[Boost-bugs] [Boost C++ Libraries] #7319: Take care of c++std-lib-32966 issue

Subject: [Boost-bugs] [Boost C++ Libraries] #7319: Take care of c++std-lib-32966 issue
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-09-02 08:32:23

#7319: Take care of c++std-lib-32966 issue
------------------------------+---------------------------------------------
 Reporter:  viboes            |       Owner:  anthonyw
     Type:  Bugs              |      Status:  new     
Milestone:  To Be Determined  |   Component:  thread  
  Version:  Boost 1.51.0      |    Severity:  Problem 
 Keywords:                    |  
------------------------------+---------------------------------------------
 Take care of the issue raised by Howard Hinnant in

 [c++std-lib-32966] Public service announcement concerning
 ~condition_variable_any()

 "Both condition_variable and condition_variable_any are based on the POSIX
 pthread_cond_t.  One of the very subtle behaviors of pthread_cond_t is
 that it is ok for a pthread_cond_t to be destroyed after all waiting
 threads have been signaled (assuming no new threads initiate a wait).
 There's even an example demonstrating this at
 http://www.unix.org/online.html under the specification for
 pthread_cond_destroy.

 This subtlety is reflected in the Requires clause for the destructor of
 both condition_variable and condition_variable_any:

 > Requires: There shall be no thread blocked on *this. [Note: That is, all
 threads shall have been notified; they may subsequently block on the lock
 specified in the wait. This relaxes the usual rules, which would have
 required all wait calls to happen before destruction. Only the
 notification to unblock the wait must happen before destruction. The user
 must take care to ensure that no threads wait on *this once the destructor
 has been started, especially when the waiting threads are calling the wait
 functions in a loop or using the overloads of wait, wait_for, or
 wait_until that take a predicate. — end note ]

 To be *perfectly* clear, the following is ok:


 {{{
   Thread A                    Thread B
    ...                        lk.lock()
    ...                        cv.wait(lk)
   lk.lock()                      ...
   cv.notify_one()                ...
   cv.~condition_variable_any()   ...
   lk.unlock()                    ...
     ...                       finally exits cv.wait  // ok, not a data
 race
 }}}

 "

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7319>
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