//readers-writer
//args: 

public class readers_writer {

    static java.util.Random rand;
    static {rand = new java.util.Random(System.currentTimeMillis());}

    public static void main(String[] args) {
	
	if (args.length != 2) {
	    System.out.println("Usage: prod_cons prod_random cons_random");
	    System.exit(1);
	}
	int prodrand = Integer.parseInt(args[0]);
	int consrand = Integer.parseInt(args[1]);
	
	SharedMemory shmem = new SharedMemory();
	new Writer(shmem,prodrand);
	new Reader(shmem,consrand);
	new Reader(shmem,consrand);
	new Reader(shmem,consrand);
    }
}

class SharedMemory {
    private int readers;
    private boolean writer_has;
    private static class Writing {}
    Writing writing = new Writing();   //list of waiting readers

    //synch'ed so only one writer at a itme
    public synchronized void write() {
	writer_has = true;
	System.out.println("write IN");
	try {
	    Thread.sleep(300);  //pause so some reader(s) can wait
	} catch (InterruptedException e) {}
	/*
	if (readers > 0)   
	    try {
		System.out.println("Writer waiting...");
		wait();
	    } catch (InterruptedException e) {
		System.out.println("Writer interrupted");
	    }
	*/
	synchronized (writing) {
	    writing.notifyAll();    //tell all waiting readers
	}
	writer_has = false;
	System.out.println("write OUT");
    }

    public void read() {
	System.out.println("read IN");
	while (writer_has) {
	    System.out.println("Reader waiting...");
	    try {
		synchronized (writing) {
		    writing.wait();
		}
	    } catch (InterruptedException e) {}
	}
	
	System.out.println("read OUT");
    }


}


//needs exclusive access to shared memory object
class Writer implements Runnable {
    SharedMemory shmem;
    int randwait;

    Writer(SharedMemory shmem, int prodrand) {
	this.shmem = shmem;
	this.randwait = prodrand;
	System.out.println("Writer running: ");
	new Thread(this,"Writer").start();
    }

    public void run() {
	int worktime;
	while (true) {
	    try {
		worktime = prod_cons.rand.nextInt(randwait);
		System.out.println("Writer work: "+worktime);
		Thread.sleep(worktime);
	    } catch (InterruptedException e) {
		System.out.println("Writer sleep interrupted");
	    }
	    shmem.write();
	}
    }
}


//readers can have simultaneous access to shared memory object
class Reader implements Runnable {
    SharedMemory shmem;
    int randwait;

    Reader(SharedMemory shmem, int consrand) {
	this.shmem = shmem;
	this.randwait = consrand;
	System.out.println("Reader running: ");
	new Thread(this,"Reader").start();
    }

    public void run() {
	int worktime;
	while (true) {
	    shmem.read();
	    try {
		worktime = prod_cons.rand.nextInt(randwait);
		System.out.println("Reader work: "+worktime);
		Thread.sleep(worktime);
	    } catch (InterruptedException e) {
		System.out.println("Reader sleep interrupted");
	    }
	}
    }
}