cancel_cleanup.c

/*
 * cancel_cleanup.c
 *
 * Demonstrate use of a cleanup handler to release resources and
 * restore invariants on cancellation of a wait.
 */
#include <pthread.h>
#include "errors.h"

#define THREADS 5

/*
 * Control structure shared by the test threads, containing
 * the synchronization and invariant data.
 */
typedef struct control_tag {
    int                 counter, busy;
    pthread_mutex_t     mutex;
    pthread_cond_t      cv;
} control_t;

control_t control =
    {0, 1, PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER};

/*
 * This routine is installed as the cancellation cleanup
 * handler around the cancellable condition wait. It will
 * be called by the system when the thread is cancelled.
 */
void cleanup_handler (void *arg)
{
    control_t *st = (control_t *)arg;
    int status;

    st->counter--;
    printf ("cleanup_handler: counter == %d\n", st->counter);
    status = pthread_mutex_unlock (&st->mutex);
    if (status != 0)
        err_abort (status, "Unlock in cleanup handler");
}

/*
 * Multiple threads are created running this routine (controlled
 * by the THREADS macro). They maintain a "counter" invariant,
 * which expresses the number of running threads. They specify a
 * nonzero value to pthread_cleanup_pop to run the same
 * "finalization" action when cancellation does not occur.
 */
void *thread_routine (void *arg)
{
    int status;

    pthread_cleanup_push (cleanup_handler, (void*)&control);

    status = pthread_mutex_lock (&control.mutex);
    if (status != 0)
        err_abort (status, "Mutex lock");
    control.counter++;

    while (control.busy) {
        status = pthread_cond_wait (&control.cv, &control.mutex);
        if (status != 0)
            err_abort (status, "Wait on condition");
    }

    pthread_cleanup_pop (1);
    return NULL;
}

int main (int argc, char *argv[])
{
    pthread_t thread_id[THREADS];
    int count;
    void *result;
    int status;

    for (count = 0; count < THREADS; count++) {
        status = pthread_create (
            &thread_id[count], NULL, thread_routine, NULL);
        if (status != 0)
            err_abort (status, "Create thread");
    }

    sleep (2);

    for (count = 0; count < THREADS; count++) {
        status = pthread_cancel (thread_id[count]);
        if (status != 0)
            err_abort (status, "Cancel thread");

        status = pthread_join (thread_id[count], &result);
        if (status != 0)
            err_abort (status, "Join thread");
        if (result == PTHREAD_CANCELED)
            printf ("thread %d cancelled\n", count);
        else
            printf ("thread %d was not cancelled\n", count);
    }
    return 0;    
}