pthread_cleanup_push(3) - Linux manual page (original) (raw)
pthreadcleanuppush(3) Library Functions Manual pthreadcleanuppush(3)
NAME top
pthread_cleanup_push, pthread_cleanup_pop - push and pop thread
cancelation clean-up handlersLIBRARY top
POSIX threads library (_libpthread_, _-lpthread_)SYNOPSIS top
**#include <pthread.h>**
**void pthread_cleanup_push(typeof(void (void *)) ***_routine_**, void ***_arg_**);**
**void pthread_cleanup_pop(int** _execute_**);**DESCRIPTION top
These functions manipulate the calling thread's stack of thread-
cancelation 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 cancelation clean-up handler is popped from the stack and
executed in the following circumstances:
• 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.
• When a thread terminates by calling [pthread_exit(3)](../man3/pthread%5Fexit.3.html), 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.)
• 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)](../man3/longjmp.3.html) ([siglongjmp(3)](../man3/siglongjmp.3.html)) 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)](../man3/setjmp.3.html) ([sigsetjmp(3)](../man3/sigsetjmp.3.html)). Likewise,
calling [longjmp(3)](../man3/longjmp.3.html) ([siglongjmp(3)](../man3/siglongjmp.3.html)) from inside a clean-up handler
produces undefined results unless the jump buffer was also filled
by [setjmp(3)](../man3/setjmp.3.html) ([sigsetjmp(3)](../man3/sigsetjmp.3.html)) inside the handler.RETURN VALUE top
These functions do not return a value.ERRORS top
There are no errors.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────────────────┼───────────────┼─────────┤
│ **pthread_cleanup_push**(), │ Thread safety │ MT-Safe │
│ **pthread_cleanup_pop**() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘VERSIONS top
On glibc, 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.STANDARDS top
POSIX.1-2008.HISTORY top
POSIX.1-2001. glibc 2.0.EXAMPLES top
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 cancelation
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
cancelation 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
cancelation 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 _cleanuppoparg_ 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 _cleanuppoparg_:
$ **./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 <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.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 curr;
printf("New thread started\n");
pthread_cleanup_push(cleanup_handler, NULL);
curr = time(NULL);
while (!done) {
pthread_testcancel(); /* A cancelation point */
if (curr < time(NULL)) {
curr = time(NULL);
printf("cnt = %d\n", cnt); /* A cancelation 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);
}SEE ALSO top
[pthread_cancel(3)](../man3/pthread%5Fcancel.3.html), [pthread_cleanup_push_defer_np(3)](../man3/pthread%5Fcleanup%5Fpush%5Fdefer%5Fnp.3.html),
[pthread_setcancelstate(3)](../man3/pthread%5Fsetcancelstate.3.html), [pthread_testcancel(3)](../man3/pthread%5Ftestcancel.3.html), [pthreads(7)](../man7/pthreads.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-12-13 pthreadcleanuppush(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)