CodeSamples/intro/initrace.c

/*
 * initrace.c: simple program demonstrating racy initialization.
 *
 * 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.
 *
 * Copyright (c) 2008 Paul E. McKenney, IBM Corporation.
 */

#include "../api.h"

int nkids = 1;
atomic_t counter;
atomic_t start_count;
int goflag;
#define GOFLAG_INIT  0
#define GOFLAG_START 1
#define GOFLAG_STOP  2

spinlock_t mutex;
int initialized;
DEFINE_PER_THREAD(int, doneflag);

void *init_test(void *arg)
{
	while (goflag != GOFLAG_STOP) {
		while (goflag == GOFLAG_INIT)
			poll(NULL, 0, 1);
		if (goflag == GOFLAG_STOP)
			break;
		atomic_inc(&start_count);
		while (atomic_read(&start_count) != nkids)
			continue;

		/* --- Lock-free checked initialization --- */
		if (!initialized) {
			spin_lock(&mutex);
			initialized = 1;
			atomic_inc(&counter);
			spin_unlock(&mutex);
		}
		/* --- End of lock-free checked initialization --- */

		__get_thread_var(doneflag) = 1;
		while (goflag == GOFLAG_START)
			poll(NULL, 0, 1);
		atomic_inc(&counter);
	}
	return NULL;
}

void usage(char *progname)
{
	fprintf(stderr,
		"Usage: %s [ #threads ]\n", progname);
	exit(-1);
}

int main(int argc, char *argv[])
{
	int done;
	int i;
	int iter;

	smp_init();

	if (argc > 1) {
		nkids = strtoul(argv[1], NULL, 0);
		if (nkids > NR_THREADS) {
			fprintf(stderr, "nkids = %d too large, max = %d\n",
				nkids, NR_THREADS);
			usage(argv[0]);
		}
	}
	printf("Number of threads: %d\n", nkids);

	spin_lock_init(&mutex);
	goflag = GOFLAG_INIT;
	for (i = 0; i < nkids; i++)
		create_thread(init_test, NULL);

	for (iter = 0; iter < 100; iter++) {
		spin_lock(&mutex);
		for_each_thread(i) {
			per_thread(doneflag, i) = 0;
		}
		__get_thread_var(doneflag) = 1;
		atomic_set(&counter, 0);
		atomic_set(&start_count, 0);
		initialized = 0;
		spin_unlock(&mutex);
		spin_lock(&mutex);
		goflag = GOFLAG_START;
		spin_unlock(&mutex);
		poll(NULL, 0, 1);
		done = 0;
		while (!done) {
			done = 1;
			for (i = 0; i < nkids; i++)
				if (!per_thread(doneflag, i)) {
					done = 0;
					break;
				}
			poll(NULL, 0, 1);
		}
		if (atomic_read(&counter) != 1) {
			printf("Double initialization, counter = %d\n",
			       atomic_read(&counter));
			exit(-1);
		} else {
			printf("Iteration %d succeeded\n", iter);
		}
		spin_lock(&mutex);
		atomic_set(&counter, 0);
		spin_unlock(&mutex);
		spin_lock(&mutex);
		goflag = GOFLAG_INIT;
		while (atomic_read(&counter) < nkids)
			poll(NULL, 0, 1);
		spin_unlock(&mutex);
		spin_lock(&mutex);
		atomic_set(&counter, 0);
		spin_unlock(&mutex);
	}

	goflag = GOFLAG_STOP;

	wait_all_threads();

	exit(0);
}