pthread_setcancelstate(3) — Linux manual page

pthread_...celstate(3)  Library Functions Manual  pthread_...celstate(3)

NAME

       pthread_setcancelstate, pthread_setcanceltype - set cancelability
       state and type

LIBRARY

       POSIX threads library (libpthread, -lpthread)

SYNOPSIS

       #include <pthread.h>

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

DESCRIPTION

       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:

       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
              cancelation request.

       PTHREAD_CANCEL_DISABLE
              The thread is not cancelable.  If a cancelation 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 cancelation request is deferred until the thread next
              calls a function that is a cancelation point (see
              pthreads(7)).  This is the default cancelability type in
              all new threads, including the initial thread.

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

       PTHREAD_CANCEL_ASYNCHRONOUS
              The thread can be canceled at any time.  (Typically, it
              will be canceled immediately upon receiving a cancelation
              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()       │                     │         │
       └───────────────────────────────┴─────────────────────┴─────────┘

STANDARDS

       POSIX.1-2008.

HISTORY

       glibc 2.0 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
       cancelation 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 cancelation
       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 cancelation 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 cancelation
       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 cancelation 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().

EXAMPLES

       See pthread_cancel(3).

SEE ALSO

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

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Linux man-pages 6.9.1          2024-05-02         pthread_...celstate(3)

Pages that refer to this page: pthread_cancel(3), pthread_cleanup_push(3), pthread_cleanup_push_defer_np(3), pthread_kill_other_threads_np(3), pthread_testcancel(3), pthreads(7)

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