👤
Home Man
Search
Today's Posts
Register

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:
Select Section of Man Page:
Select Man Page Repository:

Linux 2.6 - man page for pthread_cleanup_pop (linux section 3)

PTHREAD_CLEANUP_PUSH(3) 	    Linux Programmer's Manual		  PTHREAD_CLEANUP_PUSH(3)

NAME
       pthread_cleanup_push, pthread_cleanup_pop - push and pop thread cancellation clean-up han-
       dlers

SYNOPSIS
       #include <pthread.h>

       void pthread_cleanup_push(void (*routine)(void *),
				 void *arg);
       void pthread_cleanup_pop(int execute);

       Compile and link with -pthread.

DESCRIPTION
       These functions manipulate the calling thread's stack of thread-cancellation clean-up han-
       dlers.	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.

RETURN VALUE
       These functions do not return a value.

ERRORS
       There are no errors.

CONFORMING TO
       POSIX.1-2001.

NOTES
       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 vari-
       ables 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.

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
       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  ter-
       minate 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);
       }

SEE ALSO
       pthread_cancel(3),      pthread_cleanup_push_defer_np(3),       pthread_setcancelstate(3),
       pthread_testcancel(3), pthreads(7)

COLOPHON
       This  page  is  part of release 3.55 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)


All times are GMT -4. The time now is 08:27 PM.

Unix & Linux Forums Content Copyrightę1993-2018. All Rights Reserved.
×
UNIX.COM Login
Username:
Password:  
Show Password