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: Gaetano Mendola (mendola_at_[hidden])
Date: 2012-12-05 15:05:14

On 05/12/2012 19.57, Vicente J. Botet Escriba wrote:
> Le 05/12/12 18:39, Gaetano Mendola a écrit :
>> On 05/12/2012 18.08, Anthony Williams wrote:
>>> On 05/12/12 15:59, Gaetano Mendola wrote:
>>>> On 05/12/2012 16.29, Vicente Botet wrote:
>>>>> 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 ?
>>>
>>> Your code had two bugs. Firstly, it called interrupt and timed_join on
>>> the same thread object from multiple threads. Secondly, it called
>>> interrupt and timed_join in a loop without ever checking the result of
>>> timed_join.
>>>
>>> Vicente's quote from the docs addresses the second issue: if timed_join
>>> returns true then looping round to call interrupt and timed_join again
>>> is now a precondition violation, and thus undefined behaviour.
>>
>> Then I'm not reading well the precondition.
>>
>> this->get_id(): the thread id of the instance on which I'm calling the
>> boost::thread::interrupt().
>>
>> boost::this_thread::get_id(): gives the caller thread id.
>>
>> from documentation I'm reading that if an instance of boost::thread
>> doesn't refer to a thread of execution then it returns a
>> default-constructed boost::thread::id that represents Not-a-Thread.
>>
>> This means that in case of an already joined thread this->get_id()
>> returns a default-constructed boost::thread::id, how can that be equal
>> to current (caller) thread id?
>>
>> I'm reading the precondition as: "you can not time_join your self"
>>
>> Indeed looking at 1.52 code in the interrupt method I can read:
>>
>> if (this_thread::get_id() == get_id()) {
>>   boost::throw_exception(
>>     thread_resource_error(
>>       system::errc::resource_deadlock_would_occur,
>>       "boost thread: trying joining itself"));
>> }
>>
>> **boost thread: trying joining itself**
>>
>> I'm sure I'm still missing something.
>>
>>
> My bad. You are right the pre-conditions in 1.48 is not the correct one.
> I have updated the documentation for join() since 1.50 and since 1.52
> for all the other join functions. In particular
>
>
>         Member function |timed_join()|
>
> <http://www.boost.org/doc/libs/1_52_0/doc/html/thread/thread_management.html#thread.thread_management.thread.timed_join>
>
>
>
> bool  timed_join(const  system_time&  wait_until);
>
> template<typename  TimeDuration>
> bool  timed_join(TimeDuration  const&  rel_time);
>
> Preconditions:
>
>     the thread is joinable.
>
>
> So you are right there is a bug up to 1.51, with a fix on 1.52.
>
> Sorry for the troubles this issue could caused you.

I believe boost project deserve a wiki documentation site.

Gaetano Mendola

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