C/C++ CODE FOR READER WRITER PROBLEM: READER's PRIORITY

READER WRITER PROBLEM USING SEMAPHORES : READER's PRIORITY

A famous problem in system programming in the context of concurrency is Reader-Writer problem.Here we are considering that we have a single memory location and various readers and writers want to access it.Here we will be implementing Reader's priority over writer.Just keep in mind the following things:

• Multiple readers can enter the critical section or read at the same time.
• Only one writer can enter the critical section or write at a particular time.
• Writer and reader can't be simultaneously present in the critical section.

The following code illustrates the concept:

#include<stdio.h>

#include<semaphore.h>

#include<pthread.h>

int rc=0,val,wc=0;

pthread_mutex_t mutex1,mread;

pthread_t tr1,tw1,tr2,tw2,tw3;

pthread_attr_t tr1attr,tw1attr,tr2attr,tw2attr,tw3attr;

void *reader();

void *writer();

int main()

{

pthread_mutex_init(&mutex1,NULL);

pthread_mutex_init(&mread,NULL);

pthread_attr_init(&tr1attr);

pthread_attr_init(&tr2attr);

pthread_attr_init(&tw1attr);

pthread_attr_init(&tw2attr);

pthread_attr_init(&tw3attr);

printf("\n Writer 1 created");

pthread_create(&tw1,&tw1attr,writer,NULL);

printf("\n Reader 1 created");

pthread_create(&tr1,&tr1attr,reader,NULL);

printf("\n Writer 2 created");

pthread_create(&tw2,&tw2attr,writer,NULL);

printf("\n Reader 2 created");

pthread_create(&tr2,&tr2attr,reader,NULL);

printf("\n Writer 3 created");

pthread_create(&tw3,&tw3attr,writer,NULL);

pthread_join(tw1,NULL);

pthread_join(tr1,NULL);

pthread_join(tw2,NULL);

pthread_join(tr2,NULL);

pthread_join(tw3,NULL);

return 0;

}

void *writer()

{

pthread_mutex_lock(&mutex1);

wc++;

printf("\n Enter data:  ");

scanf("%d",&val);

pthread_mutex_unlock(&mutex1);

printf("\n writer %d levng",wc);

pthread_exit(0);

}

void *reader()

{

pthread_mutex_lock(&mread);

rc++;

if(rc==1)

pthread_mutex_lock(&mutex1);

pthread_mutex_unlock(&mread);

printf("\n Value read by reader %d: %d",rc,val);

pthread_mutex_lock(&mread);

rc--;

if(rc==0)

pthread_mutex_unlock(&mutex1);

pthread_mutex_unlock(&mread);

printf("\n Reader %d levng",rc+1);

pthread_exit(0);

}

I have used Linux's text editor to write the code.To run this code you have to type this in the terminal:

1) gcc -pthread yourfilename.c

2) ./a.out

You will be able to see the output on terminal screen.Interested in WRITER's PRIORITY?