[PATCH] [libcxx] Fix bug in shared_timed_mutex that could cause a program to hang.

[Eric Fiselier]

Hi mclow.lists,

The summary of the bug, provided by STL: 

In shared_timed_mutex::try_lock_until() (line 195 in 3.6.0), you need to deliver a notification.  The scenario is:
 
* There are N threads holding the shared lock.
* One thread calls try_lock_until() to attempt to acquire the exclusive lock.  It sets the "I want to write" bool/bit, then waits for the N readers to drain away.
* K more threads attempt to acquire the shared lock, but they notice that someone said "I want to write", so they block on a condition_variable.
* At least one of the N readers is stubborn and doesn't release the shared lock.
* The wannabe-writer times out, gives up, and unsets the "I want to write" bool/bit.
 
At this point, a notification (it needs to be notify_all) must be delivered to the condition_variable that the K wannabe-readers are waiting on.  Otherwise, they can block forever without waking up.

http://reviews.llvm.org/D8796

Files:
  include/shared_mutex
  test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/stl_bug.pass.cpp

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D8796.23116.patch
Type: text/x-patch
Size: 3611 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20150402/f57baffd/attachment.bin>