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bohc:
谢谢,搞了两天了,现在才算是找到问题所在,解决了。
文件在使用FileChannel.map后不能被删除(Windows上) -
zhang0000jun:
在jdk1.8中执行正好和楼主的结果相反,请指教
从Java视角理解CPU缓存(CPU Cache) -
在世界的中心呼喚愛:
forenroll 写道请问楼主的那个分析工具cachemis ...
从Java视角理解CPU缓存(CPU Cache) -
xgj1988:
我这里打出的结果是: 0 L1-dcache-load-mis ...
从Java视角理解CPU缓存(CPU Cache) -
thebye85:
请教下大神,为什么频繁的park会导致大量context sw ...
从Java视角理解CPU上下文切换(Context Switch)
4 Gen_Event 行为
这一章应该与gen_event(3)
结合起来看,gen_event(3)
对所有接口函数和回调函数都有详细描述.
4.1 事件处理原则
在OTP中, an event manager is a named object to which events can be sent. An event could be, for example, an error, an alarm or some information that should be logged.
In the event manager, zero, one or several event handlers are installed. When the event manager is notified about an event, the event will be processed by all the installed event handlers. For example, an event manager for handling errors can by default have a handler installed which writes error messages to the terminal. If the error messages during a certain period should be saved to a file as well, the user adds another event handler which does this. When logging to file is no longer necessary, this event handler is deleted.
An event manager is implemented as a process and each event handler is implemented as a callback module.
The event manager essentially maintains a list of {Module, State}
pairs, where each Module
is an event handler, and State
the internal state of that event handler.
4.2 Example
The callback module for the event handler writing error messages to the terminal could look like:
java 代码
- -module(terminal_logger).
- -behaviour(gen_event).
- -export([init/1, handle_event/2, terminate/2]).
- init(_Args) ->
- {ok, []}.
- handle_event(ErrorMsg, State) ->
- io:format("***Error*** ~p~n", [ErrorMsg]),
- {ok, State}.
- terminate(_Args, _State) ->
- ok.
The callback module for the event handler writing error messages to a file could look like:
java 代码
- -module(file_logger).
- -behaviour(gen_event).
- -export([init/1, handle_event/2, terminate/2]).
- init(File) ->
- {ok, Fd} = file:open(File, read),
- {ok, Fd}.
- handle_event(ErrorMsg, Fd) ->
- io:format(Fd, "***Error*** ~p~n", [ErrorMsg]),
- {ok, Fd}.
- terminate(_Args, Fd) ->
- file:close(Fd).
The code is explained in the next sections.
4.3 Starting an Event Manager
To start an event manager for handling errors, as described in the example above, call the following function:
java 代码
- gen_event:start_link({local, error_man})
This function spawns and links to a new process, an event manager.
The argument, {local, error_man}
specifies the name. In this case, the event manager will be locally registered as error_man
.
If the name is omitted, the event manager is not registered. Instead its pid must be used. The name could also be given as {global, Name}
, in which case the event manager is registered using global:register_name/2
.
gen_event:start_link
must be used if the event manager is part of a supervision tree, i.e. is started by a supervisor. There is another function gen_event:start
to start a stand-alone event manager, i.e. an event manager which is not part of a supervision tree.
4.4 Adding an Event Handler
Here is an example using the shell on how to start an event manager and add an event handler to it:
1> gen_event:start({local, error_man}).
{ok,<0.31.0>}
2> gen_event:add_handler(error_man, terminal_logger, []).
ok
This function sends a message to the event manager registered as error_man
, telling it to add the event handler terminal_logger
. The event manager will call the callback function terminal_logger:init([])
, where the argument [] is the third argument to add_handler
. init
is expected to return {ok, State}
, where State
is the internal state fo the event handler.
java 代码
- init(_Args) ->
- {ok, []}.
Here, init
does not need any indata and ignores its argument. Also, for terminal_logger
the internal state is not used. For file_logger
, the internal state is used to save the open file descriptor.
java 代码
- init(_Args) ->
- {ok, Fd} = file:open(File, read),
- {ok, Fd}.
4.5 Notifying About Events
3> gen_event:notify(error_man, no_reply).
***Error*** no_reply
ok
error_man
is the name of the event manager and no_reply
is the event.
The event is made into a message and sent to the event manager. When the event is received, the event manager calls handle_event(Event, State)
for each installed event handler, in the same order as they were added. The function is expected to return a tuple {ok, State1}
, where State1
is a new value for the state of the event handler.
In terminal_logger
:
- handle_event(ErrorMsg, State) ->
- io:format("***Error*** ~p~n", [ErrorMsg]),
- {ok, State}.
- In file_logger:
- handle_event(ErrorMsg, Fd) ->
- io:format(Fd, "***Error*** ~p~n", [ErrorMsg]),
- {ok, Fd}.
4.6 Deleting an Event Handler
4> gen_event:delete_handler(error_man, terminal_logger, []).
ok
This function sends a message to the event manager registered as error_man
, telling it to delete the event handler terminal_logger
. The event manager will call the callback function terminal_logger:terminate([], State)
, where the argument [] is the third argument to delete_handler
. terminate
should be the opposite of init
and do any necessary cleaning up. Its return value is ignored.
For terminal_logger
, no cleaning up is necessary:
java 代码
- terminate(_Args, Fd) ->
- file:close(Fd).
For file_logger
, the file descriptor opened in init
needs to be closed:
java 代码
- terminate(_Args, Fd) ->
- file:close(Fd).
4.7 Stopping
When an event manager is stopped, it will give each of the installed event handlers the chance to clean up by calling terminate/2
, the same way as when deleting a handler.
4.7.1 In a Supervision Tree
If the event manager is part of a supervision tree, no stop function is needed. The event manager will automatically be terminated by its supervisor. Exactly how this is done is defined by a shutdown strategy set in the supervisor.
4.7.2 Stand-Alone Event Managers
An event manager can also be stopped by calling:
> gen_event:stop(error_man).
ok
发表评论
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ubuntu安装otp R11B 的一些记录
2007-11-16 12:30 2781新的ubuntu系统会缺少一些工具 和lib. 用apt-ge ... -
emulator调试日志: driver篇
2007-10-08 16:35 2273--------- driver篇 ------------- ... -
修正Programming Erlang中linked driver实例的小问题
2007-10-08 14:50 2445也许很多人碰上过, 用example1_lid:sta ... -
emulator调试日志: port篇
2007-10-06 16:14 2371------------------ port 篇 ----- ... -
supervisor一小技巧
2007-09-04 13:20 1777simple_one_for_one可以让supervisor ... -
gen_server
2007-08-29 21:52 1898State用来存数据, 任何erlang term都行 ge ... -
application
2007-08-29 02:01 1717用pman 可以看出application controlle ... -
epmd源码学习
2007-07-26 10:14 1998注: 此处节点是指分布式中分布在各终端的点, 而结点是指存在数 ... -
Tracing和dbg
2007-07-15 21:49 2532代码不必用特殊的标记(比如debug_info)来编译,也可以 ... -
ets,dets与大数据存储
2007-07-15 12:49 4931ets与dets都是用来存大数据的机制 ets是Erl ... -
用telnet来与ejabberd交互
2007-07-11 15:41 3195看了一篇文章,觉得用telnet来调试ejabberd也是一种 ... -
ejabberd管理页面和客户端
2007-07-11 00:23 9721转战到97机器。在ejabber.config加上这么一行. ... -
ejabberd在linux平台的安装与配置
2007-07-05 21:17 11919这些天捣鼓了下ejabberd,准备研究它的代码,做为榜样~ ... -
mnesia相关笔记
2007-06-29 12:17 2311当前版本OTP 5.5的mensia建表的表名可以和记录名不一 ... -
OTP设计原则:应用
2007-06-27 00:32 19077 Applications This chapter sh ... -
erlang网络编程的几个性能调优和注意点
2007-06-26 09:56 17848前些天给echo_server写了 ... -
erlc
2007-06-24 15:08 3799erlc 命令 erlc 概要 编译器 描述 Th ... -
echo_server
2007-06-23 14:45 2435代码 -module(echo_server ... -
OTP设计原则:Supervisor行为
2007-06-22 12:15 27035 Supervisor Behaviour This s ... -
OTP设计原则:Gen_Fsm 行为
2007-06-22 11:56 27083 Gen_Fsm 行为 This chapter shou ...
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