Ingo Weinhold 2ea2527fe4 R/W lock implementation:
* Changed the rw_lock_{read,write}_unlock() return values to void. They
  returned a value != B_OK only in case of user error and no-one checked them
  anyway.
* Optimized rw_lock_read_[un]lock(). They are inline now and as long as
  there's no contending write locker, they will only perform an atomic_add().
* Changed the semantics of nested locking after acquiring a write lock: Read
  and write locks are counted separately, so read locks no longer implicitly
  become write locks. This does e.g. make degrading a write lock to a read
  lock by way of read_lock + write_unlock (as used in the VM) actually work.

These changes speed up the -j8 Haiku image build on my machine by a few
percent, but more interestingly they reduce the total kernel time by 25 %.
Apparently we get more contention on other locks, now.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@34830 a95241bf-73f2-0310-859d-f6bbb57e9c96
2009-12-31 17:03:41 +00:00
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