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 Botet (vicente.botet_at_[hidden])
Date: 2012-12-05 10:29:28

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 handle is no longer valid, and you should exit the loop.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.

Best,
Vicente

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