cvs commit: src/sys/kern kern_rwlock.c

[John Baldwin]

jhb         2006-04-18 18:27:54 UTC

  FreeBSD src repository

  Modified files:
    sys/kern             kern_rwlock.c 
  Log:
  Adaptively spin before blocking on the turnstile if an rwlock is write
  locked.  In general the adaptive spinning is similar to the same code
  for mutexes with some extra trickiness in rw_wunlock_hard().  Specifically,
  even though both wait bits might be set and we might have a turnstile with
  at least one waiting thread, there might not be any threads blocked on the
  queue we are not waking up (they might all be spinning), and we should
  only preserve the waiting flag for the queue we aren't waking up if there
  are in fact threads blocked on that queue.  Secondly, there might not be
  any threads blocked on the queue we have chosen to waken threads from
  (there might only be threads blocked on the other queue and the threads
  for this queue are all spinning) in which case we disown the turnstile
  instead of doing a braodcast and unpend.
  
  Revision  Changes    Path
  1.7       +88 -7     src/sys/kern/kern_rwlock.c