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application模块

applictaion:get_all_env().
applictaion:get_all_env(App).

get_env/1/2

格式:

applictaion:get_env(Par).
applictaion:get_env(App, Par).

实例:

application:get_env(octopus).

set_env/2/3

格式:

applictaion:set_env(App, Key, Value).

实例:

applictaion:set_env(octopus, port, 80).

start/1/2

结构:

start(Application) -> ok | {error, Reason}
start(Application, Type) -> ok | {error, Reason}
类型:
Application = atom()
Type = restart_type()
Reason = term()

步骤:

1.如果没有reload,先调用reload/1加载
2.检查env下参数applications下的app是否全部启动,如没有,返回:{error,{not_started,App}}
3.建立application master用于以后管理子进程
4.查env下参数mod的值Module,并执行Module:start/2函数

Type参数:

默认为temporary
可选参数:permanent | transient | temporary

permanent: 如果app终止了,那么整个系统都会停止工作.通过调用application:stop/1 手动终止app的情况除外
transient: 如果 app 以 normal 的原因终止, 没有影响. 任何其他终止原因都会导致整个系统关闭
temporary: application 可以以任何原因终止, 只会产生报告, 没有其他任何影响

Module:start/2

结构:

Module:start(StartType, StartArgs) -> {ok, Pid} | {ok, Pid, State} | {error, Reason}
类型:
StartType =
      normal |
      {takeover, Node :: node()} |
      {failover, Node :: node()}
StartArgs = term()
Pid = pid()
State = term()

说明:

当调用application:start/1/2时调用,并启动此application的进程
if此application是基于OTP设计原则的结构作为supervision树,则means:
  启动top supervisor tree

StartType参数:

normal: 如是normal启动
normal:  if the application is distributed and started at the current node
          because of a failover from another node, and the application
          specification key start_phases == undefined.
{takeover,Node} if the application is distributed and started at the current node
                  because of a takeover from Node, either because takeover/2 has
                  been called or because the current node has higher priority than Node.
{failover,Node} if the application is distributed and started at the current node
                 because of a failover from Node, and the application
                 specification key start_phases /= undefined.

StartArgs:

env中mod参数给定的值

返回值:

{ok,Pid} or {ok,Pid,State}
State: 任何值，当application stop时会传递给Module:prep_stop/1

Module:stop/1

结构:

Module:stop(State)
类型
State = term()

说明:

if 函数 Module:prep_stop/1存在, State是它的返回值,
if 函数 Module:prep_stop/1不存在, State是 Module:start/2的返回值

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