PTHREAD_MUTEXATTR(3)

NAME
pthread_mutexattr_init, pthread_mutexattr_destroy, pthread_mutexattr_setprioceiling, pthread_mutexattr_getprioceiling, pthread_mutexattr_setprotocol, pthread_mutexattr_getprotocol, pthread_mutexattr_settype, pthread_mutexattr_gettype, pthread_mutexattr_getpshared, pthread_mutexattr_setpshared - mutex attribute operations

LIBRARY
libpthread

SYNOPSIS
#include <pthread.h>
int
pthread_mutexattr_init(pthread_mutexattr_t *attr);
int
pthread_mutexattr_destroy(pthread_mutexattr_t *attr);
int
pthread_mutexattr_setprioceiling(pthread_mutexattr_t *attr, int prioceiling);
int
pthread_mutexattr_getprioceiling(pthread_mutexattr_t *attr, int *prioceiling);
int
pthread_mutexattr_setprotocol(pthread_mutexattr_t *attr, int protocol);
int
pthread_mutexattr_getprotocol(pthread_mutexattr_t *attr, int *protocol);
int
pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type);
int
pthread_mutexattr_gettype(pthread_mutexattr_t * restrict attr, int * restrict type);
int
pthread_mutexattr_getpshared(const pthread_mutexattr_t * __restrict attr, int * __restrict pshared);
int
pthread_mutexattr_setpshared(pthread_mutexattr_t * attr, int pshared);

DESCRIPTION
Mutex attributes are used to specify parameters to pthread_mutex_init(). Like with thread attributes, one attribute object can be used in multiple calls to pthread_mutex_init(3), with or without modifications between calls.

The pthread_mutexattr_init() function initializes attr with all the default mutex attributes.

The pthread_mutexattr_destroy() function destroys attr.

The pthread_mutexattr_settype() functions set the mutex type value of the attribute. Valid mutex types are:

PTHREAD_MUTEX_NORMAL
    This type of mutex does not check for usage errors. It will deadlock if reentered, and result in undefined behavior if a locked mutex is unlocked by another thread. Attempts to unlock an already unlocked PTHREAD_MUTEX_NORMAL mutex will result in undefined behavior.

PTHREAD_MUTEX_ERRORCHECK
    These mutexes do check for usage errors. If an attempt is made to relock a PTHREAD_MUTEX_ERRORCHECK mutex without first dropping the lock, an error will be returned. If a thread attempts to unlock a PTHREAD_MUTEX_ERRORCHECK mutex that is locked by another thread, an error will be returned. If a thread attempts to unlock a PTHREAD_MUTEX_ERRORCHECK thread that is unlocked, an error will be returned.

PTHREAD_MUTEX_RECURSIVE
    These mutexes allow recursive locking. An attempt to relock a PTHREAD_MUTEX_RECURSIVE mutex that is already locked by the same thread succeeds. An equivalent number of pthread_mutex_unlock(3) calls are needed before the mutex will wake another thread waiting on this lock. If a thread attempts to unlock a PTHREAD_MUTEX_RECURSIVE mutex that is locked by another thread, an error will be returned. If a thread attempts to unlock a PTHREAD_MUTEX_RECURSIVE thread that is unlocked, an error will be returned.

    It is advised that PTHREAD_MUTEX_RECURSIVE mutexes are not used with condition variables. This is because of the implicit unlocking done by pthread_cond_wait(3) and pthread_cond_timedwait(3).

PTHREAD_MUTEX_DEFAULT
    Also this type of mutex will cause undefined behavior if reentered. Unlocking a PTHREAD_MUTEX_DEFAULT mutex locked by another thread will result in undefined behavior. Attempts to unlock an already unlocked PTHREAD_MUTEX_DEFAULT mutex will result in undefined behavior.

    This is the default mutex type for pthread_mutexattr_init().

The pthread_mutexattr_gettype() functions copy the type value of the attribute to the location pointed to by the second parameter.

The pthread_mutexattr_getpshared() function obtains the value of the process-shared attribute from the attributes object referenced by attr.

The pthread_mutexattr_setpshared() function is used to set the process-shared attribute in an initialised attributes object referenced by attr.

The pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions shall get and set the protocol attribute of a mutex attributes object pointed to by attr which was previously created by the function pthread_mutexattr_init().

The pthread_mutexattr_getprioceiling() and pthread_mutexattr_setprioceiling() functions, shall get and set the priority ceiling attribute of a mutex attributes object pointed to by attr which was previously created by the function pthread_mutexattr_init().

RETURN VALUES
If successful, these functions return 0. Otherwise, an error number is returned to indicate the error.

ERRORS
The pthread_mutexattr_init() function shall fail if:

[ENOMEM]
    Insufficient memory exists to initialize the mutex attributes object.

The pthread_mutexattr_settype() function shall fail if:

[EINVAL]
    The value specified either by type or attr is invalid.

No error numbers are defined for the pthread_mutexattr_destroy() and pthread_mutexattr_gettype() functions.

pthread_mutexattr_setprioceiling() may fail if:

[EINVAL]
    Invalid value for attr, or invalid value for prioceiling.

pthread_mutexattr_getprioceiling() may fail if:

[EINVAL]
    Invalid value for attr.

pthread_mutexattr_setprotocol() may fail if:

[EINVAL]
    Invalid value for attr, or invalid value for protocol.

pthread_mutexattr_getprotocol() may fail if:

[EINVAL]
    Invalid value for attr.

pthread_mutexattr_getpshared() and pthread_mutexattr_setpshared() may fail if:

[EINVAL]
    the value specified by attr is invalid.

SEE ALSO
pthread_mutex_init(3)

STANDARDS
These functions conform to p1003.1-2001.

BUGS
The pthread_mutexattr_getpshared() and pthread_mutexattr_setpshared() functions are hidden by default since only thread shared attributes are supported.