Question

Process Synchronization Assignment: Readers-Writers Problem . Consider readers and writers share a bounded array. ii. Writers write an integer on the array. iii. Readers read and display contents of the array. iv. Writers will not be allowed to write if there is a reader reading the array. v. Only one writer can access the array at a time. But many readers can access the array at the same time. vi. All readers are blocked if there is a writer writing the array. vii. Implement the above situations with at least 2 writer threads and 3 reader threads. vill. Your program must be implemented in Java only. tes)

Answer 1

import java.util.concurrent.Semaphore;

class ReaderWritersProblem {

static Semaphore readLock = new Semaphore(1);
static Semaphore writeLock = new Semaphore(1);
static int rCount = 0;

static class Read implements Runnable {
@Override
public void run() {
try {
//Acquire Section
readLock.acquire();
rCount++;
if (rCount == 1) {
writeLock.acquire();
}
readLock.release();

//Reading section
System.out.println("Thread "+Thread.currentThread().getName() + " is READING");
Thread.sleep(1500);
System.out.println("Thread "+Thread.currentThread().getName() + " has FINISHED READING");

//Releasing section
readLock.acquire();
rCount--;
if(rCount == 0) {
writeLock.release();
}
readLock.release();
} catch (InterruptedException e) {
System.out.println(e.getMessage());
}
}
}

static class Write implements Runnable {
@Override
public void run() {
try {
writeLock.acquire();
System.out.println("Thread "+Thread.currentThread().getName() + " is WRITING");
Thread.sleep(2500);
System.out.println("Thread "+Thread.currentThread().getName() + " has finished WRITING");
writeLock.release();
} catch (InterruptedException e) {
System.out.println(e.getMessage());
}
}
}

public static void main(String[] args) throws Exception {
Read read = new Read();
Write write = new Write();
Thread tr1 = new Thread(read);
tr1.setName("Reader1");
   Thread tr2 = new Thread(write);
   tr2.setName("Writer1");
Thread tr3 = new Thread(read);
tr3.setName("Reader2");
Thread tr4 = new Thread(write);
tr4.setName("Writer2");
Thread tr5 = new Thread(read);
tr5.setName("Reader3");
tr1.start();
   tr2.start();
tr3.start();
tr4.start();
tr5.start();
}
}