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-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 {
+        }
+    }
+}