push и pop обработчики очистки отмены потоков (push and pop thread cancellation clean-up handlers)
Имя (Name)
pthread_cleanup_push, pthread_cleanup_pop - push and pop thread
cancellation clean-up handlers
Синопсис (Synopsis)
#include <pthread.h>
void pthread_cleanup_push(void (*routine)(void *), void *arg);
void pthread_cleanup_pop(int execute);
Compile and link with -pthread.
Описание (Description)
These functions manipulate the calling thread's stack of thread-
cancellation clean-up handlers. A clean-up handler is a function
that is automatically executed when a thread is canceled (or in
various other circumstances described below); it might, for
example, unlock a mutex so that it becomes available to other
threads in the process.
The pthread_cleanup_push() function pushes routine onto the top
of the stack of clean-up handlers. When routine is later
invoked, it will be given arg as its argument.
The pthread_cleanup_pop() function removes the routine at the top
of the stack of clean-up handlers, and optionally executes it if
execute is nonzero.
A cancellation clean-up handler is popped from the stack and
executed in the following circumstances:
1. When a thread is canceled, all of the stacked clean-up
handlers are popped and executed in the reverse of the order
in which they were pushed onto the stack.
2. When a thread terminates by calling pthread_exit(3), all
clean-up handlers are executed as described in the preceding
point. (Clean-up handlers are not called if the thread
terminates by performing a return from the thread start
function.)
3. When a thread calls pthread_cleanup_pop() with a nonzero
execute argument, the top-most clean-up handler is popped and
executed.
POSIX.1 permits pthread_cleanup_push() and pthread_cleanup_pop()
to be implemented as macros that expand to text containing '{'
and '}', respectively. For this reason, the caller must ensure
that calls to these functions are paired within the same
function, and at the same lexical nesting level. (In other
words, a clean-up handler is established only during the
execution of a specified section of code.)
Calling longjmp(3) (siglongjmp(3)) produces undefined results if
any call has been made to pthread_cleanup_push() or
pthread_cleanup_pop() without the matching call of the pair since
the jump buffer was filled by setjmp(3) (sigsetjmp(3)).
Likewise, calling longjmp(3) (siglongjmp(3)) from inside a clean-
up handler produces undefined results unless the jump buffer was
also filled by setjmp(3) (sigsetjmp(3)) inside the handler.
Возвращаемое значение (Return value)
These functions do not return a value.
Ошибки (Error)
There are no errors.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│pthread_cleanup_push(), │ Thread safety │ MT-Safe │
│pthread_cleanup_pop() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008.
Примечание (Note)
On Linux, the pthread_cleanup_push() and pthread_cleanup_pop()
functions are implemented as macros that expand to text
containing '{' and '}', respectively. This means that variables
declared within the scope of paired calls to these functions will
be visible within only that scope.
POSIX.1 says that the effect of using return, break, continue, or
goto to prematurely leave a block bracketed
pthread_cleanup_push() and pthread_cleanup_pop() is undefined.
Portable applications should avoid doing this.
Примеры (Examples)
The program below provides a simple example of the use of the
functions described in this page. The program creates a thread
that executes a loop bracketed by pthread_cleanup_push() and
pthread_cleanup_pop(). This loop increments a global variable,
cnt, once each second. Depending on what command-line arguments
are supplied, the main thread sends the other thread a
cancellation request, or sets a global variable that causes the
other thread to exit its loop and terminate normally (by doing a
return).
In the following shell session, the main thread sends a
cancellation request to the other thread:
$ ./a.out
New thread started
cnt = 0
cnt = 1
Canceling thread
Called clean-up handler
Thread was canceled; cnt = 0
From the above, we see that the thread was canceled, and that the
cancellation clean-up handler was called and it reset the value
of the global variable cnt to 0.
In the next run, the main program sets a global variable that
causes other thread to terminate normally:
$ ./a.out x
New thread started
cnt = 0
cnt = 1
Thread terminated normally; cnt = 2
From the above, we see that the clean-up handler was not executed
(because cleanup_pop_arg was 0), and therefore the value of cnt
was not reset.
In the next run, the main program sets a global variable that
causes the other thread to terminate normally, and supplies a
nonzero value for cleanup_pop_arg:
$ ./a.out x 1
New thread started
cnt = 0
cnt = 1
Called clean-up handler
Thread terminated normally; cnt = 0
In the above, we see that although the thread was not canceled,
the clean-up handler was executed, because the argument given to
pthread_cleanup_pop() was nonzero.
Program source
#include <pthread.h>
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#define handle_error_en(en, msg) \
do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
static int done = 0;
static int cleanup_pop_arg = 0;
static int cnt = 0;
static void
cleanup_handler(void *arg)
{
printf("Called clean-up handler\n");
cnt = 0;
}
static void *
thread_start(void *arg)
{
time_t start, curr;
printf("New thread started\n");
pthread_cleanup_push(cleanup_handler, NULL);
curr = start = time(NULL);
while (!done) {
pthread_testcancel(); /* A cancellation point */
if (curr < time(NULL)) {
curr = time(NULL);
printf("cnt = %d\n", cnt); /* A cancellation point */
cnt++;
}
}
pthread_cleanup_pop(cleanup_pop_arg);
return NULL;
}
int
main(int argc, char *argv[])
{
pthread_t thr;
int s;
void *res;
s = pthread_create(&thr, NULL, thread_start, NULL);
if (s != 0)
handle_error_en(s, "pthread_create");
sleep(2); /* Allow new thread to run a while */
if (argc > 1) {
if (argc > 2)
cleanup_pop_arg = atoi(argv[2]);
done = 1;
} else {
printf("Canceling thread\n");
s = pthread_cancel(thr);
if (s != 0)
handle_error_en(s, "pthread_cancel");
}
s = pthread_join(thr, &res);
if (s != 0)
handle_error_en(s, "pthread_join");
if (res == PTHREAD_CANCELED)
printf("Thread was canceled; cnt = %d\n", cnt);
else
printf("Thread terminated normally; cnt = %d\n", cnt);
exit(EXIT_SUCCESS);
}
Смотри также (See also)
pthread_cancel(3), pthread_cleanup_push_defer_np(3),
pthread_setcancelstate(3), pthread_testcancel(3), pthreads(7)
