Lock With a Nonblocking Mutex

pthread_mutex_trylock(3THR)

Use pthread_mutex_trylock(3THR) to attempt to lock the mutex pointed to by mutex. (For Solaris threads, see "mutex_trylock(3THR)".)

Prototype:
int	pthread_mutex_trylock(pthread_mutex_t *mutex); 

#include <pthread.h>

pthread_mutex_t mutex;
int ret;

ret = pthread_mutex_trylock(&mutex); /* try to lock the mutex */

pthread_mutex_trylock() is a nonblocking version of pthread_mutex_lock(). If the mutex object referenced by mutex is currently locked (by any thread, including the current thread), the call returns immediately. Otherwise, the mutex is locked and the calling thread is the owner.

Return Values

pthread_mutex_trylock() returns zero after completing successfully. Any other returned value indicates that an error occurred. When any of the following conditions occurs, the function fails and returns the corresponding value.

EBUSY

The mutex could not be acquired because the mutex pointed to by mutex was already locked.

EAGAIN

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

If the symbol _POSIX_THREAD_PRIO_INHERIT is defined, the mutex is initialized with the protocol attribute value PTHREAD_PRIO_INHERIT, and the robustness argument of pthread_mutexattr_setrobust_np() is PTHREAD_MUTEX_ROBUST_NP the function fails and returns:

EOWNERDEAD

The last owner of this mutex died while holding the mutex. This mutex is now owned by the caller. The caller must attempt to make the state protected by the mutex consistent.

If the caller is able to make the state consistent, call pthread_mutex_consistent_np() for the mutex and unlock the mutex. Subsequent calls to pthread_mutex_lock() will behave normally.

If the caller is unable to make the state consistent, do not call pthread_mutex_init() for the mutex, but unlock the mutex. Subsequent calls to pthread_mutex_trylock() fail to acquire the mutex and return an ENOTRECOVERABLE error code.

If the owner that acquired the lock with EOWNERDEAD dies, the next owner acquires the lock with EOWNERDEAD.

ENOTRECOVERABLE

The mutex you are trying to acquire is protecting state left irrecoverable by the mutex's previous owner that died while holding the lock. The mutex has not been acquired. This condition can occur when the lock was previously acquired with EOWNERDEAD and the owner was unable to cleanup the state and had unlocked the mutex without making the mutex state consistent.

ENOMEM

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