sync_bounded_queue::wait_pull_front( lve ) might throw

[enniobarbaro@…]

Expected behavior:

A call to to sync_bounded_queue<T>::wait_pull_front can only throw via T's assignment operator. If the queue is closed, this is reported via the return value.

Actual behavior:

sync_bounded_queue<T>::wait_pull_front might spuriously throw a sync_queue_is_closed error.

Line 486 of sync_bounded_queue.hpp (current github master) checks if the queue is empty and closed; however the very next line calls the one-argument overload of wait_until_not_empty, which might throw if the queue became closed and empty in the meantime. wait_pull_front should use the overload of wait_until_not_empty which returns a closed flag.

[viboes]

​https://github.com/boostorg/thread/commit/51b367df53bc2f9a3f720cc062d997fb4eb89571