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
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
|
(************************************************************************)
(* * The Coq Proof Assistant / The Coq Development Team *)
(* v * INRIA, CNRS and contributors - Copyright 1999-2018 *)
(* <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
type 'a t
type key
val create : int -> string -> 'a t
(** [create i f] creates an empty persistent table
with initial size i associated with file [f] *)
val open_in : string -> 'a t
(** [open_in f] rebuilds a table from the records stored in file [f].
As marshaling is not type-safe, it migth segault.
*)
val find : 'a t -> key -> 'a
(** find has the specification of Hashtable.find *)
val add : 'a t -> key -> 'a -> unit
(** [add tbl key elem] adds the binding [key] [elem] to the table [tbl].
(and writes the binding to the file associated with [tbl].)
If [key] is already bound, raises KeyAlreadyBound *)
val close : 'a t -> unit
(** [close tbl] is closing the table.
Once closed, a table cannot be used.
i.e, find,add will raise UnboundTable *)
val memo : string -> (key -> 'a) -> (key -> 'a)
(** [memo cache f] returns a memo function for [f] using file [cache] as persistent table.
Note that the cache will only be loaded when the function is used for the first time *)
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 create i f =
let flags = [O_WRONLY; O_TRUNC;O_CREAT] in
{
outch = out_channel_of_descr (openfile f flags 0o666);
status = Open ;
htbl = Table.create i
}
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.replace 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 = htbl
}
with InvalidTableFormat ->
(* The file is corrupted *)
begin
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 = outch ;
status = Open ;
htbl = htbl
}
end
let close t =
let {outch = outch ; status = status ; htbl = tbl} = t in
match t.status with
| Closed -> () (* don't do it twice *)
| Open ->
close_out outch ;
Table.clear tbl ;
t.status <- Closed
let add t k e =
let {outch = outch ; status = status ; htbl = tbl} = t in
if status == Closed
then raise UnboundTable
else
let fd = descr_of_out_channel outch in
begin
Table.replace tbl k e ;
do_under_lock Write fd
(fun _ ->
Marshal.to_channel outch (k,e) [Marshal.No_sharing] ;
flush outch
)
end
let find t k =
let {outch = outch ; status = 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
end
(* Local Variables: *)
(* coding: utf-8 *)
(* End: *)
|
