Johan Nilsson wrote:
Yuval Ronen wrote:
Howard Hinnant wrote:
N2184 takes the minimalist approach. It is easier to add functionality (and the associated expense) than to subtract it. There are many things the N2184::thread does not directly support. I believe this is a feature, not a bug. This is true under the assumption that we need to target the least common denominator. Try/timed joins for example come for free on Windows. So you are imposing an unnecessary mutex+cv overhead for everyone wanting to use try/timed joins there.
I've decided to adopt a different approach and suggest a way to equalize ('harmonise' in EU terms :-) ) the platforms via the join2 extensions. In a perfect world, this would lead to everyone enjoying _zero overhead_ try/timed joins in a few years once pthread implementors adopt the extensions.
Yes, I agree that this can be considered idealistic; but the other option is to not even give them a chance to offer the functionality as there would be no portable C++ way to take advantage of it. I'm far from being an expert on the Windows internals, but maybe what seems to "zero overhead" try/timed join is not really zero overhead, and
Peter Dimov wrote: the overhead is there, just hidden somewhere inside. If that's the case, then the "idealistic" way to go is to get Windows to supply a true zero overhead join.
Basically you're just waiting for a thread handle to become signalled, much as waiting for an event, mutex or whatever. No more overhead than that, AFAIK.
One overhead I can think of is the need to call CloseHandle after the WaitForSingleObject, which means another OS call (kernel?). This doesn't exist on pthreads where calling pthread_join is enough. So in case of a single joiner, it seems pthreads is better, at least with respect to the CloseHandle call (and there might be other issues). Is the CloseHandle overhead significant? I really don't know. If it's not much, and there's really a way to implement zero-overhead multi/try/times joins, then that would certainly change my perspective.