|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
PTHREAD_CLEANUP_PUSH(3) Linux Programmer's Manual PTHREAD_CLEANUP_PUSH(3)
pthread_cleanup_push, pthread_cleanup_pop - push and pop thread can‐
cellation 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
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.
These functions do not return a value.
There are no errors.
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() │ │ │
└────────────────────────┴───────────────┴─────────┘
POSIX.1-2001, POSIX.1-2008.
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.
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);
}
pthread_cancel(3), pthread_cleanup_push_defer_np(3),
pthread_setcancelstate(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 2015-07-23 PTHREAD_CLEANUP_PUSH(3)
Pages that refer to this page: pthread_cancel(3), pthread_cleanup_push_defer_np(3), pthread_exit(3), pthread_setcancelstate(3), pthread_testcancel(3), pthreads(7)