PTHREAD_MUTEXATTR(3)

PTHREAD_MUTEXATTR(3) | Library Functions Manual | 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

POSIX Threads Library (libpthread, -lpthread)

# 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 IEEE Std 1003.1-2001 (“POSIX.1”).

# BUGS

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

June 12, 2016 | NetBSD 8.0