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.

              Even with deferred cancellation, a cancellation point in an
              asynchronous signal handler may still be acted upon and the effect
              is as if it was an asynchronous cancellation.

              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.

       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).

       │Interface                               Attribute           Value   │
       │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 pthread_setcanceltype().

       See pthread_cancel(3).

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

       This page is part of release 5.11 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

Linux                              2021-03-22          PTHREAD_SETCANCELSTATE(3)