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|
(************************************************************************)
(* * The Coq Proof Assistant / The Coq Development Team *)
(* v * INRIA, CNRS and contributors - Copyright 1999-2019 *)
(* <O___,, * (see CREDITS file for the list of authors) *)
(* \VV/ **************************************************************)
(* // * This file is distributed under the terms of the *)
(* * GNU Lesser General Public License Version 2.1 *)
(* * (see LICENSE file for the text of the license) *)
(************************************************************************)
(* *)
(* A persistent hashtable *)
(* *)
(* Frédéric Besson (Inria Rennes) 2009-2014 *)
(* *)
(************************************************************************)
module type PHashtable = sig
(* see documentation in [persistent_cache.mli] *)
type 'a t
type key
val open_in : string -> 'a t
val find : 'a t -> key -> 'a
val add : 'a t -> key -> 'a -> unit
val memo : string -> (key -> 'a) -> key -> 'a
val memo_cond : string -> (key -> bool) -> (key -> 'a) -> key -> 'a
end
open Hashtbl
module PHashtable (Key : HashedType) : PHashtable with type key = Key.t = struct
open Unix
type key = Key.t
module Table = Hashtbl.Make (Key)
exception InvalidTableFormat
exception UnboundTable
type mode = Closed | Open
type 'a t = {outch : out_channel; mutable status : mode; htbl : 'a Table.t}
let finally f rst =
try
let res = f () in
rst (); res
with reraise ->
(try rst () with any -> raise reraise);
raise reraise
let read_key_elem inch =
try Some (Marshal.from_channel inch) with
| End_of_file -> None
| e when CErrors.noncritical e -> raise InvalidTableFormat
(**
We used to only lock/unlock regions.
Is-it more robust/portable to lock/unlock a fixed region e.g. [0;1]?
In case of locking failure, the cache is not used.
**)
type lock_kind = Read | Write
let lock kd fd =
let pos = lseek fd 0 SEEK_CUR in
let success =
try
ignore (lseek fd 0 SEEK_SET);
let lk = match kd with Read -> F_RLOCK | Write -> F_LOCK in
lockf fd lk 1; true
with Unix.Unix_error (_, _, _) -> false
in
ignore (lseek fd pos SEEK_SET);
success
let unlock fd =
let pos = lseek fd 0 SEEK_CUR in
try
ignore (lseek fd 0 SEEK_SET);
lockf fd F_ULOCK 1
with Unix.Unix_error (_, _, _) ->
()
(* Here, this is really bad news --
there is a pending lock which could cause a deadlock.
Should it be an anomaly or produce a warning ?
*);
ignore (lseek fd pos SEEK_SET)
(* We make the assumption that an acquired lock can always be released *)
let do_under_lock kd fd f =
if lock kd fd then finally f (fun () -> unlock fd) else f ()
let open_in f =
let flags = [O_RDONLY; O_CREAT] in
let finch = openfile f flags 0o666 in
let inch = in_channel_of_descr finch in
let htbl = Table.create 100 in
let rec xload () =
match read_key_elem inch with
| None -> ()
| Some (key, elem) -> Table.add htbl key elem; xload ()
in
try
(* Locking of the (whole) file while reading *)
do_under_lock Read finch xload;
close_in_noerr inch;
{ outch =
out_channel_of_descr (openfile f [O_WRONLY; O_APPEND; O_CREAT] 0o666)
; status = Open
; htbl }
with InvalidTableFormat ->
(* The file is corrupted *)
close_in_noerr inch;
let flags = [O_WRONLY; O_TRUNC; O_CREAT] in
let out = openfile f flags 0o666 in
let outch = out_channel_of_descr out in
do_under_lock Write out (fun () ->
Table.iter
(fun k e -> Marshal.to_channel outch (k, e) [Marshal.No_sharing])
htbl;
flush outch);
{outch; status = Open; htbl}
let add t k e =
let {outch; status; htbl = tbl} = t in
if status == Closed then raise UnboundTable
else
let fd = descr_of_out_channel outch in
Table.add tbl k e;
do_under_lock Write fd (fun _ ->
Marshal.to_channel outch (k, e) [Marshal.No_sharing];
flush outch)
let find t k =
let {outch; status; htbl = tbl} = t in
if status == Closed then raise UnboundTable
else
let res = Table.find tbl k in
res
let memo cache f =
let tbl = lazy (try Some (open_in cache) with _ -> None) in
fun x ->
match Lazy.force tbl with
| None -> f x
| Some tbl -> (
try find tbl x
with Not_found ->
let res = f x in
add tbl x res; res )
let memo_cond cache cond f =
let tbl = lazy (try Some (open_in cache) with _ -> None) in
fun x ->
match Lazy.force tbl with
| None -> f x
| Some tbl ->
if cond x then begin
try find tbl x
with Not_found ->
let res = f x in
add tbl x res; res
end
else f x
end
(* Local Variables: *)
(* coding: utf-8 *)
(* End: *)
|
