rwlock_main.c

/*
 * rwlock_main.c
 *
 * Demonstrate use of read-write locks as implemented by
 * rwlock.c
 *
 * Special notes: On a Solaris system, call thr_setconcurrency()
 * to allow interleaved thread execution, since threads are not
 * timesliced.
 */
#include "rwlock.h"
#include "errors.h"

#define THREADS         5
#define DATASIZE        15
#define ITERATIONS      10000

/*
 * Keep statistics for each thread.
 */
typedef struct thread_tag {
    int         thread_num;
    pthread_t   thread_id;
    int         updates;
    int         reads;
    int         interval;
} thread_t;

/*
 * Read-write lock and shared data
 */
typedef struct data_tag {
    rwlock_t    lock;
    int         data;
    int         updates;
} data_t;

thread_t threads[THREADS];
data_t data[DATASIZE];

/*
 * Thread start routine that uses read-write locks
 */
void *thread_routine (void *arg)
{
    thread_t *self = (thread_t*)arg;
    int repeats = 0;
    int iteration;
    int element = 0;
    int status;

    for (iteration = 0; iteration < ITERATIONS; iteration++) {
        /*
         * Each "self->interval" iterations, perform an
         * update operation (write lock instead of read
         * lock).
         */
        if ((iteration % self->interval) == 0) {
            status = rwl_writelock (&data[element].lock);
            if (status != 0)
                err_abort (status, "Write lock");
            data[element].data = self->thread_num;
            data[element].updates++;
            self->updates++;
            status = rwl_writeunlock (&data[element].lock);
            if (status != 0)
                err_abort (status, "Write unlock");
        } else {
            /*
             * Look at the current data element to see whether
             * the current thread last updated it. Count the
             * times, to report later.
             */
            status = rwl_readlock (&data[element].lock);
            if (status != 0)
                err_abort (status, "Read lock");
            self->reads++;
            if (data[element].data == self->thread_num)
                repeats++;
            status = rwl_readunlock (&data[element].lock);
            if (status != 0)
                err_abort (status, "Read unlock");
        }
        element++;
        if (element >= DATASIZE)
            element = 0;
    }

    if (repeats > 0)
        printf (
            "Thread %d found unchanged elements %d times\n",
            self->thread_num, repeats);
    return NULL;
}

int main (int argc, char *argv[])
{
    int count;
    int data_count;
    int status;
    unsigned int seed = 1;
    int thread_updates = 0;
    int data_updates = 0;

#ifdef sun
    /*
     * On Solaris 2.5, threads are not timesliced. To ensure
     * that our threads can run concurrently, we need to
     * increase the concurrency level to THREADS.
     */
    DPRINTF (("Setting concurrency level to %d\n", THREADS));
    thr_setconcurrency (THREADS);
#endif

    /*
     * Initialize the shared data.
     */
    for (data_count = 0; data_count < DATASIZE; data_count++) {
        data[data_count].data = 0;
        data[data_count].updates = 0;
        status = rwl_init (&data[data_count].lock);
        if (status != 0)
            err_abort (status, "Init rw lock");
    }

    /*
     * Create THREADS threads to access shared data.
     */
    for (count = 0; count < THREADS; count++) {
        threads[count].thread_num = count;
        threads[count].updates = 0;
        threads[count].reads = 0;
        threads[count].interval = rand_r (&seed) % 71;
        status = pthread_create (&threads[count].thread_id,
            NULL, thread_routine, (void*)&threads[count]);
        if (status != 0)
            err_abort (status, "Create thread");
    }

    /*
     * Wait for all threads to complete, and collect
     * statistics.
     */
    for (count = 0; count < THREADS; count++) {
        status = pthread_join (threads[count].thread_id, NULL);
        if (status != 0)
            err_abort (status, "Join thread");
        thread_updates += threads[count].updates;
        printf ("%02d: interval %d, updates %d, reads %d\n",
            count, threads[count].interval,
            threads[count].updates, threads[count].reads);
    }

    /*
     * Collect statistics for the data.
     */
    for (data_count = 0; data_count < DATASIZE; data_count++) {
        data_updates += data[data_count].updates;
        printf ("data %02d: value %d, %d updates\n",
            data_count, data[data_count].data, data[data_count].updates);
        rwl_destroy (&data[data_count].lock);
    }

    printf ("%d thread updates, %d data updates\n",
        thread_updates, data_updates);
    return 0;
}