erlang学习笔记（并发程序设计）

 See Also： http://www.erlang.org/course/concurrent_programming.html

Definitions

Creating a new process

Simple message passing

An Echo Process

Selective Message Reception

Selection of Any Message

A Telephony Example

Pids can be sent in messages

Registered Processes

The Client Server Model

Timeouts

 

Definitions定义

Process 轻量级进程，系统会有许多同时运行的process
Message	进程间通过消息通讯
Timeout	超时机制
Registered Process	注册了名称的进程
Client/Server Model

Creating a new process创建一个新进程

 

Pid1进程中执行如下代码
Pid2 = spawn(Mod,Func,Args)
Pid2是新进程的标识，只有Pid1知道

 

Simple Message Passing消息传递

 

%mesTest.erl

-module(mesTest).
-export([recvTest/0]).

recvTest() ->
        receive
                finished ->
                        io:format("program stopped!~n",[]);
                {From,Msg} ->
                        io:format("Received ~p ~p~n", [From,Msg])
        end.

1> c(mesTest).
{ok,mesTest}
2> Pid2 = spawn(mesTest,recvTest,[]).
<0.39.0>
3> Pid2!{self(),"Hello Pid2"}.
Receoved <0.32.0> "Hello Pid2"
{<0.32.0>,"Hello Pid2"}
4> Pid2!{self(),"Hello Pid2"}.	%Pid2进程已经结束
{<0.32.0>,"Hello Pid2"}
5>

self() 返回自身进程的pid

From 和 Msg 匹配收到的消息 （也可以调用Pid2!finished）

如果From之前已经被bound数据，那只有Msg会收到内容

An Echo Process

% echo.erl
-module(echo).
-export([go/0, loop/0]).
 
go() ->
Pid2 = spawn(echo, loop, []),
Pid2 ! {self(), hello},
receive 
{Pid2, Msg} ->
io:format("P1 ~w~n",[Msg])
end,
Pid2 ! stop.

loop() ->
receive
{From, Msg} -> 
From ! {self(), Msg},
loop();
stop ->
true
end.

执行echo:go().

Selective Message Reception

% echo.erl
-module(echo).
-export([test/0,selective/0,bfunc/1]).

selective() ->
        receive
                foo ->
                        io:format("Received foo from A~n",[])
        end,
        receive
                bar ->
                        io:format("Received bar from B~n",[])
        end.

bfunc(Cpid) ->
        Cpid ! bar.

test() ->
        Cpid = spawn(echo, selective, []),
        spawn(echo, bfunc, [Cpid]),
timer:sleep(1000),
        Cpid ! foo.
1> c(echo).
{ok,echo}
2> echo:test().
Received foo from A
foo
Received bar from B

Selection of Any Message

-module(echo).
-export([test/0,selective/0,bfunc/1]).
selective() ->
        receive
                Msg ->
                        io:format("Received ~w ~n",[Msg])
        end,
        receive
                Msg2 ->
                        io:format("Received ~w ~n",[Msg2])
        end.

bfunc(Cpid) ->
        Cpid ! bar.

test() ->
        Cpid = spawn(echo, selective, []),
        spawn(echo, bfunc, [Cpid]),
        timer:sleep(1000),
        Cpid ! foo.

1> c(echo).
{ok,echo}
2> echo:test().
Received bar
Received foo
foo

A Telephony Example

%这个例子没能理解

 

Pids can be sent in messages

% A 把自己的Pid发送给B，B再将A的pid给C，最终C直接向A回话
% echo.erl
-module(echo).
-export([test/0,bfunc/0,cfunc/0]).

cfunc() ->
        receive
                {_,Apid} ->
                        Apid ! foo
        end.

bfunc() ->
        receive
                {Cpid,Apid} ->
                        Cpid ! {"Call A",Apid}
        end.

test() ->
        %create b and c process
        Bpid = spawn(echo,bfunc,[]),
        Cpid = spawn(echo,cfunc,[]),

        Bpid ! {Cpid,self()},
        receive
                Mes ->
                        io:format("Received ~w from C ~n",[Mes])
        end.

1> c(echo).
{ok,echo}
2> echo:test().
Received foo from C
ok

Registered Processes

register(Alias, Pid) Registers the process Pid with the name Alias.

% echo.erl
-module(echo).
-export([test/0,bfunc/0,cfunc/0]).

cfunc() ->
        receive
                {_,Apid} ->
                        Apid ! foo
        end.

bfunc() ->
        receive
                {_,Apid} ->
                        cpid ! {"Call A",Apid}
        end.

test() ->
        %create b and c process
        Bpid = spawn(echo,bfunc,[]),
        Cpid = spawn(echo,cfunc,[]),
        register(cpid,Cpid),	%BPid可以通过cpid直接向C发送消息了

        Bpid ! {Cpid,self()},
        receive
                Mes ->
                        io:format("Received ~w from C ~n",[Mes])
        end.

Client Server Model

% myserver.erl
-module(myserver).
-export([start/0,server/0,request/1]).

handle(Reqdata) ->
        "Hello " ++ Reqdata.

server() ->
        io:format("server id = ~w ~n",[self()]),
        receive
                [From,{request,X}] ->
                        Resp = handle(X),
                        From ! {reply,Resp},
                        server()
        end.

start() ->
        register(serverid,spawn(myserver,server,[])).

request(Name) ->
        serverid ! [self(),{request,Name}],
        receive
                {reply,Res} ->
                        io:format("Get ~p from server!",[Res])
        after 5000 ->
                io:format("No response from server~n",[]),
                exit(timeout)
        end.

1> c(myserver).
{ok,myserver}
2> myserver:start().
server id = <0.39.0>
true
3> myserver:request("PJ").
server id = <0.39.0>
Get "Hello PJ" from server!ok
4>

Uses of Timeouts