Description

   This routine locks a mutex with behavior that depends upon the
   type of mutex, as follows:

   o  If a normal or default mutex is specified, a deadlock can
      result if the current owner of the mutex calls this routine in
      an attempt to lock the mutex a second time. (The deadlock is
      not detected or reported.)

   o  If a recursive mutex is specified, the current owner of the
      mutex can relock the same mutex without blocking. The lock
      count is incremented for each recursive lock within the
      thread.

   o  If an errorcheck mutex is specified and the current owner
      tries to lock the mutex a second time, this routine reports
      the [EDEADLK] error. If the mutex is locked by another thread,
      the calling thread waits for the mutex to become available.

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

   The thread that has locked a mutex becomes its current owner and
   remains its owner until the same thread has unlocked it. This
   routine returns with the mutex in the locked state and with the
   calling thread as the mutex's current owner.

   A recursive or errorcheck mutex records the identity of the
   thread that locks it, allowing debuggers to display this
   information. In most cases, normal and default mutexes do not
   record the owning thread's identity.