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yap-6.3/LGPL/thread_pool.pl
2011-09-05 01:11:35 +02:00

419 lines
13 KiB
Prolog

/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@uva.nl
WWW: http://www.swi-prolog.org
Copyright (C): 2008, University of Amsterdam
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
As a special exception, if you link this library with other files,
compiled with a Free Software compiler, to produce an executable, this
library does not by itself cause the resulting executable to be covered
by the GNU General Public License. This exception does not however
invalidate any other reasons why the executable file might be covered by
the GNU General Public License.
*/
:- module(thread_pool,
[ thread_pool_create/3, % +Pool, +Size, +Options
thread_pool_destroy/1, % +Pool
thread_create_in_pool/4, % +Pool, :Goal, -Id, +Options
current_thread_pool/1, % ?Pool
thread_pool_property/2 % ?Pool, ?Property
]).
:- use_module(library(error)).
:- use_module(library(lists)).
:- use_module(library(option)).
:- use_module(library(rbtrees)).
:- use_module(library(debug)).
/** <module> Resource bounded thread management
The module library(thread_pool) manages threads in pools. A pool defines
properties of its member threads and the maximum number of threads that
can coexist in the pool. The call thread_create_in_pool/4 allocates a
thread in the pool, just like thread_create/3. If the pool is fully
allocated it can be asked to wait or raise an error.
The library has been designed to deal with server application that
recieve a variety of requests, such as HTTP servers. Simply starting a
thread for each request is a bit too simple minded for such servers:
* Creating many CPU intensive threads often leads to a slow-down
rather than a speedup.
* Creating many memory intensive threads may exhaust resources
* Tasks that require little CPU and memory but take long waiting
for external resources can run many threads.
Using this library, one can define a pool for each set of tasks with
comparable characteristics and create threads in this pool. Unlike the
worker-pool model, threads are not started immediately. Depending on the
design, both approaches can be attractive.
The library is implemented by means of a manager thread with the fixed
thread id =|__thread_pool_manager|=. All state is maintained in this
manager thread, which receives and processes requests to create and
destroy pools, create threads in a pool and handle messages from
terminated threads. Thread pools are _not_ saved in a saved state and
must therefore be recreated using the initialization/1 directive or
otherwise during startup of the application.
@see http_handler/3 and http_spawn/2.
*/
:- meta_predicate
thread_create_in_pool(+, 0, -, +).
%% thread_pool_create(+Pool, +Size, +Options) is det.
%
% Create a pool of threads. A pool of threads is a declaration for
% creating threads with shared properties (stack sizes) and a
% limited number of threads. Threads are created using
% thread_create_in_pool/4. If all threads in the pool are in use,
% the behaviour depends on the =wait= option of
% thread_create_in_pool/4 and the =backlog= option described
% below. Options are passed to thread_create/3, except for
%
% * backlog(+MaxBackLog)
% Maximum number of requests that can be suspended. Default
% is =infinite=. Otherwise it must be a non-negative integer.
% Using backlog(0) will never delay thread creation for this
% pool.
%
% The pooling mechanism does _not_ interact with the =detached=
% state of a thread. Threads can be created both =detached= and
% normal and must be joined using thread_join/2 if they are not
% detached.
%
% @bug The thread creation option =at_exit= is reserved for
% internal use by this library.
thread_pool_create(Name, Size, Options) :-
pool_manager(Manager),
thread_self(Me),
thread_send_message(Manager, create_pool(Name, Size, Options, Me)),
wait_reply.
%% thread_pool_destroy(+Name) is det.
%
% Destroy the thread pool named Name.
%
% @error existence_error(thread_pool, Name).
thread_pool_destroy(Name) :-
pool_manager(Manager),
thread_self(Me),
thread_send_message(Manager, destroy_pool(Name, Me)),
wait_reply.
%% current_thread_pool(?Name) is nondet.
%
% True if Name refers to a defined thread pool.
current_thread_pool(Name) :-
pool_manager(Manager),
thread_self(Me),
thread_send_message(Manager, current_pools(Me)),
wait_reply(Pools),
( atom(Name)
-> memberchk(Name, Pools)
; member(Name, Pools)
).
%% thread_pool_property(?Name, ?Property) is nondet.
%
% True if Property is a property of thread pool Name. Defined
% properties are:
%
% * options(Options)
% Thread creation options for this pool
% * free(Size)
% Number of free slots on this pool
% * size(Size)
% Total number of slots on this pool
% * members(ListOfIDs)
% ListOfIDs is the list or threads running in this pool
% * running(Running)
% Number of running threads in this pool
% * backlog(Size)
% Number of delayed thread creations on this pool
thread_pool_property(Name, Property) :-
current_thread_pool(Name),
pool_manager(Manager),
thread_self(Me),
thread_send_message(Manager, pool_properties(Me, Name, Property)),
wait_reply(Props),
( nonvar(Property)
-> memberchk(Property, Props)
; member(Property, Props)
).
%% thread_create_in_pool(+Pool, :Goal, -Id, +Options) is det.
%
% Create a thread in Pool. Options overrule default thread
% creation options associated to the pool. In addition, the
% following option is defined:
%
% * wait(+Boolean)
% If =true= (default) and the pool is full, wait until a
% member of the pool completes. If =false=, throw a
% resource_error.
%
% @error resource_error(threads_in_pool(Pool)) is raised if wait
% is =false= or the backlog limit has been reached.
% @error existence_error(thread_pool, Pool) if Pool does not
% exist.
thread_create_in_pool(Pool, Goal, Id, Options) :-
select_option(wait(Wait), Options, ThreadOptions, true),
pool_manager(Manager),
thread_self(Me),
thread_send_message(Manager,
create(Pool, Goal, Me, Wait, ThreadOptions)),
wait_reply(Id).
/*******************************
* START MANAGER *
*******************************/
%% pool_manager(-ThreadID) is det.
%
% ThreadID is the thread (alias) identifier of the manager. Starts
% the manager if it is not running.
pool_manager(TID) :-
TID = '__thread_pool_manager',
( thread_running(TID)
-> true
; with_mutex('__thread_pool', create_pool_manager(TID))
).
thread_running(Thread) :-
catch(thread_property(Thread, status(Status)),
E, true),
( var(E)
-> ( Status == running
-> true
; thread_join(Thread, _),
print_message(warning, thread_pool(manager_died(Status))),
fail
)
; E = error(existence_error(thread, Thread), _)
-> fail
; throw(E)
).
create_pool_manager(Thread) :-
thread_running(Thread), !.
create_pool_manager(Thread) :-
rb_new(State0),
thread_create(manage_thread_pool(State0), _,
[ alias(Thread)
]).
/*******************************
* MANAGER LOGIC *
*******************************/
%% manage_thread_pool(+State)
manage_thread_pool(State0) :-
thread_get_message(Message),
( update_thread_pool(Message, State0, State)
-> debug(thread_pool(state), 'Message ~p --> ~p', [Message, State]),
manage_thread_pool(State)
; format(user_error, 'Update failed: ~p~n', [Message])
).
update_thread_pool(create_pool(Name, Size, Options, For), State0, State) :- !,
( rb_insert_new(State0,
Name, tpool(Options, Size, Size, WP, WP, []),
State)
-> thread_send_message(For, thread_pool(true))
; reply_error(For, permission_error(create, thread_pool, Name)),
State = State0
).
update_thread_pool(destroy_pool(Name, For), State0, State) :- !,
( rb_delete(State0, Name, State)
-> thread_send_message(For, thread_pool(true))
; reply_error(For, existence_error(thread_pool, Name)),
State = State0
).
update_thread_pool(current_pools(For), State, State) :- !,
rb_keys(State, Keys),
debug(thread_pool(current), 'Reply to ~w: ~p', [For, Keys]),
reply(For, Keys).
update_thread_pool(pool_properties(For, Name, P), State, State) :- !,
( rb_lookup(Name, Pool, State)
-> findall(P, pool_property(P, Pool), List),
reply(For, List)
; reply_error(For, existence_error(thread_pool, Name))
).
update_thread_pool(Message, State0, State) :-
arg(1, Message, Name),
( rb_lookup(Name, Pool0, State0)
-> update_pool(Message, Pool0, Pool),
rb_update(State0, Name, Pool, State)
; State = State0,
( Message = create(Name, _, For, _, _)
-> reply_error(For, existence_error(thread_pool, Name))
; true
)
).
pool_property(options(Options),
tpool(Options, _Free, _Size, _WP, _WPT, _Members)).
pool_property(backlog(Size),
tpool(_, _Free, _Size, WP, WPT, _Members)) :-
diff_list_length(WP, WPT, Size).
pool_property(free(Free),
tpool(_, Free, _Size, _, _, _)).
pool_property(size(Size),
tpool(_, _Free, Size, _, _, _)).
pool_property(running(Count),
tpool(_, Free, Size, _, _, _)) :-
Count is Size - Free.
pool_property(members(IDList),
tpool(_, _, _, _, _, IDList)).
diff_list_length(List, Tail, Size) :-
'$skip_list'(Length, List, Rest),
( Rest == Tail
-> Size = Length
; type_error(difference_list, List/Tail)
).
%% update_pool(+Message, +Pool0, -Pool) is det.
%
% Deal with create requests and completion messages on a given
% pool. There are two messages:
%
% * create(PoolName, Goal, ForThread, Wait, Options)
% Create a new thread on behalve of ForThread. There are
% two cases:
% * Free slots: create the thread
% * No free slots: error or add to waiting
% * exitted(PoolName, Thread)
% A thread completed. If there is a request waiting,
% create a new one.
update_pool(create(Name, Goal, For, _, MyOptions),
tpool(Options, Free0, Size, WP, WPT, Members0),
tpool(Options, Free, Size, WP, WPT, Members)) :-
succ(Free, Free0), !,
thread_self(Me),
merge_options(MyOptions, Options, ThreadOptions),
( option(at_exit(_), ThreadOptions)
-> reply_error(For, permission_error(specify, option, at_axit)),
Members = Members0
; Exit = thread_send_message(Me, exitted(Name, Id)),
catch(thread_create(Goal, Id,
[ at_exit(Exit)
| ThreadOptions
]),
E, true),
( var(E)
-> Members = [Id|Members0],
reply(For, Id)
; reply_error(For, E),
Members = Members0
)
).
update_pool(Create,
tpool(Options, 0, Size, WP, WPT0, Members),
tpool(Options, 0, Size, WP, WPT, Members)) :-
Create = create(Name, _Goal, For, Wait, _Options), !,
option(backlog(BackLog), Options, infinite),
( can_delay(Wait, BackLog, WP, WPT0)
-> WPT0 = [Create|WPT],
debug(thread_pool, 'Delaying ~p', [Create])
; WPT = WPT0,
reply_error(For, resource_error(threads_in_pool(Name)))
).
update_pool(exitted(_Name, Id),
tpool(Options, Free0, Size, WP0, WPT, Members0),
Pool) :-
succ(Free0, Free),
delete(Members0, Id, Members1),
Pool1 = tpool(Options, Free, Size, WP, WPT, Members1),
( WP0 == WPT
-> WP = WP0,
Pool = Pool1
; WP0 = [Waiting|WP],
debug(thread_pool, 'Start delayed ~p', [Waiting]),
update_pool(Waiting, Pool1, Pool)
).
can_delay(true, infinite, _, _) :- !.
can_delay(true, BackLog, WP, WPT) :-
diff_list_length(WP, WPT, Size),
BackLog > Size.
/*******************************
* UTIL *
*******************************/
reply(To, Term) :-
thread_send_message(To, thread_pool(true(Term))).
reply_error(To, Error) :-
thread_send_message(To, thread_pool(error(Error, _))).
wait_reply :-
thread_get_message(thread_pool(Result)),
( Result == true
-> true
; Result == fail
-> fail
; throw(Result)
).
wait_reply(Value) :-
thread_get_message(thread_pool(Reply)),
( Reply = true(Value0)
-> Value = Value0
; Reply == fail
-> fail
; throw(Reply)
).
/*******************************
* MESSAGES *
*******************************/
:- multifile
prolog:message/3.
% Print messages
prolog:message(thread_pool(Message)) -->
message(Message).
prolog:message(manager_died(Status)) -->
[ 'Thread-pool: manager died on status ~p; restarting'-[Status] ].