pthread_mutex_init Syntax

int pthread_mutex_init(pthread_mutex_t *restrict mp,
          const pthread_mutexattr_t *restrict mattr);

#include <pthread.h>

pthread_mutex_t mp = PTHREAD_MUTEX_INITIALIZER;
pthread_mutexattr_t mattr;
int ret;

/* initialize a mutex to its default value */
ret = pthread_mutex_init(&mp, NULL);

/* initialize a mutex */
ret = pthread_mutex_init(&mp, &mattr); 

When the mutex is initialized, the mutex is in an unlocked state. The mutex can be in memory that is shared between processes or in memory private to a process.

For a mutex that is being initialized with the PTHREAD_MUTEX_ROBUST_NP attribute, the mutex memory must be cleared to zero before initialization.

The effect of mattr set to NULL is the same as passing the address of a default mutex attribute object, but without the memory overhead.

Use the macro PTHREAD_MUTEX_INITIALIZER to initialize statically defined mutexes to their default attributes.

Do not reinitialize or destroy a mutex lock while other threads are using the mutex. Program failure results if either action is not done correctly. If a mutex is reinitialized or destroyed, the application must be sure the mutex is not currently in use.