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       pthread_setcancelstate, pthread_setcanceltype - set cancelability state and type


       #include <pthread.h>

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

       Compile and link with -pthread.


       The  pthread_setcancelstate()  sets  the  cancelability state of the calling 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:

              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.

              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:

              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.

              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

       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.


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


       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.


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

       │InterfaceAttributeValue   │
       │pthread_setcancelstate(), │ Thread safety       │ MT-Safe │
       │pthread_setcanceltype()   │                     │         │
       │pthread_setcancelstate(), │ Async-cancel-safety │ AC-Safe │
       │pthread_setcanceltype()   │                     │         │


       POSIX.1-2001, POSIX.1-2008.


       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.

   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)), 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

       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_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.

   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_setcanceltype().


       See pthread_cancel(3).


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


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