On 27/04/2013 09.05, Vicente J. Botet Escriba wrote:
Le 22/04/13 10:16, Michael Marcin a écrit :
On 4/21/2013 11:30 PM, Vicente J. Botet Escriba wrote:
Hi,
Back on topic of latches and barriers. I was reading up on Java's CyclicBarrier and found its await return value pretty interesting and probably fairly free to implement.
"...each invocation of await() returns the arrival index of that thread at the barrier."
"the arrival index of the current thread, where index getParties() - 1 indicates the first to arrive and zero indicates the last to arrive."
To do this in boost::thread::barrier you would just have to cache m_count right after the decrement and return it instead of the current true/false.
Yes, boost::barrier return true for the last wait. The change would be quite simple, but what would be he utility of such an index?
I have implemented a first prototype of a latch class that could be used also as a barrier. I don't know if the name is the good one then. I have also implemented a completion_latch class that is able to call a function when the counter reaches zero. I'm not satisfied with the current implementation as it needs a lot of synchronization.
The change set is https://svn.boost.org/trac/boost/changeset/84055. To see the sources, you would need to update the trunk or to take a look at https://svn.boost.org/svn/boost/trunk/boost/thread/
Please let me know what do you think.
As reported in another reply I believe as it is misses some features. Immagine indeed the following two scenarios: Thread T1 needs to wait that another thread T2 have executed a certain operation at least N times. In this case (with the precondition of count_down that counter > 0) T2 has to track how many count_down it has executed (knowing then the initial value and there is no way to know given a latch his current value) or issue a "try_wait" before the each count_down and this IMHO seems a bit awkward. Rubbing salt to the wound imagine if T1 has to wait that T2 and T3 have done a certain operation N times (in total). In this way T2 and T3 have to sync at start and communicate each other how many count_down they have executed, the trick of issuing a "try_wait" in this case doesn't work. In my opinion the solution of both use cases is to remove the precondition. Regards Gaetano Mendola