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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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pthread_s...ncelstate(3) Library Functions Manualpthread_s...ncelstate(3)
pthread_setcancelstate, pthread_setcanceltype - set cancelability
state and type
POSIX threads library (libpthread, -lpthread)
#include <pthread.h>
int pthread_setcancelstate(int state, int *oldstate);
int pthread_setcanceltype(int type, int *oldtype);
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.
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.1-2008.
glibc 2.0 POSIX.1-2001.
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().
See pthread_cancel(3).
pthread_cancel(3), pthread_cleanup_push(3), pthread_testcancel(3),
pthreads(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-02-02. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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man-pages@man7.org
Linux man-pages 6.10 2024-07-23 pthread_s...ncelstate(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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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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