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/* Part of SWISH
Author: Jan Wielemaker
E-mail: J.Wielemaker@cs.vu.nl
WWW: http://www.swi-prolog.org
Copyright (C): 2018, VU University Amsterdam
CWI Amsterdam
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/
:- module(http_dyn_workers,
[
]).
:- use_module(library(http/thread_httpd)).
:- use_module(library(debug)).
:- use_module(library(settings)).
:- use_module(library(aggregate)).
:- setting(http:max_workers, integer, 100,
"Maximum number of workers to create").
:- setting(http:worker_idle_limit, number, 10,
"Terminate a dynamic worker when idle for this time").
:- setting(http:max_load, number, 10,
"Maximum load average caused by HTTP workers").
/** <module> Dynamically schedule HTTP workers.
This module defines hooks into the HTTP framework to dynamically
schedule worker threads. Dynamic scheduling relieves us from finding a
good value for the size of the HTTP worker pool.
The decision to add a worker follows these rules:
- If the load average caused by the worker threads exceeds
http:max_load, no worker is added.
- Wait for some time, depending on how close we are to the
http:max_workers limit.
- If the worker is still needed, add it.
The policy depends on three settings:
- http:max_workers
The maximum number of workers that will be created. Default is
100.
- http:worker_idle_limit
The number of seconds a dynamic worker waits for a new job. If
no job arrives in time it terminates. Default is 10 seconds.
- http:max_load
Max load average created by __the HTTP server__, i.e. the amount
of CPU time consumed per second. Default is 10.
*/
%! http:schedule_workers(+Dict)
%
% Called if there is no immediately free worker to handle the
% incomming request. The request is forwarded to the thread
% =|__http_scheduler|= as the hook is called in time critical code.
:- multifile
http:schedule_workers/1.
http:schedule_workers(Dict) :-
get_time(Now),
catch(thread_send_message('__http_scheduler', no_workers(Now, Dict)),
error(existence_error(message_queue, _), _),
fail),
!.
http:schedule_workers(Dict) :-
create_scheduler,
http:schedule_workers(Dict).
create_scheduler :-
catch(thread_create(http_scheduler, _,
[ alias('__http_scheduler'),
inherit_from(main),
debug(false),
detached(true)
]),
error(_,_),
fail).
http_scheduler :-
get_time(Now),
http_scheduler(_{ waiting:0,
time:Now
}).
http_scheduler(State) :-
( thread_self(Me),
thread_get_message(Me, Task, [timeout(10)])
-> true
; Task = update_load_avg
),
( catch(reschedule(Task, State, State1),
Error,
( print_message(warning, Error),
fail))
-> !,
http_scheduler(State1)
; http_scheduler(State)
).
%! reschedule(+Message, +State0, -State) is semidet.
reschedule(no_workers(Reported, Dict), State0, State) :-
update_load_avg(Dict, State0, State, Load),
setting(http:max_load, MaxLoad),
( Load > MaxLoad
-> debug(http(scheduler), 'Load ~1f > ~1f; not adding workers',
[ Load, MaxLoad ])
; aggregate_all(count, http_current_worker(Dict.port, _), Workers),
setting(http:max_workers, MaxWorkers),
Wait is 0.001*(MaxWorkers/max(1, MaxWorkers-Workers)),
get_time(Now),
Sleep is Wait + Reported-Now,
debug(http(scheduler), 'Waiting: ~w; active: ~w; sleep: ~3f; load: ~1f',
[Dict.waiting, Workers, Sleep, Load]),
sleep(Sleep),
accept_queue(Dict, Queue),
message_queue_property(Queue, size(Newsize)),
( Newsize == 0
-> debug(http(scheduler), 'Drained', [])
; debug(http(scheduler), 'Size is ~w: adding worker', [Newsize]),
setting(http:worker_idle_limit, MaxIdle),
http_add_worker(Dict.port,
[ max_idle_time(MaxIdle)
])
)
).
reschedule(update_load_avg, State0, State) :-
update_load_avg(_{}, State0, State, _).
update_load_avg(_Dict, State, State, Load) :-
_{stamp:Last, load:Load} :< State.get(load),
get_time(Now),
Now - Last < 10.
update_load_avg(Dict, State0, State, Load) :-
server_port(Dict, State0, State1, Port),
!,
aggregate_all(sum(CPU), worker_cpu(Port, CPU), CPU1),
get_time(Now),
( LoadDict = State1.get(load),
_{stamp:Last, cpu:LastCPU} :< LoadDict
-> Load0 is (CPU1-LastCPU)/(Now-Last),
smooth_load(LoadDict, Load0, Load),
State = State1.put(load, _{stamp:Now, cpu:CPU1, load:Load})
; State = State1.put(load, _{stamp:Now, cpu:CPU1}),
Load = 0
).
update_load_avg(_, _, _, 0).
worker_cpu(Port, CPU) :-
http_current_worker(Port, Thread),
catch(thread_statistics(Thread, cputime, CPU), _, fail).
server_port(_Dict, State, State, Port) :-
Port = State.get(port),
!.
server_port(Dict, State0, State, Port) :-
Port = Dict.get(port),
State = State0.put(port, Port).
smooth_load(LoadDict, Load0, Load) :-
OldLoad = LoadDict.get(load),
!,
Load is (5*OldLoad+Load0)/6.
smooth_load(_, Load, Load).
%! accept_queue(+Dict, -Queue)
%
% As of 7.7.16, `queue` is a member of the provided dict. For older
% versions we need a hack.
accept_queue(Dict, Queue) :-
Queue = Dict.get(queue),
!.
accept_queue(Dict, Queue) :-
thread_httpd:current_server(Dict.port, _, _, Queue, _, _),
!.
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