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

static int counter; // shared resource
static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

void incr_counter(void *p) {
    do {
        usleep(10); // Let's have a time slice between mutex locks
        pthread_mutex_lock(&mutex);
        counter++;
        printf("%d\n", counter);
        sleep(1);
        pthread_mutex_unlock(&mutex);
    } while ( 1 );
}

void reset_counter(void *p) {
    char buf[10];
    int  num = 0;
    int  rc;
    pthread_mutex_lock(&mutex); // block mutex just to show message
    printf("Enter the number and press 'Enter' to initialize the counter with new value anytime.\n");
    sleep(3);
    pthread_mutex_unlock(&mutex); // unblock blocked mutex so another thread may work
    do {
        if ( gets(buf) != buf ) return; // NO fool-protection ! Risk of overflow !
        num = atoi(buf);
        if ( (rc = pthread_mutex_trylock(&mutex)) == EBUSY ) {
            printf("Mutex is already locked by another process.\n\
Let's lock mutex using pthread_mutex_lock().\n");
            pthread_mutex_lock(&mutex);
        } else if ( rc == 0 ) {
            printf("WOW! You are on time! Congratulation!\n");
        } else { 
            printf("Error: %d\n", rc);
            return;
        }
        counter = num;
        printf("New value for counter is %d\n", counter);
        pthread_mutex_unlock(&mutex);
    } while ( 1 );
}

int main(int argc, char ** argv) {
    pthread_t thread_1;
    pthread_t thread_2;

    counter = 0;

    pthread_create(&thread_1, NULL, (void *)&incr_counter, NULL);
    pthread_create(&thread_2, NULL, (void *)&reset_counter, NULL);

    pthread_join(thread_2, NULL);

    return 0;
}