Date: Wed, 10 Feb 2010 12:46:46 -0500 (EST) From: Daniel Eischen <deischen@freebsd.org> To: Randall Stewart <rrs@lakerest.net> Cc: threads@freebsd.org Subject: Re: Thinking about kqueue's and pthread_cond_wait Message-ID: <Pine.GSO.4.64.1002101232240.13876@sea.ntplx.net> In-Reply-To: <3CF3033E-FD13-405B-9DC6-DDE9DF4FBF37@lakerest.net> References: <3581A86D-9C9C-4E08-9AD3-CD550B180CED@lakerest.net> <Pine.GSO.4.64.1002101202060.13656@sea.ntplx.net> <3CF3033E-FD13-405B-9DC6-DDE9DF4FBF37@lakerest.net>
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On Wed, 10 Feb 2010, Randall Stewart wrote: > > On Feb 10, 2010, at 9:04 AM, Daniel Eischen wrote: > >> On Wed, 10 Feb 2010, Randall Stewart wrote: >> >>> All: >>> >>> I have once again come around to thinking about joining pthread cond waits >>> and >>> kqueue's. >>> >>> After thinking about it, I think its doable.. with something like a: >>> >>> pthread_cond_wait_kqueue_np(kev, cond, mtx, ucontext) >>> >>> Then you can use kev inside a kqueue i.e. >>> ret = kevent(kq, kev, 1, outkev, 1, NULL); >>> >>> Now when you saw the event: >>> if (kev.filter == EVFILT_UMTX){ /* not sure about the name here */ >>> pthread_kqueue_cond_wait_ret_np(kev, cond, mtx, ucontext) >>> do_user_action(cond,mtx, ucontext); >>> } >>> >>> Which would fill in the cond/mtx and ucontext for the user. >>> >>> Now does this sound useful to anyone.. i.e. should I spend the time >>> making it work? >>> >>> The only down side to this is that it would have to allocate memory so >>> one would need to do a: >>> >>> pthread_kqueue_cond_wait_free_np(kev) >>> >>> After you were done.. and I think it would be best for this to >>> be a ONE_SHOT.. i.e. you have to re-arm it if the event happens... >>> Of course until you free it that can be as simple as passing the kev >>> back down again (i.e. no pthread_cond_wait_kqueue_np() needed). >>> >>> Comments? Thoughts? i.e. especially is it worthwhile doing? >> >> Please don't mess with the pthread_ API like that :-) If you >> really want to munge them together, see my email to you a few >> weeks ago last time you brought it up.' > > If I remember right your email was basically don't do it... I will > go dig through the archives and re-read it all. No, it was to add an interface or two to the kqueue/kevent API, not to modify the pthread_ API (which shouldn't know anything about kqueues). I really think the OS is already given us the tools we need to do the job simply enough. You can easily use a pipe, socketpair, or EVFILT_SIGNAL to wakeup a thread stuck in kevent(). You can additionally use a mutex to protect data shared between thread waiting in kevent() and other threads. I don't see what problem this is trying to solve and I think whatever solution you come up with involving mutexes/CVs is not going to be any simpler and may even be more complex and messy. Mutexes and CVs are userland library thingies, not kernel entities. Yes, the umtx is a kernel entity, but it alone does not give you mutexes and CVs. So when you want to mix kqueues and mutexes/CVs, you are involving another userland library and this is what makes it messy. -- DE
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