threads/thread_incr_rwlock.c

This is threads/thread_incr_rwlock.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.

Download threads/thread_incr_rwlock.c

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

threadFunc()
main()

/* thread_incr_rwlock.c

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

static volatile int glob = 0;
static pthread_rwlock_t rwlock;

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_rwlock_wrlock(&rwlock);
        if (s != 0)
            errExitEN(s, "pthread_rwlock_wrlock");

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

        s = pthread_rwlock_unlock(&rwlock);
        if (s != 0)
            errExitEN(s, "pthread_rwlock_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_rwlock_init(&rwlock, NULL);
    if (s != 0)
        errExitEN(s, "pthread_rwlock_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);
}

Download threads/thread_incr_rwlock.c

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