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PTHREAD_SETCANCELSTATE(P)  POSIX Programmer's Manual PTHREAD_SETCANCELSTATE(P)



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

NAME
       pthread_setcancelstate, pthread_setcanceltype, pthread_testcancel - set
       cancelability state

SYNOPSIS
       #include <pthread.h>

       int pthread_setcancelstate(int state, int *oldstate);
       int pthread_setcanceltype(int type, int *oldtype);
       void pthread_testcancel(void);


DESCRIPTION
       The  pthread_setcancelstate()  function	shall  atomically both set the
       calling thread's cancelability state to the indicated state and	return
       the  previous  cancelability  state  at the location referenced by old-
       state.  Legal  values   for   state   are   PTHREAD_CANCEL_ENABLE   and
       PTHREAD_CANCEL_DISABLE.

       The  pthread_setcanceltype()  function  shall  atomically  both set the
       calling thread's cancelability type to the indicated  type  and	return
       the  previous cancelability type at the location referenced by oldtype.
       Legal values for	 type  are  PTHREAD_CANCEL_DEFERRED  and  PTHREAD_CAN-
       CEL_ASYNCHRONOUS.

       The  cancelability state and type of any newly created threads, includ-
       ing the thread in which main() was first invoked, shall be PTHREAD_CAN-
       CEL_ENABLE and PTHREAD_CANCEL_DEFERRED respectively.

       The  pthread_testcancel() function shall create a cancellation point in
       the calling thread. The pthread_testcancel()  function  shall  have  no
       effect if cancelability is disabled.

RETURN VALUE
       If successful, the pthread_setcancelstate() and pthread_setcanceltype()
       functions shall return  zero;  otherwise,  an  error  number  shall  be
       returned to indicate the error.

ERRORS
       The pthread_setcancelstate() function may fail if:

       EINVAL The specified state is not PTHREAD_CANCEL_ENABLE or PTHREAD_CAN-
	      CEL_DISABLE.


       The pthread_setcanceltype() function may fail if:

       EINVAL The   specified	type   is   not	  PTHREAD_CANCEL_DEFERRED   or
	      PTHREAD_CANCEL_ASYNCHRONOUS.


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

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       The pthread_setcancelstate() and pthread_setcanceltype() functions con-
       trol the points at which a thread may be asynchronously	canceled.  For
       cancellation  control  to be usable in modular fashion, some rules need
       to be followed.

       An object can be considered to be a generalization of a procedure.   It
       is  a  set  of  procedures  and	global variables written as a unit and
       called by clients not known by the object. Objects may depend on	 other
       objects.

       First,  cancelability  should  only  be disabled on entry to an object,
       never explicitly enabled. On exit from  an  object,  the	 cancelability
       state should always be restored to its value on entry to the object.

       This follows from a modularity argument: if the client of an object (or
       the client of an object that uses that object) has disabled cancelabil-
       ity,  it	 is  because  the  client  does not want to be concerned about
       cleaning up if the thread is canceled while executing some sequence  of
       actions. If an object is called in such a state and it enables cancela-
       bility and a cancellation request is pending for that thread, then  the
       thread is canceled, contrary to the wish of the client that disabled.

       Second, the cancelability type may be explicitly set to either deferred
       or asynchronous upon entry to an object.	 But as with the cancelability
       state,  on  exit from an object the cancelability type should always be
       restored to its value on entry to the object.

       Finally, only functions that are	 cancel-safe  may  be  called  from  a
       thread that is asynchronously cancelable.

FUTURE DIRECTIONS
       None.

SEE ALSO
       pthread_cancel() , 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,  Copyright  (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.opengroup.org/unix/online.html .



IEEE/The Open Group		     2003	     PTHREAD_SETCANCELSTATE(P)
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