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Date: Wed, 10 Oct 2012 21:12:33 +0200
From: Rickard Green <rick...@erlang.org>
Organization: Erlang/OTP, Ericsson AB
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To: Zhemzhitsky Sergey <Sergey_Zhemzhit...@troika.ru>
Cc: Erlang Questions <erlang-questi...@erlang.org>
Subject: Re: [erlang-questions] Port Driver. erl_drv_thread_join and
 ErlDrvTid reuse.
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>>From time to time erl_drv_thread_join returns error EDEADLK=3D35, i.e. th=
e current thread (scheduler thread) tries to join itself.
>
> According to the documentation =93A Thread identifier may be reused very =
quickly after a thread has terminated. Therefore, if a thread corresponding=
 to one of the involved thread identifiers has terminated since the thread =
identifier was saved, the result of erl_drv_equal_tids() might not give the=
 expected result.=94
>
> I suppose that thread terminates earlier then erl_drv_thread_join call ha=
ppens, so ErlDrvTid is already reused.
>

This reuse will not cause problems for erl_drv_thread_join() as long as =

it is used correctly (a tid wont be reused until after the thread has =

been joined). erl_drv_thread_join() will also refuse to join threads not =

created by erl_drv_thread_create(), and would in case the scheduler =

thread tried to join itself fail with EINVAL.

> So the question is how to use erl_drv_thread_join properly and how to gua=
rantee that the saved ErlDrvTid value points to the same data that was retu=
rned from erl_drv_thread_create?
>

It is important that the thread is joined once and *only* once. Are you =

sure that you don't do two calls to erl_drv_thread_join() for the same =

thread?

Regards,
Rickard
-- =

Rickard Green, Erlang/OTP, Ericsson AB.
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