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2013-08-31T16:48:27.683
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Here is Circular Bounded Queue which is (supposed to be)thread safe and provides a blocking <code>take</code> operation. <pre><code>public class CircularQueue<T> { private final int MAX_SIZE; private final AtomicReferenceArray<T> buffer; private final AtomicInteger start; private final AtomicInteger end; private final AtomicInteger len; private final ReentrantLock rwlock; private final Condition readCondition; public CircularQueue(int size) { MAX_SIZE = size; buffer = new AtomicReferenceArray<T>(size); start = new AtomicInteger(0); end = new AtomicInteger(0); len = new AtomicInteger(0); rwlock = new ReentrantLock(true); readCondition = rwlock.newCondition(); } /** * Adds to tail of the queue */ public void put(T val) { try { rwlock.lock(); buffer.set(end.get(), val); end.set((end.get() + 1) % MAX_SIZE); if (len.get() == MAX_SIZE) { // overwrite start.set((start.get() + 1) % MAX_SIZE); } else { len.incrementAndGet(); } readCondition.signal(); } finally { rwlock.unlock(); } } /** * Blocking removeFront operation * @return */ public T take() { T val = null; try { rwlock.lock(); while (len.get() == 0) { try { readCondition.await(); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } } val = buffer.get(start.get()); buffer.set(start.get(), null); start.set((start.get() + 1) % MAX_SIZE); len.decrementAndGet(); } finally { rwlock.unlock(); } return val; } public int size() { int curLen = 0; try { rwlock.lock(); curLen = len.get(); } finally { rwlock.unlock(); } return curLen; } } </code></pre> There are many operations which are yet to be added like <code>poll</code>, <code>offer</code> etc. But you can test this out with some threads : It is going to hang your JVM if it runs correctly. <pre><code>public static void main(String[] args) { final int MAX_QUEUE_SIZE = 4; final CircularQueue<Integer> q = new CircularQueue<Integer>(MAX_QUEUE_SIZE); new Thread(new Runnable() { @Override public void run() { for (int i = 0; i < MAX_QUEUE_SIZE; ++i) { try { Thread.sleep(1000); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } System.out.println("Putting: from " + Thread.currentThread().getName() + " " + i); q.put(i); } for (int i = 0; i < MAX_QUEUE_SIZE; ++i) { System.out.println("Trying to get from " + Thread.currentThread().getName() + " " + q.take()); } } }).start(); new Thread(new Runnable() { @Override public void run() { for (int i = 10; i < 10 + MAX_QUEUE_SIZE; ++i) { try { Thread.sleep(1001); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } System.out.println("Putting: from " + Thread.currentThread().getName() + " " + i); q.put(i); } for (int i = 0; i < MAX_QUEUE_SIZE; ++i) { System.out.println("Trying to get from " + Thread.currentThread().getName() + " " + q.take()); } } }).start(); } </code></pre> Your output should probably match <pre><code>Putting: from Thread-0 0 Putting: from Thread-1 10 Putting: from Thread-0 1 Putting: from Thread-1 11 Putting: from Thread-0 2 Putting: from Thread-1 12 Putting: from Thread-0 3 Trying to get from Thread-0 11 Trying to get from Thread-0 2 Trying to get from Thread-0 12 Trying to get from Thread-0 3 Putting: from Thread-1 13 Trying to get from Thread-1 13 </code></pre> The other take operations from Thread-1 are waiting for a corresponding put operation since Thread-1 is slightly slower than Thread-0.
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