threadtest.c

#include <pthread.h>
#include <stdio.h>

#define NUM_WAITING_THREADS 20
#define NUM_WORKING_THREADS 20

pthread_mutex_t quux;


void waste_some_time(int cycles) {
    int i, v;
    for(i=0; i < cycles; i++) {
        v = i^2;
    }
}


void *waiting_thread(void *threadid) {
    long tid;
    tid = (long)threadid;
    printf("%ld: this is a waiting thread, trying to lock\n", tid);
    pthread_mutex_lock(&quux);
    printf("%ld: got my lock, unlocking and exiting\n", tid);
    pthread_mutex_unlock(&quux);
    pthread_exit(NULL);
}


void *working_thread(void *threadid) {
    long tid;
    tid = (long)threadid;
    printf("%ld: this is a working thread\n", tid);
    waste_some_time(100000000);
    pthread_exit(NULL);
}


int main (int argc, char *argv[])
{
    pthread_t threads[NUM_WAITING_THREADS + NUM_WORKING_THREADS];
    int rc;
    long t;

    pthread_mutex_init(&quux, NULL);
    pthread_mutex_lock(&quux);

    for(t=0; t < NUM_WAITING_THREADS; t++){
        printf("In main: creating waiting thread %ld\n", t);
        rc = pthread_create(&threads[t], NULL, waiting_thread, (void *)t);
        if (rc){
            printf("ERROR; return code from pthread_create() is %d\n", rc);
            exit(-1);
        }
    }

    for(; t < NUM_WAITING_THREADS + NUM_WORKING_THREADS; t++) {
        printf("In main: creating working thread %ld\n", t);
        rc = pthread_create(&threads[t], NULL, working_thread, (void *)t);
        if (rc){
            printf("ERROR; return code from pthread_create() is %d\n", rc);
            exit(-1);
        }
    }

    printf("wasting some time in main thread\n");
    waste_some_time(100000000);

    printf("main thread done, unlocking\n");
    pthread_mutex_unlock(&quux);

    pthread_mutex_destroy(&quux);

    pthread_exit(NULL);
}