Lock a Mutex

pthread_mutex_lock(3T)

Prototype:
int	pthread_mutex_lock(pthread_mutex_t *mutex); 

#include <pthread.h>

pthread_mutex_t mp;
int ret;

ret = pthread_ mutex_lock(&mp); /* acquire the mutex */

Use pthread_mutex_lock(3T) to lock the mutex pointed to by mutex. When pthread_mutex_lock() returns, the mutex is locked and the calling thread is the owner. If the mutex is already locked and owned by another thread, the calling thread blocks until the mutex becomes available. (For Solaris threads, see "mutex_lock(3T)".)

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 which is unlocked, undefined behaviour 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 one. 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 zero, 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 which is unlocked, an error will be returned.

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

Return Values

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

EAGAIN

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

EDEADLK

The current thread already owns the mutex.