отправить запрос на отмену в поток (send a cancellation request to a thread)
Имя (Name)
pthread_cancel - send a cancellation request to a thread
Синопсис (Synopsis)
#include <pthread.h>
int pthread_cancel(pthread_t thread);
Compile and link with -pthread.
Описание (Description)
The pthread_cancel() function sends a cancellation request to the
thread thread. Whether and when the target thread reacts to the
cancellation request depends on two attributes that are under the
control of that thread: its cancelability state and type.
A thread's cancelability state, determined by
pthread_setcancelstate(3), can be enabled (the default for new
threads) or disabled. If a thread has disabled cancellation,
then a cancellation request remains queued until the thread
enables cancellation. If a thread has enabled cancellation, then
its cancelability type determines when cancellation occurs.
A thread's cancellation type, determined by
pthread_setcanceltype(3), may be either asynchronous or deferred
(the default for new threads). Asynchronous cancelability means
that the thread can be canceled at any time (usually immediately,
but the system does not guarantee this). Deferred cancelability
means that cancellation will be delayed until the thread next
calls a function that is a cancellation point. A list of
functions that are or may be cancellation points is provided in
pthreads(7).
When a cancellation requested is acted on, the following steps
occur for thread (in this order):
1. Cancellation clean-up handlers are popped (in the reverse of
the order in which they were pushed) and called. (See
pthread_cleanup_push(3).)
2. Thread-specific data destructors are called, in an unspecified
order. (See pthread_key_create(3).)
3. The thread is terminated. (See pthread_exit(3).)
The above steps happen asynchronously with respect to the
pthread_cancel() call; the return status of pthread_cancel()
merely informs the caller whether the cancellation request was
successfully queued.
After a canceled thread has terminated, a join with that thread
using pthread_join(3) obtains PTHREAD_CANCELED as the thread's
exit status. (Joining with a thread is the only way to know that
cancellation has completed.)
Возвращаемое значение (Return value)
On success, pthread_cancel() returns 0; on error, it returns a
nonzero error number.
Ошибки (Error)
ESRCH No thread with the ID thread could be found.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│pthread_cancel() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008.
Примечание (Note)
On Linux, cancellation is implemented using signals. Under the
NPTL threading implementation, the first real-time signal (i.e.,
signal 32) is used for this purpose. On LinuxThreads, the second
real-time signal is used, if real-time signals are available,
otherwise SIGUSR2 is used.
Примеры (Examples)
The program below creates a thread and then cancels it. The main
thread joins with the canceled thread to check that its exit
status was PTHREAD_CANCELED. The following shell session shows
what happens when we run the program:
$ ./a.out
thread_func(): started; cancellation disabled
main(): sending cancellation request
thread_func(): about to enable cancellation
main(): thread was canceled
Program source
#include <pthread.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#define handle_error_en(en, msg) \
do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
static void *
thread_func(void *ignored_argument)
{
int s;
/* Disable cancellation for a while, so that we don't
immediately react to a cancellation request. */
s = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL);
if (s != 0)
handle_error_en(s, "pthread_setcancelstate");
printf("thread_func(): started; cancellation disabled\n");
sleep(5);
printf("thread_func(): about to enable cancellation\n");
s = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
if (s != 0)
handle_error_en(s, "pthread_setcancelstate");
/* sleep() is a cancellation point. */
sleep(1000); /* Should get canceled while we sleep */
/* Should never get here. */
printf("thread_func(): not canceled!\n");
return NULL;
}
int
main(void)
{
pthread_t thr;
void *res;
int s;
/* Start a thread and then send it a cancellation request. */
s = pthread_create(&thr, NULL, &thread_func, NULL);
if (s != 0)
handle_error_en(s, "pthread_create");
sleep(2); /* Give thread a chance to get started */
printf("main(): sending cancellation request\n");
s = pthread_cancel(thr);
if (s != 0)
handle_error_en(s, "pthread_cancel");
/* Join with thread to see what its exit status was. */
s = pthread_join(thr, &res);
if (s != 0)
handle_error_en(s, "pthread_join");
if (res == PTHREAD_CANCELED)
printf("main(): thread was canceled\n");
else
printf("main(): thread wasn't canceled (shouldn't happen!)\n");
exit(EXIT_SUCCESS);
}
Смотри также (See also)
pthread_cleanup_push(3), pthread_create(3), pthread_exit(3),
pthread_join(3), pthread_key_create(3),
pthread_setcancelstate(3), pthread_setcanceltype(3),
pthread_testcancel(3), pthreads(7)
