hibernate的妙用
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关于erlang进程hibernate的好处,去过这次erlang大会的同学应该已经都知道了
简单的理解:
hibernate可以使你闲置的erlang进程马上进行gc,因为进程处于receive状态下是不会gc的
我在性能调优时发现,gc对于消息发送速度的影响还是非常大的
关于erlang gc问题也可以参看这个
Recently, as part of RabbitMQ server development, we ran into an interesting issue regarding Erlang’s per-process garbage collection. If a process is idle — not doing any work at all, simply waiting for an external event — then its garbage-collector will not run until it starts working again. The solution is to hibernate idle processes, which causes a very aggressive garbage-collection run and puts the process into a suspended state, from which it will wake when a message next arrives.
所以查看rabbitMQ源代码可以看到里面的gen_server/fsm等进程统统都会使用hibernate
下面解释下如何让进程hibernate,这里需要注意的是一个进程hiberate后,会清空stack栈,也就是说之前的调用关系全部没有了,也就是说hibernate所在的函数永远不会返回,待有新消息时,进程从hibernate(M,F,A)里指定的M:F处开始运行
gen_server和gen_fsm都提供了hibernate的方式,2种方法
第一种:
在gen_server,或gen_fsm回调接口返回时,指定hibernate
实际这个Time1可以指定为hibernate,则重新回到main loop时会直接hibernate
这种方法可能使你的进程频繁hibernate又被唤醒,效率不是很好
正确的方式应该是,当你预期你的进程一段时间内不会收到消息才hibernate
所以推荐下面的方法,直接看下示例代码:
运行:
总体上是让进程在main_loop里先timeout也就是证明一段时间内都没有消息到达,然后gen_fsm进程是发送{'gen_event',timeout}消息处理timeout事件的,所以要在每个Mod:StateName处都加个处理timeout的分支,来进行timeout处理,也就是hibernate掉自己,重新进入的是enter_loop 函数,这个东西很有用呐,大家可以查看源码,我就不多说了
另外,示例中可以看到,hibernate会清空stack,但是不会影响你的进程字典和ets等其它东西,可以放心用了
简单的理解:
hibernate可以使你闲置的erlang进程马上进行gc,因为进程处于receive状态下是不会gc的
我在性能调优时发现,gc对于消息发送速度的影响还是非常大的
关于erlang gc问题也可以参看这个
引用
Recently, as part of RabbitMQ server development, we ran into an interesting issue regarding Erlang’s per-process garbage collection. If a process is idle — not doing any work at all, simply waiting for an external event — then its garbage-collector will not run until it starts working again. The solution is to hibernate idle processes, which causes a very aggressive garbage-collection run and puts the process into a suspended state, from which it will wake when a message next arrives.
所以查看rabbitMQ源代码可以看到里面的gen_server/fsm等进程统统都会使用hibernate
下面解释下如何让进程hibernate,这里需要注意的是一个进程hiberate后,会清空stack栈,也就是说之前的调用关系全部没有了,也就是说hibernate所在的函数永远不会返回,待有新消息时,进程从hibernate(M,F,A)里指定的M:F处开始运行
gen_server和gen_fsm都提供了hibernate的方式,2种方法
第一种:
在gen_server,或gen_fsm回调接口返回时,指定hibernate
- {next_state, NStateName, NStateData, Time1}
{next_state, NStateName, NStateData, Time1}
实际这个Time1可以指定为hibernate,则重新回到main loop时会直接hibernate
这种方法可能使你的进程频繁hibernate又被唤醒,效率不是很好
正确的方式应该是,当你预期你的进程一段时间内不会收到消息才hibernate
所以推荐下面的方法,直接看下示例代码:
- %% ====================================================================
- %% Interface Function
- %% ====================================================================
- join(UserId)->
- io:format("join UserId=~p~n",[UserId]),
- gen_fsm:sync_send_event(?MODULE, {join,UserId}).
- start()->
- gen_fsm:send_event(?MODULE,start).
- %% ====================================================================
- %% Callback Function
- %% ====================================================================
- wait_player({join,UserId},_From, State) ->
- print_inner_data(State),
- put(p,get(p)+1),
- ets:insert(State#state.players,{p,UserId}),
- Count=State#state.count+1,
- if
- Count =:= 3 ->
- io:format("jump to next phrase -> start~n"),
- {reply,next_phrase,wait_start,State,5000};
- true->
- NewState=State#state{count=Count},
- {reply,stand_still,wait_player,NewState,5000}
- end.
- wait_player(timeout,State)->
- io:format("timeout happened when wait_player,let's hibernate~n"),
- proc_lib:hibernate(gen_fsm, enter_loop, [?MODULE, [], wait_player,State]).
- wait_start(start,State)->
- print_inner_data(State),
- io:format("recv start event ~n"),
- {next_state,wait_start,State,5000};
- wait_start(timeout,State)->
- io:format("timeout happened when wait_start,let's hibernate~n"),
- proc_lib:hibernate(gen_fsm, enter_loop, [?MODULE, [], wait_start,State]).
- start_link()->
- gen_fsm:start_link({local,?MODULE}, ?MODULE, [] ,[]).
- init([])->
- put(p,0),
- {ok,
- wait_player,
- #state
- {
- count=0,
- players=ets:new(players,[bag])
- },
- 5000
- }.
- print_inner_data(State)->
- io:format("inner data: dict=~p,ets=~p~n",[get(p),ets:tab2list(State#state.players)]).
%% ====================================================================%% Interface Function%% ====================================================================join(UserId)->io:format("join UserId=~p~n",[UserId]),gen_fsm:sync_send_event(?MODULE, {join,UserId}).start()->gen_fsm:send_event(?MODULE,start).%% ====================================================================%% Callback Function%% ====================================================================wait_player({join,UserId},_From, State) ->print_inner_data(State),put(p,get(p)+1),ets:insert(State#state.players,{p,UserId}),Count=State#state.count+1,ifCount =:= 3 ->io:format("jump to next phrase -> start~n"),{reply,next_phrase,wait_start,State,5000};true->NewState=State#state{count=Count},{reply,stand_still,wait_player,NewState,5000}end.wait_player(timeout,State)->io:format("timeout happened when wait_player,let's hibernate~n"),proc_lib:hibernate(gen_fsm, enter_loop, [?MODULE, [], wait_player,State]).wait_start(start,State)-> print_inner_data(State), io:format("recv start event ~n"), {next_state,wait_start,State,5000};wait_start(timeout,State)->io:format("timeout happened when wait_start,let's hibernate~n"),proc_lib:hibernate(gen_fsm, enter_loop, [?MODULE, [], wait_start,State]).start_link()->gen_fsm:start_link({local,?MODULE}, ?MODULE, [] ,[]).init([])->put(p,0),{ok, wait_player, #state{count=0,players=ets:new(players,[bag])},5000}.print_inner_data(State)->io:format("inner data: dict=~p,ets=~p~n",[get(p),ets:tab2list(State#state.players)]).
运行:
- 2> {ok,Pid}=fsm:start_link().
- {ok,<0.39.0>}
- 3> process_info(Pid,total_heap_size).
- {total_heap_size,233}
- 4> fsm:join(123).
- join UserId=123
- inner data: dict=0,ets=[]
- stand_still
- timeout happened when wait_player,let's hibernate
- 5> process_info(Pid,total_heap_size).
- {total_heap_size,33}
- 6> fsm:join(456).
- join UserId=456
- inner data: dict=1,ets=[{p,123}]
- stand_still
2> {ok,Pid}=fsm:start_link().{ok,<0.39.0>}3> process_info(Pid,total_heap_size).{total_heap_size,233}4> fsm:join(123).join UserId=123inner data: dict=0,ets=[]stand_stilltimeout happened when wait_player,let's hibernate5> process_info(Pid,total_heap_size).{total_heap_size,33}6> fsm:join(456).join UserId=456inner data: dict=1,ets=[{p,123}]stand_still
总体上是让进程在main_loop里先timeout也就是证明一段时间内都没有消息到达,然后gen_fsm进程是发送{'gen_event',timeout}消息处理timeout事件的,所以要在每个Mod:StateName处都加个处理timeout的分支,来进行timeout处理,也就是hibernate掉自己,重新进入的是enter_loop 函数,这个东西很有用呐,大家可以查看源码,我就不多说了
另外,示例中可以看到,hibernate会清空stack,但是不会影响你的进程字典和ets等其它东西,可以放心用了
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