06_readers_writers_2.c

#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
#include <time.h>
#include <sched.h>
#include "queue.h"


#define max 6
int rc=0,w=0;
sem_t mutex,wrt;
pthread_attr_t tattr;
pthread_t tid[max];
int ret;
struct sched_param param;
struct Queue *wq, *rq;
struct QNode *qn;

void *reader(void *arg)
{
    srand(time(0));
    int id = *((int *) arg);
    FILE *f;
    while(1)
    {
        printf("Reader %d arrived",id);
		if(!isQueueEmpty(rq))
			printf(", Waiting in read queue\n");
		else
			printf("\n");
		enQueue(rq, id);
        printf("Read Queue: ");
		printQueue(rq);
        printf("\n");
        while(w>0);
           // goto b;
        int t=(rand()%3)+1;
        sem_wait(&mutex);
        rc++;
        if(rc==1)
            sem_wait(&wrt);
        sem_post(&mutex);

        f = fopen("Object.txt","r");
        sleep(1);
        char str[100];
        if( fgets (str, 60, f)!=NULL ) {
            printf("Reader %d reads %s from the file\n",id,str);
        }
        fclose(f);
        
        sem_wait(&mutex);
        rc--;
        qn = deQueue(rq);
        printf("Read Queue: ");
		printQueue(rq);
        printf("\n");
        if(rc==0)
            sem_post(&wrt);
        sem_post(&mutex);    
       
        //b:   sleep(t);
        
    }
    pthread_exit(0);
}

void *writer(void *arg)
{
    srand(time(0));
    int id = *((int *) arg);
    FILE *f;
    while(1)
    {
        w++;
        int t=(rand()%3)+2;
        printf("Writer %d arrived",id);
		if(!isQueueEmpty(wq))
			printf(", Waiting in write queue\n");
		else
			printf("\n");
		enQueue(wq, id);
        printf("Writer Queue: ");
		printQueue(wq);
        printf("\n");
        sem_wait(&wrt);
        f = fopen("Object.txt","w");
         sleep(1);
        int n=rand()%10;
        fprintf(f,"%d",n);
        printf("Writer %d writes %d to the file\n",id,n);
        fclose(f);
        sem_post(&wrt);
        qn = deQueue(wq);
        printf("Writer Queue: ");
		printQueue(wq);
        printf("\n");
        w--;
        sleep(t);
    }
    pthread_exit(0);
}
int main()
{
    wq = createQueue();
    rq = createQueue();

    srand(time(0));
    int id[max],i;
    FILE *f;

    sem_init(&wrt,0,1);
    sem_init(&mutex,0,1);
    
    id[0]=0;
    id[1]=0;
    id[2]=1;
    id[3]=1;
    id[4]=2;
    id[5]=2;
    f = fopen("Object.txt","w");
    int n = rand();
    fprintf(f,"%d",n);
    fclose(f);
    ret=pthread_create(&tid[0],&tattr,writer,(void *) &id[0]);
    printf("Writer %d created\n",id[0]);
    pthread_create(&tid[1],NULL,reader,(void *) &id[1]);
    printf("Reader %d created\n",id[1]);
    ret=pthread_create(&tid[2],&tattr,writer,(void *) &id[2]);
    printf("Writer %d created\n",id[2]);
    pthread_create(&tid[3],NULL,reader,(void *) &id[3]);
    printf("Reader %d created\n",id[3]);
    ret=pthread_create(&tid[4],&tattr,writer,(void *) &id[4]);
    printf("Writer %d created\n",id[4]);
    pthread_create(&tid[5],NULL,reader,(void *) &id[5]);
    printf("Reader %d created\n",id[5]);
    for(i=0;i<max;i++)
        pthread_join(tid[i],NULL);

       return 0;

}