first attempt u05-4

u05-4/Semaphore.java

@@ -0,0 +1,19 @@
+class Semaphore {
+	private int value;
+
+	public Semaphore(int value) {
+		this.value = value;
+	}
+
+	synchronized public void acquire() throws InterruptedException {
+		while (this.value <= 0) {
+			wait();
+		}
+		this.value--;
+	}
+
+	synchronized public void release() {
+		this.value++;
+		notify();
+	}
+}

u05-4/WorkQueue.java

@@ -0,0 +1,95 @@
+import java.util.LinkedList;
+import java.util.NoSuchElementException;
+import java.util.Queue;
+import java.util.concurrent.Semaphore;
+
+class WorkQueue {
+	private Queue<Task> tasks = new LinkedList<Task>();
+	private Semaphore readSemaphore;
+	private Semaphore writeSemaphore;
+
+	public WorkQueue(int maxSize) {
+		readSemaphore = new Semaphore(0);
+		writeSemaphore = new Semaphore(maxSize);
+	}
+
+	public void producer() throws InterruptedException {
+		writeSemaphore.acquire();
+
+		Task t = new Task();
+		tasks.add(t);
+
+		readSemaphore.release();
+	}
+
+	public void consumer() throws InterruptedException {
+
+		Task t;
+
+		readSemaphore.acquire();
+
+		// for some reason, consumer can get here without tasks in the list. how to fix?
+		System.out.println(tasks.size());
+		if (tasks.isEmpty()) {
+			// SHOULD never be reached
+			System.out.println("!!! No tasks in the queue");
+			return;
+		}
+		try {
+			t = tasks.remove();
+		} catch (NoSuchElementException e) {
+			System.out.println("!!! No taks in queue (BUT STILL TRIED ACCESSING)");
+			return;
+		}
+
+		writeSemaphore.release();
+
+		t.run();
+	}
+
+	public void printTaksSize() {
+		System.out.println("Tasks in queue: " + tasks.size());
+	}
+
+
+	public static void main(String[] args) {
+		WorkQueue w = new WorkQueue(10);
+		Thread[] producers = new Thread[5];
+		Thread[] consumers = new Thread[5];
+		for (int i = 1; i <= 2; i++) {
+			final int i_final = i;
+			producers[i] = new Thread(() -> {
+				try {
+					for (int j = 0; j < 10; j++) {
+						w.producer();
+						System.out.println("Producer " + i_final + " produced task " + j);
+						w.printTaksSize();
+						// Thread.sleep(100);
+					}
+				} catch (InterruptedException e) {
+					Thread.currentThread().interrupt();
+				}
+			});
+			consumers[i] = new Thread(() -> {
+				try {
+					for (int j = 0; j < 10; j++) {
+						w.consumer();
+						w.printTaksSize();
+						System.out.println("Consumer " + i_final + " consumed task " + j);
+						// Thread.sleep(100);
+					}
+				} catch (InterruptedException e) {
+					Thread.currentThread().interrupt();
+				}
+			});
+			producers[i].start();
+			consumers[i].start();
+		}
+	}
+}
+
+class Task implements Runnable{
+	public void run() {
+		// System.out.println("Task is running");
+	}
+}