threads/thread_incr_spinlock.c

This is threads/thread_incr_spinlock.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 33.

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

Distribution version

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

threadFunc()
main()

/* thread_incr_spinlock.c

   This program employs two POSIX threads that increment the same global
   variable, synchronizing their access using a spinlock. As a consequence,
   updates are not lost. Compare with thread_incr.c, thread_incr_mutex.c,
   and thread_incr_rwlock.c
*/
#include <pthread.h>
#include "tlpi_hdr.h"

static volatile int glob = 0;
static pthread_spinlock_t splock;

static void *                   /* Loop 'arg' times incrementing 'glob' */
threadFunc(void *arg)
{
    int loops = *((int *) arg);
    int loc, s;

    for (int j = 0; j < loops; j++) {
        s = pthread_spin_lock(&splock);
        if (s != 0)
            errExitEN(s, "pthread_spin_lock");

        loc = glob;
        loc++;
        glob = loc;

        s = pthread_spin_unlock(&splock);
        if (s != 0)
            errExitEN(s, "pthread_spin_unlock");
    }

    return NULL;
}

int
main(int argc, char *argv[])
{
    int loops = (argc > 1) ? getInt(argv[1], GN_GT_0, "num-loops") : 10000000;

    int s = pthread_spin_init(&splock, 0);
    if (s != 0)
        errExitEN(s, "pthread_spin_init");

    pthread_t t1, t2;
    s = pthread_create(&t1, NULL, threadFunc, &loops);
    if (s != 0)
        errExitEN(s, "pthread_create");
    s = pthread_create(&t2, NULL, threadFunc, &loops);
    if (s != 0)
        errExitEN(s, "pthread_create");

    s = pthread_join(t1, NULL);
    if (s != 0)
        errExitEN(s, "pthread_join");
    s = pthread_join(t2, NULL);
    if (s != 0)
        errExitEN(s, "pthread_join");

    printf("glob = %d\n", glob);
    exit(EXIT_SUCCESS);
}

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.