userthreads.c

/*
 * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
 *      The President and Fellows of Harvard College.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
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 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Test multiple user level threads inside a process. The program
 * forks 3 threads off 2 to functions, each of which displays a string
 * every once in a while.
 *
 * This won't do much of anything unless you implement user-level
 * threads.
 *
 * It also makes various assumptions about the thread API. In
 * particular, it believes (1) that you create a thread by calling
 * "threadfork()" and passing the address for execution of the new
 * thread to begin at, (2) that if the parent thread exits any child
 * threads will keep running, and (3) child threads will exit if they
 * return from the function they started in. If any or all of these
 * assumptions are not met by your user-level threads, you will need
 * to patch this test accordingly.
 *
 * This is also a rather basic test and you'll probably want to write
 * some more of your own.
 */


#include <unistd.h>
#include <stdio.h>

#define NTHREADS  3
#define MAX       1<<25

/* counter for the loop in the threads : 
   This variable is shared and incremented by each 
   thread during his computation */
volatile int count = 0;

/* the 2 threads : */
void ThreadRunner(void);
void BladeRunner(void);

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

    (void)argc;
    (void)argv;

    for (i=0; i<NTHREADS; i++) {
        if (i)
            threadfork(ThreadRunner);
        else
            threadfork(BladeRunner);
    }

    printf("Parent has left.\n");
    return 0;
}

/* multiple threads will simply print out the global variable.
   Even though there is no synchronization, we should get some 
   random results.
*/

void
BladeRunner()
{
    while (count < MAX) {
        if (count % 500 == 0)
            printf("Blade ");
        count++;
    }
}

void
ThreadRunner()
{
    while (count < MAX) {
        if (count % 513 == 0)
            printf(" Runner\n");
        count++;
    }
}