/* 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"). /** Dynamically schedule HTTP workers. Most code doesn't need to use this directly; instead use library(http/http_server), which combines this library with the typical HTTP libraries that most servers need. 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), ( Workers >= MaxWorkers -> debug(http(scheduler), 'Reached max workers (~D); not adding workers', [ MaxWorkers ]) ; Wait is 0.001*(MaxWorkers/max(1, MaxWorkers-Workers)), get_time(Now), Sleep is max(0.001, 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, _, _), !.