On Feb 4, 2011, at 12:54 PM, Ion Gaztañaga wrote:
El 04/02/2011 3:05, Howard Hinnant escribió:
In this set condition_variable_any and unique_lock are in C++0x. I hope to propose shared_lock and shared_mutex for tr2 and ultimately c++1x. Field experience here (good or bad) would help. Here is a tutorial and implementation of the shared and upgrade mutexes and locks:
http://home.roadrunner.com/~hinnant/mutexes/locking.html
Here is an implementation of condition_variable_any:
http://llvm.org/svn/llvm-project/libcxx/trunk/include/condition_variable
Thanks Howard! Just two comments:
a) Windows Vista condition variables natively supports Slim Reader/Writer Locks (http://msdn.microsoft.com/en-us/library/ms686304%28v=VS.85%29.aspx), the implementation could take advantage of this if shared_mutex is based on this primitive.
<nod> Agreed.
b) Is there any reason to store shared_ptr<mutex> instead of a mutex?
Yes. I missed this subtlety for years. I think it was Peter Dimov who pointed it out to me: Thread A notfies the condition_variable_any, which thread B is waiting on. Then thread A destructs the condition_variable_any before thread B wakes and returns from the wait. This is supposed to work. The POSIX condition variable also works this way. The shared_ptr is used to share ownership of the mutex between the condition_variable_any, and the thread running the wait function. If the condition_variable_any destructs while the wait is running, the mutex stays alive long for the wait function to lock and unlock it, and then destructs when the wait returns. -Howard