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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 10:59:19

On 05/12/2012 16.29, Vicente Botet wrote:
> Gaetano Mendola-3 wrote
>> 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 handle is no longer valid, and you should exit the loop.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?).
> From the 1.48 documentation
> "Member function timed_join()
> bool timed_join(const system_time& wait_until);
> template<typename TimeDuration>
> bool timed_join(TimeDuration const& rel_time);
> Preconditions:
> this->get_id()!=boost::this_thread::get_id()
> Postconditions:
> If *this refers to a thread of execution on entry, and timed_join
> returns true, that thread of execution has completed, and *this no longer
> refers to any thread of execution. If this call to timed_join returns false,
> *this is unchanged.
> "
> Your second call doesn't satisfy the pre-conditions, so that the outcome of
> this second call is undefined.

That precondition tests that your are not interrupting yourself doesn't
say anything about thread safety. Am I missing something ?

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