Manual Pages for UNIX Operating System command usage for man pthread_mutexattr_settype

Standard C Library Functions        pthread_mutexattr_gettype(3C)



NAME
     pthread_mutexattr_gettype, pthread_mutexattr_settype  -  get
     or set mutex type

SYNOPSIS
     cc -mt [ flag... ] file... -lpthread [ library... ]
     #include 

     int pthread_mutexattr_gettype(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 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 will
                                 deadlock. Attempting to unlock a
                                 mutex   locked  by  a  different
                                 thread  results   in   undefined
                                 behavior.  Attempting  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 will
                                 return with an error.  A  thread
                                 attempting  to  unlock  a  mutex
                                 that another thread  has  locked
                                 will  return  with  an  error. A
                                 thread attempting to  unlock  an
                                 unlocked  mutex will return with
                                 an error.






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Standard C Library Functions        pthread_mutexattr_gettype(3C)



     PTHREAD_MUTEX_RECURSIVE     A thread  attempting  to  relock
                                 this mutex without first unlock-
                                 ing it will succeed  in  locking
                                 the    mutex.    The   relocking
                                 deadlock  that  can  occur  with
                                 mutexes          of         type
                                 PTHREAD_MUTEX_NORMAL      cannot
                                 occur  with  this type of mutex.
                                 Multiple  locks  of  this  mutex
                                 require   the   same  number  of
                                 unlocks  to  release  the  mutex
                                 before    another   thread   can
                                 acquire  the  mutex.  A   thread
                                 attempting  to  unlock  a  mutex
                                 that another thread  has  locked
                                 will  return  with  an  error. A
                                 thread attempting to  unlock  an
                                 unlocked  mutex will return with
                                 an error. This type of mutex  is
                                 only supported for mutexes whose
                                 process  shared   attribute   is
                                 PTHREAD_PROCESS_PRIVATE.


     PTHREAD_MUTEX_DEFAULT       Attempting to recursively lock a
                                 mutex  of  this  type results in
                                 undefined  behavior.  Attempting
                                 to  unlock  a mutex of this type
                                 that was not locked by the  cal-
                                 ling thread results in undefined
                                 behavior. Attempting to unlock a
                                 mutex  of  this type that is not
                                 locked  results   in   undefined
                                 behavior.  An  implementation is
                                 allowed to map this mutex to one
                                 of the other mutex types.


RETURN VALUES
     Upon successful completion, the  pthread_mutexattr_settype()
     function  returns  0. Otherwise, an error number is returned
     to indicate the error.


     Upon successful completion, the  pthread_mutexattr_gettype()
     function  returns  0 and stores the value of the type attri-
     bute of attr in the object referenced by the type parameter.
     Otherwise an error number is returned to indicate the error.

ERRORS
     The             pthread_mutexattr_gettype()              and
     pthread_mutexattr_settype() functions will fail if:



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Standard C Library Functions        pthread_mutexattr_gettype(3C)



     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.


ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe                     |
    |_____________________________|_____________________________|
    | Standard                    | See standards(5).           |
    |_____________________________|_____________________________|


SEE ALSO
     pthread_cond_timedwait(3C),  pthread_cond_wait(3C),   attri-
     butes(5), standards(5)

NOTES
     Application should not use a  PTHREAD_MUTEX_RECURSIVE  mutex
     with  condition  variables  because the implicit unlock per-
     formed for pthread_cond_wait()  or  pthread_cond_timedwait()
     will  not  actually release the mutex (if it had been locked
     multiple times). If this occurs, no other thread can satisfy
     the condition of the predicate.

















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