上面的例子中,因为 “Pong” 在 “ping” 进程开始前已经创建完成,所以才能将 “pong” 进程的进程标识符作为参数传递给进程 “ping”。
这也就说,“ping” 进程必须通过某种途径获得 “pong” 进程的进程标识符后才能将消息发送 “pong” 进程。
然而,某些情况下,进程需要相互独立地启动,而这些进程之间又要求知道彼此的进程标识符,前面提到的这种方式就不能满足要求了。因此,Erlang 提供了为每个进程提供一个名称绑定的机制,这样进程间通信就可以通过进程名来实现,而不需要知道进程的进程标识符了。为每个进程注册一个名称需要用到内置函数 register:
register(some_atom, Pid)
接下来,让我们一起上面的 ping pong 示例程序。这一次,我们为 “pong” 进程赋予了一名进程名称 pong:
-module(tut16). -export([start/0, ping/1, pong/0]). ping(0) -> pong ! finished, io:format("ping finished~n", []); ping(N) -> pong ! {ping, self()}, receive pong -> io:format("Ping received pong~n", []) end, ping(N - 1). pong() -> receive finished -> io:format("Pong finished~n", []); {ping, Ping_PID} -> io:format("Pong received ping~n", []), Ping_PID ! pong, pong() end. start() -> register(pong, spawn(tut16, pong, [])), spawn(tut16, ping, [3]).
2> c(tut16). {ok, tut16} 3> tut16:start(). <0.38.0> Pong received ping Ping received pong Pong received ping Ping received pong Pong received ping Ping received pong ping finished Pong finished
start/0 函数如下:
register(pong, spawn(tut16, pong, [])),
创建 “pong” 进程的同时还赋予了它一个名称 pong。在 “ping” 进程中,通过如下的形式发送消息:
pong ! {ping, self()},
ping/2 变成了 ping/1。这是因为不再需要参数 Pong_PID 了。