removes a specific thread from a sleep queue. sleepq_resume_thread()
resumes scheduling of a thread that has been previously removed from a
sleep queue.
- sleepq_catch_signals() just removes a thread from the queue it was just
added to when a pending signal is found.
- sleepq_signal() and sleepq_broadcast() remove threads from a queue,
drop the queue lock, and then resume all the previously removed threads.
This doesn't completely fix the sched_lock <-> sleepq chain LOR, but it
makes it a little better as we no longer call setrunnble() with a sleep
queue lock held meaning if setrunnable() tries to wakeup the swapper we
don't try to lock two sleep queue chains at the same time.
condition where kse_wakeup() doesn't yet see them in (interruptible)
sleep queues. Also add an upcall check to sleepqueue_catch_signals()
suggested by jhb.
This commit should fix recent mysql hangs.
Reviewed by: jhb, davidxu
Mysql'd by: Robin P. Blanchard <robin.blanchard at gactr uga edu>
might be enqueued on a sleep queue but not be asleep when the timeout fires
if it is blocked on a lock trying to check for pending signals before going
to sleep. In the case of fixing up the TDF_TIMEOUT race, however, the
thread must be marked asleep.
Reported by: kan (the bogus one)
to queue threads sleeping on a wait channel similar to how turnstiles are
used to queue threads waiting for a lock. This subsystem will be used as
the backend for sleep/wakeup and condition variables initially. Eventually
it will also be used to replace the ithread-specific iwait thread
inhibitor.
Sleep queues are also not locked by sched_lock, so this splits sched_lock
up a bit further increasing concurrency within the scheduler. Sleep queues
also natively support timeouts on sleeps and interruptible sleeps allowing
for the reduction of a lot of duplicated code between the sleep/wakeup and
condition variable implementations. For more details on the sleep queue
implementation, check the comments in sys/sleepqueue.h and
kern/subr_sleepqueue.c.
