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 calling thread to the value given in state.  The previ-
       ous 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.

CONFORMING TO
       POSIX.1-2001.

NOTES
       For details of what happens when a thread is canceled, see pthread_cancel(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 operations that may block  for  long
       periods, since that will render the thread unresponsive to cancellation requests.

       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)), acquire  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 cancellation occur before the resources were reserved, while  they
       were  reserved,  or  after they were released?  Furthermore, some internal data structures (e.g., the linked list of free
       blocks managed by the malloc(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 asyn-
       chronously  canceled  are  called  async-cancel-safe  functions.   POSIX.1-2001  only  requires  that  pthread_cancel(3),
       pthread_setcancelstate(), and pthread_setcanceltype() 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.

       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.1-2001 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_setcanceltype().

EXAMPLE
       See pthread_cancel(3).

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

COLOPHON
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-11-24                                  PTHREAD_SETCANCELSTATE(3)