[英]GenServer doesn't trap_exit when started with start_link
I found that when trying to trap exit signal, starting a GenServer with GenServer.start
then Process.link
the pid has very different outcome than running GenServer.start_link
. 我发现当尝试捕获退出信号时,使用
GenServer.start
启动GenServer.start
然后进行Process.link
,pid与运行GenServer.start_link
结果GenServer.start_link
。
Here's the experiment code I used to demonstrate the problem: 这是我用来演示问题的实验代码:
defmodule Foo do
defmodule Server do
def init(_) do
Process.flag(:trap_exit, true)
{:ok, nil}
end
def handle_info({:EXIT, from, reason}, _) do
IO.inspect({:kill_signal, from, reason})
{:noreply, nil}
end
end
def foo() do
Process.flag(:trap_exit, true)
# version 1
{:ok, pid} = GenServer.start_link(Server, nil)
# version 2
# {:ok, pid} = GenServer.start(Server, nil)
# Process.link(pid)
# print process info
IO.inspect({self(), pid, Process.info(pid)})
Process.exit(pid, :reason)
:timer.sleep(200)
end
end
Foo.foo
With version 1, the EXIT signal cause the Server
to exit without being caught in its handle_info
block, but with version 2, the signal was correctly intercepted and processed in handle_info
block, and therefore Server
is not terminated. 对于版本1,EXIT信号导致
Server
退出而不会被其handle_info
块捕获,但是对于版本2,信号在handle_info
块中被正确拦截和处理,因此Server
不会终止。 I also notice that the Process.info
of these two ways to start a GenServer are identical. 我还注意到,启动GenServer的这两种方式的
Process.info
是相同的。
I tried the same thing with spawn_link
and spawn
, but they all behaves as expected - EXIT signal all being caught - there's no difference: 我用
spawn_link
和spawn
尝试了同样的事情,但它们都表现得像预期的那样 - EXIT信号都被捕获 - 没有区别:
defmodule Foo do
def loop do
Process.flag(:trap_exit, true)
receive do
msg -> IO.inspect(msg)
end
loop
end
def foo() do
Process.flag(:trap_exit, true)
# version 1
pid = spawn_link(&loop/0)
# version 2
# pid = spawn(&loop/0)
# Process.link(pid)
# print process info
IO.inspect({self(), pid, Process.info(pid)})
Process.exit(pid, :reason)
:timer.sleep(200)
end
end
Foo.foo
By the way I'm using Elixir 1.8.1 on Erlang/OTP 21, if it matters. 顺便说一句,我在Erlang / OTP 21上使用Elixir 1.8.1,如果重要的话。
I want to know what causes the difference in behaviors, is this a bug or by design, and how I can trap EXIT correctly if I want to call start+link atomically. 我想知道导致行为差异的原因,这是一个错误还是设计,以及如果我想以原子方式调用start + link,我如何正确捕获EXIT。
handle_info
is not being called because the one sending the exit signal is the parent process. handle_info
未被调用,因为发送退出信号的是父进程。 GenServer and all other behaviours handles the parent exit signal and always shuts down when the parent does, mainly because if you are in a supervision tree and your supervisor shuts down, you want to terminate immediately too as at that moment all bets are off. GenServer和所有其他行为处理父出口信号并在父进程时始终关闭,主要是因为如果您在监督树中并且您的主管关闭,您希望立即终止,因为此时所有投注都已关闭。 If you replace this:
如果你替换这个:
Process.exit(pid, :reason)
By: 通过:
spawn fn -> Process.exit(pid, :reason) end
You can see handle_info
called as another process is sending the exit signal. 您可以看到
handle_info
被调用,因为另一个进程正在发送退出信号。
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