Re: [boost] [thread 1.48] Multiple interrupt/timed_join leads to deadlock

Subject: Re: [boost] [thread 1.48] Multiple interrupt/timed_join leads to deadlock
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-12-05 12:35:59

Le 05/12/12 16:59, Gaetano Mendola a écrit :
> 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 handle is no longer valid, and you should exit the loop.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 ?
>
Hi,

no function is considered been thread-safe until it is stated explicitly.

Vicente