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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
PTHREAD_SETCANCELSTATE(3) Linux Programmer's ManualPTHREAD_SETCANCELSTATE(3)
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:
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 cancellation request.
PTHREAD_CANCEL_DISABLE
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:
PTHREAD_CANCEL_DEFERRED
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.
PTHREAD_CANCEL_ASYNCHRONOUS
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
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 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 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 release 4.12 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
https://www.kernel.org/doc/man-pages/.
Linux 2015-08-08 PTHREAD_SETCANCELSTATE(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)