How do you write a c program for reader writer problem?

Answer 1

/* program to study Reader/Writer problem with Semaphore along with output*/

#include<stdio.h>

#include<pthread.h>

#include<semaphore.h>

void reader1();

void writer1();

void reader2();

void writer2();

sem_t rsem;

sem_t wsem;

sem_t x,y,z;

int rc=0, wc=0,p=0;

int main()

{

int r,w,i=0,ch=2;

pthread_t t1[5],t2[5];

printf ("\n\nEnter the number of READERS: ");

scanf ("%d", &r);

printf ("\n\nEnter the number of WRITERS: ");

scanf ("%d", &w);

printf ("\n\nMENU\n\n\t1.READERS HAVE PRIORITY");

printf ("\n\n\t2.WRITER HAVE PRIORITY");

printf ("\n\n\tENTER YOUR CHOICE:");

scanf ("%d", &ch);

sem_init(&rsem, 0, 1);

sem_init(&wsem, 0, 1);

sem_init(&x, 0, 1);

sem_init(&y, 0, 1);

sem_init(&z, 0, 1);

if (ch==1)

{

for (i=0;i<r;i++)

pthread_create(&t1[i], NULL, (void *)reader1, (void *)i );

for (i=0; i<w; i++)

pthread_create(&t2[i], NULL, (void *)writer1, (void *)i);

//pthread_create(&t1[w-1], NULL, (void *)reader1, (void *)(w-1) );

//pthread_create(&t2[r-1], NULL, (void *)writer1, (void *)(r-1) );

for (i=0;i<r;i++)

pthread_join(t1[i], NULL);

for (i=0;i<w;i++)

pthread_join(t2[i], NULL);

}

else if (ch==2)

{

//pthread_create(&t2[0], NULL, (void *)writer2, 0);

//pthread_create(&t1[0], NULL, (void *)reader2, 0);

for (i=0;i<r;i++)

pthread_create(&t2[i], NULL, (void *)reader2, (void *)i );

for (i=1;i<w;i++)

pthread_create(&t1[i], NULL, (void *)writer2, (void *)i );

//pthread_create (&t2[r-1], NULL, (void *)writer2, (void *)(r-1) );

//pthread_create (&t1[w-1], NULL, (void *)reader2, (void *)(w-1) );

for(i=0; i<r; i++)

pthread_join(t1[i], NULL);

for(i=0; i<w; i++)

pthread_join(t2[i], NULL);

}

else

printf ("\nINVALID CHOICE....PROGRAM TERMINATED.");

sem_destroy(&rsem);

sem_destroy(&wsem);

return 0;

} // main function close

void reader1 (void *i)

{ int i1;

for(i1=0;i1<10;i1++)

{

sem_wait(&x);

rc++;

if (rc==1)

sem_wait(&wsem);

sem_post(&x);

printf ("\n\t \t \t \tREADER %d IS READING NOW %d", (int)i,p);

sem_wait(&x);

rc--;

if(rc==0)

sem_post(&wsem);

sem_post(&x);

sleep(2);

//printf ("\nREADER %d HAS FINISHED READING\n");

}

}

void writer1(void *i)

{ int i1;

for(i1=0;i1<10;i1++)

{ sem_wait(&wsem);

p++;

printf ("\nWRITER %d IS WRITING NOW %d", (int) i,p);

sem_post(&wsem);

if ((int)i % 2 == 0)sleep(1); else sleep(6);

// printf ("\nWRITER %d HAS FINISHED WRITING\n");

}

}

void reader2(void *i)

{

sem_wait(&z);

sem_wait(&rsem);

sem_wait(&x);

rc++;

if(rc==1)

sem_wait(&wsem);

printf ("\nREADER %d IS READING NOW", (int)i);

sem_post(&x);

sem_post(&rsem);

sem_post(&z);

sleep(1);

sem_wait(&x);

rc--;

if (rc==0)

sem_post(&wsem);

sem_post(&x);

//printf ("\nREADER %d HAS FINISHED READING\n");

}

void writer2(void *i)

{

sem_wait(&y);

wc++;

if (wc==1)

sem_wait(&rsem);

sem_post(&y);

sem_wait(&wsem);

printf ("\nWRITER %d IS WRITING NOW", (int) i);

sem_post(&wsem);

sem_wait(&y);

wc--;

if(wc==0)

sem_post(&rsem);

sem_post(&y);

sleep(1);

//printf ("\nWRITER %d HAS FINISHED WRITING\n");

}

/*

student@student-desktop:~/Documents$ ./rdwrt

Enter the number of READERS: 4

Enter the number of WRITERS: 4

MENU

1.READERS HAVE PRIORITY

2.WRITER HAVE PRIORITY

ENTER YOUR CHOICE:1

READER 0 IS READING NOW

READER 1 IS READING NOW

READER 2 IS READING NOW

READER 1 IS READING NOW

READER 2 IS READING NOW

READER 3 IS READING NOW

READER 1 HAS FINISHED READING

READER 0 HAS FINISHED READING

READER 1 HAS FINISHED READING

READER 2 HAS FINISHED READING

READER 2 HAS FINISHED READING

READER 3 HAS FINISHED READING

WRITER 0 IS WRITING NOW

WRITER 0 HAS FINISHED WRITING

WRITER 1 IS WRITING NOW

WRITER 1 HAS FINISHED WRITING

WRITER 2 IS WRITING NOW

WRITER 2 HAS FINISHED WRITING

WRITER 3 IS WRITING NOW

WRITER 3 HAS FINISHED WRITING

student@student-desktop:~/Documents$ ./rdwrt

Enter the number of READERS: 4

Enter the number of WRITERS: 4

MENU

1.READERS HAVE PRIORITY

2.WRITER HAVE PRIORITY

ENTER YOUR CHOICE:2

WRITER 0 IS WRITING NOW

WRITER 0 HAS FINISHED WRITING

WRITER 1 IS WRITING NOW

WRITER 1 HAS FINISHED WRITING

WRITER 2 IS WRITING NOW

WRITER 2 HAS FINISHED WRITING

WRITER 3 IS WRITING NOW

WRITER 3 HAS FINISHED WRITING

READER 1 IS READING NOW

READER 0 IS READING NOW

READER 2 IS READING NOW

READER 3 IS READING NOW

READER 2 HAS FINISHED READING

READER 1 HAS FINISHED READING

READER 0 HAS FINISHED READING

READER 3 HAS FINISHED READING

*/

Written by: Fabianski Benjamin