Date: Wed, 27 Jul 2005 08:48:57 +0200 From: "Norbert Koch" <NKoch@demig.de> To: "Scott Long" <scottl@samsco.org> Cc: "Freebsd-Hackers@Freebsd. Org" <freebsd-hackers@freebsd.org> Subject: RE: await & asleep Message-ID: <001801c59277$432fd960$4801a8c0@ws-ew-3.W2KDEMIG> In-Reply-To: <42E65A9F.4010504@samsco.org>
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> > The functions await() and asleep() in kern_synch.c > > are marked as EXPERIMENTAL/UNTESTED. > > Is this comment still valid? Does anyone have used > > those functions successfully? Should I better not > > use them in my device driver code for RELENG_4? > > How do I correctly cancel a request (as I should do > > according to the man page): "asleep (NULL, 0, NULL, 0)"? > > The await family was removed in 5.x and beyond, so trying to > use them in 4.x will make your driver very unportable. There > are better ways than await to handle delayed events. Ok, my [classical] situation is this: 1. an interrupt handler writes into a queue 2. a read function reading from the queue pseudo code using asleep()/await() (no error handling): read() { forever { while ! empty_queue() { uiomove(&uio, ...); if (uio->uio_resid == 0) { return 0; } } asleep(& read_queue, ...); if (empty_queue ()) { error = await (...); } else { asleep (NULL, ...); } } } If I want to do that with plain tsleep() I have to use spl??() to lock the empty_queue() call and not lose a wakeup() from the interrupt handler. But if I add error checks the code becomes very ugly compared to the solution above. I never wrote a driver under 5.X. As I understand I would use a mutex to access the queue and call msleep() to sleep with the mutex unlocked. (That seems to simulate pthread_cond_timedwait(), doesn't it?) pseudo code: read() { forever { while ! empty_queue() { uiomove(&uio, ...); if (uio->uio_resid == 0) { return 0; } } mtx_lock (&mutex); if (empty_queue ()) { error = msleep (&queue, &mutex, ...); }; mtx_unlock (&mutex); } } How would you suggest to do that under 4.X in an _elegant_ way w/o asleep/await? Norbert
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