1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
|
(************************************************************************)
(* * The Coq Proof Assistant / The Coq Development Team *)
(* v * Copyright INRIA, CNRS and contributors *)
(* <O___,, * (see version control and CREDITS file for authors & dates) *)
(* \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}
(* XXX: Move to Fun.protect once in Ocaml 4.08 *)
let fun_protect ~(finally : unit -> unit) work =
let finally_no_exn () =
let exception Finally_raised of exn in
try finally ()
with e ->
let bt = Printexc.get_raw_backtrace () in
Printexc.raise_with_backtrace (Finally_raised e) bt
in
match work () with
| result -> finally_no_exn (); result
| exception work_exn ->
let work_bt = Printexc.get_raw_backtrace () in
finally_no_exn ();
Printexc.raise_with_backtrace work_exn work_bt
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
let () =
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 ?
*)
()
in
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 fun_protect f ~finally:(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: *)
|
