CEEOPMT

C library interface: pthread_mutex_trylock()

CEEOPMT conditionally acquires (locks) the mutex referred to by mutex. Conditionally means the call always returns immediately, whether or not the lock is acquired. If the mutex is already locked, the mutex is not acquired. When successful, this function returns with the mutex in the locked state with the calling thread as its owner.

Syntax

void CEEOPMT (mutex, [fc])

CEE_MUTEX   *mutex;
FEED_BACK   *fc;

CEEOPMT

Call this CWI interface as follows:

L     R15,CEECAALEOV-CEECAA(,R12)     CAA address is in R12
L     R15,0296(,R15)
BALR  R14,R15

mutex (input)

The mutex to be locked conditionally.

fc (output/optional)

The feedback code returned by the service. It indicates the degree of success in locking the mutex conditionally. The following message identifiers and associated severities can be returned by the service in the feedback code fc.

Condition	Description category	Description value
CEE000	Severity	0
	Msg_No	0000
	Message	The service completed successfully.
CEE4S9	Severity	3
	Msg_No	5001
	Message	The service is unavailable unless POSIX(ON) runtime option specified and z/OS UNIX System Services are started.
CEE5I5	Severity	3
	Msg_No	5701
	Message	The pthread_mutex_t object specified by mutex is not valid (not initialized).
CEE5I8	Severity	4
	Msg_No	5704
	Message	Address exception while referencing storage allocated by mutex initialization for pthread_mutex_t object specified by mutex.
CEE5IB	Severity	0
	Msg_No	5707
	Message	The pthread_mutex_t object specified by mutex is busy.
CEE5IO	Severity	4
	Msg_No	5720
	Message	Thread forced by quiesce.
CEE5IS	Severity	0
	Msg_No	5724
	Message	Not enough resource (other than memory).
CEE5K4	Severity	3
	Msg_No	5764
	Message	The mutex specified by mutex was not initialized.
CEE5K6	Severity	3
	Msg_No	5766
	Message	An addressing exception occurred referencing a lock object.
CEE5K7	Severity	4
	Msg_No	5767
	Message	Address exception while referencing system storage allocated by lock object initialization.
CEE5KQ	Severity	3
	Msg_No	5786
	Message	The callable service BPX1SLK failed during shared lock processing. The system return code was return_code, the reason code was reason_code, X'00'.

Usage Notes:

If the CEEOPXS service was used to give the mutex the attribute RECURSIVE before the mutex was initialized with the CEEOPMI service, the thread which locked the mutex can relock it with lock service, CEEOPML, or trylock service, CEEOPMT. In other words, trylock returns with success rather than busy feedback code, if the thread already owns a recursive mutex. Only when the mutex is nonrecursive, which is the default attribute for mutexes, does trylock return the busy feedback code if the mutex is already locked.
A recursive mutex must be unlocked as many times as it has been locked and relocked to relinquish ownership.
Only the owning thread (the thread that acquired a mutex) can unlock it.