| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON | The Linux Programming Interface |
PTHREAD_CLEANUP_PUSH(3) Linux Programmer's Manual PTHREAD_CLEANUP_PUSH(3)
pthread_cleanup_push, pthread_cleanup_pop - push and pop thread cancellation
clean-up handlers
#include <pthread.h>
void pthread_cleanup_push(void (*routine)(void *),
void *arg);
void pthread_cleanup_pop(int execute);
Compile and link with -pthread.
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 only established 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.
These functions do not return a value.
There are no errors.
POSIX.1-2001.
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 only be visible within 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.
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.
#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);
}
pthread_cancel(3), pthread_cleanup_push_defer_np(3),
pthread_setcancelstate(3), pthread_testcancel(3), pthreads(7)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2008-11-24 PTHREAD_CLEANUP_PUSH(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface