semaphore

main.c

/*****************************
 * Fernlehre Semaphore Example
 * File: main.c
 * Author: Granzer Wolfgang
 * Version: 1.0
 * Date: 30.4.2012
 **/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>

#include <semaphore.h>

/*
 *   TODO: Add code here for semaphore data structure
 *
 *      Available Semaphore operations are:
 *          int sem_init (sem_t *sem, int pshared, unsigned int value);
 *          int sem_wait (sem_t *sem);
 *          int sem_post (sem_t *sem);
 */


// forward declaration
void* threadIWorker(void* param);
void* threadJWorker(void* param);

int loopFlag = 1;

sem_t s1;
sem_t s2;

/**
 * Main Program.
 */
int main(int argc, const char* argv[])
{
    pthread_t threadI, threadJ;

    /*
     *   TODO: Add code here to initialize the semaphore.
     */

    sem_init(&s1, 0, 1);
    sem_init(&s2, 0, 0);

    printf("Example Semaphore\n");
    printf("----------------------------\n");
    printf("Starting Thread I ...\n");
    printf("Starting Thread J ...\n");
    printf("Press q <enter> to exit\n");

    pthread_create(&threadI, NULL, threadIWorker, NULL);


    pthread_create(&threadJ, NULL, threadJWorker, NULL);


    while (loopFlag)
    {
        char c = getchar();
        if (c == 'q')
        {
            printf("Bye ...\n");
            loopFlag = 0;
        }

    }
    pthread_join(threadI, NULL);
    pthread_join(threadJ, NULL);

    return 0;
}

/**
 * Thread I
 */
void* threadIWorker(void* param)
{
    while (loopFlag)
    {
        /*
         *   TODO: Enter critical section.
         */

        sem_wait(&s1);

        printf("I: =========\n");
        usleep(100000*(rand()%10));
        printf("I: Do\n");
        usleep(100000*(rand()%10));
        printf("I: some\n");
        usleep(100000*(rand()%10));
        printf("I: usefull\n");
        usleep(100000*(rand()%10));
        printf("I: stuff\n");
        usleep(100000*(rand()%10));
        printf("I: within\n");
        usleep(100000*(rand()%10));
        printf("I: a\n");
        usleep(100000*(rand()%10));
        printf("I: critical\n");
        usleep(100000*(rand()%10));
        printf("I: section\n");
        usleep(100000*(rand()%10));
        printf("I: =========\n");

        /*
         *   TODO: Leave critical section.
         */
        sem_post(&s2);
        usleep(100000*(rand()%10));
    }
    return 0;
}

/**
 * Thread J
 */
void* threadJWorker(void* param)
{
    while(loopFlag)
    {
        /*
         *   TODO: Enter critical section.
         */
        sem_wait(&s2);

        printf("J: =========\n");
        usleep(100000*(rand()%10));
        printf("J: Do\n");
        usleep(100000*(rand()%10));
        printf("J: some\n");
        usleep(100000*(rand()%10));
        printf("J: usefull\n");
        usleep(100000*(rand()%10));
        printf("J: stuff\n");
        usleep(100000*(rand()%10));
        printf("J: within\n");
        usleep(100000*(rand()%10));
        printf("J: a\n");
        usleep(100000*(rand()%10));
        printf("J: critical\n");
        usleep(100000*(rand()%10));
        printf("J: section\n");
        usleep(100000*(rand()%10));
        printf("J: =========\n");

        /*
         *   TODO: Leave critical section.
         */

        sem_post(&s1);

        usleep(100000*(rand()%10));
    }
    return 0;
}