threads/thread_cleanup.c

/* thread_cleanup.c

   An example of thread cancellation using the POSIX threads API:
   demonstrate the use of pthread_cancel() and cleanup handlers.
*/
#include <pthread.h>
#include "tlpi_hdr.h"

static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
static int glob = 0;                    /* Predicate variable */

static void     /* Free memory pointed to by 'arg' and unlock mutex */
cleanupHandler(void *arg)
{
    int s;

    printf("cleanup: freeing block at %p\n", arg);
    free(arg);

    printf("cleanup: unlocking mutex\n");
    s = pthread_mutex_unlock(&mtx);
    if (s != 0)
        errExitEN(s, "pthread_mutex_unlock");
}

static void *
threadFunc(void *arg)
{
    int s;
    void *buf = NULL;                   /* Buffer allocated by thread */

    buf = malloc(0x10000);              /* Not a cancellation point */
    printf("thread:  allocated memory at %p\n", buf);

    s = pthread_mutex_lock(&mtx);       /* Not a cancellation point */
    if (s != 0)
        errExitEN(s, "pthread_mutex_lock");

    pthread_cleanup_push(cleanupHandler, buf);

    while (glob == 0) {
        s = pthread_cond_wait(&cond, &mtx);     /* A cancellation point */
        if (s != 0)
            errExitEN(s, "pthread_cond_wait");
    }

    printf("thread:  condition wait loop completed\n");
    pthread_cleanup_pop(1);             /* Executes cleanup handler */
    return NULL;
}

int
main(int argc, char *argv[])
{
    pthread_t thr;
    void *res;
    int s;

    s = pthread_create(&thr, NULL, threadFunc, NULL);
    if (s != 0)
        errExitEN(s, "pthread_create");

    sleep(2);                   /* Give thread a chance to get started */

    if (argc == 1) {            /* Cancel thread */
        printf("main:    about to cancel thread\n");
        s = pthread_cancel(thr);
        if (s != 0)
            errExitEN(s, "pthread_cancel");

    } else {                    /* Signal condition variable */
        printf("main:    about to signal condition variable\n");

        s = pthread_mutex_lock(&mtx);   /* See the TLPI page 679 erratum */
        if (s != 0)
            errExitEN(s, "pthread_mutex_lock");

        glob = 1;

        s = pthread_mutex_unlock(&mtx); /* See the TLPI page 679 erratum */
        if (s != 0)
            errExitEN(s, "pthread_mutex_unlock");

        s = pthread_cond_signal(&cond);
        if (s != 0)
            errExitEN(s, "pthread_cond_signal");
    }

    s = pthread_join(thr, &res);
    if (s != 0)
        errExitEN(s, "pthread_join");
    if (res == PTHREAD_CANCELED)
        printf("main:    thread was canceled\n");
    else
        printf("main:    thread terminated normally\n");

    exit(EXIT_SUCCESS);
}