On Fri, Feb 25, 2011 at 1:51 AM, Russ Cox <r...@swtch.com> wrote: > > your layout in your first email (i think) assumes that wakeup > > can be called twice. > > it doesn't. the scenario in my first email has exactly one > sleep and one wakeup. > > the canonical problem you have to avoid when implementing > sleep and wakeup is that the wakeup might happen before > the sleep has gotten around to sleeping. >
There is a pattern in DragonFly BSD for use with tsleep (tsleep is evolutionarily related to p9's sleep, though the descent is tortuous), tsleep_interlock. tsleep_interlock(WAITCHAN); /* Kick off some operation or release some higher level lock or w/e */ tsleep(WAITCHAN, ...); tsleep_interlock queues a process but does not actually go to sleep. If a wakeup happens after the tsleep_interlock but before tsleep has fully slept, the process does not sleep in tsleep(). I do not know if a similar design would be feasible given Plan 9's sleep/wakeup; at first glance, it looks to be so - sleep_interlock would look similar to sleep's front-end, but it would not 'gotolabel(&m->sched)'. -- vs
