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Subject: Re: [boost] [thread 1.48] Multiple interrupt/timed_join leads to deadlock
From: Gaetano Mendola (mendola_at_[hidden])
Date: 2012-12-05 08:45:24

On 05/12/2012 13.42, Vicente J. Botet Escriba wrote:
> Le 05/12/12 12:33, Gaetano Mendola a écrit :
>> On 05/12/2012 09.16, Anthony Williams wrote:
>>> On 04/12/12 18:32, Gaetano Mendola wrote:
>>>> Hi all,
>>>> I was investigating a rare deadlock when issuing an interrupt and
>>>> a timed_join in parallel. I come out with the the following code
>>>> showing the behavior.
>>>> The deadlock is rare so sometime you need to wait a bit.
>>>> I couldn't try it with boost 1.52 because the code is invalid
>>>> due the precondition of "thread joinable" when issuing the
>>>> timed_join.
>>> That's a hint.
>>>> Is the code not valid or a real bug?
>>> The code is invalid: you keep trying to interrupt and join even after
>>> the thread has been joined! Once the thread has been joined, the thread
>>> handle is no longer valid, and you should exit the loop.
>> I haven't seen this statement in the documentation.
>> The loop was meant to exploit exactly this, then you are confirming
>> that interrupting a joined thread is not valid. How do I safely
>> interrupt then a thread?
>> There is no "atomic" check_joinable_then_interrupt, whatching at the
>> interrupt code it seems that the check is done inside. I'm lost.
> Boost.Thread and std::thread are designed so that there is only one
> owner of the thread. That is only one thread can join/interrupt a thread
> safely.

Unless I have totally missed it the documentation doesn't mention
anything about thread safety (would that be an hint about it?).

Googling for it comes out exactly this question on stackoverflow:

and the answer was: "And it appears that yes, it is thread-safe."

I have added now the answer stating the opposite.

Gaetano Mendola

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