PTHREAD_MUTEXATTR(3)

NAME
pthread_mutexattr_init, pthread_mutexattr_destroy, pthread_mutexattr_setprioceiling, pthread_mutexattr_getprioceiling, pthread_mutexattr_setprotocol, pthread_mutexattr_getprotocol, pthread_mutexattr_setpshared, pthread_mutexattr_getpshared, pthread_mutexattr_setrobust, pthread_mutexattr_getrobust, pthread_mutexattr_settype, pthread_mutexattr_gettype - 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(const pthread_mutexattr_t *attr, int *prioceiling);
int
pthread_mutexattr_setprotocol(pthread_mutexattr_t *attr, int protocol);
int
pthread_mutexattr_getprotocol(const pthread_mutexattr_t *restrict attr, int *restrict protocol);
int
pthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int shared);
int
pthread_mutexattr_getpshared(const pthread_mutexattr_t *attr, int *shared);
int
pthread_mutexattr_setrobust(pthread_mutexattr_t *attr, int robust);
int
pthread_mutexattr_getrobust(pthread_mutexattr_t *attr, int *robust);
int
pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type);
int
pthread_mutexattr_gettype(const pthread_mutexattr_t *restrict attr, int *restrict type);

DESCRIPTION
Mutex attributes are used to specify parameters to pthread_mutex_init(). One attribute object can be used in multiple calls to pthread_mutex_init(), 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_setprioceiling() function sets the priority ceiling for the mutex, used by threads executed under the PTHREAD_PRIO_PROTECT protocol.

The pthread_mutexattr_setprotocol() function specifies the protocol to be followed in utilizing mutexes. The protocol argument can take one of the following values:

PTHREAD_PRIO_NONE
    Priority and scheduling of the thread owning this mutex is not affected by its mutex ownership.

PTHREAD_PRIO_INHERIT
    Request priority-inheritance protocol, where the thread owning the mutex is executed at the highest priority among priorities of all threads waiting on any mutex owned by this thread.

PTHREAD_PRIO_PROTECT
    Request priority-inheritance protocol, where the thread owning the mutex is executed at highest priority among priorities or priority ceilings of all threads waiting on any mutex owned by this thread.

The pthread_mutexattr_setpshared() function sets the process-shared attribute of attr to the value specified in pshared. The argument pshared may have one of the following values:

PTHREAD_PROCESS_PRIVATE
    The mutex may only be used by threads in the same process as the one that created the object.

PTHREAD_PROCESS_SHARED
    The mutex may be used by threads in processes other than the one that created the object, assuming other processes share access to the memory where the mutex was allocated.
See libthr(3) for details of the implementation of the shared mutexes, and their limitations.

The pthread_mutexattr_setrobust() function specifies robustness attribute of the mutex. Possible values for the robust argument are

PTHREAD_MUTEX_STALLED
    No special actions are taken if the thread owning the mutex is terminated without unlocking the mutex lock. This can lead to deadlocks if no other thread can unlock the mutex. This is the default value.

PTHREAD_MUTEX_ROBUST
    If the process containing the owning thread of a robust mutex, or owning thread, terminates while holding the mutex lock, the next thread that acquires the mutex is notified about the termination by the return value EOWNERDEAD from the locking function. Then, either pthread_mutex_consistent(3) can be used to repair the mutex lock state, or pthread_mutex_unlock(3) can unlock the mutex lock but also put it an unusable state, where all further attempts to acquire it result in the ENOTRECOVERABLE error.

The pthread_mutexattr_settype() function sets the type of the mutex. The type affects the behavior of calls which lock and unlock the mutex. The possible values for the type argument are

PTHREAD_MUTEX_NORMAL
    Both recursive locking, and unlocking when the lock is not owned by the current thread, cause an error to be returned from the corresponding functions. This matches PTHREAD_MUTEX_ERRORCHECK but somewhat contradicts the behavior mandated by POSIX.

PTHREAD_MUTEX_ERRORCHECK
    Both recursive locking, and unlocking when the lock is not owned by the current thread, cause an error returned from the corresponding functions.

PTHREAD_MUTEX_RECURSIVE
    Recursive locking is allowed. Attempt to unlock when current thread is not an owner of the lock causes an error to be returned.

PTHREAD_MUTEX_DEFAULT
    The FreeBSD implementation maps this type to PTHREAD_MUTEX_ERRORCHECK type.

The pthread_mutexattr_get*() functions copy the value of the attribute that corresponds to each function name to the location pointed to by the second function parameter.

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

ERRORS
The pthread_mutexattr_init() function will fail if:

[ENOMEM]
    Out of memory.

The pthread_mutexattr_destroy() function will fail if:

[EINVAL]
    Invalid value for attr.

The pthread_mutexattr_setprioceiling() function will fail if:

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

The pthread_mutexattr_getprioceiling() function will fail if:

[EINVAL]
    Invalid value for attr.

The pthread_mutexattr_setprotocol() function will fail if:

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

The pthread_mutexattr_getprotocol() function will fail if:

[EINVAL]
    Invalid value for attr.

The pthread_mutexattr_setpshared() function will fail if:

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

The pthread_mutexattr_getpshared() function will fail if:

[EINVAL]
    Invalid value for attr.

The pthread_mutexattr_settype() function will fail if:

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

The pthread_mutexattr_gettype() function will fail if:

[EINVAL]
    Invalid value for attr.

The pthread_mutexattr_setrobust() function will fail if:

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

The pthread_mutexattr_getrobust() function will fail if:

[EINVAL]
    Invalid value for attr.

SEE ALSO
libthr(3), pthread_mutex_init(3)

STANDARDS
The pthread_mutexattr_init() and pthread_mutexattr_destroy() functions conform to p1003.1-96

The pthread_mutexattr_setprioceiling(), pthread_mutexattr_getprioceiling(), pthread_mutexattr_setprotocol(), pthread_mutexattr_getprotocol(), pthread_mutexattr_setpshared(), pthread_mutexattr_getpshared(), pthread_mutexattr_settype(), and pthread_mutexattr_gettype() functions conform to susv2. The pthread_mutexattr_setrobust() and pthread_mutexattr_getrobust() functions conform to susv4.