erlang gen_fsm编程框架

本文是erlang中的gen_fsm编程框架，在我们使用这个模型的时候，如果在这些代码的基础上进行开发的话，会收到事半功倍的效果。

%%%-------------------------------------------------------------------

%%% File    : eb_atm.erl

%%% Author  : Mitchell Hashimoto

%%% Description : The ATM backend for ErlyBank

%%%

%%% Created :  6 Sep 2008 by Mitchell Hashimoto

%%%-------------------------------------------------------------------

-module(eb_atm).

-behaviour(gen_fsm).

%% API

-export([start_link/0]).

%% gen_fsm callbacks

-export([init/1, state_name/2, state_name/3, handle_event/3,

         handle_sync_event/4, handle_info/3, terminate/3, code_change/4]).

-define(SERVER, ?MODULE).

%%====================================================================

%% API

%%====================================================================

%%--------------------------------------------------------------------

%% Function: start_link() -> ok,Pid} | ignore | {error,Error}

%% Description:Creates a gen_fsm process which calls Module:init/1 to

%% initialize. To ensure a synchronized start-up procedure, this function

%% does not return until Module:init/1 has returned.

%%--------------------------------------------------------------------

start_link() ->

  gen_fsm:start_link({local, ?SERVER}, ?MODULE, [], []).

%%====================================================================

%% gen_fsm callbacks

%%====================================================================

%%--------------------------------------------------------------------

%% Function: init(Args) -> {ok, StateName, State} |

%%                         {ok, StateName, State, Timeout} |

%%                         ignore                              |

%%                         {stop, StopReason}

%% Description:Whenever a gen_fsm is started using gen_fsm:start/[3,4] or

%% gen_fsm:start_link/3,4, this function is called by the new process to

%% initialize.

%%--------------------------------------------------------------------

init([]) ->

  {ok, state_name, nobody}.

%%--------------------------------------------------------------------

%% Function:

%% state_name(Event, State) -> {next_state, NextStateName, NextState}|

%%                             {next_state, NextStateName,

%%                                NextState, Timeout} |

%%                             {stop, Reason, NewState}

%% Description:There should be one instance of this function for each possible

%% state name. Whenever a gen_fsm receives an event sent using

%% gen_fsm:send_event/2, the instance of this function with the same name as

%% the current state name StateName is called to handle the event. It is also

%% called if a timeout occurs.

%%--------------------------------------------------------------------

state_name(_Event, State) ->

  {next_state, state_name, State}.

%%--------------------------------------------------------------------

%% Function:

%% state_name(Event, From, State) -> {next_state, NextStateName, NextState} |

%%                                   {next_state, NextStateName,

%%                                     NextState, Timeout} |

%%                                   {reply, Reply, NextStateName, NextState}|

%%                                   {reply, Reply, NextStateName,

%%                                    NextState, Timeout} |

%%                                   {stop, Reason, NewState}|

%%                                   {stop, Reason, Reply, NewState}

%% Description: There should be one instance of this function for each

%% possible state name. Whenever a gen_fsm receives an event sent using

%% gen_fsm:sync_send_event/2,3, the instance of this function with the same

%% name as the current state name StateName is called to handle the event.

%%--------------------------------------------------------------------

state_name(_Event, _From, State) ->

  Reply = ok,

  {reply, Reply, state_name, State}.

%%--------------------------------------------------------------------

%% Function:

%% handle_event(Event, StateName, State) -> {next_state, NextStateName,

%%                                                NextState} |

%%                                          {next_state, NextStateName,

%%                                                NextState, Timeout} |

%%                                          {stop, Reason, NewState}

%% Description: Whenever a gen_fsm receives an event sent using

%% gen_fsm:send_all_state_event/2, this function is called to handle

%% the event.

%%--------------------------------------------------------------------

handle_event(_Event, StateName, State) ->

  {next_state, StateName, State}.

%%--------------------------------------------------------------------

%% Function:

%% handle_sync_event(Event, From, StateName,

%%                   State) -> {next_state, NextStateName, NextState} |

%%                             {next_state, NextStateName, NextState,

%%                              Timeout} |

%%                             {reply, Reply, NextStateName, NextState}|

%%                             {reply, Reply, NextStateName, NextState,

%%                              Timeout} |

%%                             {stop, Reason, NewState} |

%%                             {stop, Reason, Reply, NewState}

%% Description: Whenever a gen_fsm receives an event sent using

%% gen_fsm:sync_send_all_state_event/2,3, this function is called to handle

%% the event.

%%--------------------------------------------------------------------

handle_sync_event(Event, From, StateName, State) ->

  Reply = ok,

  {reply, Reply, StateName, State}.

%%--------------------------------------------------------------------

%% Function:

%% handle_info(Info,StateName,State)-> {next_state, NextStateName, NextState}|

%%                                     {next_state, NextStateName, NextState,

%%                                       Timeout} |

%%                                     {stop, Reason, NewState}

%% Description: This function is called by a gen_fsm when it receives any

%% other message than a synchronous or asynchronous event

%% (or a system message).

%%--------------------------------------------------------------------

handle_info(_Info, StateName, State) ->

  {next_state, StateName, State}.

%%--------------------------------------------------------------------

%% Function: terminate(Reason, StateName, State) -> void()

%% Description:This function is called by a gen_fsm when it is about

%% to terminate. It should be the opposite of Module:init/1 and do any

%% necessary cleaning up. When it returns, the gen_fsm terminates with

%% Reason. The return value is ignored.

%%--------------------------------------------------------------------

terminate(_Reason, _StateName, _State) ->

  ok.

%%--------------------------------------------------------------------

%% Function:

%% code_change(OldVsn, StateName, State, Extra) -> {ok, StateName, NewState}

%% Description: Convert process state when code is changed

%%--------------------------------------------------------------------

code_change(_OldVsn, StateName, State, _Extra) ->

  {ok, StateName, State}.

%%--------------------------------------------------------------------

%%% Internal functions

%%--------------------------------------------------------------------