gen_server源码杂记

调用gen_server启动的方法
gen_server :start_link ( { local, ?MODULE } , ?MODULE , [ ] , [ ] ) .
参数分别是Name,Mod,Arg,Options

Options里可以设置timeout

gen.erl里的简单小函数取得timeout

timeout(Options) ->
    case opt(timeout, Options) of
	{ok, Time} ->
	    Time;
	_ ->
	    infinity
    end.

spawn_opts(Options) ->
    case opt(spawn_opt, Options) of
	{ok, Opts} ->
	    Opts;
	_ ->
	    []
    end.

opt(Op, [{Op, Value}|_]) ->
    {ok, Value};
opt(Op, [_|Options]) ->
    opt(Op, Options);
opt(_, []) ->
    false.

gen_server启动流程大体如下：
在我们的程序里启动一般调用如下：

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

gen_server.erl 里

start_link(Name, Mod, Args, Options) ->
    gen:start(?MODULE, link, Name, Mod, Args, Options).

gen.erl里基本是这样

do_spawn(GenMod, link, Mod, Args, Options) ->
    Time = timeout(Options),
    proc_lib:start_link(?MODULE, init_it,
			[GenMod, self(), self(), Mod, Args, Options], 
			Time,...

proc_lib是一个关于进程的工具类，提供了同步启动进程的机制

start_link(M,F,A,Timeout,SpawnOpts) when is_atom(M), is_atom(F), is_list(A) ->
    Pid = proc_lib:spawn_opt(M, F, A, ensure_link(SpawnOpts)),
    sync_wait(Pid, Timeout).

sync_wait(Pid, Timeout) ->
    receive
	{ack, Pid, Return} ->
	    Return;
	{'EXIT', Pid, Reason} ->
	    {error, Reason}
    after Timeout ->
	    unlink(Pid),
	    exit(Pid, kill),
	    flush(Pid),
	    {error, timeout}
    end.

spawn_opt系列大体就是erlang:spawn系里的一个，是异步的，先调用了本模块的init_p，存放些上下文信息到进程字典，最终会回调gen_server，一会再说

同步的关键在sync_wait这句，一看就懂了

上面的spawn经过fun的传来传去最终回到了gen_server.erl

init_it(Starter, self, Name, Mod, Args, Options) ->
    init_it(Starter, self(), Name, Mod, Args, Options);
init_it(Starter, Parent, Name0, Mod, Args, Options) ->
    Name = name(Name0),
    Debug = debug_options(Name, Options),
    case catch Mod:init(Args) of
	{ok, State} ->
	    proc_lib:init_ack(Starter, {ok, self()}), 	    
	    loop(Parent, Name, State, Mod, infinity, Debug);
	{ok, State, Timeout} ->
	    proc_lib:init_ack(Starter, {ok, self()}), 	    
	    loop(Parent, Name, State, Mod, Timeout, Debug);
	{stop, Reason} ->
	    %% For consistency, we must make sure that the
	    %% registered name (if any) is unregistered before
	    %% the parent process is notified about the failure.
	    %% (Otherwise, the parent process could get
	    %% an 'already_started' error if it immediately
	    %% tried starting the process again.)
	    unregister_name(Name0),
	    proc_lib:init_ack(Starter, {error, Reason}),
	    exit(Reason);
	ignore ->
	    unregister_name(Name0),
	    proc_lib:init_ack(Starter, ignore),
	    exit(normal);
	{'EXIT', Reason} ->
	    unregister_name(Name0),
	    proc_lib:init_ack(Starter, {error, Reason}),
	    exit(Reason);
	Else ->
	    Error = {bad_return_value, Else},
	    proc_lib:init_ack(Starter, {error, Error}),
	    exit(Error)
    end.

看见这句了吧
catch Mod:init(Args)