Erlang gen_server转换错误的返回值

Question

我尝试将消息转发给gen_server:

 gen_server:cast({global, ID}, {watchers}).

处理程序是:

handle_cast({watchers}, State) ->
    case State#table_state.watchers of
    [] ->
        {reply, no_watchers, State};
    _ ->
        {reply, State#table_state.watchers, State}
    end;

但是当我执行gen_server:castgen_server时会终止并出现错误:

=ERROR REPORT==== 29-Apr-2011::18:26:07 ===
** Generic server 1 terminating 
** Last message in was {'$gen_cast',{watchers}}
** When Server state == {table_state,1,"1",11,[]}
** Reason for termination == 
** {bad_return_value,{reply, no_watchers, {table_state,3,"3",11,[]}}}

我为什么要这样bad_return_value？

Answer 1

您无法使用演员表回复(请参阅gen_server文档).这是投射异步消息而不是使用调用的重点.

在您的情况下,您想要返回一个回复,所以请gen_server:call/2改用.