PTHREAD_MUTEXATTR_GETTYPE(3P)                       POSIX Programmer's Manual                      PTHREAD_MUTEXATTR_GETTYPE(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       pthread_mutexattr_gettype, pthread_mutexattr_settype - get and set the mutex type attribute

SYNOPSIS
       #include <pthread.h>

       int pthread_mutexattr_gettype(const pthread_mutexattr_t *restrict attr,
              int *restrict type);
       int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type);


DESCRIPTION
       The pthread_mutexattr_gettype() and pthread_mutexattr_settype() functions, respectively, shall get and set the mutex type
       attribute. This attribute is set in the type parameter to these functions. The default value of  the  type  attribute  is
       PTHREAD_MUTEX_DEFAULT.

       The type of mutex is contained in the type attribute of the mutex attributes. Valid mutex types include:

       PTHREAD_MUTEX_NORMAL

              This  type  of mutex does not detect deadlock. A thread attempting to relock this mutex without first unlocking it
              shall deadlock.  Attempting to unlock a mutex locked by a different thread results in undefined behavior. Attempt-
              ing to unlock an unlocked mutex results in undefined behavior.

       PTHREAD_MUTEX_ERRORCHECK

              This  type  of  mutex provides error checking. A thread attempting to relock this mutex without first unlocking it
              shall return with an error. A thread attempting to unlock a mutex which another thread  has  locked  shall  return
              with an error. A thread attempting to unlock an unlocked mutex shall return with an error.

       PTHREAD_MUTEX_RECURSIVE

              A  thread  attempting  to  relock  this  mutex  without first unlocking it shall succeed in locking the mutex. The
              relocking deadlock which can occur with mutexes of type PTHREAD_MUTEX_NORMAL cannot occur with this type of mutex.
              Multiple  locks  of this mutex shall require the same number of unlocks to release the mutex before another thread
              can acquire the mutex. A thread attempting to unlock a mutex which another thread has locked shall return with  an
              error.  A thread attempting to unlock an unlocked mutex shall return with an error.

       PTHREAD_MUTEX_DEFAULT

              Attempting to recursively lock a mutex of this type results in undefined behavior. Attempting to unlock a mutex of
              this type which was not locked by the calling thread results in undefined behavior.  Attempting to unlock a  mutex
              of this type which is not locked results in undefined behavior. An implementation may map this mutex to one of the
              other mutex types.


RETURN VALUE
       Upon successful completion, the pthread_mutexattr_gettype() function shall return zero and store the value  of  the  type
       attribute of attr into the object referenced by the type parameter. Otherwise, an error shall be returned to indicate the
       error.

       If successful, the pthread_mutexattr_settype() function shall return zero; otherwise, an error number shall  be  returned
       to indicate the error.

ERRORS
       The pthread_mutexattr_settype() function shall fail if:

       EINVAL The value type is invalid.


       The pthread_mutexattr_gettype() and pthread_mutexattr_settype() functions may fail if:

       EINVAL The value specified by attr is invalid.


       These functions shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       It  is  advised  that  an application should not use a PTHREAD_MUTEX_RECURSIVE mutex with condition variables because the
       implicit unlock performed for a pthread_cond_timedwait() or pthread_cond_wait() may not actually release the mutex (if it
       had been locked multiple times). If this happens, no other thread can satisfy the condition of the predicate.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       pthread_cond_timedwait(), the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open  Group
       Standard   is   the   referee   document.   The   original   Standard   can   be   obtained  online  at  http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                 PTHREAD_MUTEXATTR_GETTYPE(3P)