Erlang入门：构建application练习4（进程link的作用）

标签：erlang   入门教程   application   link   

1、示例项目(bank)简介

bank_server.erl是为客户服务的进程回调模块
bank_center.erl是为银行服务中心的进程回调模块
客户(bank_server)每年都要扣除年费
所有年费都交给银行服务中心(bank_center)

客户服务使用示例：
创建用户：bank_server:create_account(myname, 100).
用户存钱：myname ! {deposit, 10}.
用户取钱：myname ! {cash1, 20}.
myname ! {cash2, 30}.
查询余额：myname ! check.

银行服务中心使用示例：
查询收到的年费总额：bank_center ! check.

2、启动bank_center

2.1、bank_center里有3个启动API

%% 此处?MODULE为bank_center

start()->
%% gen_server:start/3
%% 无link，无注册
{ok, Pid} = gen_server:start(?MODULE, [], []),
%% 自行注册
erlang:register(?MODULE, Pid).

start2()->
%% gen_server:start/4
%% 无link，注册为本地进程，名称为?MODULE
gen_server:start({local, ?MODULE}, ?MODULE, [], []).

start_link()->
%% gen_server:start_link/4
%% 有link，有注册
gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

2.2、在bank_app里启动bank_center

-module(bank_app).
-behaviour(application). 
-export([start/2, stop/1]). 

-include("common.hrl").

start(_Type, _Args) -> 
?I("Start ~p ...", [?MODULE]),
% bank_center:start(),
% bank_center:start2(),
bank_center:start_link(),
{ok, self()}.

stop(_State) -> 
?I("Stop ~p!", [?MODULE]),
ok.

3、创建客户进程后，和bank_center进行link

init([Money]) ->
%% 与银行服务中心进行关联
link(whereis(bank_center)),
{ok, Money}.

4、link实验

4.1、测试link的作用

bank_server:create_account(myname1, 100).

myname1 ! error.

Eshell V5.10.4 (abort with ^G)
1> bank_server:create_account(myname1, 100).
true
2> whereis(bank_center).
<0.37.0>
3> myname1 ! error.
##[<0.38.0>bank_server:141] terminate: {bad_return_value,{ok,80}}
error
4> 
=ERROR REPORT==== 16-Jan-2015::16:54:58 ===
** Generic server <0.38.0> terminating 
** Last message in was error
** When Server state == 80
** Reason for termination == 
** {bad_return_value,{ok,80}}

4> whereis(bank_center).
undefined
5> whereis(myname1). 
undefined

4.2、设置bank_center为系统进程，并且能监控客户进程的退出

init(_) ->
%% 把系统进程设置为系统进程
process_flag(trap_exit, true),
?I("Start ~p ...", [?MODULE]),
{ok, 0}.

Eshell V5.10.4 (abort with ^G)
1> bank_server:create_account(myname1, 100).
true
2> 
2> myname1 ! error.
##[<0.38.0>bank_server:141] terminate: {bad_return_value,{ok,100}}
##[<0.37.0>bank_center:81] handle_info: {'EXIT',<0.38.0>,
{bad_return_value,{ok,100}}}
error
3> 
=ERROR REPORT==== 16-Jan-2015::17:12:34 ===
** Generic server <0.38.0> terminating 
** Last message in was error
** When Server state == 100
** Reason for termination == 
** {bad_return_value,{ok,100}}

3> whereis(bank_center).
<0.37.0>
4> whereis(myname1). 
undefined

{'EXIT', <0.38.0>, {bad_return_value,{ok,100}}}

Eshell V5.10.4 (abort with ^G)
1> bank_server:create_account(myname1, 100).
true
2> myname1 ! stop2.
##[<0.38.0>bank_server:141] terminate: normal
##[<0.37.0>bank_center:81] handle_info: {'EXIT',<0.38.0>,normal}
stop2

5、完整演示代码下载

地址：http://download.csdn.net/detail/u011471961/8368973

Erlang入门：构建application练习4（进程link的作用）

标签：erlang   入门教程   application   link   

原文地址：http://blog.csdn.net/zhongruixian/article/details/42779731