Subj : Futex problem
To   : comp.programming.threads
From : JK
Date : Sat Oct 01 2005 08:58 am

Hi, I am trying to learn how to use futex and I just dont get it ;)
What is problem with this code example? The child process never stops
waiting. This is only a test, thats why it does not have any error
checking.


#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <linux/futex.h>
#include <asm/unistd.h>
#include <errno.h>

#define __NR_sys_futex __NR_futex
_syscall4(int, sys_futex, volatile int *, futex, int, op,
    int, val, struct timespec *, rel);


int main(int argc, char *argv[])
{
	int counter = 1;
	pid_t p = fork();

	if (p == 0)
	{
		printf ("before wait\n");
		sys_futex(&counter, FUTEX_WAIT, 1, NULL);
		printf ("after wait\n");
	}

	sleep (2);

	counter = 0;
	printf ("wake (%d) : %d\n", sys_futex(&counter,
             FUTEX_WAKE, 1, NULL), counter);

	sleep (2);
	return EXIT_SUCCESS;
}


OUPUT:
----------------
before wait
wake (0) : 0


Thanks,

JK

.