I have written my own solution to the Reader-Writers problems using semaphores based on the psuedocode from Wikipedia. I would like to gauge the correctness and quality of the code.
import java.util.concurrent.Semaphore;
class ReaderWritersProblem {
static Semaphore readLock = new Semaphore(1);
static Semaphore writeLock = new Semaphore(1);
static int readCount = 0;
static class Read implements Runnable {
@Override
public void run() {
try {
//Acquire Section
readLock.acquire();
readCount++;
if (readCount == 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();
readCount--;
if(readCount == 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 t1 = new Thread(read);
t1.setName("thread1");
Thread t2 = new Thread(read);
t2.setName("thread2");
Thread t3 = new Thread(write);
t3.setName("thread3");
Thread t4 = new Thread(read);
t4.setName("thread4");
t1.start();
t3.start();
t2.start();
t4.start();
}
}