Write a program to implement Reader-writer problem using mutex/ semaphore

SOFTWARE LABORATORY

Code :
#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
#include<semaphore.h>

int data=0,rdcnt=0;
sem_t mutex,writeblock;
void * reader(void * no)
{
    printf("\n\tReader %d is executing ",(int)no);
    sem_wait(&mutex);
    printf("\n\tWait  to mutex by %d reader",(int)no);
    rdcnt++;
    if(rdcnt==1)
    {
        sem_wait(&writeblock);
        printf("\n\tWait  to writerblock by %d reader",(int)no);
    }
    //sleep(2);
    printf("\n\t***Reader %d read data = %d ",(int)no,data);
    if(rdcnt==1)
    {
        sem_post(&writeblock);
        printf("\n\tSignal to writerblock by %d reader",(int)no);
    }
    sem_post(&mutex);
    printf("\n\tSignal to mutex by %d reader\n",(int)no);
}
void * writer(void * no)
{
    printf("\n\tWriter %d is executing ",(int)no);
    sem_wait(&writeblock);
    printf("\n\tWait  to writerblock by %d writer",(int)no);
    //sleep(2);
    data+=5;
    printf("\n\t***Writer %d write data = %d ",(int)no,data);
    sem_post(&writeblock);
    printf("\n\tSignal to writer by %d writer\n",(int)no);
}
int main()
{
    int no,i,ir=0,iw=0,ch;
    sem_init(&mutex,0,1);
    sem_init(&writeblock,0,1);
    printf("\nEnter no of readers and writers to create : ");
    scanf("%d",&no);
   
    pthread_t r[no],w[no];
   
   
    /*for(i=0;i<no;i++)
    {
        pthread_create(&r[i],NULL,reader,(void *)i);
        pthread_create(&w[i],NULL,writer,(void *)i);
    }*/
   
    /*for(i=0;i<no;i++)
    {
        pthread_join(r[i],NULL);
        pthread_join(w[i],NULL);
    }*/
    do
    {
        printf("\n\t1.Reader\n\t2.Writer\n\t3.terminate\n\tYour choice : ");
        scanf("%d",&ch);
        switch(ch)
        {
            case 1: pthread_create(&r[ir],NULL,reader,(void *)ir);
                    pthread_join(r[ir++],NULL);
                    break;
            case 2: pthread_create(&w[iw],NULL,writer,(void *)iw);
                    pthread_join(w[iw++],NULL);
                    break;
        }
    }while(ch!=3);
   
    sem_destroy(&mutex);
    sem_destroy(&writeblock);
}


OUTPUT :

use -lpthread while compiling .. see following lines

root@prashant-HP-ENVY-4-Notebook-PC:~/SPOS Programs/reader writer# gcc rdwr.c -lpthread
root@prashant-HP-ENVY-4-Notebook-PC:~/SPOS Programs/reader writer# ./a.out

Enter no of readers and writers to create : 2

    1.Reader
    2.Writer
    3.terminate
    Your choice : 1

    Reader 0 is executing
    Wait  to mutex by 0 reader
    Wait  to writerblock by 0 reader
    ***Reader 0 read data = 0
    Signal to writerblock by 0 reader
    Signal to mutex by 0 reader

    1.Reader
    2.Writer
    3.terminate
    Your choice : 2

    Writer 0 is executing
    Wait  to writerblock by 0 writer
    ***Writer 0 write data = 5
    Signal to writer by 0 writer

    1.Reader
    2.Writer
    3.terminate
    Your choice : 3
root@prashant-HP-ENVY-4-Notebook-PC:~/SPOS Programs/reader writer#