officially have undefined behavior, from returning an error code to raising
an assertion failure.
Also, don't bother to explicitly test for (illegal) null pointers and return
an error; they'll bomb out soon enough.
front of the sleep queue rather than the back. This is more
cache-friendly behavior and within the (lack of) constraints on wakeup
ordering imposed on equal-priority threads.
* Use a double-checked locking technique to avoid taking
the interlock in pthread_mutex_unlock().
* In pthread_mutex_lock() and pthread_mutex_trylock(), only store the
stack pointer, not the thread ID, in ptm_owner. Do the translation
to a thread ID in the slow-lock, errorcheck, and recursive mutex
cases rather than in the common path.
* Juggle where pthread__self() is called, to move it out of the fast path.
Overall, this means that neither pthread_self() nor
pthread_spin[un]lock() are used in the course of locking and unlocking
an uncontested mutex. Speeds up the fast path by 40-50%, and
eliminates about 98% of spinlocks used by a couple of large threaded
applications.
(Still a GET_MUTEX_PRIVATE() in the fast path... perhaps the type
should be in the main body of the mutex).
