Le 13/10/12 23:17, Andrzej Krzemienski a écrit :
2012/10/13 Vicente J. Botet Escriba <vicente.botet@wanadoo.fr>
Le 13/10/12 16:08, Andrzej Krzemienski a écrit :
std::future does
join without interruption. What does boost::future do? I think it should interrupt and join (or perhaps detach as per N3451).
I don't understand this. Could you clarify?
Sorry, I tried to say too much in one sentence. While std::thread's destructor terminates for joinable thread, std::future's destructor sort-of joins with the (implied) thread: it waits until the job is done. So we already have a potentially surprising suspension upon leaving the scope.
I guess you are referring to the case the std::future is created by async
0.
If the implementation chooses the launch::async policy,
*
— a call to a waiting function on an asynchronous return object that shares the shared state created
by this async call shall block until the associated thread has completed, as if joined (30.3.1.5);
C++ International Standard Otherwise
~std::future(); Effects: — releases any shared state (30.6.4); — destroys *this.
Could you explain me what waiting function is called on the future destructor that needs to block until the completion of the associated thread?
It is not any waiting function mentioned explicitly. It is the requirement in 30.6.8 para 5: "If the implementation chooses the launch::async policy, [...] the associated thread completion synchronizes with the return from the first function that successfully detects the ready status of the shared state or with the return from the last function that releases the shared state, whichever happens first."
Why the future destructor should be the last function that release the shared state? Best, Vicente