/*
 *  eventfd-sem by Davide Libenzi (Simple test for eventfd sempahore)
 *  Copyright (C) 2009  Davide Libenzi
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 *  Davide Libenzi <davidel@xmailserver.org>
 *
 */

#include <sys/types.h>
#include <sys/syscall.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>

#ifndef EFD_SEMLIKE
#define EFD_SEMLIKE (1 << 0)
#endif

#ifndef __NR_eventfd2
#if defined(__x86_64__)
#define __NR_eventfd2 290
#elif defined(__i386__)
#define __NR_eventfd2 328
#else
#error Cannot detect your architecture!
#endif
#endif


static int eventfd2(int count, int flags) {
	return syscall(__NR_eventfd2, count, flags);
}

static void xsem_wait(int fd) {
	u_int64_t cntr;

	if (read(fd, &cntr, sizeof(cntr)) != sizeof(cntr)) {
		perror("reading eventfd");
		exit(1);
	}
	fprintf(stdout, "[%u] wait completed on %d: count=%llu\n",
		getpid(), fd, cntr);
}

static void xsem_post(int fd, int count) {
	u_int64_t cntr = count;

	if (write(fd, &cntr, sizeof(cntr)) != sizeof(cntr)) {
		perror("writing eventfd");
		exit(1);
	}
}

static void sem_player(int fd1, int fd2) {
	fprintf(stdout, "[%u] posting 1 on %d\n", getpid(), fd1);
	xsem_post(fd1, 1);

	fprintf(stdout, "[%u] waiting on %d\n", getpid(), fd2);
	xsem_wait(fd2);

	fprintf(stdout, "[%u] posting 1 on %d\n", getpid(), fd1);
	xsem_post(fd1, 1);

	fprintf(stdout, "[%u] waiting on %d\n", getpid(), fd2);
	xsem_wait(fd2);

	fprintf(stdout, "[%u] posting 5 on %d\n", getpid(), fd1);
	xsem_post(fd1, 5);

	fprintf(stdout, "[%u] waiting 5 times on %d\n", getpid(), fd2);
	xsem_wait(fd2);
	xsem_wait(fd2);
	xsem_wait(fd2);
	xsem_wait(fd2);
	xsem_wait(fd2);
}

static void usage(char const *prg) {
	fprintf(stderr, "use: %s [-h]\n", prg);
}

int main (int argc, char **argv) {
	int c, fd1, fd2, status;
	pid_t cpid_poster, cpid_waiter;

	while ((c = getopt(argc, argv, "h")) != -1) {
		switch (c) {
		default:
			usage(argv[0]);
			return 1;
		}
	}
	if ((fd1 = eventfd2(0, EFD_SEMLIKE)) == -1 ||
	    (fd2 = eventfd2(0, EFD_SEMLIKE)) == -1) {
		perror("eventfd2");
		return 1;
	}
	if ((cpid_poster = fork()) == 0) {
		sem_player(fd1, fd2);
		exit(0);
	}
	if ((cpid_waiter = fork()) == 0) {
		sem_player(fd2, fd1);
		exit(0);
	}
	waitpid(cpid_poster, &status, 0);
	waitpid(cpid_waiter, &status, 0);

	return 0;
}