#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <sys/mman.h>
#include <sys/time.h>
#include <sys/wait.h>

#define MAX_WAIT_USEC (1000*1000)
#define CHILDREN 16
#define MAX_ITER 200

#define NS_PER_S 1000000000

static pthread_mutex_t *proc_lock;

static void child()
{
        int rv, i = 0;

        do {
                int wait_usec = 0;
		struct timespec abstime;

		clock_gettime(CLOCK_REALTIME, &abstime);

		abstime.tv_nsec += 1000;
		if (abstime.tv_nsec >= NS_PER_S) {
			abstime.tv_sec++;
			abstime.tv_nsec -= NS_PER_S;
		}

                while ((rv = pthread_mutex_timedlock(proc_lock, &abstime))) {
                    if (rv != ETIMEDOUT) {
			    fprintf(stderr, "BADx rv=%d\n", rv);
			    abort();
		    }
                    if (++wait_usec >= MAX_WAIT_USEC)
                        abort();
                }
		//fprintf(stderr, "[%d] rv=%d\n", getpid(), rv);

            i++;
	    usleep(1);
            if (pthread_mutex_unlock(proc_lock))
                abort();
        } while (i < MAX_ITER);

	exit(0);
}

int main(int argc, char **argv)
{
	proc_lock = mmap(NULL, sizeof(*proc_lock),
			 PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED,
			 -1, 0);

	pthread_mutexattr_t mattr;

	pthread_mutexattr_init(&mattr);
	pthread_mutexattr_setpshared(&mattr, PTHREAD_PROCESS_SHARED);
	pthread_mutexattr_setrobust(&mattr, PTHREAD_MUTEX_ROBUST);
	pthread_mutexattr_setprotocol(&mattr, PTHREAD_PRIO_INHERIT);

	pthread_mutex_init(proc_lock, &mattr);

	pthread_mutexattr_destroy(&mattr);

	for (unsigned a = 0; a < CHILDREN; a++)
		if (!fork())
			child();

	for (unsigned a = 0; a < CHILDREN; a++)
		wait(NULL);

	pthread_mutex_destroy(proc_lock);


	return 0;
}