pthread_mutex_init

, pthread_mutex_destroy

- initialize or destroy a mutex

Synopsis

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

int pthread_mutex_init(pthread_mutex_t *restrict mutex,
     const pthread_mutexattr_t *restrict attr);

int pthread_mutex_destroy(pthread_mutex_t *mutex);

pthread_mutex_t mutex= PTHREAD_MUTEX_INITIALIZER;

Description

The pthread_mutex_init() function initializes the mutex referenced by mutex with attributes specified by attr. If attr is NULL, the default mutex attributes are used; the effect is the same as passing the address of a default mutex attributes object. Upon successful initialization, the state of the mutex becomes initialized and unlocked.

Except for robust mutexes, attempting to initialize an already initialized mutex results in undefined behavior.

The pthread_mutex_destroy() function destroys the mutex object referenced by mutex; the mutex object becomes, in effect, uninitialized. A destroyed mutex object can be re-initialized using pthread_mutex_init(); the results of otherwise referencing the object after it has been destroyed are undefined.

It is safe to destroy an initialized mutex that is unlocked. Attempting to destroy a locked mutex results in undefined behavior.

In cases where default mutex attributes are appropriate, the macro PTHREAD_MUTEX_INITIALIZER can be used to initialize mutexes that are statically allocated. The effect is equivalent to dynamic initialization by a call to pthread_mutex_init() with parameter attr specified as NULL, except that no error checks are performed.

Return Values

If successful, the pthread_mutex_init() and pthread_mutex_destroy() functions return 0. Otherwise, an error number is returned to indicate the error.

Errors

The pthread_mutex_init() function will fail if:

EAGAIN

The system lacked the necessary resources (other than memory) to initialize another mutex.

EBUSY

An attempt was detected to re-initialize a robust mutex previously initialized but not yet destroyed. See pthread_mutexattr_setrobust(3C).

EINVAL

An attempt was detected to re-initialize a robust mutex previously initialized with a different set of attributes. See pthread_mutexattr_setrobust(3C).

ENOMEM

Insufficient memory exists to initialize the mutex.

EPERM

The caller does not have the privilege to perform the operation.

The pthread_mutex_init() function may fail if:

EBUSY

An attempt was detected to re-initialize the object referenced by mutex, a mutex previously initialized but not yet destroyed.

EINVAL

The value specified by attr or mutex is invalid.

The pthread_mutex_destroy() function may fail if:

EBUSY

An attempt was detected to destroy the object referenced by mutex while it is locked or referenced (for example, while being used in a pthread_cond_wait(3C) or pthread_cond_timedwait(3C)) by another thread.

EINVAL

The value specified by mutex is invalid.

Attributes

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

See Also

pthread_cond_wait(3C), pthread_mutex_lock(3C), pthread_mutexattr_setprioceiling(3C), pthread_mutexattr_setprotocol(3C), pthread_mutexattr_setpshared(3C), pthread_mutexattr_setrobust(3C), pthread_mutexattr_settype(3C), attributes(5), mutex(5), standards(5)