NAME
pthreadcleanuppush, pthreadcleanuppop - push and pop thread cancel‐
lation clean-up handlers SYNOPSIS
#include
void pthreadcleanuppush(void (*routine)(void *), void *arg); void pthreadcleanuppop(int execute); Compile and link with -pthread. DESCRIPTION
These functions manipulate the calling thread's stack of thread-cancel‐
lation 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 pthreadcleanuppush() 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 pthreadcleanuppop() 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 pthreadexit(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 pthreadcleanuppop() with a nonzero execute
argument, the top-most clean-up handler is popped and executed. POSIX.1 permits pthreadcleanuppush() and pthreadcleanuppop() 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 estab‐ lished 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 pthreadcleanuppush() or pthreadcleanuppop() without the matching call of the pair since the jump buffer was filled by setjmp(3) (sigsetjmp(3)). Likewise, calling longjmp(3) (sig‐
longjmp(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. RETURN VALUE These functions do not return a value. ERRORS There are no errors. CONFORMING TO
POSIX.1-2001. NOTES On Linux, the pthreadcleanuppush() and pthreadcleanuppop() func‐ tions 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 pthreadcleanuppush() and pthreadcleanuppop() is undefined. Portable applications should avoid doing this. EXAMPLE 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 pthreadcleanuppush() and pthreadcleanuppop(). This loop increments a global variable, cnt, once each second. Depend‐
ing 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 can‐
cellation 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 pthreadcleanuppop() was nonzero. Program source
#include
#include
#include
#include
#include
#include
#define handleerroren(en, msg) \ do { errno = en; perror(msg); exit(EXITFAILURE); } while (0) static int done = 0; static int cleanuppoparg = 0; static int cnt = 0; static void cleanuphandler(void *arg) {
printf("Called clean-up handler\n"); cnt = 0; } static void * threadstart(void *arg) { timet start, curr; printf("New thread started\n"); pthreadcleanuppush(cleanuphandler, NULL); curr = start = time(NULL); while (!done) { pthreadtestcancel(); /* A cancellation point */ if (curr < time(NULL)) { curr = time(NULL);
printf("cnt = %d\n", cnt); /* A cancellation point */ cnt++; } } pthreadcleanuppop(cleanuppoparg); return NULL; } int main(int argc, char *argv[]) { pthreadt thr; int s; void *res; s = pthreadcreate(&thr, NULL, threadstart, NULL); if (s != 0) handleerroren(s, "pthreadcreate"); sleep(2); /* Allow new thread to run a while */ if (argc > 1) { if (argc > 2) cleanuppoparg = atoi(argv[2]); done = 1; } else { printf("Canceling thread\n"); s = pthreadcancel(thr); if (s != 0) handleerroren(s, "pthreadcancel"); } s = pthreadjoin(thr, &res); if (s != 0) handleerroren(s, "pthreadjoin"); if (res == PTHREADCANCELED)
printf("Thread was canceled; cnt = %d\n", cnt); else
printf("Thread terminated normally; cnt = %d\n", cnt); exit(EXITSUCCESS); } SEE ALSO pthreadcancel(3), pthreadcleanuppushdefernp(3), pthreadsetcancel‐ state(3), pthreadtestcancel(3), pthreads(7) COLOPHON
This page is part of release 3.53 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 PTHREADCLEANUPPUSH(3)