Description

   This routine attempts to lock the mutex specified in the mutex
   argument. When a thread calls this routine, an attempt is made to
   immediately lock the mutex. If the mutex is successfully locked,
   this routine returns zero (0) and the calling thread becomes the
   mutex's current owner. If the specified mutex is locked when a
   thread calls this routine, the calling thread does not wait for
   the mutex to become available.

   The behavior of this routine is as follows:

   o  For a normal, default, or errorcheck mutex: if the mutex
      is locked by any thread (including the calling thread) when
      this routine is called, this routine returns [EBUSY] and the
      calling thread does not wait to acquire the lock.

   o  For a normal or errorcheck mutex: if the mutex is not owned,
      this routine returns zero (0) and the mutex becomes locked by
      the calling thread.

   o  For a recursive mutex: if the mutex is owned by the current
      thread, this routine returns zero (0) and the mutex lock count
      is incremented. (To unlock a recursive mutex, each call to
      pthread_mutex_trylock() must be matched by a call to pthread_
      mutex_unlock().)

   Use the pthread_mutexattr_settype() routine to set the mutex type
   attribute (normal, default, recursive, or errorcheck).