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|
(************************************************************************)
(* v * The Coq Proof Assistant / The Coq Development Team *)
(* <O___,, * INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2012 *)
(* \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) 2009-2011 *)
(* *)
(************************************************************************)
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 x ->
(try rst ()
with _ -> raise x
); raise x
let read_key_elem inch =
try
Some (Marshal.from_channel inch)
with
| End_of_file -> None
| _ -> raise InvalidTableFormat
(** In win32, it seems that we should unlock the exact zone
that has been locked, and not the whole file *)
let locked_start = ref 0
let lock fd =
locked_start := lseek fd 0 SEEK_CUR;
lockf fd F_LOCK 0
let rlock fd =
locked_start := lseek fd 0 SEEK_CUR;
lockf fd F_RLOCK 0
let unlock fd =
let pos = lseek fd 0 SEEK_CUR in
ignore (lseek fd !locked_start SEEK_SET);
lockf fd F_ULOCK 0;
ignore (lseek fd pos SEEK_SET)
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 *)
rlock finch;
finally
(fun () -> xload () )
(fun () ->
unlock finch ;
close_in_noerr inch ;
) ;
{
outch = out_channel_of_descr (openfile f [O_WRONLY;O_APPEND;O_CREAT] 0o666) ;
status = Open ;
htbl = htbl
}
with InvalidTableFormat ->
(* Try to keep as many entries as possible *)
begin
let flags = [O_WRONLY; O_TRUNC;O_CREAT] in
let out = (openfile f flags 0o666) in
let outch = out_channel_of_descr out in
lock out;
(try
Table.iter
(fun k e -> Marshal.to_channel outch (k,e) [Marshal.No_sharing]) htbl;
flush outch ;
with _ -> () )
;
unlock out ;
{ 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.add tbl k e ;
lock fd;
ignore (lseek fd 0 SEEK_END);
Marshal.to_channel outch (k,e) [Marshal.No_sharing] ;
flush outch ;
unlock fd
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 (open_in cache) in
fun x ->
let tbl = Lazy.force tbl in
try
find tbl x
with
Not_found ->
let res = f x in
add tbl x res ;
res
end
(* Local Variables: *)
(* coding: utf-8 *)
(* End: *)
|
