aboutsummaryrefslogtreecommitdiffhomepage
path: root/plugins/micromega/persistent_cache.ml
blob: 387a5251417c62fbabcb08e2f1a70c1a06049e5c (plain)
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
(************************************************************************)
(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
(* <O___,, *   INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2017     *)
(*   \VV/  **************************************************************)
(*    //   *      This file is distributed under the terms of the       *)
(*         *       GNU Lesser General Public License Version 2.1        *)
(************************************************************************)
(*                                                                      *)
(*  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: *)