threads/prod_no_condvar.c

This is threads/prod_no_condvar.c, an example to accompany the book, The Linux Programming Interface.

This file is not printed in the book; it is a supplementary file for Chapter 30.

The source code file is copyright 2010, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

  Cover of The Linux Programming Interface

Function list (Bold in this list means a function is not static)

/* prod_no_condvar.c

   A simple POSIX threads producer-consumer example that doesn't use
   a condition variable.

   See also prod_condvar.c.
*/
#include <time.h>
#include <pthread.h>
#include "tlpi_hdr.h"

static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;

static int avail = 0;
static void *
threadFunc(void *arg)
{
    int cnt = atoi((char *) arg);
    int s, j;

    for (j = 0; j < cnt; j++) {
        sleep(1);

        /* Code to produce a unit omitted */

        s = pthread_mutex_lock(&mtx);
        if (s != 0)
            errExitEN(s, "pthread_mutex_lock");

        avail++;        /* Let consumer know another unit is available */

        s = pthread_mutex_unlock(&mtx);
        if (s != 0)
            errExitEN(s, "pthread_mutex_unlock");
    }

    return NULL;
}
int
main(int argc, char *argv[])
{
    pthread_t tid;
    int s, j;
    int totRequired;            /* Total number of units that all
                                   threads will produce */
    int numConsumed;            /* Total units so far consumed */
    Boolean done;
    time_t t;

    t = time(NULL);

    /* Create all threads */

    totRequired = 0;
    for (j = 1; j < argc; j++) {
        totRequired += atoi(argv[j]);

        s = pthread_create(&tid, NULL, threadFunc, argv[j]);
        if (s != 0)
            errExitEN(s, "pthread_create");
    }

    /* Use a polling loop to check for available units */

    numConsumed = 0;
    done = FALSE;

    for (;;) {
        s = pthread_mutex_lock(&mtx);
        if (s != 0)
            errExitEN(s, "pthread_mutex_lock");

        while (avail > 0) {             /* Consume all available units */

            /* Do something with produced unit */

            numConsumed ++;
            avail--;
            printf("T=%ld: numConsumed=%d\n", (long) (time(NULL) - t),
                    numConsumed);

            done = numConsumed >= totRequired;
        }

        s = pthread_mutex_unlock(&mtx);
        if (s != 0)
            errExitEN(s, "pthread_mutex_unlock");

        if (done)
            break;

        /* Perhaps do other work here that does not require mutex lock */

    }

    exit(EXIT_SUCCESS);
}

 

Download threads/prod_no_condvar.c

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.