pthread_mutex_lock(3C)					   Standard C Library Functions 				    pthread_mutex_lock(3C)

NAME

       pthread_mutex_lock, pthread_mutex_trylock, pthread_mutex_unlock - lock or unlock a mutex

SYNOPSIS

       cc -mt [ flag... ] file... -lpthread [ library... ]
       #include <pthread.h>

       int pthread_mutex_lock(pthread_mutex_t *mutex);

       int pthread_mutex_trylock(pthread_mutex_t *mutex);

       int pthread_mutex_unlock(pthread_mutex_t *mutex);

DESCRIPTION

       The  mutex  object referenced by mutex is locked by calling pthread_mutex_lock(). If the mutex is already locked, the calling thread blocks
       until the mutex becomes available. This operation returns with the mutex object referenced by mutex in the locked state	with  the  calling
       thread as its owner.

       If the mutex type is  PTHREAD_MUTEX_NORMAL, deadlock detection is not provided. Attempting to relock the mutex causes deadlock. If a thread
       attempts to unlock a mutex that it has not locked or a mutex that is unlocked, undefined behavior results.

       If the mutex type is  PTHREAD_MUTEX_ERRORCHECK, then error checking is provided. If a thread attempts to relock a mutex that it has already
       locked,	an  error  will  be returned. If a thread attempts to unlock a mutex that it has not locked or a mutex which is unlocked, an error
       will be returned.

       If the mutex type is  PTHREAD_MUTEX_RECURSIVE, then the mutex  maintains the concept of a lock count. When a thread successfully acquires a
       mutex  for  the first time, the lock count is set to 1. Every time a thread relocks this mutex, the lock count is  incremented by one. Each
       time the thread unlocks the mutex, the lock count is decremented by one. When the lock count reaches  0, the mutex  becomes  available  for
       other  threads  to  acquire.  If  a thread  attempts to unlock a mutex that it has not locked or a mutex that is unlocked, an error will be
       returned.

       If the mutex type is  PTHREAD_MUTEX_DEFAULT, attempting to recursively lock the mutex results in undefined behavior. Attempting to   unlock
       the  mutex  if  it  was	not locked by the calling thread results in undefined behavior. Attempting to unlock the mutex if it is not locked
       results in undefined behavior.

       The pthread_mutex_trylock() function 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 fails immediately with EBUSY.

       The  pthread_mutex_unlock()  function  releases	the mutex object referenced by mutex. The manner in which a mutex is released is dependent
       upon the mutex's type attribute. If there are threads blocked on the mutex  object  referenced  by  mutex  when	pthread_mutex_unlock()	is
       called,	resulting  in  the mutex  becoming available, the scheduling policy is used to determine  which thread will acquire the mutex. (In
       the case of  PTHREAD_MUTEX_RECURSIVE mutexes, the mutex becomes available when the count reaches  0 and the calling thread  no  longer  has
       any locks on this mutex.)

       If  a  signal is delivered to a thread waiting for a mutex, upon return from the signal handler the thread resumes waiting for the mutex as
       if it was not interrupted.

RETURN VALUES

       If successful, the  pthread_mutex_lock() and  pthread_mutex_unlock() functions return  0. Otherwise, an error number is returned  to  indi-
       cate the error.

       The   pthread_mutex_trylock() function returns  0 if a lock on the mutex object referenced by mutex is acquired. Otherwise, an error number
       is returned to indicate the error.

ERRORS

       The  pthread_mutex_lock() and pthread_mutex_trylock() functions will fail if:

       EAGAIN	 The mutex could not be acquired because the maximum number of recursive locks for mutex has been exceeded.

       EINVAL	 The mutex was created with the protocol attribute having the value PTHREAD_PRIO_PROTECT and  the  calling  thread's  priority	is
		 higher than the mutex's current priority ceiling.

       EPERM	 The  mutex  was  created  with  the protocol attribute having the value PTHREAD_PRIO_PROTECT and the calling thread is not in the
		 real-time class (SCHED_RR or SCHED_FIFO scheduling class).

       The  pthread_mutex_trylock() function will fail if:

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

       The  pthread_mutex_lock(), pthread_mutex_trylock() and pthread_mutex_unlock() functions may fail if:

       EINVAL	 The value specified by mutex does not refer to an initialized mutex object.

       The  pthread_mutex_lock() function may fail if:

       EDEADLK	  The current thread already owns the mutex.

       ENOMEM	  The limit on the number of simultaneously held mutexes has been exceeded.

       The  pthread_mutex_unlock() function will fail if:

       EPERM	The mutex type is PTHREAD_MUTEX_ERRORCHECK or the mutex is a robust mutex, and the current thread does not own the mutex.

       When a thread makes a call to pthread_mutex_lock() or pthread_mutex_trylock(), if the mutex is initialized with	the  robustness  attribute
       having the value PTHREAD_MUTEX_ROBUST (see pthread_mutexattr_getrobust(3C)), the call will return these error values if:

       EOWNERDEAD	  The last owner of this mutex died while holding the mutex, or the process containing the owner of the mutex unmapped the
			  memory containing the mutex or performed one of the exec(2) functions. This mutex is now owned by the caller. The caller
			  must	now  attempt  to  make	the  state protected by the mutex consistent. If it is able to clean up the state, then it
			  should call pthread_mutex_consistent() for the mutex and unlock the mutex. Subsequent calls to pthread_mutex_lock()  and
			  pthread_mutex_trylock()  will  behave  normally,  as	before.  If  the  caller  is  not  able  to  clean  up	the state,
			  pthread_mutex_consistent() should not be called for the mutex, but the mutex should be  unlocked.  Subsequent  calls	to
			  pthread_mutex_lock() and pthread_mutex_trylock() will fail to acquire the mutex with the error value ENOTRECOVERABLE. If
			  the owner who acquired the lock with EOWNERDEAD dies, the next owner will acquire the lock with EOWNERDEAD.

       ENOTRECOVERABLE	  The mutex trying to be acquired was protecting the state that has been left irrecoverable by the mutex's last owner. The
			  mutex  has  not  been  acquired. This condition can occur when the lock was previously acquired with EOWNERDEAD, and the
			  owner was not able to clean up the state and unlocked the mutex without calling pthread_mutex_consistent().

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Committed 		   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+
       |Standard		     |See standards(5). 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       pthread_mutex_consistent(3C), pthread_mutex_init(3C),  pthread_mutexattr_setprotocol(3C),  pthread_mutexattr_setrobust(3C),  pthread_mutex-
       attr_settype(3C), attributes(5), standards(5)

NOTES

       In  the	current  implementation of threads, pthread_mutex_lock(), pthread_mutex_unlock(), mutex_lock(), mutex_unlock(), pthread_mutex_try-
       lock(), and mutex_trylock() do not validate the mutex type.  Therefore, an uninitialized mutex or a mutex with an  invalid  type  does  not
       return  EINVAL. Interfaces for mutexes with an invalid type have unspecified behavior.

       Uninitialized  mutexes that are allocated locally may contain junk data. Such mutexes need to be initialized using  pthread_mutex_init() or
       mutex_init().

SunOS 5.11							    11 Nov 2008 					    pthread_mutex_lock(3C)