Erlang进程简单的主动负载管制实现

我们知道Erlang的调度器是公平的,当进程的时间片用完了后,会强制切出,但是这个粒度是比较粗的。比如说进程进行了大量的Io操作,这个操作换成时间片是不准确的,会导致某些CPU计算密集型的比较吃亏,IO密集型的合算。

 
为了避免这个情况,IO密集型的经常可以互动要求短暂放弃执行,最简单的方法就是用消息等待机制。当进程在等消息的时候,就会被切出,我们就达到目的。
 
我们可以参考mnesia的实现:
%%mnesia_dumper.erl:L1181
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%                                                      
%% Load regulator                                                                                                           
%%                                                                                                                          
%% This is a poor mans substitute for a fair scheduler algorithm                                                            
%% in the Erlang emulator. The mnesia_dumper process performs many                                                          
%% costly BIF invokations and must pay for this. But since the                                                              
%% Emulator does not handle this properly we must compensate for                                                            
%% this with some form of load regulation of ourselves in order to                                                          
%% not steal all computation power in the Erlang Emulator ans make                                                          
%% other processes starve. Hopefully this is a temporary solution.                                                          
 
start_regulator() ->
    case mnesia_monitor:get_env(dump_log_load_regulation) of
        false ->
            nopid;
        true ->
            N = ?REGULATOR_NAME,
            case mnesia_monitor:start_proc(N, ?MODULE, regulator_init, [self()]) of
                {ok, Pid} ->
                    Pid;
                {error, Reason} ->
                    fatal("Failed to start ~n: ~p~n", [N, Reason])
            end
    end.
 
regulator_init(Parent) ->
    %% No need for trapping exits.                                                                                          
    %% Using low priority causes the regulation                                                                             
    process_flag(priority, low),
    register(?REGULATOR_NAME, self()),
    proc_lib:init_ack(Parent, {ok, self()}),
    regulator_loop().
 
regulator_loop() ->
    receive
        {regulate, From} ->
            From ! {regulated, self()},
            regulator_loop();
        {stop, From} ->
            From ! {stopped, self()},
            exit(normal)
    end.
 
regulate(nopid) ->
    ok;
regulate(RegulatorPid) ->
    RegulatorPid ! {regulate, self()},
    receive
        {regulated, RegulatorPid} -> ok
    end.
祝玩得开心!

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