[erlang-questions] Sending a message to a process that no longer exists

Hynek Vychodil <>
Tue Dec 9 12:09:13 CET 2008


or also look at do_call/4 and wait_resp_mon/3 in gen.erl

2008/12/9 Robert Virding <>

> Using erlang:monitor/2 is better as the process could die after you check
> it is alive but before it replies.
>
> Do you know that it will alwys reply?
>
> Check the module io.erl in stdlib which uses erlang:monitor/2 to make sure
> that io servers are alive long enough to reply to an io request. There is a
> bit of trickery needed when removing the monitor with erlang:demonitor/1 to
> make sure no 'DOWN' messages are left in the mailbox. N.B. monitoring stacks
> so you have to be careful to remove as many as you add.
>
> If you are going to send many requests in one go to the process it would be
> better to wrap the whole "transaction" with monitor/demonitor.
>
> Robert
>
> 2008/12/9 Rapsey <>
>
>> Or you can use a monitor (erlang:monitor/2), to receive a message when a
>> process dies.
>> Or you can check if a proces is alive with: erlang:is_process_alive(PID)
>>
>>
>> Sergej
>>
>>
>> On Tue, Dec 9, 2008 at 7:40 AM, Bernard Duggan <> wrote:
>>
>>> Jack Orenstein wrote:
>>> > On Dec 9, 2008, at 12:58 AM, Rapsey wrote:
>>> >
>>> >
>>> >> Using the send operator is very common. To avoid endless waiting in
>>> >> a receive statement you can use after:
>>> >>
>>> >> receive
>>> >>         {Server, Response} ->
>>> >>             ?DUMP({send_and_receive, received, Response}),
>>> >>             Response
>>> >>        after 1000 ->
>>> >>              void
>>> >>   end.
>>> >>
>>> >
>>> > But this won't distinguish a dead process from a slow one.
>>> >
>>> If you want to ensure the process is running, you can use
>>> process_flag(trap_exit, true),
>>> and then spawn_link(), instead of spawn() to create the server process.
>>> Then, in your receive block above add a pattern
>>>
>>> {'EXIT', Server, Reason}
>>>
>>> This will be sent to you when the server process exits for whatever
>>> reason.
>>>
>>> Cheers,
>>>
>>> Bernard
>>>
>>
>>
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>
>
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-- 
--Hynek (Pichi) Vychodil
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