1/* Part of SWISH 2 3 Author: Jan Wielemaker 4 E-mail: J.Wielemaker@cs.vu.nl 5 WWW: http://www.swi-prolog.org 6 Copyright (C): 2018, VU University Amsterdam 7 CWI Amsterdam 8 All rights reserved. 9 10 Redistribution and use in source and binary forms, with or without 11 modification, are permitted provided that the following conditions 12 are met: 13 14 1. Redistributions of source code must retain the above copyright 15 notice, this list of conditions and the following disclaimer. 16 17 2. Redistributions in binary form must reproduce the above copyright 18 notice, this list of conditions and the following disclaimer in 19 the documentation and/or other materials provided with the 20 distribution. 21 22 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 23 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 24 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 25 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 26 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 27 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 28 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 29 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 30 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 32 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 33 POSSIBILITY OF SUCH DAMAGE. 34*/ 35 36:- module(http_dyn_workers, 37 [ 38 ]). 39:- use_module(library(http/thread_httpd)). 40:- use_module(library(debug)). 41:- use_module(library(settings)). 42:- use_module(library(aggregate)). 43 44:- setting(http:max_workers, integer, 100, 45 "Maximum number of workers to create"). 46:- setting(http:worker_idle_limit, number, 10, 47 "Terminate a dynamic worker when idle for this time"). 48:- setting(http:max_load, number, 10, 49 "Maximum load average caused by HTTP workers").

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. */

84:- multifile 85 http:schedule_workers/1. 86 87http:schedule_workers(Dict) :- 88 get_time(Now), 89 catch(thread_send_message('__http_scheduler', no_workers(Now, Dict)), 90 error(existence_error(message_queue, _), _), 91 fail), 92 !. 93http:schedule_workers(Dict) :- 94 create_scheduler, 95 http:schedule_workers(Dict). 96 97create_scheduler :- 98 catch(thread_create(http_scheduler, _, 99 [ alias('__http_scheduler'), 100 inherit_from(main), 101 debug(false), 102 detached(true) 103 ]), 104 error(_,_), 105 fail). 106 107http_scheduler :- 108 get_time(Now), 109 http_scheduler(_{ waiting:0, 110 time:Now 111 }). 112 113http_scheduler(State) :- 114 ( thread_self(Me), 115 thread_get_message(Me, Task, [timeout(10)]) 116 -> true 117 ; Task = update_load_avg 118 ), 119 ( catch(reschedule(Task, State, State1), 120 Error, 121 ( print_message(warning, Error), 122 fail)) 123 -> !, 124 http_scheduler(State1) 125 ; http_scheduler(State) 126 ).

130reschedule(no_workers(Reported, Dict), State0, State) :- 131 update_load_avg(Dict, State0, State, Load), 132 setting(http:max_load, MaxLoad), 133 ( Load > MaxLoad 134 -> debug(http(scheduler), 'Load ~1f > ~1f; not adding workers', 135 [ Load, MaxLoad ]) 136 ; aggregate_all(count, http_current_worker(Dict.port, _), Workers), 137 setting(http:max_workers, MaxWorkers), 138 Wait is 0.001*(MaxWorkers/max(1, MaxWorkers-Workers)), 139 get_time(Now), 140 Sleep is Wait + Reported-Now, 141 debug(http(scheduler), 'Waiting: ~w; active: ~w; sleep: ~3f; load: ~1f', 142 [Dict.waiting, Workers, Sleep, Load]), 143 sleep(Sleep), 144 accept_queue(Dict, Queue), 145 message_queue_property(Queue, size(Newsize)), 146 ( Newsize == 0 147 -> debug(http(scheduler), 'Drained', []) 148 ; debug(http(scheduler), 'Size is ~w: adding worker', [Newsize]), 149 setting(http:worker_idle_limit, MaxIdle), 150 http_add_worker(Dict.port, 151 [ max_idle_time(MaxIdle) 152 ]) 153 ) 154 ). 155reschedule(update_load_avg, State0, State) :- 156 update_load_avg(_{}, State0, State, _). 157 158update_load_avg(_Dict, State, State, Load) :- 159 _{stamp:Last, load:Load} :< State.get(load), 160 get_time(Now), 161 Now - Last < 10. 162update_load_avg(Dict, State0, State, Load) :- 163 server_port(Dict, State0, State1, Port), 164 !, 165 aggregate_all(sum(CPU), worker_cpu(Port, CPU), CPU1), 166 get_time(Now), 167 ( LoadDict = State1.get(load), 168 _{stamp:Last, cpu:LastCPU} :< LoadDict 169 -> Load0 is (CPU1-LastCPU)/(Now-Last), 170 smooth_load(LoadDict, Load0, Load), 171 State = State1.put(load, _{stamp:Now, cpu:CPU1, load:Load}) 172 ; State = State1.put(load, _{stamp:Now, cpu:CPU1}), 173 Load = 0 174 ). 175update_load_avg(_, _, _, 0). 176 177worker_cpu(Port, CPU) :- 178 http_current_worker(Port, Thread), 179 catch(thread_statistics(Thread, cputime, CPU), _, fail). 180 181server_port(_Dict, State, State, Port) :- 182 Port = State.get(port), 183 !. 184server_port(Dict, State0, State, Port) :- 185 Port = Dict.get(port), 186 State = State0.put(port, Port). 187 188smooth_load(LoadDict, Load0, Load) :- 189 OldLoad = LoadDict.get(load), 190 !, 191 Load is (5*OldLoad+Load0)/6. 192smooth_load(_, Load, Load).