pthread_mutex_trylock() should never block

[Igor Sysoev]

The current pthread_mutex_trylock() implementation in both libpthread (libkse)
and libthr can block if mutex is locked by another thread.

libphtread calls THR_LOCK_ACQUIRE() and it can be blocked.  

libthr's pthread_mutex_trylock() is too heavy - it calls 3 syscalls:
sigprocmask()/umtx_lock()/sigprocmask() and can be blocked too.


SUSv2 states:
[ http://www.opengroup.org/onlinepubs/007908799/xsh/pthread_mutex_lock.html ]

--------
The function pthread_mutex_trylock() is identical to pthread_mutex_lock()
except that if the mutex object referenced by mutex is currently locked
(by any thread, including the current thread), the call returns immediately.

[ ... ]

The pthread_mutex_trylock() function will fail if:

[EBUSY]
    The mutex could not be acquired because it was already locked.

[ ... ]

The pthread_mutex_lock() function may fail if:

[EDEADLK]
    The current thread already owns the mutex.
--------


Igor Sysoev
http://sysoev.ru/en/