lab11-2.c

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <malloc.h>
#include <semaphore.h>

sem_t mutex1,wsem,mutex2,mutex3,rsem;

int rdcount=0;
int wrcount=0;

delay()
{
  int i,j;
  for(i=0;i<1000000;++i)
   {
    for(j=0;j<1000;j++)
    {
      }
      }
}
void * reader(void * p)
{
  int q=(int)p;
  do
  {
     printf("reader%d is interested\n",q);
    sem_wait(&mutex3);
        sem_wait(&rsem);
        sem_wait(&mutex1);
            rdcount++;
            if(rdcount==1)
                sem_wait(&wsem);
        sem_post(&mutex1);
        sem_post(&rsem);
    sem_post(&mutex3);
    /////////////////////////
    
    printf("reader%d is reading\n",q);
    delay();
    
    /////////////////////////
    sem_wait(&mutex1);
      rdcount--;
      if(rdcount==0)
         sem_post(&wsem);
    sem_post(&mutex1);
    printf("reader%d has read\n",q);
    
  }while(1);
}
void * writer(void * p)
{
  int q=(int)p;
  do
  {
  
  printf("writer%d is interested\n",q);
     sem_wait(&mutex2);
        wrcount++;
        if(wrcount==1)
            sem_wait(&rsem);
     sem_post(&mutex2);
     
     sem_wait(&wsem);
            
     /////////////////
      
      printf("writer %d is writing\n",q);
      delay();
     ////////////////
     sem_post(&wsem);
     sem_wait(&mutex2);
        wrcount--;
        if(wrcount==0)
          sem_post(&rsem);
     sem_post(&mutex2);
     printf("writer %d is written\n",q);
     delay();
  }while(1);
}

main()
{
  
  int i;
  
  sem_init(&mutex1,0,1);
  sem_init(&mutex2,0,1);
  sem_init(&mutex3,0,1);
  sem_init(&wsem,0,1);
  sem_init(&rsem,0,1);
  
  pthread_t thread[6];
  pthread_t thread2[2];
  
   int t,re;
    t=0;
    for(t=0;t<3;++t)
    {
    re=pthread_create(&thread[t],NULL,reader,(void *)t);
    printf("thread reader%d created.............\n",t);
    if(re)
    {
            printf("error");
            exit(-1);
    }
    }
    //---------------------------------------------------------------
    
    for(t=0;t<2;++t)
    {
    re=pthread_create(&thread2[t],NULL,writer,(void *)t);
    printf("thread writer%d created.............\n",t);
    if(re)
    {
            printf("error");
            exit(-1);
    }
    }
    
    //--------------------------------------------------------------------
    for(t=3;t<6;++t)
    {
    re=pthread_create(&thread[t],NULL,reader,(void *)t);
    printf("thread reader%d created.............\n",t);
    if(re)
    {
            printf("error");
            exit(-1);
    }
    }
    
    
    
    
    
   // =====================================================================
    
    
    
    
    
    for(t=0;t<6;++t)
    {
    pthread_join(thread[t],NULL);
    
    }
    pthread_join(thread2[0],NULL);
    pthread_join(thread2[1],NULL);
}