Programming Erlang读书笔记9: 并行程序里的错误

使用BIF link将两个节点连接起来，如果其中一个节点B退出，则另一个节点A会收到{'EXIT', B, Why}的信号

可以创建一个on_exit(Pid, Fun)方法来捕获某个Pid进程的死掉:

on_exit(Pid, Fun) ->
  spawn(fun() ->
      process_flag(trap_exit, true),
      link(Pid),
      receive
        {'EXIT', Pid, Why} ->
          Fun(Why)
      end
    end).

Erlang可以远程捕获和处理错误(跨机器)

调用BIF process_flag(trap_exit, true)来将一个正常的进程转换为一个可以trap exits的系统进程

trap_exit  Exit Signal  Action
true          kill        Die: Broadcast the exit signal killed to the link set.
true           X          Add {'EXIT', Pid, X} to the mailbox.
false         normal      Continue: Do-nothing signal vanishes.
false         kill        Die: Broadcast the exit signal killed to the link set.
false          X          Die: Broadcast the exit signal X to the link set.

Idiom1: I Don't Care If a Process I Created Crashes

Pid = spawn(fun() -> ... end)

Idiom2: I Want to Die If a Process I Created Crashes

Pid = spawn_link(fun() -> ... end)

Idiom3: I Want to Handle Errors If a Process I Create Crashes

...
process_flag(trap_exit, true),
Pid = spawn_link(fun() -> ... end),
...
loop(...).

loop(State) ->
  receive
    {'EXIT', SomePid, Reason} ->
      %% do something with the error
      loop(State1);
    ...
  end

Error Handling Primitives

@spec spawn_link(Fun) -> Pid

@spec process_flag(trap_exit, true)

@spec link(Pid) -> true

@spec unlink(Pid) -> true

@spec exit(Why) -> none()

@spec exit(Pid, Why) -> true

@spec erlang:monitor(process, Item) -> MonitorRef