;;; coq-par-compile.el --- parallel compilation of required modules

;; This file is part of Proof General.

;; Portions © Copyright 1994-2012  David Aspinall and University of Edinburgh
;; Portions © Copyright 2003-2018  Free Software Foundation, Inc.
;; Portions © Copyright 2001-2017  Pierre Courtieu
;; Portions © Copyright 2010, 2016  Erik Martin-Dorel
;; Portions © Copyright 2011-2013, 2016-2017  Hendrik Tews
;; Portions © Copyright 2015-2017  Clément Pit-Claudel

;; Authors: Hendrik Tews
;; Maintainer: Hendrik Tews <hendrik@askra.de>

;; License:     GPL (GNU GENERAL PUBLIC LICENSE)

;;; Commentary:
;;
;; This file implements compilation of required modules.  The
;; compilation is done in parallel in the background (in contrast to
;; what you find in coq-seq-compile.el).
;;
;;
;;; TODO
;;
;; - fix -I current-dir argument for coqc invocations
;; - on error, try to put location info into the error message
;; - use file-attribute-modification-time and similar functions when
;;   dropping support for emacs 25 (emacs 26.1 released on 05/2018)
;; - use define-error when dropping support for emacs 24 (25.1
;;   released on 09/2016)
;;
;; Note that all argument computations inherit `coq-autodetected-version': when
;; changing compilers, all compilation jobs must be terminated.  This is
;; consistent with the fact that the _CoqProject file is not reparsed.
;;
;; tests wanted:
;; - unlock checks for ancestors of failed jobs in different cases
;; - two require jobs, where the first finishes, while the second is
;;   in a state before waiting-dep
;; - a job depending on a failed dependee, where the dependee has been finished before

;;; Code:

(defvar queueitems)       ; dynamic scope in p-s-extend-queue-hook
(eval-when-compile (require 'cl-lib))
(require 'coq-compile-common)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Multiple file handling -- parallel compilation of required modules
;;

;; This file implements parallel background compilation. It makes sure
;; that only a certain number (`coq-max-background-compilation-jobs')
;; of coqdep and coqc processes are running in the background.
;;
;; In this file, compilation jobs are uninterned lisp symbols that
;; store all important information in their property list. New
;; compilation jobs are created when Require commands are parsed and
;; when the output of coqdep is processed. If there is space, new jobs
;; are directly launched. Otherwise, they are put into a queue
;; (`coq-par-compilation-queue') to be launched when some other
;; process terminates.
;;
;; Dependencies between files are reflected with suitable links. They
;; are established when the coqdep output is processed. A job with
;; dependencies waits for the dependencies to finish before it
;; continues with coqc.
;;
;; There are two differend kinds of compilation jobs. First, ordinary
;; files, whose dependencies must be determined with coqdep and which
;; might need to be compiled after all their dependencies are ready.
;; These compilation jobs are called 'file jobs here. Apart from 'file
;; jobs there are the Require commands in the asserted region. For
;; each Require command one must determine the modules/files (its
;; dependencies) that must be compiled before the Require command can
;; be processed. Require commands are tracked with 'require jobs here.
;; Typically, a 'require job has a number of 'file jobs as
;; dependencies. coqdep must be run on both, 'require and 'file jobs
;; to determine their dependencies. For 'require jobs this is done in
;; a temporary file. coqc must only be run on 'file jobs.
;;
;; It is pretty clear how to process these compilation jobs. The
;; problems are:
;;
;; 1- where to put the Require command itself and the items that follow it
;; 2- make sure ancestors are properly locked
;; 3- error reporting
;; 4- using -quick and the handling of .vo/.vio prerequisites for Coq < 8.11
;; 5- using -vos for Coq >= 8.11
;;
;;
;; For 1- where to put the Require command and the items that follow it:
;;
;; The Require command and the items that follow cannot stay in
;; proof-action-list, as otherwise they would be sent to the prover
;; long before the compilation finishes. I therefore cut
;; proof-action-list into pieces and leave only the items before the
;; first Require on proof-action-list. The others are put into the
;; 'queueitems property of the 'require command that is created for
;; the Require. When such a 'require job gets ready, it puts the items
;; back into proof-action-list and lets Proof General process them as
;; usual.
;;
;; All 'require commands are linked with so-called 'queue-dependent
;; links, such that later 'require jobs can be delayed until earlier
;; ones are ready. The later 'require job is said to be a queue
;; dependant of the earlier one.
;;
;;
;; For 2- make sure ancestors are properly locked:
;;
;; Consider "Require a. Require b." where a and b depend on c. Locking
;; must be done such that c is only unlocked, when "Require a" is
;; undone and not when "Require b" is undone alone. During compilation
;; files are locked just before coqdep is started on them (after they
;; have been identified as a dependency). At that time the 'lock-state
;; property of the job is set to 'locked. Ancestors are then
;; propagated upwards in the dependency tree and stored in the
;; 'ancestors property of jobs. When a require job is retired all
;; direct and indirect ancestors with 'lock-state 'locked are stored
;; in the 'coq-locked-ancestors property of the span belonging to that
;; require command (in the 'require-span property). The 'lock-state is
;; then set to 'asserted, such that any other require job will ignore
;; these jobs. A span delete action will unlock all uncestors in the
;; 'coq-locked-ancestors property.
;;
;; The 'ancestors property holds a hash that is used as a set, to
;; avoid exponential duplication of ancestors, see Proof General
;; issue 499.
;;
;;
;; For 3- error reporting:
;;
;; Depending on `coq-compile-keep-going' compilation can continue
;; after an error or stop immediately. For stopping immediately,
;; processing is aborted with a signal that eventually leads to
;; `coq-par-emergency-cleanup', which kills all compilation jobs,
;; retracts the queue region and resets all internal data.
;;
;; For `coq-compile-keep-going', the failing job, all ordinary
;; dependants and all queue dependants are marked with 'failed. All
;; ancestors that have already been registered in such a failed job
;; are treated in the following way: If the ancestor is (via a
;; different dependency path) an ancestor of a job that is still being
;; compiled, then the ancestor is kept locked. Otherwise the ancestor
;; is unlocked. Failed jobs continue with their normal state
;; transition, but omit certain steps (eg., running coqc). If a coqc
;; compilation finishes and all dependants are marked as failed, the
;; ancestors are also treated in the way described before. If a failed
;; require job is retired, nothing is done (especially its span is not
;; asserted), unless it is the last compilation job. If the last
;; compilation job is marked as failed when it is retired, then the
;; whole queue region is retracted.
;;
;; When a failing require command follows a bunch of commands that
;; take a while to process, it may happen, that the last failing
;; require command is ready to be retired before the preceeding
;; commands have been processed. In this case the retirement (in
;; particular, unlocking the queue region) must be delayed until proof
;; action list is empty. This is done by adding an empty action into
;; `proof-action-list' that calls the retirement function
;; `coq-par-kickoff-queue-maybe' again. Further
;; `coq--par-delayed-last-job' must be set to disable the cycle
;; detection that is otherwise automatically started if no background
;; job is active and the last require job has not been retired yet.
;;
;;
;; For 4- using -quick and the handling of .vo/.vio prerequisites for Coq < 8.11
;;
;; There are now two ways available to speed up compilation,
;; -quick/-vio and -vos. For Coq >= 8.5 and < 8.11 -quick/-vio is
;; available and coq-compile-quick is consulted in order to determine
;; whether to use it. For Coq >= 8.11 -vos is available and
;; coq-compile-vos is consulted. The following paragraph descripes the
;; complications with -quick/-vio.

;; Coq accepts both .vo and .vio files for importing modules
;; regardless of it is running with -quick or not. However, it is
;; unclear which file is loaded when both, .vo and .vio, of a
;; dependency are present. Therefore I delete a .vio file when I
;; decide to rebuild a .vo file and vica versa. coqdep delivers
;; dependencies for both, .vio and .vo files. These dependencies are
;; identical for .vio and vo (last checked for coq trunk in October
;; 2016). For deciding whether prerequisites must be recompiled the
;; full path returned form coqdep is relevant. Because it seems odd to
;; store a full path without a .vo or .vio suffix I decided to always
;; store the .vo object file name in the 'vo-file property of
;; compilation jobs. Only when all dependencies are ready, in
;; `coq-par-job-needs-compilation' I decide whether to build a .vio or
;; .vo file and if already present .vo or .vio files must be deleted.
;; Only at that point the relevant property 'required-obj-file is set.
;;
;;
;; For 5- using -vos for Coq >= 8.11
;;
;; When Coq >= 8.11 is detected, -vos is used and coq-compile-vos is
;; consulted in order to find out whether to compile to .vos or to .vo
;; files. For people switching PG or switching to Coq 8.11, there is a
;; backward compatibility path: When coq-compile-vos is nil, the
;; decision is derived from coq-compile-quick.
;;
;; The logic here to decide whether compilation is needed or not,
;; assumes coq is used consistently without randomly deleting files.
;; Because coqc always produces an empty .vos file when compiling to
;; .vo, it can never happen, that a .vo file is present without .vos
;; file or that a .vo file is more recent then the corresponding .vos
;; file. This simplifies the logic for deciding about recompilation
;; quite a bit.
;;
;; For Coq >= 8.11, vio to vo compilation is disabled for obvious
;; reasons and in this version of Proof General, there is no similar
;; feature.
;;
;; 
;; Properties of compilation jobs
;;
;;   'name            - some unique string, only used for debugging
;;   'queueitems      - holds items from proof-action-list on
;;                      require jobs
;;   'vo-file         - the .vo file for the module that this job has
;;                      to make up-to-date. This slot is filled when the
;;                      job is created and independent of whether a .vio
;;                      or .vo file must be made up-to-date. Only present
;;                      in file jobs.
;;   'required-obj-file - contains the .vio or .vo to be produced or nil
;;                        if that has not yet been decided. May contain
;;                        nil if no file needs to be rebuild at all. Nil
;;                        on require jobs.
;;   'obj-mod-time    - modification time of 'required-obj-file, stored
;;                      here in case compilation is not needed for file
;;                      jobs, to avoid double stat calls;
;;   'use-quick       - 'vio if `coq-par-job-needs-compilation' decided to use
;;                      -quick for Coq older than 8.11; 'vos if it decided to
;;                      to use -vos for Coq 8.11 or newer, nil if it decided
;;                      to use .vo compilation, no compilation is necessary or
;;                      for require jobs.
;;   'type            - the type of the job, either 'require or 'file
;;   'state           - the state of the job, see below
;;   'coqc-dependants - list of parent jobs that depend on this job,
;;                      when this job finishes it propagates the
;;                      necessary information to it's parent jobs and
;;                      decreases their 'coqc-dependency-count
;;   'coqc-dependency-count - number of unfinished child jobs
;;                            increased for every subjob spawned
;;                            during coqdep output processing
;;                            File job waits with coqc until this
;;                            count reaches 0 again. Require jobs wait with
;;                            their transition to 'ready.
;;   'youngest-coqc-dependency - slot to accumulate the most recent
;;                               modification time of some ancestor
;;                               value; might be an Emacs time or
;;                               'just-compiled; not really needed in require
;;                               jobs but present there to simplify the code
;;   'queue-dependant - next top-level job, only present in require jobs
;;   'queue-dependant-waiting - t if this is a require job that has
;;                              to wait until previous require jobs
;;                              finish. In this waiting time, dependencies
;;                              are compiled, but queue items are only
;;                              put back into proof-action-list when
;;                              this property becomes nil
;;   'src-file        - the .v file name, only in file jobs
;;   'load-path       - value of coq-load-path, propagated to all
;;                      dependencies
;;   'ancestors       - set of ancestor jobs, implemented as hash
;;			mapping jobs to t; for file jobs
;;			this set includes the job itself; the hash is
;;			necessary to avoid an exponentially growing
;;			number of duplicates
;;   'lock-state      - nil for require jobs, 'unlocked if the file
;;                      corresponding to job is not locked, 'locked if that
;;                      file has been locked, 'asserted if it has been
;;                      registered in some span in the 'coq-locked-ancestors
;;                      property already
;;   'require-span    - holds the span with the require command for require jobs
;;   'vio2vo-needed   - t if a subsequent vio2vo process is required to
;;                      build the .vo file. Otherwiese nil.
;;   'failed          - t if coqdep or coqc for the job or one dependee failed.
;;   'visited         - used in the dependency cycle detection to mark
;;                      visited jobs
;;   'current-dir     - current directory or default-directory of the buffer
;;                      that contained the require command. Only present in
;;                      require jobs. Only needed for 8.4 compatibility.
;;   'temp-require-file  - temporary file name just containing the require
;;                         command of a require job for determining the files
;;                         needed for that require. Must be deleted after
;;                         coqdep finished.
;;
;; 
;; Properties of processes
;;
;; A lot of the necessary actions are started from inside a process
;; sentinel. The property list of processes stores the necessary
;; information for that in the following properties.
;;
;;   'coq-compilation-job       - the compilation job that started
;;                                this process
;;   'coq-process-continuation  - the continuation to be called when
;;                                the process finishes. Either
;;                                coq-par-process-coqdep-result or
;;                                coq-par-coqc-continuation or
;;                                coq-par-vio2vo-continuation
;;   'coq-process-output        - the output of the process
;;   'coq-process-command       - the command for error reporting
;;                                (as string list)
;;   'coq-par-process-killed    - t if this process has been killed from PG
;;   'coq-process-rm            - if not nil, a file to be deleted when
;;                                the process does not finish successfully,
;;                                i.e., when the continuation is not called.
;;
;;
;; State transition of file jobs
;;
;;     'enqueued-coqdep -> 'waiting-dep -> 'enqueued-coqc -> 'ready
;;
;; State transition for require jobs
;;
;;     'enqueued-coqdep -> 'waiting-dep -> 'waiting-queue -> 'ready
;;
;; State explanation
;;
;;   'enqueued-coqdep - coqdep is running or the job enqueued, waiting
;;                      for a slot to start coqdep
;;   'waiting-dep     - coqdep finished, dependencies determined, waiting for
;;                      the dependencies
;;   'enqueued-coqc   - dependencies ready, coqc is running, or the job is
;;                      enqueued, waiting for a slot to start coqc
;;   'waiting-queue   - XXX
;;   'ready           - ready, the result might be missing when 'failed
;;
;;
;; Over its live time, a compilation job might get passed through the
;; following functions. Some of them might be skipped or executed more
;; then once.
;;
;; | functions for file jobs          | state            | comment                              |
;; |----------------------------------+------------------+--------------------------------------|
;; | coq-par-create-file-job          | 'enqueued-coqdep | job creation                         |
;; | coq-par-start-coqdep-on-file     |                  | lock files                           |
;; | coq-par-process-coqdep-result    | 'waiting-dep     | create dependee/child jobs           |
;; | coq-par-decrease-coqc-dependency |                  | dependee/child finished coqc         |
;; | coq-par-compile-job-maybe        | 'enqueued-coqc   |                                      |
;; | -- start coqc                    |                  |                                      |
;; | coq-par-coqc-continuation        |                  |                                      |
;; | coq-par-kickoff-coqc-dependants  | 'ready           |                                      |
;; | coq-par-start-vio2vo             |                  |                                      |
;; | coq-par-vio2vo-continuation      |                  |                                      |
;;
;;
;; | function for require jobs        | state            | comment                              |
;; |----------------------------------+------------------+--------------------------------------|
;; | coq-par-create-require-job       | 'enqueued-coqdep | job creation                         |
;; | coq-par-start-coqdep-on-require  |                  | lock files                           |
;; | coq-par-process-coqdep-result    | 'waiting-dep     | create dependee/child jobs           |
;; | coq-par-decrease-coqc-dependency |                  | dependee/child finished coqc         |
;; | coq-par-kickoff-queue-maybe      | 'waiting-queue   |                                      |
;; | coq-par-retire-top-level-job     |                  |                                      |
;; | coq-par-kickoff-queue-maybe cont | 'ready           |                                      |
;; | coq-par-require-processed        |                  | in dummy action in proof-action-list |
;; | coq-par-run-vio2vo-queue         |                  | called via timer                     |
;;
;;
;; The following _is_ outdated.
;; To print the states of the compilation jobs for debugging, eval
;; 
;; (let ((clones))
;;   (maphash (lambda (k v)
;; 	     (message "%s type %s for %s state %s dep of %s queue dep of %s"
;; 		      (get v 'name)
;; 		      (get v 'type)
;; 		      (get v 'src-file)
;; 		      (get v 'state)
;; 		      (mapcar (lambda (p) (get p 'name))
;; 			      (get v 'coqc-dependants))
;; 		      (get v 'queue-dependant))
;; 	     (mapc (lambda (p) (when (eq (get p 'type) 'clone)
;; 				 (push p clones)))
;; 		   (get v 'coqc-dependants)))
;; 	   coq--compilation-object-hash)
;;   (mapc (lambda (v)
;; 	  (message "%s type %s for %s state %s dep of %s queue dep of %s"
;; 		   (get v 'name)
;; 		   (get v 'type)
;; 		   (get v 'src-file)
;; 		   (get v 'state)
;; 		   (mapcar (lambda (p) (get p 'name))
;; 			   (get v 'coqc-dependants))
;; 		   (get v 'queue-dependant)))
;; 	clones))


;;; Variables

(defvar coq--current-background-jobs 0
  "Number of currently running background jobs.")

(defvar coq--compilation-object-hash nil
  "Hash for storing the compilation jobs.
This hash only stores file jobs and no require jobs.  They
are stored in order to avoid double compilation.  The jobs stored
in here are uninterned symbols that carry all important
information in their property list.  See the documentation in the
source file \"coq-par-compile.el\". The hash always maps .vo file
names to compilation jobs, regardless of ``-quick''.")

(defvar coq--last-compilation-job nil
  "Pointer to the last require compilation job.
Used to link top-level jobs with queue dependencies.")

(defvar coq--compile-vio2vo-in-progress nil
  "Set to t iff vio2vo is running in background.")

(defvar coq--compile-vio2vo-delay-timer nil
  "Holds the timer for the vio2vo delay.")

(defvar coq--compile-vio2vo-start-id 0
  "Integer counter to detect races for `coq-par-require-processed'.
Assume compilation for the last top-level ``Require'' command
finishes but executing the ``Require'' takes so long that the
user can assert a next ``Require'' and that the second
compilation finishes before the first ``Require'' has been
processed. In this case there are two `coq-par-require-processed'
callbacks active, of which the first one must be ignored. For
each new callback this counter is incremented and when there is a
difference the call to `coq-par-require-processed' is ignored.")

(defvar coq--par-next-id 1
  "Increased for every job and process, to get unique job names.
The names are only used for debugging.")

(defvar coq--par-delayed-last-job nil
  "Inform the cycle detection that there is a delayed top-level job.
The retirement of failing require jobs must be delayed until
`proof-action-list' is empty, to avoid retracting commands before
the first failing require. This is done by adding the call to
`coq-par-kickoff-queue-maybe' to the end of `proof-action-list'.
This variable is t during this time to disable cycle detection,
which is otherwise started when `coq--last-compilation-job' has
not been retired but no compilation process is running in the
background.")


;;; utility functions

(defun split-list-at-predicate (l pred)
  "Split L into several lists at points where PRED is t.
Splits L into several lists, such that
- their concatenation equals the original L
- every element for which PRED returns t starts a new list
- except for the first list, PRED is t for every car of every result list
- the first result list contains the first elements of L for which PRED is nil
L is modified in place and the list structure in L is reused for
the result."
  (let ((result (list l))
	previous
	(current l))
    (while current
      (when (funcall pred (car current))
	(if previous
	    (progn
	      (setcdr previous nil)
	      (push current result))
	  ;; handle case where pred is t for the car of the original l
	  (setq result (list l nil))))
      (setq previous current)
      (setq current (cdr current)))
    (nreverse result)))

(defun coq-par-time-less (time-1 time-2)
  "Compare extended times.
The arguments can be an emacs time (a list of 2 to 4 integers,
see `current-time') or the symbol 'just-compiled, where the
latter is greater then everything else."
  (cond
   ((eq time-2 'just-compiled) t)
   ((eq time-1 'just-compiled) nil)
   (t (time-less-p time-1 time-2))))

(defun coq-par-init-compilation-hash ()
  "(Re-)Initialize `coq--compilation-object-hash'."
  (setq coq--compilation-object-hash (make-hash-table :test 'equal)))

(defun merge-hash-content (target source)
  "Add all elements of hash SOURCE to hash TARGET.
Keys present in TARGET and in SOURCE are replaced in TARGET with
their SOURCE binding."
  (maphash
   (lambda (key val) (puthash key val target))
   source))

;;; generic queues
;; Standard implementation with two lists.

(defun coq-par-new-queue ()
  "Create a new empty queue."
  (cons nil nil))

(defun coq-par-enqueue (queue x)
  "Insert X in queue QUEUE."
  (push x (car queue)))

(defun coq-par-dequeue (queue)
  "Dequeue the next item from QUEUE."
  (let ((res (pop (cdr queue))))
    (unless res
      (setcdr queue (nreverse (car queue)))
      (setcar queue nil)
      (setq res (pop (cdr queue))))
    res))


;;; job queue

;; XXX local variable -- check all defvars for local variables
(defvar coq-par-compilation-queue (coq-par-new-queue)
  "Queue of compilation jobs that wait for a free core to get started.
Use `coq-par-job-enqueue' and `coq-par-job-dequeue' to access the
queue.")

(defun coq-par-job-enqueue (job)
  "Insert JOB in the queue of waiting compilation jobs."
  (coq-par-enqueue coq-par-compilation-queue job)
  (when coq--debug-auto-compilation
    (message "%s: enqueue job in waiting queue" (get job 'name))))

(defun coq-par-job-dequeue ()
  "Dequeue the next job from the compilation queue."
  (let ((res (coq-par-dequeue coq-par-compilation-queue)))
    (when coq--debug-auto-compilation
      (if res
	  (message "%s: dequeue" (get res 'name))
	(message "compilation queue empty")))
    res))


;;; vio2vo queue

(defvar coq-par-vio2vo-queue (coq-par-new-queue)
  "Queue of jobs that need a vio2vo process.
Use `coq-par-vio2vo-enqueue' and `coq-par-vio2vo-dequeue' to
access the queue.")

(defun coq-par-vio2vo-enqueue (job)
  "Insert JOB in the queue for vio2vo processing."
  (coq-par-enqueue coq-par-vio2vo-queue job)
  (when coq--debug-auto-compilation
    (message "%s: enqueue job in vio2vo queue" (get job 'name))))

(defun coq-par-vio2vo-dequeue ()
  "Dequeue the next job from the vio2vo queue."
  (let ((res (coq-par-dequeue coq-par-vio2vo-queue)))
    (when coq--debug-auto-compilation
      (if res
	  (message "%s: vio2vo dequeue" (get res 'name))
	(message "vio2vo queue empty")))
    res))


;;; error symbols

;; coq-compile-error-coqdep
;;
;; This error is signaled with one data item -- the file name

(put 'coq-compile-error-coqdep 'error-conditions
     '(error coq-compile-error coq-compile-error-coqdep))
(put 'coq-compile-error-coqdep 'error-message
     "Coq compilation error: coqdep fails in")

;; coq-compile-error-coqc
;;
;; This error is signaled with one data item -- the file name

(put 'coq-compile-error-coqc 'error-conditions
     '(error coq-compile-error coq-compile-error-coqc))
(put 'coq-compile-error-coqc 'error-message
     "Coq compilation error: coqc fails in")

;; coq-compile-error-command-start
;;
;; This error is signaled with two data items --
;; a list consisting of the command and the system error message,
;; the command itself is a string list of the command name and the options

(put 'coq-compile-error-command-start 'error-conditions
     '(error coq-compile-error coq-compile-error-command-start))
(put 'coq-compile-error-command-start 'error-message
     "Coq compilation error:")

;; coq-compile-error-circular-dep
;;
;; This error is signaled with one data item -- an indication about
;; the circularity, which is the error message to be appended to the
;; contents of 'error-message.

(put 'coq-compile-error-circular-dep 'error-conditions
     '(error coq-compile-error coq-compile-error-circular-dep))
(put 'coq-compile-error-circular-dep 'error-message
     "Coq compilation error: Circular dependency")

;; coq-compile-error-rm
;;
;; Signaled when we have to delete a .vio or .vo file for consistency and
;; that deletion fails.
;;
;; This error is signaled with one data item -- the file-error error
;; description. Its car is the error symbol `file-error' and the cdr are
;; the data items for this error. They seem to be a list of strings with
;; different parts of the error message.

(put 'coq-compile-error-rm 'error-conditions
     '(error coq-compile-error coq-compile-error-rm))
(put 'coq-compile-error-rm 'error-message
     "Cannot remove outdated file.")


;;; find circular dependencies in non-ready compilation jobs

(defun coq-par-find-dependency-circle-for-job (job path)
  "Find a dependency cycle in the dependency subtree of JOB.
Do a depth-first-search to find the cycle. JOB is the current
node and PATH the stack of visited nodes. Jobs in state
'enqueue-coqc can be ignored, because they can never participate
in a cycle."
  ;; CORRECTNESS ARGUMENT FOR THIS FUNCTION
  ;;
  ;; An outside-cycle job is a job for which the whole upward segment
  ;; of the dependency graph does not contain any cycle (and therefore
  ;; neither job itself belongs to any cycle nor is there a path
  ;; starting in job and leading to a cycle). Any job is either
  ;; outside-cycle or there exists an upward path containing the job
  ;; and a cycle above it.
  ;; The visited-condition is that all jobs marked visited are
  ;; outside-cycle jobs.
  ;; 
  ;; The precondition of this function is that
  ;; - PATH does not contain any job twice,
  ;; - PATH is an reversed upward path where JOB is a dependant of the
  ;;   head of PATH, and
  ;; - the visited-condition holds.
  ;;
  ;; This function returns nil and the visited condition holds at
  ;; return, if the precondition holds and JOB is outside-cycle.
  ;; Proved by induction on the length of the maximal upward path.
  ;; 
  ;; This function returns a cycle (and not nil) if the precondition
  ;; holds and JOB is not outside-cycle. Proved by induction on the
  ;; distance to the first repeated job on the right-most upward path
  ;; containing a cycle. Here, right is the direction of the head of
  ;; the 'coqc-dependants list.
  (let (cycle (p path))
    ;; path is reversed. A potential cycle goes from the beginning of
    ;; path to the first occurence of job.
    (while p
      (when (eq (car p) job)
	(setcdr p nil)
	(setq cycle path))
      (setq p (cdr p)))
    (if cycle
	cycle
      (setq path (cons job path))
      (setq p (get job 'coqc-dependants))
      (while (and p (not cycle))
        ;; XXX when clause does not make sense: job is a dependee or
        ;; dependency of (car p), therefore (car p) can only be in
        ;; state 'waiting-dep
        ;; XXX only recurse for dependants not visited yet
	(when (eq (get (car p) 'state) 'waiting-dep)
          ;; XXX should not be called on visited ancestors?
	  (setq cycle (coq-par-find-dependency-circle-for-job (car p) path)))
	(setq p (cdr p)))
      (put job 'visited t)
      cycle)))

(defun coq-par-find-dependency-circle ()
  "Find a dependency cycle in compilation jobs of state 'waiting-dep.
If no circle is found return nil, otherwise the list of files
belonging to the circle.  Jobs in state 'enqueue-coqc can be
ignored, because they can never participate in a cycle."
  (let (cycle)
    (maphash (lambda (key job) (put job 'visited nil))
	     coq--compilation-object-hash)
    (maphash
     (lambda (key job)
       (when (and (not cycle) (not (get job 'visited))
		  (eq (get job 'state) 'waiting-dep))
	 (setq cycle (coq-par-find-dependency-circle-for-job job nil))))
     coq--compilation-object-hash)
    (mapcar (lambda (j) (get j 'src-file)) cycle)))


;;; map coq module names to files, using synchronously running coqdep

(defun coq-par-coqdep-arguments (lib-src-file coq-load-path)
  "Compute the command line arguments for invoking coqdep on LIB-SRC-FILE.
Argument COQ-LOAD-PATH must be `coq-load-path' from the buffer
that triggered the compilation, in order to provide correct
load-path options to coqdep."
  (nconc (coq-coqdep-prog-args coq-load-path
                               (file-name-directory lib-src-file)
                               (coq--pre-v85))
         (list lib-src-file)))

(defun coq-par-coqc-arguments (lib-src-file coq-load-path)
  "Compute the command line arguments for invoking coqc on LIB-SRC-FILE.
Argument COQ-LOAD-PATH must be `coq-load-path' from the buffer
that triggered the compilation, in order to provide correct
load-path options to coqdep."
  (nconc (coq-coqc-prog-args coq-load-path (file-name-directory lib-src-file) (coq--pre-v85))
         (list lib-src-file)))

(defun coq-par-analyse-coq-dep-exit (status output command)
  "Analyse output OUTPUT of coqdep command COMMAND with exit status STATUS.
Returns the list of .vo dependencies if there is no error. Otherwise,
writes an error message into `coq-compile-response-buffer', makes
this buffer visible and returns a string.

This function does always return .vo dependencies, regardless of the
value of `coq-compile-quick'. If necessary, the conversion into .vio
or .vos files must be done elsewhere."
  ;; (when coq--debug-auto-compilation
  ;;   (message "analyse coqdep output \"%s\"" output))
  (if (or
       (not (eq status 0))
       (string-match coq-coqdep-error-regexp output))
      (progn
	;; display the error
	(coq-compile-display-error (mapconcat 'identity command " ") output t)
        (if (eq status 0)
            "unsatisfied dependencies"
          (format "coqdep exist status %d" status)))
    ;; In 8.5, coqdep produces two lines. Match with .* here to
    ;; extract only a part of the first line.
    ;; We could match against (concat "^[^:]*" obj-file "[^:]*: \\(.*\\)")
    ;; to select the right line for either .vo or .vio dependencies.
    ;; However, we want to accept a .vo prerequisite for a .vio target
    ;; if it is recent enough. Therefore we actually need module dependencies
    ;; instead of file dependencies and we derive them from the .vo line.
    (when (string-match "\\`[^:]*: \\(.*\\)" output)
      (cl-remove-if-not
       (lambda (f) (string-match-p "\\.vo\\'" f))
       (split-string (match-string 1 output))))))


;;; manage background jobs

(defun coq-par-kill-all-processes ()
  "Kill all background coqc, coqdep or vio2vo compilation processes.
Return t if some process was killed."
  ;; need to first mark processes as killed, because delete process
  ;; starts running sentinels in the order processes terminated, so
  ;; after the first delete-process we see sentinentels of non-killed
  ;; processes running
  (let ((kill-needed))
    (mapc
     (lambda (process)
       (when (process-get process 'coq-compilation-job)
	 (process-put process 'coq-par-process-killed t)
	 (setq kill-needed t)))
     (process-list))
    (when kill-needed
      (message "Kill all Coq background compilation processes"))
    (mapc
     (lambda (process)
       (when (process-get process 'coq-compilation-job)
	 (process-put process 'coq-par-process-killed t)
	 (delete-process process)
	 (when coq--debug-auto-compilation
	   (message "%s %s: kill it"
		    (get (process-get process 'coq-compilation-job) 'name)
		    (process-name process)))))
     (process-list))
    (setq coq--current-background-jobs 0)
    kill-needed))

(defun coq-par-unlock-all-ancestors-on-error ()
  "Unlock ancestors which are not in an asserted span.
Used for unlocking ancestors on compilation errors."
  (when coq--compilation-object-hash
    (maphash
     (lambda (key job)
       (when (eq (get job 'lock-state) 'locked)
         (coq-unlock-ancestor (get job 'src-file))
	 (put job 'lock-state 'unlocked)))
     coq--compilation-object-hash)))

(defun coq-par-kill-and-cleanup ()
  "Kill all background compilation, cleanup internal state and unlock ancestors.
This is the common core of `coq-par-emergency-cleanup' and
`coq-par-user-interrupt'.  Returns t if there actually was a
background job that was killed."
  (let (proc-killed)
    (when coq--debug-auto-compilation
      (message "kill all jobs and cleanup state"))
    (setq proc-killed (coq-par-kill-all-processes))
    (setq coq-par-compilation-queue (coq-par-new-queue))
    (setq coq--last-compilation-job nil)
    (setq coq-par-vio2vo-queue (coq-par-new-queue))
    (setq coq--compile-vio2vo-in-progress nil)
    (when coq--compile-vio2vo-delay-timer
      (cancel-timer coq--compile-vio2vo-delay-timer)
      (setq coq--compile-vio2vo-delay-timer nil))
    (coq-par-unlock-all-ancestors-on-error)
    (setq proof-second-action-list-active nil)
    (coq-par-init-compilation-hash)
    proc-killed))

(defun coq-par-emergency-cleanup ()
  "Emergency cleanup for errors in parallel background compilation.
This is the function that cleans everything up when some
background compilation process detected a severe error.  When
`coq-compile-keep-going' is nil, all errors are severe.  When
`coq-compile-keep-going' is t, coqc and coqdep errors are
not severe.  This function is also used for the user action to
kill all background compilation.

On top of `coq-par-kill-and-cleanup', this function resets the
queue region (and thus `proof-action-list' and signals an
interrupt to the proof shell."
  (interactive)				; needed for menu
  (when coq--debug-auto-compilation
    (message "emergency cleanup"))
  (coq-par-kill-and-cleanup)
  (when proof-action-list
    (setq proof-shell-interrupt-pending t))
  (proof-release-lock)
  (proof-detach-queue))

(defun coq-par-user-interrupt ()
  "React to a generic user interrupt with cleaning up everything.
This function cleans up background compilation when the proof
assistant died (`proof-shell-handle-error-or-interrupt-hook') or
when the user interrupted Proof General (with \\[proof-interrupt-process] or
`proof-interrupt-process' leading to
`proof-shell-signal-interrupt-hook').

On top of `coq-par-kill-and-cleanup', this function only sets the
dynamic variable `prover-was-busy' to tell the proof shell that
the user actually had a reason to interrupt.  However, in the
special case where `proof-action-list' is nil and
`coq--last-compilation-job' not, this function also clears the
queue region and releases the proof shell lock.  This has the nice
side effect, that `proof-interrupt-process' does not send an
interrupt signal to the prover."
  (let (proc-killed
	(was-busy (or coq--last-compilation-job
		      coq--compile-vio2vo-in-progress
		      coq--compile-vio2vo-delay-timer)))
    (when coq--debug-auto-compilation
      (message "cleanup on user interrupt"))
    (setq proc-killed (coq-par-kill-and-cleanup))
    (unless proof-action-list
      (when coq--debug-auto-compilation
	(message "clear queue region and proof shell lock"))
      (proof-release-lock)
      (proof-detach-queue))
    (when (and (boundp 'prover-was-busy)
	       (or proc-killed was-busy))
      (setq prover-was-busy t))))

(defun coq-par-process-filter (process output)
  "Store OUTPUT from coq background compilation."
  (process-put process 'coq-process-output
	       (concat (process-get process 'coq-process-output) output)))

(defun coq-par-start-process (command arguments continuation job file-rm)
  "Start asynchronous compilation job for COMMAND.
This function starts COMMAND with arguments ARGUMENTS for
compilation job JOB, making sure that CONTINUATION runs when the
process finishes successfully. FILE-RM, if non-nil, denotes a
file to be deleted when the process does not finish successfully."
  ;;(message "CPSP %s %s %s %s %s" command arguments continuation job file-rm)
  (let ((process-connection-type nil)	; use pipes
	(process-name (format "pro-%s" coq--par-next-id))
	process)
    (setq coq--par-next-id (1+ coq--par-next-id))
    (with-current-buffer (or proof-script-buffer (current-buffer))
      (when coq--debug-auto-compilation
	(message "%s %s: start %s %s in %s"
		 (get job 'name) process-name
		 command (mapconcat 'identity arguments " ")
		 default-directory))
      (condition-case err
	  ;; If the command is wrong, start-process aborts with an
	  ;; error. However, in Emacs 23.4.1. it will leave a process
	  ;; behind, which is in a very strange state: running with no
	  ;; pid. Emacs 24.2 fixes this.
	  (setq process (apply 'start-process process-name
			       nil	; no process buffer
			       command arguments))
	(error
	 (when coq--debug-auto-compilation
           (message "%s %s: error in start process, %s"
		    (get job 'name) process-name
                    (if file-rm
                        (format "rm %s" file-rm)
                      "no file removal")))         
	 (when file-rm
	   (ignore-errors (delete-file file-rm)))
	 (signal 'coq-compile-error-command-start
		 (list (cons command arguments) (nth 2 err)))))
      (set-process-filter process 'coq-par-process-filter)
      (set-process-sentinel process 'coq-par-process-sentinel)
      (set-process-query-on-exit-flag process nil)
      (setq coq--current-background-jobs (1+ coq--current-background-jobs))
      (process-put process 'coq-compilation-job job)
      (process-put process 'coq-process-continuation continuation)
      (process-put process 'coq-process-command (cons command arguments))
      (process-put process 'coq-process-output "")
      (process-put process 'coq-process-rm file-rm))))

(defun coq-par-process-sentinel (process event)
  "Sentinel for all background processes.
Runs when process PROCESS terminated because of EVENT. It
determines the exit status and calls the continuation function
that has been registered with that process. Normal compilation
errors are reported with an error message inside the callback.
Starts as many queued jobs as possible. If, at the end, no job is
running in the background but compilation has not been finished,
then there must be a cycle in the dependencies, which is found
and reported here. The cycle detection is skipped, if the
retirement of the last compilation job has been delayed per
`coq--par-delayed-last-job'. All signals are caught inside this
function and reported appropriately."
  (condition-case err
      (if (process-get process 'coq-par-process-killed)
	  (progn
	    (when coq--debug-auto-compilation
	      (message "%s %s: skip sentinel, process killed, %s"
		       (get (process-get process 'coq-compilation-job) 'name)
		       (process-name process)
		       (if (process-get process 'coq-process-rm)
			   (format "rm %s"
				   (process-get process 'coq-process-rm))
			 "no file removal")))
	    (when (process-get process 'coq-process-rm)
	      (ignore-errors
		(delete-file (process-get process 'coq-process-rm))))
	    (when (eq (process-get process 'coq-process-continuation)
		      'coq-par-vio2vo-continuation)
	      (when coq--debug-auto-compilation
		(message "%s: reenqueue for vio2vo"
			 (get (process-get process 'coq-compilation-job) 'name)))
	      (coq-par-vio2vo-enqueue
	       (process-get process 'coq-compilation-job))))
	(let (exit-status)
	  (when coq--debug-auto-compilation
	    (message "%s %s: process status changed to %s"
		     (get (process-get process 'coq-compilation-job) 'name)
		     (process-name process)
		     event))
	  (cond
	   ((eq (process-status process) 'exit)
	    (setq exit-status (process-exit-status process)))
	   (t (setq exit-status "abnormal termination")))
	  (setq coq--current-background-jobs
		(max 0 (1- coq--current-background-jobs)))
	  (funcall (process-get process 'coq-process-continuation)
		   process exit-status)
	  (coq-par-start-jobs-until-full)
	  (when (and coq--compile-vio2vo-in-progress
		     (eq coq--current-background-jobs 0))
	    (setq coq--compile-vio2vo-in-progress nil)
	    (message "vio2vo compilation finished"))
	  (when (and
		 (not coq--par-delayed-last-job)
		 (eq coq--current-background-jobs 0)
		 coq--last-compilation-job)
	    (let ((cycle (coq-par-find-dependency-circle)))
	      (if cycle
                  ;; XXX cycle may contain a file job -> check code and adapt
                  ;; cycle printing
		  (signal 'coq-compile-error-circular-dep
			  (mapconcat 'identity cycle " -> "))
		(error "Deadlock in parallel compilation"))))))
    ;; coq-compile-error-start can be signaled inside the continuation
    ;; function, if that tries to start new jobs
    ;; XXX catch this error also in coq-par-preprocess-require-commands
    (coq-compile-error-command-start
     (coq-par-emergency-cleanup)
     (message "%s \"%s\" in \"%s\""
	      (get (car err) 'error-message)
	      (nth 2 err) (mapconcat 'identity (cadr err) " ")))
    (coq-compile-error
     (coq-par-emergency-cleanup)
     (message "%s %s" (get (car err) 'error-message) (cdr err)))
    (error
     (message "Error in sentinel of process %s, error %s"
	      (process-name process) err)
     (coq-par-emergency-cleanup)
     (signal (car err) (cdr err)))))


;;; vio2vo compilation

(defun coq-par-run-vio2vo-queue ()
  "Start delayed vio2vo compilation."
  ;; XXX this assert can be triggered - just start a compilation
  ;; shortly before the timer triggers
  (cl-assert (not coq--last-compilation-job)
	  nil "normal compilation and vio2vo in parallel 3")
  (setq coq--compile-vio2vo-in-progress t)
  (setq coq--compile-vio2vo-delay-timer nil)
  (when coq--debug-auto-compilation
    (message "Start vio2vo processing for %d jobs"
	     (+ (length (car coq-par-vio2vo-queue))
		(length (cdr coq-par-vio2vo-queue)))))
  (coq-par-start-jobs-until-full))

(defun coq-par-require-processed (race-counter)
  "Callback for `proof-action-list' to signal completion of the last Require.
This function ensures that vio2vo compilation starts after
`coq-compile-vio2vo-delay' seconds after the last module has been
loaded into Coq. When background compilation is successful, this
callback is inserted with a dummy item into proof-action-list
somewhere after the last require command."
  ;; When the user asserts new stuff while the (previously) last
  ;; require command is being processed, `coq--last-compilation-job'
  ;; might get non-nil. In this case there is a new last compilation
  ;; job that will eventually trigger vio2vo compilation.
  (unless (or coq--last-compilation-job
	      (not (eq race-counter coq--compile-vio2vo-start-id)))
    (setq coq--compile-vio2vo-delay-timer
	  (run-at-time coq-compile-vio2vo-delay nil
		       'coq-par-run-vio2vo-queue))))

(defun coq-par-callback-queue-item (callback)
  "Create queue item containing just CALLBACK.
Create a queue item for `proof-action-list' containing just
CALLBACK. CALLBACK must be a function taking a span as argument.
The command list in the produced queue item is nil, therefore the
item will be processed as comment and only the callback will be called."
  ;; A proof-action-list item has the form of
  ;;            (SPAN COMMANDS ACTION [DISPLAYFLAGS])
  ;; If COMMANDS is nil, the item is processed as comment and not sent
  ;; to the proof assistant, only the callback is called, see
  ;; proof-shell.el.
  (list nil nil callback))


;;; background job tasks

(defun coq-par-dependencies-ready (job)
  "Return t if all dependencies of compilation job JOB are ready."
  (eq (get job 'coqc-dependency-count) 0))

(defun coq-par-add-coqc-dependency (dependee dependant)
  "Add normal Coq dependency from child job DEPENDEE to parent job DEPENDANT."
  (put dependant 'coqc-dependency-count
       (1+ (get dependant 'coqc-dependency-count)))
  (push dependant (get dependee 'coqc-dependants))
  (when coq--debug-auto-compilation
    (message "%s -> %s: add coqc dependency"
	     (get dependee 'name) (get dependant 'name))))

(defun coq-par-add-queue-dependency (dependee dependant)
  "Add queue dependency from require job DEPENDEE to require job DEPENDANT.
The require item of DEPENDANT comes after those of DEPENDEE.
Therefore DEPENDANT must wait for DEPENDEE to finish. "
  (cl-assert (and (not (get dependant 'queue-dependant-waiting))
                  (not (get dependee 'queue-dependant)))
	  nil "queue dependency cannot be added")
  (put dependant 'queue-dependant-waiting t)
  (put dependee 'queue-dependant dependant)
  (when coq--debug-auto-compilation
    (message "%s -> %s: add queue dependency"
	     (get dependee 'name) (get dependant 'name))))

(defun coq-par-job-needs-compilation-quick (job)
  "Determine whether JOB needs to get compiled and do some side effects.
This function contains most of the logic nesseary to support
quick compilation according to `coq-compile-quick' for coq < 8.11.  Taking
`coq-compile-quick' into account, it determines if a compilation
is necessary.  The property 'required-obj-file is set either to
the file that we need to produce or to the up-to-date object
file.  If compilation is needed, property 'use-quick is set to `vio' when
-quick/-vio will be used.  If no compilation is needed, property
'obj-mod-time remembers the time stamp of 'required-obj-file.
Indepent of whether compilation is required, .vo or .vio files
that are in the way are deleted.  Note that the coq documentation
does not contain a statement, about what file is loaded, if both
a .vo and a .vio file are present.  To be on the safe side, I
therefore delete a file if it might be in the way.  Sets the
'vio2vo-needed property on job if necessary."
  (let* ((vo-file (get job 'vo-file))
	 (vio-file (coq-library-vio-of-vo-file vo-file))
	 (vo-obj-time (nth 5 (file-attributes vo-file)))
	 (vio-obj-time (nth 5 (file-attributes vio-file)))
	 (dep-time (get job 'youngest-coqc-dependency))
	 (src-time (nth 5 (file-attributes (get job 'src-file))))
	 file-to-delete max-obj-time vio-is-newer
	 other-file other-obj-time result)
    (when coq--debug-auto-compilation
      (message
       (concat "%s: compare mod times: vo mod %s, vio mod %s, src mod %s, "
	       "youngest dep %s; vo < src : %s, vio < src : %s, "
	       "vo < dep : %s, vio < dep : %s")
       (get job 'name)
       (if vo-obj-time (current-time-string vo-obj-time) "-")
       (if vio-obj-time (current-time-string vio-obj-time) "-")
       (if src-time (current-time-string src-time) "-")
       (if (eq dep-time 'just-compiled) "just compiled"
	 (current-time-string dep-time))
       (if vo-obj-time (time-less-p vo-obj-time src-time) "-")
       (if vio-obj-time (time-less-p vio-obj-time src-time) "-")
       (if vo-obj-time (coq-par-time-less vo-obj-time dep-time) "-")
       (if vio-obj-time (coq-par-time-less vio-obj-time dep-time) "-")))
    ;; Compute first the max of vo-obj-time and vio-obj-time and remember
    ;; which of both is newer. This is only meaningful if at least one of
    ;; the .vo or .vio file exists.
    (cond
     ((and vio-obj-time vo-obj-time
	   (time-less-or-equal vo-obj-time vio-obj-time))
      (setq max-obj-time vio-obj-time)
      (setq vio-is-newer t))
     ((and vio-obj-time vo-obj-time)
      (setq max-obj-time vo-obj-time))
     (vio-obj-time
      (setq max-obj-time vio-obj-time)
      (setq vio-is-newer t))
     (t
      (setq max-obj-time vo-obj-time)))
    ;; Decide if and what to compile.
    (if (or (eq dep-time 'just-compiled) ; a dep has been just compiled
	    (and (not vo-obj-time) (not vio-obj-time)) ; no obj exists
	    ;; src younger than any obj?
	    (time-less-or-equal max-obj-time src-time)
	    ;; dep younger than any obj?
	    (time-less-or-equal max-obj-time dep-time))
	;; compilation is definitely needed
	(progn
	  (setq result t)
	  (if (coq-compile-prefer-quick)
	      (progn
		(put job 'required-obj-file vio-file)
		(put job 'use-quick 'vio)
		(when vo-obj-time
		  (setq file-to-delete vo-file))
		(when (eq coq-compile-quick 'quick-and-vio2vo)
		  (put job 'vio2vo-needed t)))
	    (put job 'required-obj-file vo-file)
	    (when vio-obj-time
	      (setq file-to-delete vio-file)))
	  (when coq--debug-auto-compilation
	    (message
	     (concat "%s: definitely need to compile to %s; delete %s")
	     (get job 'name)
	     (get job 'required-obj-file)
	     (if file-to-delete file-to-delete "noting"))))
      ;; Either the .vio or the .vo file exists and one of .vio or .vo is
      ;; younger than the source and the youngest dependency. Might not
      ;; need to compile.
      (if (eq coq-compile-quick 'ensure-vo)
	  (progn
	    (put job 'required-obj-file vo-file)
	    (if (or (not vio-is-newer) ; vo is newest
		    (and vo-obj-time   ; vo is older than vio
			               ; but still newer than src or dep
			 (time-less-p src-time vo-obj-time)
			 (time-less-p dep-time vo-obj-time)))
		;; .vo is newer than src and youngest dep - don't compile
		(progn
		  (put job 'obj-mod-time vo-obj-time)
		  ;; delete vio if it is outdated or newer than vo
		  (when (and vio-obj-time
			     (or vio-is-newer
				 (time-less-or-equal vio-obj-time src-time)
				 (time-less-or-equal vio-obj-time dep-time)))
		    (setq file-to-delete vio-file))
		  (when coq--debug-auto-compilation
		    (message "%s: vo up-to-date 1; delete %s"
			     (get job 'name)
			     (if file-to-delete file-to-delete "noting"))))
	      ;; .vo outdated - need to compile
	      (setq result t)
	      ;; delete vio if it is outdated
	      (when (and vio-obj-time
			 (or (time-less-or-equal vio-obj-time src-time)
			     (time-less-or-equal vio-obj-time dep-time)))
		(setq file-to-delete vio-file))
	      (when coq--debug-auto-compilation
		(message "%s: need to compile to vo; delete %s"
			 (get job 'name)
			 (if file-to-delete file-to-delete "noting")))))
	;; There is an up-to-date .vio or .vo file and the user does not
	;; insist on either .vio or .vo - no need to compile.
	;; Ensure to delete outdated .vio or .vo files.
	;; First store the other obj file in other-file and other-obj-time.
	(if vio-is-newer
	    (setq other-file vo-file
		  other-obj-time vo-obj-time)
	  (setq other-file vio-file
		other-obj-time vio-obj-time))
	(if (and other-obj-time
		 (time-less-p src-time other-obj-time)
		 ;; dep-time is neither nil nor 'just-compiled here
		 (time-less-p dep-time other-obj-time))
	    ;; Both the .vio and .vo exist and are up-to-date. Coq
	    ;; loads the younger one but we continue with the older
	    ;; one to avoid recompilation for the case where a vio2vo
	    ;; process took a long time for a dependency.
	    (progn
	      (put job 'required-obj-file other-file)
	      (put job 'obj-mod-time other-obj-time)
	      (when coq--debug-auto-compilation
		(message (concat "%s: .vio and .vo up-to-date, "
				 "continue with the older %s")
			 (get job 'name)
			 (if vio-is-newer ".vio" ".vo"))))
	  ;; The other obj file does not exist or is outdated.
	  ;; Delete the outdated if it exists.
	  (when other-obj-time
	    (setq file-to-delete other-file))
	  (if vio-is-newer
	      (progn
		(put job 'required-obj-file vio-file)
		(put job 'obj-mod-time vio-obj-time)
		(when (eq coq-compile-quick 'quick-and-vio2vo)
		  (put job 'vio2vo-needed t))
		(when coq--debug-auto-compilation
		  (message "%s: vio up-to-date; delete %s"
			   (get job 'name)
			   (if file-to-delete file-to-delete "noting"))))
	    (put job 'required-obj-file vo-file)
	    (put job 'obj-mod-time vo-obj-time)
	    (when coq--debug-auto-compilation
	      (message "%s: vo up-to-date 2; delete %s"
		       (get job 'name)
		       (if file-to-delete file-to-delete "noting")))))))
    (when file-to-delete
      (condition-case err
	  (delete-file file-to-delete)
	(file-error
	 (signal 'coq-compile-error-rm err))))
    result))

(defun coq-par-job-needs-compilation-vos (job)
  "Determine whether JOB needs to get compiled.
This function decides whether JOB needs to get compiled for coq
>= 8.11 and whether a .vo or a .vos should be produced. For the
latter, `coq-compile-vos' is consulted and, if that is `nil',
coq-compile-quick, see `coq-compile-prefer-vos'. This function
assumes that coq is used consistently and that a .vo file cannot
be present without a .vos file that has the same time stamp or
has been created more recently. As result, this function sets the
property 'use-quick to `vos' if JOB should be compiled with -vos.
If compilation is needed, 'required-obj-file is set.
If no compilation is needed, 'obj-mod-time is set to the time stamp of
the .vos or .vo file, depending on `coq-compile-prefer-vos'."
  (let* ((vo-file (get job 'vo-file))
         (vos-file (coq-library-vos-of-vo-file vo-file))
         (dep-time (get job 'youngest-coqc-dependency))
	 (src-time (nth 5 (file-attributes (get job 'src-file))))
         (vos-obj-time (nth 5 (file-attributes vos-file)))
         result)
    (when coq--debug-auto-compilation
      (message "%s: compare mod times: vos mod %s, src mod %s, youngest dep %s"
               (get job 'name)
               (if vos-obj-time (current-time-string vos-obj-time) "-")
               (if src-time (current-time-string src-time) "-")
               (if (eq dep-time 'just-compiled) "just compiled"
	         (current-time-string dep-time))))
    (if (or (eq dep-time 'just-compiled) ; a dep has been just compiled
            (not vos-obj-time)           ; neither vos nor vo present
	    ;; src younger than vos?
	    (time-less-or-equal vos-obj-time src-time)
	    ;; dep younger than vos?
	    (time-less-or-equal vos-obj-time dep-time))
	;; compilation needed
        (if (coq-compile-prefer-vos)
            (progn
    	      (put job 'required-obj-file vos-file)
	      (put job 'use-quick 'vos)
              (setq result t))
          (put job 'required-obj-file vo-file)
          (setq result t))
      ;; maybe need to compile if vo is required
      (if (coq-compile-prefer-vos)
          ;; vo not required and vos is fine - no compilation
          (put job 'obj-mod-time vos-obj-time)
        ;; vo required, may need to compile
        (let ((vo-obj-time (nth 5 (file-attributes vo-file))))
          (when coq--debug-auto-compilation
            (message "%s: ensure-vo: vo mod %s"
                     (get job 'name)
                     (if vo-obj-time (current-time-string vo-obj-time) "-")))
          (if (or (not vo-obj-time)     ; vo not present
	          ;; src younger than vo?
	          (time-less-or-equal vo-obj-time src-time)
	          ;; dep younger than vo?
	          (time-less-or-equal vo-obj-time dep-time))
	      ;; compilation needed
              (progn
                (put job 'required-obj-file vo-file)
                (setq result t))
            ;; vo is fine - no compilation
            (put job 'obj-mod-time vo-obj-time)))))
    result))


(defun coq-par-job-needs-compilation (job)
  "Determine if JOB nees to get compiled and possibly do some side effects.
This function calls `coq-par-job-needs-compilation-vos for coq >=
8.11 and `coq-par-job-needs-compilation-quick' otherwise. Returns
t if a compilation is required and sets the 'use-quick property
depending on wheter -quick/-vio or -vos should be used.
If compilation is needed, 'required-obj-file is set.  Property
'obj-mod-time is set when no compilation is needed."
  (if (coq--post-v811)
      (coq-par-job-needs-compilation-vos job)
    (coq-par-job-needs-compilation-quick job)))

(defun coq-par-retire-top-level-job (job)
  "Register ancestors and start queue items.
JOB must be a successful require job.

This function performs the essential tasks for successful require
jobs when they transition from 'waiting-queue to 'ready:
- Registering ancestors in the span and recording this fact in
  the 'lock-state property.
- Moving queue items back to `proof-action-list' and start their
  execution.
- Insert `coq-par-require-processed' as callback if this is the
  last top-level job, such that vio2vo compilation will start
  eventually."
  (cl-assert (and (not (get job 'failed)) (eq (get job 'type) 'require))
	  nil "coq-par-retire-top-level-job precondition failed")
  (let ((span (get job 'require-span))
	(items (get job 'queueitems)))
    (when coq-lock-ancestors
      (maphash
       (lambda (anc-job not-used)
         (cl-assert (not (eq (get anc-job 'lock-state) 'unlocked))
                    nil "bad ancestor lock state")
         (when (eq (get anc-job 'lock-state) 'locked)
           (put anc-job 'lock-state 'asserted)
           (push (get anc-job 'src-file)
                 (span-property span 'coq-locked-ancestors))))
       (get job 'ancestors)))
    ;; XXX each require job must have items, right?
    (when items
      (when (and (not (coq--post-v811))
                 (eq coq-compile-quick 'quick-and-vio2vo)
		 (eq coq--last-compilation-job job))
	(let ((vio2vo-counter
	       (setq coq--compile-vio2vo-start-id
		     (1+ coq--compile-vio2vo-start-id))))
	  ;; Insert a notification callback for when the last require
	  ;; queue item has been processed.
	  (setq items
		(cons
		 (car items)		; this is the require
		 (cons
		  (coq-par-callback-queue-item
		   `(lambda (span) (coq-par-require-processed ,vio2vo-counter)))
		  (cdr items))))))
      (proof-add-to-queue items 'advancing)
      (when coq--debug-auto-compilation
	(message "%s: add %s items to action list"
		 (get job 'name) (length items)))
      ;; this function should only be called once for each require job
      ;; resetting queueitems is on the save side in any case
      (put job 'queueitems nil))))

(defun coq-par-kickoff-queue-maybe (job)
  "Transition require job JOB to 'waiting-queue and maybe to 'ready.
This function can only be called for require jobs. It further
must not be called if JOB is in state 'enqueued-coqdep or in
state 'waiting-dep with some not yet finished dependencies. This
function is called when all dependencies of JOB are ready to put
JOB into state 'waiting-dep. When in state 'waiting-dep, this
function is also called, when the queue dependency of JOB has
transitioned to 'ready (inside this function).

First JOB is put into state 'waiting-dep. If there is still a
queue dependency, nothing else happens and JOB waits until the
queue dependee calls this function again when it is ready.

If there is no queue dependency, then require job JOB must be
retired and transition to 'ready. This means:
- for successful require jobs, ancestors are registered in the
  'queue-span and marked as 'asserted in their 'lock-state
  property
- processing of items in 'queueitems is started (if JOB is successful)
- a possible queue dependant gets it's dependency cleared, and,
  if possible the 'waiting-queue -> 'ready transition
  is (recursively) done for the dependant
- if this job is the last top-level compilation
  job (`coq--last-compilation-job') then the last compilation job
  and `proof-second-action-list-active' are cleared and vio2vo
  processing is triggered.
- If compilation failed, the (failing) last top-level job is
  delayed until `proof-action-list' is empty, possibly by
  registering this call as a callback in an empty
  proof-action-list item. When proof-action-list is empty, the
  queue span is deleted, remaining spans are cleared and the
  `proof-shell-busy' lock is freed."
  (cl-assert (and (eq (get job 'type) 'require)
                  (or (eq (get job 'state) 'waiting-queue)
                      (and (eq (get job 'state) 'waiting-dep)
                           (coq-par-dependencies-ready job))))
             nil "coq-par-kickoff-queue-maybe precondition failed")
  (put job 'state 'waiting-queue)
  (if (get job 'queue-dependant-waiting)
      (when coq--debug-auto-compilation
        (message "%s: no queue kickoff because waiting for queue dependency"
                 (get job 'name)))
    ;; first require job in the queue of require jobs
    (when coq--debug-auto-compilation
      (message "%s: has itself no queue dependency" (get job 'name)))
    (unless (get job 'failed)
      (coq-par-retire-top-level-job job))
    (when (get job 'failed)
      ;; Reset coq--par-delayed-last-job for the case that this
      ;; function was called from a callback in proof-action-list. If
      ;; called from elsewhere, this does not harm.
      (setq coq--par-delayed-last-job nil))
    (if (and (get job 'failed)
	     (eq coq--last-compilation-job job)
	     proof-action-list)
	(progn
	  (when coq--debug-auto-compilation
	    (message "%s: delay queue kickoff until action list is empty"
		     (get job 'name)))
	  (setq coq--par-delayed-last-job t)
	  (proof-add-to-queue
	   (list (coq-par-callback-queue-item
		  `(lambda (span) (coq-par-kickoff-queue-maybe ',job))))
	   'advancing))
      (put job 'state 'ready)
      (when coq--debug-auto-compilation
	(message "%s: ready" (get job 'name)))
      (let ((dependant (get job 'queue-dependant)))
	(if dependant
	    (progn
	      (cl-assert (not (eq coq--last-compilation-job job))
		      nil "coq--last-compilation-job invariant error")
	      (put dependant 'queue-dependant-waiting nil)
              ;; dependant might still wait for dependencies or even
              ;; for coqdep to finish
              (if (eq (get dependant 'state) 'waiting-queue)
                  (progn
                    (when coq--debug-auto-compilation
                      (message
                       "%s -> %s: clear queue dependency, kickoff queue at %s"
                       (get job 'name) (get dependant 'name)
                       (get dependant 'name)))
                    (coq-par-kickoff-queue-maybe dependant)
                    (when coq--debug-auto-compilation
                      (message "%s: queue kickoff finished"
                               (get job 'name))))
                (when coq--debug-auto-compilation
                  (message
                   "%s -> %s: clear queue dependency, no queue kickoff for %s"
                   (get job 'name) (get dependant 'name)
                   (get dependant 'name)))))
          ;; XXX no dependant - this must be the last require job
	  (when (eq coq--last-compilation-job job)
	    (when (get job 'failed)
	      ;; proof-action-list is empty, see above
	      ;; variables that hold the queue span are buffer local
	      (with-current-buffer (or proof-script-buffer (current-buffer))
		(proof-script-clear-queue-spans-on-error nil))
	      (proof-release-lock)
	      (when (and (not (coq--post-v811))
                         (eq coq-compile-quick 'quick-and-vio2vo))
		(cl-assert (not coq--compile-vio2vo-delay-timer)
			nil "vio2vo timer set before last compilation job")
		(setq coq--compile-vio2vo-delay-timer
		      (run-at-time coq-compile-vio2vo-delay nil
				   'coq-par-run-vio2vo-queue))))
	    (setq coq--last-compilation-job nil)
	    (setq proof-second-action-list-active nil)
	    (when coq--debug-auto-compilation
	      (message "clear last compilation job"))
	    (message "Library compilation %s"
		     (if (get job 'failed) "failed" "finished successfully")))
	  (when coq--debug-auto-compilation
	    (message "%s: no queue dependant, queue kickoff finished"
		     (get job 'name))))))))

(defun coq-par-compile-job-maybe (job)
  "Compile JOB after dependencies are ready or start next transitions.
This function can only be called for 'file jobs. It must also be
called for failed jobs to finish all necessary transitions.
First JOB is put into state 'enqueued-coqc.  Then it is determined
if JOB needs compilation, what file must be produced (depending
on `coq-compile-quick') and if a .vio or .vo file must be
deleted.  If necessary, deletion happens immediately.  If JOB needs
compilation, compilation is started or the JOB is enqueued and
JOB stays in 'enqueued-coqc for the time being.  Otherwise, the
transition 'enqueued-coqc -> 'ready is triggered."
  (cl-assert (eq (get job 'type) 'file)
	  nil "wrong job type in coq-par-compile-job-maybe")
  (put job 'state 'enqueued-coqc)
  ;; Note that coq-par-job-needs-compilation sets 'required-obj-file
  ;; if compilation is needed (but it might also get set if no
  ;; compilation is needed). For Coq < 8.11 .vo or .vio files that are
  ;; in the way are deleted. It also sets the 'vio2vo-needed property
  ;; if needed.
  (if (and (not (get job 'failed)) (coq-par-job-needs-compilation job))
      (coq-par-start-or-enqueue job)
    (when coq--debug-auto-compilation
      (message "%s: %s, no compilation"
	       (get job 'name)
	       (if (get job 'failed) "failed" "up-to-date")))
    (when (get job 'vio2vo-needed)
      (coq-par-vio2vo-enqueue job))
    (coq-par-kickoff-coqc-dependants job nil)))

(defun coq-par-decrease-coqc-dependency (dependant dependee-time
						   dependee-anc-hash)
  "Clear Coq dependency and update dependee information in DEPENDANT.
This function handles a Coq dependency from child dependee to
parent dependant when the dependee has finished compilation (ie.
is in state 'ready).  DEPENDANT must be in state
'waiting-dep.  The time of the most recent ancestor is updated, if
necessary using DEPENDEE-TIME.  DEPENDEE-TIME must be an Emacs
time or 'just-compiled.  The ancestors of dependee in hash
DEPENDEE-ANC-HASH are propagated to DEPENDANT.  The dependency
count of DEPENDANT is decreased and, if it reaches 0, the next
transition is triggered for DEPENDANT.  For 'file jobs this is
'waiting-dep -> 'enqueued-coqc and for 'require jobs this is
'waiting-dep -> 'waiting-queue.

This function must be called for failed jobs to complete all
necessary transitions."

  ;(message "%s: CPDCD with time %s" (get dependant 'name) dependee-time)
  (cl-assert (eq (get dependant 'state) 'waiting-dep)
	  nil "wrong state of parent dependant job")
  (when (coq-par-time-less (get dependant 'youngest-coqc-dependency)
			   dependee-time)
    (put dependant 'youngest-coqc-dependency dependee-time))
  (merge-hash-content (get dependant 'ancestors) dependee-anc-hash)
  (put dependant 'coqc-dependency-count
       (1- (get dependant 'coqc-dependency-count)))
  (cl-assert (<= 0 (get dependant 'coqc-dependency-count))
	  nil "dependency count below zero")
  (when coq--debug-auto-compilation
    (message "%s: coqc dependency count down to %d"
	     (get dependant 'name) (get dependant 'coqc-dependency-count)))
  (when (coq-par-dependencies-ready dependant)
    (cond
     ;;; XXX rewrite with if
     ((eq (get dependant 'type) 'file)
      (coq-par-compile-job-maybe dependant))
     ((eq (get dependant 'type) 'require)
      (coq-par-kickoff-queue-maybe dependant)))))

(defun coq-par-kickoff-coqc-dependants (job just-compiled)
  "Handle transition to state 'ready for file job JOB.
This function can only be called for file jobs and it must also
be called for failed jobs to complete all necessary transitions.
This function is called after compilation has been finished (with
JUST-COMPILED being t) or after determining that compilation was
not necessary or failed (with JUST-COMPILED being nil). This
function sets 'youngest-coqc-dependency to the maximal (youngest)
time stamp of the vo file for this job and all its ancestors.
This function also decreases the dependency counter on all
dependants, propagates 'youngest-coqc-dependency and the
ancestors and starts any necessary state transitions on the
dependants. Finally, if this job has not failed, but all
dependants are marked as failed already, then the ancestors are
unlocked as necessary.

For the case that JUST-COMPILED is nil and that JOB has not
failed, this function relies on 'obj-mod-time has been set
before."
  (cl-assert (not (eq (get job 'type) 'require))
             nil "kickoff-coqc-dependants called for require job")
  ;; most actions are not relevant for failed jobs, but do not harm
  (let ((ancestor-hash (get job 'ancestors))
	(dependant-alive nil)
        ;; take max (youngest) time of this job and all ancestors
        ;;
        ;; If this job has just been compiled then it is clearly
        ;; 'just-compiled. Otherwise it must be 'obj-mod-time, because
        ;; if some ancestore were newer, this just would have been
        ;; compiled. For failed jobs obj-mod-time might be nil, but
        ;; this does not matter.
        (dep-time (if just-compiled 'just-compiled
                    (get job 'obj-mod-time))))
    (put job 'youngest-coqc-dependency dep-time)
    (when coq--debug-auto-compilation
      (message "%s: kickoff %d coqc dependencies with time %s"
	       (get job 'name) (length (get job 'coqc-dependants))
	       (if (eq dep-time 'just-compiled)
		   'just-compiled
		 (current-time-string dep-time))))
    ;; In the recursion coq-par-kickoff-coqc-dependants ->
    ;; coq-par-decrease-coqc-dependency -> coq-par-compile-job-maybe
    ;; -> coq-par-kickoff-coqc-dependants jobs on the path upwards
    ;; must be in state 'ready, otherwise coq-par-ongoing-compilation
    ;; might take one of those as witness for an ongoing compilation.
    (put job 'state 'ready)
    (dolist (dependant (get job 'coqc-dependants))
      (coq-par-decrease-coqc-dependency dependant dep-time ancestor-hash)
      (unless (get dependant 'failed)
	(setq dependant-alive t)))
    (when coq--debug-auto-compilation
      (message (concat "%s: coqc kickoff finished, %s dependant alive")
	       (get job 'name)
	       (if dependant-alive "some" "no")))
    (when (and (not dependant-alive)
               (not (get job 'failed)))
      ;; job has not failed (see first assert), but all dependants
      ;; have 'failed set
      (coq-par-unlock-job-ancestors-on-error job))))

(defun coq-par-start-coqdep-on-require (job)
  "Start coqdep for require job JOB.
Write the require statement in JOB into a temporary file and
start coqdep on it. 

This function may be called asynchronously, if the require job
was queued."
  ;; get coq-load-path from job
  ;; check that this really includes the current dir in the arguments
  (let ((load-path
         ;; For coq < 8.5 coqdep needs the current working directory
         ;; in the load path. This differs from the directory containing
         ;; 'temp-require-file. Therefore we add it here and tweek
         ;; coq-load-path-include-current such that coq-coqdep-prog-args
         ;; does not add the directory containing 'temp-require-file to
         ;; load-path.
         (if (and coq-load-path-include-current (coq--pre-v85))
             (cons (get job 'current-dir) (get job 'load-path))
           (get job 'load-path)))
        (coq-load-path-include-current nil)
        (require-command
         (mapconcat 'identity (nth 1 (car (get job 'queueitems))) " ")))
    (put job 'temp-require-file
         (make-temp-file "ProofGeneral-coq" nil ".v" require-command))
    (when coq--debug-auto-compilation
      (message "%s: start coqdep for require job for file %s"
	       (get job 'name)
	       (get job 'temp-require-file)))
    (coq-par-start-process
     coq-dependency-analyzer
     (coq-par-coqdep-arguments (get job 'temp-require-file) load-path)
     'coq-par-process-coqdep-result
     job
     (get job 'temp-require-file))))

(defun coq-par-start-coqdep-on-file (job)
  "Start coqdep for file job JOB.
Lock the source file and start the coqdep background process."
  (when (and coq-lock-ancestors
             ;; the lock state property is initialized from all as
             ;; locked registered files in `proof-included-files-list'
	     (eq (get job 'lock-state) 'unlocked))
    (proof-register-possibly-new-processed-file (get job 'src-file))
    (puthash job t (get job 'ancestors))
    (put job 'lock-state 'locked))
  (coq-par-start-process
   coq-dependency-analyzer
   (coq-par-coqdep-arguments (get job 'src-file) (get job 'load-path))
   'coq-par-process-coqdep-result
   job
   nil))

(defun coq-par-start-coqc (job)
  "Start coqc background compilation for JOB.
Depending on property 'use-quick, vos or quick compilation may be
used."
  (message "Recompile %s%s"
           (cond
            ((eq (get job 'use-quick) 'vos) "-vos ")
            ((eq (get job 'use-quick) 'vio) "-quick ")
            (t ""))
           (get job 'src-file))
  (let ((arguments
         (coq-par-coqc-arguments (get job 'src-file) (get job 'load-path))))
    (cond
     ((eq (get job 'use-quick) 'vos) (push "-vos" arguments))
     ((eq (get job 'use-quick) 'vio) (push "-quick" arguments))
     (t t))
    (coq-par-start-process
     coq-compiler
     arguments
     'coq-par-coqc-continuation
     job
     (get job 'required-obj-file))))

(defun coq-par-start-vio2vo (job)
  "Start vio2vo background job."
  (let ((arguments (coq-include-options (get job 'load-path)))
	(module (coq-module-of-src-file (get job 'src-file)))
	(default-directory
	  (file-name-directory (file-truename (get job 'src-file)))))
    (when coq--debug-auto-compilation
      (message "%s: start vio2vo for %s"
	       (get job 'name)
	       (get job 'src-file)))
    (message "vio2vo %s" (get job 'src-file))
    (coq-par-start-process
     ;; in 8.9.1 and before only coqtop accepts -schedule-vio2vo
     ;; after change 103f59e only coqc accepts -schedule-vio2vo
     (if (coq--post-v810) coq-compiler coq-prog-name)
     (nconc arguments (list "-schedule-vio2vo" "1" module))
     'coq-par-vio2vo-continuation
     job
     (get job 'vo-file))))

(defun coq-par-start-task (job)
  "Start the background job for which JOB is waiting.
JOB was at the head of the compilation queue and now either
coqdep, coqc or vio2vo is started for it. This function may be called
synchronously or asynchronously."
  (let ((job-state (get job 'state)))
    (cond
     ((and (eq job-state 'enqueued-coqdep) (eq (get job 'type) 'require))
      (coq-par-start-coqdep-on-require job))
     ((eq job-state 'enqueued-coqdep)
      (coq-par-start-coqdep-on-file job))
     ((eq job-state 'enqueued-coqc)
      (coq-par-start-coqc job))
     ((eq job-state 'ready)
      (coq-par-start-vio2vo job))
     (t (cl-assert nil nil "coq-par-start-task with invalid job")))))

(defun coq-par-start-jobs-until-full ()
  "Start background jobs until the limit is reached.
This function may be called synchronously or asynchronously."
  (let ((max-jobs (if coq--compile-vio2vo-in-progress
		      coq--internal-max-vio2vo-jobs
		    coq--internal-max-jobs))
	next-job)
    (while (and (< coq--current-background-jobs max-jobs)
		(setq next-job (if coq--compile-vio2vo-in-progress
				   (coq-par-vio2vo-dequeue)
				 (coq-par-job-dequeue))))
      (coq-par-start-task next-job))))
  
(defun coq-par-start-or-enqueue (new-job)
  "Start NEW-JOB or put it into the queue of waiting jobs.
NEW-JOB goes already into the waiting queue, if the number of
background jobs is one below the limit.  This is in order to leave
room for Proof General. This function might be called
synchronously or asynchronously."
  (if (< (1+ coq--current-background-jobs) coq--internal-max-jobs)
      (coq-par-start-task new-job)
    (coq-par-job-enqueue new-job)))

(defun coq-par-job-init-common (coq-load-path type)
  "Common initialization for 'require and 'file jobs.
Create a new job of type TYPE and initialize all common fields of
require and file jobs that need an initialization different from
nil."
  (let ((new-job (make-symbol "coq-compile-job-symbol")))
    (put new-job 'name (format "job-%d" coq--par-next-id))
    (setq coq--par-next-id (1+ coq--par-next-id))
    (put new-job 'coqc-dependency-count 0)
    (put new-job 'type type)
    (put new-job 'state 'enqueued-coqdep)
    ;; The ancestor modification time is not really needed in require
    ;; jobs, however, if the field is present, we can treat require
    ;; and file jobs more uniformely.
    (put new-job 'youngest-coqc-dependency '(0 0))
    (put new-job 'ancestors (make-hash-table :size 7 :rehash-size 2.1))
    (put new-job 'load-path coq-load-path)
    new-job))

(defun coq-par-create-require-job (coq-load-path require-items require-span)
  "Create a new require job for REQUIRE-SPAN.
Create a new require job and initialize its fields. COQ-LOAD-PATH
is the load path configured for the current scripting buffer,
that is passed down to all dependencies and used in all
compilations. REQUIRE-ITEMS are the non-require commands
following the REQUIRE-SPAN, they are temporarily stored in the
new require job outside of `proof-action-list'. 

The current directory (from `default-directory') is stored in
property 'current-dir for <8.5 compatibility, where coqdep did
not search the current directory.

This function is called synchronously when asserting. The new
require job is neither started nor enqueued here - the caller
must do this."
  (let ((new-job (coq-par-job-init-common coq-load-path 'require)))
    (put new-job 'require-span require-span)
    (put new-job 'queueitems require-items)
    (put new-job 'current-dir default-directory)
    (when coq--debug-auto-compilation
      (let* ((require-item (car require-items))
             (require-command (mapconcat 'identity (nth 1 require-item) " ")))
        (message "%s: create require job for %s"
                 (get new-job 'name) require-command)))
    new-job))

;; XXX what happens when job exists but has been unlocked because
;; there was some error and it was not used anywhere back then, but
;; job is now needed as a dependency of some other file?
;; XXX what happens if the job exists and is failed?
(defun coq-par-create-file-job (module-vo-file coq-load-path dep-src-file)
  "Create a new file job for MODULE-VO-FILE.
DEP-SRC-FILE is the source file whose coqdep output we are just
processing and which depends on MODULE-VO-FILE. This argument is
only used in the error message, when MODULE-VO-FILE happens to
coincide with the current scripting buffer (which means we
detected a dependency cycle).

If there is a file job for MODULE-VO-FILE, just return this.
Otherwise, create a new file job and initialize its fields. In
particular, initialize its 'lock-state property from the set of
as locked registered files in `proof-included-files-list'.

If a new job is created it is started or enqueued right away."
  (cond
   ((gethash module-vo-file coq--compilation-object-hash))
   (t
    (let ((new-job (coq-par-job-init-common coq-load-path 'file)))
      ;; fields 'required-obj-file and obj-mod-time are implicitely set to nil
      (put new-job 'vo-file module-vo-file)
      (put new-job 'src-file (coq-library-src-of-vo-file module-vo-file))
      (when (equal (get new-job 'src-file)
		   (buffer-file-name proof-script-buffer))
        ;; test this error case - maybe need more files participating
        ;; in the circle?
	(signal 'coq-compile-error-circular-dep
		(concat dep-src-file " -> scripting buffer")))
      (puthash module-vo-file new-job coq--compilation-object-hash)
      (when coq--debug-auto-compilation
	(message "%s: create %s compilation for %s"
		 (get new-job 'name) (get new-job 'type) module-vo-file))
      ;; if the user single-steps through multiple requires, then the
      ;; compilation for the previous require might have been finished
      ;; and cleared, then we might have visited and locked this file
      ;; already
      (if (member (file-truename (get new-job 'src-file))
		  proof-included-files-list)
	  (put new-job 'lock-state 'asserted)
	(put new-job 'lock-state 'unlocked))
      (message "Check %s" (get new-job 'src-file))
      (coq-par-start-or-enqueue new-job)
      new-job))))

(defun coq-par-ongoing-compilation (job)
  "Determine if the source file for JOB needs to stay looked.
Return t if job has a direct or indirect dependant that has not
failed yet and that is in a state before 'ready. Also,
return t if JOB has a dependant that is a top-level job which has
not yet failed."
  ;; This function is called on jobs with 'lock-state 'locked. A job
  ;; that is 'asserted has all its ancestors 'asserted as well.
  ;; Therefore all direct and indirect dependants of job (i.e.,
  ;; everything above) cannot be 'asserted. In a stable state all
  ;; dependants must be 'locked. But when this function is called,
  ;; ancestors from some failing job are unlocked in no particular
  ;; order, therefore some dependant might already be 'unlocked.
  (cl-assert (not (eq (get job 'lock-state) 'asserted))
	  nil "coq-par-ongoing-compilation precondition failed")
  (cond
   ((get job 'failed)
    nil)
   ((or (eq (get job 'state) 'waiting-dep)
	(eq (get job 'state) 'enqueued-coqc)
	;; top-level job that has compilation finished but has not
	;; been asserted yet and has not been set to 'failed (see
	;; first cond check)
	(eq (get job 'state) 'waiting-queue)
	;; Note that job cannot be a top-level in state 'ready,
	;; because we started from job with 'lock-state property equal
	;; to 'locked. Top-level job in state 'ready have all
	;; dependees with 'lock-state equal to 'asserted.
	)
    t)
   ;; The following recursive clause needs to match file and require
   ;; jobs that were ready, before the current mark-failing or
   ;; unlocking-ancestors procedure started. Additionally, it also
   ;; needs to match dependants that are right now inside
   ;; coq-par-kickoff-coqc-dependants in the loop to propagate their
   ;; ancestors to their dependants. Therefore it is important that
   ;; coq-par-kickoff-coqc-dependants sets the state to 'ready quite
   ;; early.
   ((eq (get job 'state) 'ready)
    ;; internal ready job
    (let ((dependants (get job 'coqc-dependants))
	  (res nil)
	  dep)
      (while (and (not res) (setq dep (pop dependants)))
	(setq res (coq-par-ongoing-compilation dep)))
      res))
   (t
    (cl-assert nil nil
	    "impossible ancestor state %s on job %s"
	    (get job 'state) (get job 'name)))))

;; XXX check whether this needs to be called only when job is set to 'failed
;; - when job was set to failed earlier, then the ancestors should have been
;; unlocked earlier too
(defun coq-par-unlock-job-ancestors-on-error (job)
  "Unlock those ancestors of JOB that need to be unlocked.
For a failing job JOB, an ancestor needs to stay looked if there
is still some compilation going on for which this ancestor is a
dependee or if a top level job with JOB as ancestor has finished
it's compilation successfully.  In all other cases the ancestor
must be unlocked."
  (maphash
   (lambda (anc-job not-used)
     (when (and (eq (get anc-job 'lock-state) 'locked)
                (not (coq-par-ongoing-compilation anc-job)))
       (when coq--debug-auto-compilation
         (message "%s: %s unlock because no ongoing compilation"
                  (get anc-job 'name) (get anc-job 'src-file)))
       (coq-unlock-ancestor (get anc-job 'src-file))
       (put anc-job 'lock-state 'unlocked)))
   (get job 'ancestors)))

(defun coq-par-mark-queue-failing (job)
  "Mark require JOB and its queue dependants with 'failed.
Mark JOB with 'failed and unlock ancestors as appropriate.
Recurse for queue dependants."
  (unless (get job 'failed)
    (put job 'failed t)
    (cl-assert (not (eq (get job 'state) 'ready))
	    nil "coq-par-mark-queue-failing impossible state")
    (when coq--debug-auto-compilation
      (message "%s: mark as failed, %s"
	       (get job 'name)
	       (if (eq (get job 'state) 'waiting-queue)
		   "and unlock ancestors"
		 "wait")))
    (coq-par-unlock-job-ancestors-on-error job)
    (when (get job 'queue-dependant)
      (coq-par-mark-queue-failing (get job 'queue-dependant)))))

(defun coq-par-mark-job-failing (job)
  "Mark all dependants of JOB as failing and unlock ancestors as appropriate.
Set the 'failed property on all direct and indirect dependants of
JOB.  Along the way, unlock ancestors as determined by
`coq-par-ongoing-compilation'."
  (unless (get job 'failed)
    (put job 'failed t)
    (when coq--debug-auto-compilation
      (message "%s: mark as failed and unlock free ancestors" (get job 'name)))
    (coq-par-unlock-job-ancestors-on-error job)
    (dolist (dependant (get job 'coqc-dependants))
      (coq-par-mark-job-failing dependant))
    (when (get job 'queue-dependant)
      (coq-par-mark-queue-failing (get job 'queue-dependant)))))

(defun coq-par-process-coqdep-result (process exit-status)
  "Coqdep continuation function: Process coqdep output.
This function analyses the coqdep output of PROCESS.  In case of
error, the job is marked as failed or compilation is aborted via
a signal (depending on `coq-compile-keep-going').  If there was no
coqdep error, the following actions are taken.
- temp-require-file for require jobs is deleted
- the job that started PROCESS is put into sate 'waiting-dep
- a new job is created for every dependency.  If this new job is
  not immediately ready, a dependency is registered from the
  new job to the current job.  For dependencies that are 'ready
  already, the most recent ancestor modification time is
  propagated.
- if there are no dependencies (especially if coqdep failed) or
  all dependencies are ready already, the next transition is
  triggered. For file jobs the next transition goes to
  'enqueued-coqc, for require jobs it goes to 'waiting-queue.
- otherwise the current job is left alone until somebody
  decreases its dependency count to 0.

The argument EXIT-STATUS must be the exit status of PROCESS, it
is directly passed to `coq-par-analyse-coq-dep-exit'."
  (let ((job (process-get process 'coq-compilation-job))
	(dependencies-or-error
	 (coq-par-analyse-coq-dep-exit
	  exit-status
	  (process-get process 'coq-process-output)
	  (process-get process 'coq-process-command)))
	job-max-time dependee-failed)
    (if (stringp dependencies-or-error)
        (progn
          (when coq--debug-auto-compilation
            (message "%s coqdep error %s" (get job 'name) dependencies-or-error))
          (if coq-compile-keep-going
              (coq-par-mark-job-failing job)
            (signal 'coq-compile-error-coqdep (get job 'src-file))))

      ;; no coqdep error -- work on dependencies
      (when coq--debug-auto-compilation
	(message "%s: dependencies of %s are %s"
		 (get job 'name)
                 (if (eq (get job 'type) 'file)
                     (get job 'src-file)
                   (get job 'temp-require-file))
                 dependencies-or-error))
      (when (get job 'temp-require-file)
        (ignore-errors (delete-file (get job 'temp-require-file))))      
      (setq job-max-time (get job 'youngest-coqc-dependency))
      (dolist (dep-vo-file dependencies-or-error)
	(unless (coq-compile-ignore-file dep-vo-file)
	  (let* ((dep-job (coq-par-create-file-job dep-vo-file
                                                   (get job 'load-path)
                                                   (get job 'src-file)))
		 (dep-time (get dep-job 'youngest-coqc-dependency)))
            (when (get dep-job 'failed)
              (setq dependee-failed t))
            ;; XXX what happens when dep-job failed?
	    (unless (eq (get dep-job 'state) 'ready)
              ;; the following clause is not needed for require jobs,
              ;; but it doesn't harm either, so keep the code a little
              ;; bit more simple
              (when (coq-par-time-less job-max-time dep-time)
                (setq job-max-time dep-time))
	      (coq-par-add-coqc-dependency dep-job job)))))
      (put job 'youngest-coqc-dependency job-max-time)
      (when dependee-failed
        (cl-assert coq-compile-keep-going
                   nil "compilation continues without keep going")
        (coq-par-mark-job-failing job)))
    ;; common part for job where coqdep was successful and where
    ;; coqdep failed (when coq-compile-keep-going)
    (put job 'state 'waiting-dep)
    (if (coq-par-dependencies-ready job)
	(progn
	  (when coq--debug-auto-compilation
	    (message "%s: coqc dependencies finished" (get job 'name)))
          (if (eq (get job 'type) 'file)
              (coq-par-compile-job-maybe job)
            ;; require jobs
            (coq-par-kickoff-queue-maybe job)))
      (when coq--debug-auto-compilation
	(message "%s: wait for %d dependencies"
		 (get job 'name) (get job 'coqc-dependency-count))))))

(defun coq-par-coqc-continuation (process exit-status)
  "Coqc continuation function.
If coqc failed, signal an error or mark the job as 'failed, and
unlock ancestors as appropriate.  If coqc was successful, trigger
the transition 'enqueued-coqc -> 'ready for the job
behind PROCESS."
  (let ((job (process-get process 'coq-compilation-job)))
    (if (eq exit-status 0)
	(progn
	  ;; coqc success
	  (when (get job 'vio2vo-needed)
	    (coq-par-vio2vo-enqueue job))
	  (coq-par-kickoff-coqc-dependants job t))
      ;; coqc error
      (coq-compile-display-error
       (mapconcat 'identity (process-get process 'coq-process-command) " ")
       (process-get process 'coq-process-output)
       t)
      (if coq-compile-keep-going
	  (progn
	    (coq-par-mark-job-failing job)
	    (coq-par-kickoff-coqc-dependants job nil))
	(signal 'coq-compile-error-coqc
		(get (process-get process 'coq-compilation-job) 'src-file))))))

(defun coq-par-vio2vo-continuation (process exit-status)
  "Vio2vo continuation function.
Nothing to do in case of success. Otherwise display the errors."
  (let ((job (process-get process 'coq-compilation-job)))
    (if (eq exit-status 0)
	;; success - nothing to do
	(when coq--debug-auto-compilation
	  (message "%s: vio2vo finished successfully" (get job 'name)))
      (when coq--debug-auto-compilation
	(message "%s: vio2vo failed" (get job 'name)))
      (coq-compile-display-error
       (concat
	"cd "
	(file-name-directory (file-truename (get job 'src-file)))
	"; "
	(mapconcat 'identity (process-get process 'coq-process-command) " "))
       (process-get process 'coq-process-output)
       t)
      ;; don't signal an error or abort other vio2vo processes
      )))


;;; handle Require commands when queue is extended

(defun coq-par-handle-require-list (require-items)
  "Start compilation for the required modules in the car of REQUIRE-ITEMS.
REQUIRE-ITEMS is a list of queue items, eventually to be added to
`proof-action-list', that contains just one require command in
the first element. This function starts the compilation process
for all modules and their dependencies in this require command.

This function creates one require job for the require command,
maintains `coq--last-compilation-job' and adds the delete action
to delete all ancestors to the span of the require command.
Coqdep is directly started on the require job or the job is
enqueued.

This function must be evaluated with the buffer that triggered
the compilation as current, otherwise a wrong `coq-load-path'
might be used.

This function is called synchronously when asserting."
  (let ((span (caar require-items))
        new-job)
    (when coq--debug-auto-compilation
      (let* ((require-item (car require-items))
             (require-command (mapconcat 'identity (nth 1 require-item) " ")))
        (message "handle require command \"%s\"" require-command)))
    (span-add-delete-action
     span
     `(lambda ()
	(coq-unlock-all-ancestors-of-span ,span)))
    ;; create a new require job and maintain coq--last-compilation-job
    (setq new-job (coq-par-create-require-job coq-load-path require-items span))
    (when coq--last-compilation-job
      (coq-par-add-queue-dependency coq--last-compilation-job new-job))
    (setq coq--last-compilation-job new-job)
    (when coq--debug-auto-compilation
      (message "%s: this job is the last compilation job now"
               (get coq--last-compilation-job 'name)))
    (coq-par-start-or-enqueue new-job)))
    

(defun coq-par-item-require-predicate (item)
  "Return t if ITEM contains a Require command.
Predicate for `split-list-at-predicate', used to split the new
queue items at each Require command."
  (let ((string (mapconcat 'identity (nth 1 item) " ")))
    (and string
	 (string-match coq-require-command-regexp string))))


(defun coq-par-preprocess-require-commands-internal ()
  "Worker for `coq-par-preprocess-require-commands'.
This function does all the work for
`coq-par-preprocess-require-commands', except for error
reporting.

If `coq-compile-before-require' is non-nil, this function starts
the compilation (if necessary) of the dependencies
ansynchronously in parallel in the background.

If there already is a last compilation job (`coq--last-compilation-job')
then the queue region is extended, while some background
compilation is still running.  In this case I have to preserve the
internal state.  Otherwise the hash of the compilation jobs and
the ancestor hash are reinitialized.

As next action the new queue items are splitted at each Require
command.  The items before the first Require are appended to the
last compilation job or put back into ‘proof-action-list’.  The
remaining batches of items that each start with a Require are
then processed by `coq-par-handle-require-list', which creates
require jobs as necessary.  Before processing the
first of these batches, buffers are saved with
`coq-compile-save-some-buffers' and an possibly ongoing vio2vo
compilation is stopped.

Finally, `proof-second-action-list-active' is set if I keep some
queue items because they have to wait for a compilation job.  Then
the maximal number of background compilation jobs is started.
This function is called synchronously when asserting."
  (when coq--debug-auto-compilation
    (message "%d items were added to the queue, scan for require"
	     (length queueitems)))
  (unless coq--last-compilation-job
    (coq-par-init-compilation-hash)
    (coq-init-compile-response-buffer))
  (let ((splitted-items
	 (split-list-at-predicate queueitems
				  'coq-par-item-require-predicate)))
    (if coq--last-compilation-job
	(progn
	  (put coq--last-compilation-job 'queueitems
	       (nconc (get coq--last-compilation-job 'queueitems)
		      (car splitted-items)))
	  (setq queueitems nil)
	  (message "attach first %s items to job %s"
		   (length (car splitted-items))
		   (get coq--last-compilation-job 'name)))
      (setq queueitems (car splitted-items))
      (when coq--debug-auto-compilation
	(message "attach first %s items directly to queue"
		 (length (car splitted-items)))))
    ;; XXX handle external compilation here, compile everything
    ;; with one command, use compilation-finish-functions to get
    ;; notification
    (when (cdr splitted-items)
      (when coq--compile-vio2vo-delay-timer
	(cancel-timer coq--compile-vio2vo-delay-timer)
	(setq coq--compile-vio2vo-delay-timer nil))
      (when coq--compile-vio2vo-in-progress
	(cl-assert (not coq--last-compilation-job)
		nil "normal compilation and vio2vo in parallel 2")
	;; there are only vio2vo background processes
	(coq-par-kill-all-processes)
	(setq coq--compile-vio2vo-in-progress nil))
      ;; save buffers before invoking the first coqdep
      (coq-compile-save-some-buffers)
      (dolist (require-items (cdr splitted-items))
	(coq-par-handle-require-list require-items)))
    (when coq--last-compilation-job
      (setq proof-second-action-list-active t))
    (coq-par-start-jobs-until-full)
    (when coq--debug-auto-compilation
      (if coq--last-compilation-job
	  (message "return control, waiting for background jobs")
	(message "return control, no background jobs")))))

(defun coq-par-preprocess-require-commands ()
  "Coq function for `proof-shell-extend-queue-hook' doing parallel compilation.
If `coq-compile-before-require' is non-nil, this function starts
the compilation (if necessary) of the dependencies
ansynchronously in parallel in the background.  This function only
does the error checking/reporting for
`coq-par-preprocess-require-commands-internal', which does all
the work. This function is called synchronously when asserting."
  (when coq-compile-before-require
    (condition-case err
	(coq-par-preprocess-require-commands-internal)
      (coq-compile-error
       (coq-par-emergency-cleanup)
       (message "%s %s" (get (car err) 'error-message) (cdr err)))
      (coq-unclassifiable-version
       (coq-par-emergency-cleanup)
       (if (equal (cdr err) "trunk")
	   (message
	    (concat "your Coq version \"trunk\" is too unspecific for "
		    "Proof General; please customize coq-pinned-version"))
	 (message "%s \"%s\"; consider customizing coq-pinned-version"
		  (get (car err) 'error-message) (cdr err))))
      (file-error
       (coq-par-emergency-cleanup)
       (message "Error: %s" (mapconcat 'identity (cdr err) ": ")))
      (error
       (message "Unexpected error during parallel compilation: %s"
		err)
       (coq-par-emergency-cleanup)
       (signal (car err) (cdr err))))))


(provide 'coq-par-compile)


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;;; coq-par-compile.el ends here