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 13:57:57

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.

Best,
Vcente