Properly sync PacketWriter's queue

by using a custom ArrayBlockingQueueWithShutdown. Fixes a race condition
where nextpacket() would wait for a notification that would never
arrive, because all all put(Packet) calls are still blocking.

SMACK-560

smack-core/src/main/java/org/jivesoftware/smack/util/ArrayBlockingQueueWithShutdown.java

@@ -0,0 +1,495 @@
+/**
+ *
+ * Copyright 2014 Florian Schmaus
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smack.util;
+
+import java.util.AbstractQueue;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * Like ArrayBlockingQueue but with additional {@link #shutdown()} and {@link #start} methods. Will
+ * throw {@link InterruptedException} if Queue has been shutdown on {@link #take()} and
+ * {@link #poll(long, TimeUnit)}.
+ * <p>
+ * Based on ArrayBlockingQueue of OpenJDK by Doug Lea (who released ArrayBlockingQueue as public
+ * domain).
+ * 
+ * @param <E> the type of elements held in this collection
+ */
+public class ArrayBlockingQueueWithShutdown<E> extends AbstractQueue<E> implements BlockingQueue<E> {
+
+    private final E[] items;
+
+    private int takeIndex;
+
+    private int putIndex;
+
+    private int count;
+
+    private final ReentrantLock lock;
+
+    private final Condition notEmpty;
+
+    private final Condition notFull;
+
+    private volatile boolean isShutdown = false;
+
+    private final int inc(int i) {
+        return (++i == items.length) ? 0 : i;
+    }
+
+    private final void insert(E e) {
+        items[putIndex] = e;
+        putIndex = inc(putIndex);
+        count++;
+        notEmpty.signal();
+    }
+
+    private final E extract() {
+        E e = items[takeIndex];
+        items[takeIndex] = null;
+        takeIndex = inc(takeIndex);
+        count--;
+        notFull.signal();
+        return e;
+    }
+
+    private final void removeAt(int i) {
+        if (i == takeIndex) {
+            items[takeIndex] = null;
+            takeIndex = inc(takeIndex);
+        }
+        else {
+            while (true) {
+                int nexti = inc(i);
+                if (nexti != putIndex) {
+                    items[i] = items[nexti];
+                    i = nexti;
+                }
+                else {
+                    items[i] = null;
+                    putIndex = i;
+                    break;
+                }
+            }
+        }
+        count--;
+        notFull.signal();
+    }
+
+    private final static void checkNotNull(Object o) {
+        if (o == null) {
+            throw new NullPointerException();
+        }
+    }
+
+    private final void checkNotShutdown() throws InterruptedException {
+        if (isShutdown) {
+            throw new InterruptedException();
+        }
+    }
+
+    private final boolean hasNoElements() {
+        return count == 0;
+    }
+
+    private final boolean hasElements() {
+        return !hasNoElements();
+    }
+
+    private final boolean isFull() {
+        return count == items.length;
+    }
+
+    private final boolean isNotFull() {
+        return !isFull();
+    }
+
+    public ArrayBlockingQueueWithShutdown(int capacity) {
+        this(capacity, false);
+    }
+
+    @SuppressWarnings("unchecked")
+    public ArrayBlockingQueueWithShutdown(int capacity, boolean fair) {
+        if (capacity <= 0)
+            throw new IllegalArgumentException();
+        items = (E[]) new Object[capacity];
+        lock = new ReentrantLock(fair);
+        notEmpty = lock.newCondition();
+        notFull = lock.newCondition();
+    }
+
+    /**
+     * Shutdown the Queue. Will method currently waiting for a not full/empty condition will unblock
+     * (and usually throw a InterruptedException).
+     */
+    public void shutdown() {
+        lock.lock();
+        try {
+            isShutdown = true;
+            notEmpty.signalAll();
+            notFull.signalAll();
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    /**
+     * Start the queue. Newly created instances will be started automatically, thus this only needs
+     * to be called after {@link #shutdown()}.
+     */
+    public void start() {
+        lock.lock();
+        try {
+            isShutdown = false;
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    /**
+     * Returns true if the queue is currently shut down.
+     * 
+     * @return true if the queue is shut down.
+     */
+    public boolean isShutdown() {
+        lock.lock();
+        try {
+            return isShutdown;
+        } finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public E poll() {
+        lock.lock();
+        try {
+            if (hasNoElements()) {
+                return null;
+            }
+            E e = extract();
+            return e;
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public E peek() {
+        lock.lock();
+        try {
+            return hasNoElements() ? null : items[takeIndex];
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public boolean offer(E e) {
+        checkNotNull(e);
+        lock.lock();
+        try {
+            if (isFull() || isShutdown) {
+                return false;
+            }
+            else {
+                insert(e);
+                return true;
+            }
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public void put(E e) throws InterruptedException {
+        checkNotNull(e);
+        lock.lockInterruptibly();
+
+        try {
+            while (isFull()) {
+                try {
+                    notFull.await();
+                    checkNotShutdown();
+                }
+                catch (InterruptedException ie) {
+                    notFull.signal();
+                    throw ie;
+                }
+            }
+            insert(e);
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException {
+        checkNotNull(e);
+        long nanos = unit.toNanos(timeout);
+        lock.lockInterruptibly();
+        try {
+            while (true) {
+                if (isNotFull()) {
+                    insert(e);
+                    return true;
+                }
+                if (nanos <= 0) {
+                    return false;
+                }
+                try {
+                    nanos = notFull.awaitNanos(nanos);
+                    checkNotShutdown();
+                }
+                catch (InterruptedException ie) {
+                    notFull.signal();
+                    throw ie;
+                }
+            }
+        }
+        finally {
+            lock.unlock();
+        }
+
+    }
+
+    @Override
+    public E take() throws InterruptedException {
+        lock.lockInterruptibly();
+        try {
+            checkNotShutdown();
+            try {
+                while (hasNoElements()) {
+                    notEmpty.await();
+                    checkNotShutdown();
+                }
+            }
+            catch (InterruptedException ie) {
+                notEmpty.signal();
+                throw ie;
+            }
+            E e = extract();
+            return e;
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
+        long nanos = unit.toNanos(timeout);
+        lock.lockInterruptibly();
+        try {
+            checkNotShutdown();
+            while (true) {
+                if (hasElements()) {
+                    E e = extract();
+                    return e;
+                }
+                if (nanos <= 0) {
+                    return null;
+                }
+                try {
+                    nanos = notEmpty.awaitNanos(nanos);
+                    checkNotShutdown();
+                }
+                catch (InterruptedException ie) {
+                    notEmpty.signal();
+                    throw ie;
+                }
+            }
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public int remainingCapacity() {
+        lock.lock();
+        try {
+            return items.length - count;
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public int drainTo(Collection<? super E> c) {
+        checkNotNull(c);
+        if (c == this) {
+            throw new IllegalArgumentException();
+        }
+        lock.lock();
+        try {
+            int i = takeIndex;
+            int n = 0;
+            for (; n < count; n++) {
+                c.add(items[i]);
+                items[i] = null;
+                i = inc(i);
+            }
+            if (n > 0) {
+                count = 0;
+                putIndex = 0;
+                takeIndex = 0;
+                notFull.signalAll();
+            }
+            return n;
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public int drainTo(Collection<? super E> c, int maxElements) {
+        checkNotNull(c);
+        if (c == this) {
+            throw new IllegalArgumentException();
+        }
+        if (maxElements <= 0) {
+            return 0;
+        }
+        lock.lock();
+        try {
+            int i = takeIndex;
+            int n = 0;
+            int max = (maxElements < count) ? maxElements : count;
+            for (; n < max; n++) {
+                c.add(items[i]);
+                items[i] = null;
+                i = inc(i);
+            }
+            if (n > 0) {
+                count -= n;
+                takeIndex = i;
+                notFull.signalAll();
+            }
+            return n;
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public int size() {
+        lock.lock();
+        try {
+            return count;
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+        lock.lock();
+        try {
+            return new Itr();
+        }
+        finally {
+            lock.unlock();
+        }
+    }
+
+    private class Itr implements Iterator<E> {
+        private int nextIndex;
+        private E nextItem;
+        private int lastRet;
+
+        Itr() {
+            lastRet = -1;
+            if (count == 0) {
+                nextIndex = -1;
+            }
+            else {
+                nextIndex = takeIndex;
+                nextItem = items[takeIndex];
+            }
+        }
+
+        public boolean hasNext() {
+            return nextIndex >= 0;
+        }
+
+        private void checkNext() {
+            if (nextIndex == putIndex) {
+                nextIndex = -1;
+                nextItem = null;
+            }
+            else {
+                nextItem = items[nextIndex];
+                if (nextItem == null) {
+                    nextIndex = -1;
+                }
+            }
+        }
+
+        public E next() {
+            lock.lock();
+            try {
+                if (nextIndex < 0) {
+                    throw new NoSuchElementException();
+                }
+                lastRet = nextIndex;
+                E e = nextItem;
+                nextIndex = inc(nextIndex);
+                checkNext();
+                return e;
+            }
+            finally {
+                lock.unlock();
+            }
+        }
+
+        public void remove() {
+            lock.lock();
+            try {
+                int i = lastRet;
+                if (i < 0) {
+                    throw new IllegalStateException();
+                }
+                lastRet = -1;
+                int ti = takeIndex;
+                removeAt(i);
+                nextIndex = (i == ti) ? takeIndex : i;
+                checkNext();
+            }
+            finally {
+                lock.unlock();
+            }
+        }
+    }
+
+}

smack-tcp/src/main/java/org/jivesoftware/smack/PacketWriter.java

@@ -18,11 +18,10 @@
 package org.jivesoftware.smack;
 
 import org.jivesoftware.smack.packet.Packet;
+import org.jivesoftware.smack.util.ArrayBlockingQueueWithShutdown;
 
 import java.io.IOException;
 import java.io.Writer;
-import java.util.concurrent.ArrayBlockingQueue;
-import java.util.concurrent.BlockingQueue;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
@@ -37,12 +36,16 @@ import java.util.logging.Logger;
  * @author Matt Tucker
  */
 class PacketWriter {
+    public static final int QUEUE_SIZE = 500;
+
     private static final Logger LOGGER = Logger.getLogger(PacketWriter.class.getName());
-    
+
+    private final XMPPTCPConnection connection;
+    private final ArrayBlockingQueueWithShutdown<Packet> queue = new ArrayBlockingQueueWithShutdown<Packet>(QUEUE_SIZE, true);
+
     private Thread writerThread;
     private Writer writer;
-    private XMPPTCPConnection connection;
-    private final BlockingQueue<Packet> queue;
+
     volatile boolean done;
 
     /**
@@ -51,7 +54,6 @@ class PacketWriter {
      * @param connection the connection.
      */
     protected PacketWriter(XMPPTCPConnection connection) {
-        this.queue = new ArrayBlockingQueue<Packet>(500, true);
         this.connection = connection;
         init();
     }
@@ -64,6 +66,7 @@ class PacketWriter {
         this.writer = connection.writer;
         done = false;
 
+        queue.start();
         writerThread = new Thread() {
             public void run() {
                 writePackets(this);
@@ -79,17 +82,17 @@ class PacketWriter {
      * @param packet the packet to send.
      */
     public void sendPacket(Packet packet) {
-        if (!done) {
-            try {
-                queue.put(packet);
-            }
-            catch (InterruptedException ie) {
-                LOGGER.log(Level.SEVERE, "Failed to queue packet to send to server: " + packet.toString(), ie);
-                return;
-            }
-            synchronized (queue) {
-                queue.notifyAll();
-            }
+        if (done) {
+            return;
+        }
+
+        try {
+            queue.put(packet);
+        }
+        catch (InterruptedException ie) {
+            LOGGER.log(Level.SEVERE,
+                            "Failed to queue packet to send to server: " + packet.toString(), ie);
+            return;
         }
     }
 
@@ -112,9 +115,7 @@ class PacketWriter {
      */
     public void shutdown() {
         done = true;
-        synchronized (queue) {
-            queue.notifyAll();
-        }
+        queue.shutdown();
     }
 
     /**
@@ -123,17 +124,16 @@ class PacketWriter {
      * @return the next packet for writing.
      */
     private Packet nextPacket() {
+        if (done) {
+            return null;
+        }
+
         Packet packet = null;
-        // Wait until there's a packet or we're done.
-        while (!done && (packet = queue.poll()) == null) {
-            try {
-                synchronized (queue) {
-                    queue.wait();
-                }
-            }
-            catch (InterruptedException ie) {
-                // Do nothing
-            }
+        try {
+            packet = queue.take();
+        }
+        catch (InterruptedException e) {
+            // Do nothing
         }
         return packet;
     }
@@ -191,12 +191,8 @@ class PacketWriter {
             // The exception can be ignored if the the connection is 'done'
             // or if the it was caused because the socket got closed
             if (!(done || connection.isSocketClosed())) {
-                done = true;
-                // packetReader could be set to null by an concurrent disconnect() call.
-                // Therefore Prevent NPE exceptions by checking packetReader.
-                if (connection.packetReader != null) {
-                        connection.notifyConnectionError(ioe);
-                }
+                shutdown();
+                connection.notifyConnectionError(ioe);
             }
         }
     }

smack-tcp/src/test/java/org/jivesoftware/smack/PacketWriterTest.java

@@ -0,0 +1,112 @@
+/**
+ *
+ * Copyright 2014 Florian Schmaus
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smack;
+
+import java.io.IOException;
+import java.io.Writer;
+import java.util.concurrent.BrokenBarrierException;
+import java.util.concurrent.CyclicBarrier;
+
+import org.jivesoftware.smack.packet.Message;
+import org.junit.Test;
+
+import static org.junit.Assert.fail;
+
+public class PacketWriterTest {
+    volatile boolean shutdown;
+    volatile boolean prematureUnblocked;
+
+    /**
+     * Make sure that packet writer does block once the queue reaches
+     * {@link PacketWriter#QUEUE_SIZE} and that
+     * {@link PacketWriter#sendPacket(org.jivesoftware.smack.packet.Packet)} does unblock after the
+     * interrupt.
+     * 
+     * @throws InterruptedException
+     * @throws BrokenBarrierException
+     */
+    @SuppressWarnings("javadoc")
+    @Test
+    public void shouldBlockAndUnblockTest() throws InterruptedException, BrokenBarrierException {
+        XMPPTCPConnection connection = new XMPPTCPConnection("foobar.com");
+        final PacketWriter pw = new PacketWriter(connection);
+        pw.setWriter(new BlockingStringWriter());
+        pw.startup();
+
+        for (int i = 0; i < PacketWriter.QUEUE_SIZE; i++) {
+            pw.sendPacket(new Message());
+        }
+        
+        final CyclicBarrier barrier = new CyclicBarrier(2);
+        shutdown = false;
+        prematureUnblocked = false;
+        Thread t = new Thread(new Runnable() {
+            @Override
+            public void run() {
+                try {
+                    barrier.await();
+                }
+                catch (InterruptedException | BrokenBarrierException e1) {
+                }
+                pw.sendPacket(new Message());
+                // should only return after the pw was shutdown
+                if (!shutdown) {
+                    prematureUnblocked = true;
+                }
+                try {
+                    barrier.await();
+                }
+                catch (InterruptedException | BrokenBarrierException e) {
+                }
+            }
+        });
+        t.start();
+        // This barrier is not strictly necessary, but may increases the chances that the threat
+        // will block before we call shutdown. Otherwise we may get false positives (which is still
+        // better then false negatives).
+        barrier.await();
+        // Not really cool, but may increases the chances for 't' to block in sendPacket.
+        Thread.sleep(250);
+
+        // Shutdown the packetwriter
+        pw.shutdown();
+        shutdown = true;
+        barrier.await();
+        if (prematureUnblocked) {
+            fail("Should not unblock before the thread got shutdown");
+        }
+    }
+    
+    public class BlockingStringWriter extends Writer {
+        @Override
+        public void write(char[] cbuf, int off, int len) throws IOException {
+            try {
+                Thread.sleep(Integer.MAX_VALUE);
+            }
+            catch (InterruptedException e) {
+            }
+        }
+
+        @Override
+        public void flush() throws IOException {
+        }
+
+        @Override
+        public void close() throws IOException {
+        }
+    }
+}