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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 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


       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

       │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

       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 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_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

   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


       See pthread_cancel(3).


       pthread_cancel(3),    pthread_cleanup_push(3),   pthread_testcancel(3),


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