PTHREAD_SETCANCELSTATE(3)  Linux Programmer's Manual PTHREAD_SETCANCELSTATE(3)



NAME
       pthread_setcancelstate, pthread_setcanceltype - set cancelability state
       and type

SYNOPSIS
       #include <pthread.h>

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

       Compile and link with -pthread.

DESCRIPTION
       The pthread_setcancelstate() sets the cancelability state of the	 call-
       ing  thread  to	the  value given in state.  The previous cancelability
       state of the thread is returned in the buffer pointed to	 by  oldstate.
       The state argument must have one of the following values:

       PTHREAD_CANCEL_ENABLE
	      The  thread  is  cancelable.   This is the default cancelability
	      state in all new threads, including  the	initial	 thread.   The
	      thread's	cancelability type determines when a cancelable thread
	      will respond to a cancellation request.

       PTHREAD_CANCEL_DISABLE
	      The thread is not cancelable.   If  a  cancellation  request  is
	      received, it is blocked until cancelability is enabled.

       The  pthread_setcanceltype() sets the cancelability type of the calling
       thread to the value given in type.  The previous cancelability type  of
       the  thread  is returned in the buffer pointed to by oldtype.  The type
       argument must have one of the following values:

       PTHREAD_CANCEL_DEFERRED
	      A cancellation request is deferred until the thread next calls a
	      function	that  is a cancellation point (see pthreads(7)).  This
	      is the default cancelability type in all new threads,  including
	      the initial thread.

       PTHREAD_CANCEL_ASYNCHRONOUS
	      The  thread can be canceled at any time.	(Typically, it will be
	      canceled immediately upon receiving a cancellation request,  but
	      the system doesn't guarantee this.)

       The  set-and-get	 operation  performed  by  each	 of these functions is
       atomic with respect to other threads in the process  calling  the  same
       function.

RETURN VALUE
       On  success,  these functions return 0; on error, they return a nonzero
       error number.

ERRORS
       The pthread_setcancelstate() can fail with the following error:

       EINVAL Invalid value for state.

       The pthread_setcanceltype() can fail with the following error:

       EINVAL Invalid value for type.

ATTRIBUTES
       For  an	explanation  of	 the  terms  used   in	 this	section,   see
       attributes(7).

       +--------------------------+---------------------+---------+
       |Interface		  | Attribute		| Value	  |
       +--------------------------+---------------------+---------+
       |pthread_setcancelstate(), | Thread safety	| MT-Safe |
       |pthread_setcanceltype()	  |			|	  |
       +--------------------------+---------------------+---------+
       |pthread_setcancelstate(), | Async-cancel-safety | AC-Safe |
       |pthread_setcanceltype()	  |			|	  |
       +--------------------------+---------------------+---------+
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

NOTES
       For details of what happens when a thread is canceled, see pthread_can-
       cel(3).

       Briefly disabling cancelability is useful if  a	thread	performs  some
       critical action that must not be interrupted by a cancellation request.
       Beware of disabling cancelability for long periods,  or	around	opera-
       tions  that  may	 block	for  long  periods, since that will render the
       thread unresponsive to cancellation requests.

   Asynchronous cancelability
       Setting the cancelability type to PTHREAD_CANCEL_ASYNCHRONOUS is rarely
       useful.	 Since	the  thread  could  be canceled at any time, it cannot
       safely reserve resources (e.g., allocating memory with malloc(3)),  ac-
       quire mutexes, semaphores, or locks, and so on.	Reserving resources is
       unsafe because the application has no way of knowing what the state  of
       these  resources is when the thread is canceled; that is, did cancella-
       tion occur before the resources were  reserved,	while  they  were  re-
       served,	or  after they were released?  Furthermore, some internal data
       structures (e.g., the linked list of free blocks managed	 by  the  mal-
       loc(3)  family  of  functions)  may be left in an inconsistent state if
       cancellation occurs in the middle of the function call.	 Consequently,
       clean-up handlers cease to be useful.

       Functions  that can be safely asynchronously canceled are called async-
       cancel-safe functions.  POSIX.1-2001 and POSIX.1-2008 require only that
       pthread_cancel(3),   pthread_setcancelstate(),  and  pthread_setcancel-
       type() be async-cancel-safe.  In general, other library functions can't
       be safely called from an asynchronously cancelable thread.

       One  of	the  few  circumstances in which asynchronous cancelability is
       useful is for cancellation of a thread that is in a pure	 compute-bound
       loop.

   Portability notes
       The  Linux  threading  implementations  permit the oldstate argument of
       pthread_setcancelstate() to be NULL,  in	 which	case  the  information
       about  the  previous cancelability state is not returned to the caller.
       Many other implementations also permit a	 NULL  oldstat	argument,  but
       POSIX.1	does  not  specify this point, so portable applications should
       always specify a non-NULL value in oldstate.  A precisely analogous set
       of  statements  applies	for the oldtype argument of pthread_setcancel-
       type().

EXAMPLE
       See pthread_cancel(3).

SEE ALSO
       pthread_cancel(3),   pthread_cleanup_push(3),	pthread_testcancel(3),
       pthreads(7)

COLOPHON
       This  page  is  part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest	  version     of     this    page,    can    be	   found    at
       https://www.kernel.org/doc/man-pages/.



Linux				  2015-08-08	     PTHREAD_SETCANCELSTATE(3)