Ported QueueingThreadPoolExecutor synchronization improvements from E…

…clipse Smarthome (jupnp#96)

* Ported synchronization improvements from eclipse-archived/smarthome#5113

Signed-off-by: velichko.stoykov <[email protected]>

bundles/org.jupnp/src/main/java/org/jupnp/QueueingThreadPoolExecutor.java

@@ -21,6 +21,8 @@
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -58,16 +60,17 @@
  */
 public class QueueingThreadPoolExecutor extends ThreadPoolExecutor {
 
-    private Logger logger = LoggerFactory.getLogger(QueueingThreadPoolExecutor.class);
+    private final Logger logger = LoggerFactory.getLogger(QueueingThreadPoolExecutor.class);
 
     /** we will use a core pool size of 1 since we allow to timeout core threads. */
     final static int CORE_THREAD_POOL_SIZE = 1;
 
     /** Our queue for queueing tasks that wait for a thread to become available */
-    private LinkedTransferQueue<Runnable> taskQueue = new LinkedTransferQueue<>();
+    private final BlockingQueue<Runnable> taskQueue = new LinkedTransferQueue<>();
 
     /** The thread for processing the queued tasks */
     private Thread queueThread;
+    private final ReadWriteLock lock = new ReentrantReadWriteLock(true);
 
     final private Object semaphore = new Object();
 
@@ -109,18 +112,30 @@ public static QueueingThreadPoolExecutor createInstance(String name, int threadP
      * @param runnable the task to add
      */
     protected void addToQueue(Runnable runnable) {
-        taskQueue.add(runnable);
+        lock.readLock().lock();
 
         if (queueThread == null || !queueThread.isAlive()) {
-            synchronized (this) {
+            lock.readLock().unlock();
+            lock.writeLock().lock();
+            try {
                 // check again to make sure it has not been created by another thread
                 if (queueThread == null || !queueThread.isAlive()) {
-                    logger.warn("Thread pool '{}' exhausted, queueing tasks now.", threadPoolName);
+                    logger.info("Thread pool '{}' exhausted, queueing tasks now.", threadPoolName);
                     queueThread = createNewQueueThread();
                     queueThread.start();
                 }
+
+                lock.readLock().lock();
+            } finally {
+                lock.writeLock().unlock();
             }
         }
+
+        try {
+            taskQueue.add(runnable);
+        } finally {
+            lock.readLock().unlock();
+        }
     }
 
     @Override
@@ -181,7 +196,15 @@ public void run() {
                                 logger.debug("Executing queued task of thread pool '{}'.", threadPoolName);
                                 QueueingThreadPoolExecutor.super.execute(runnable);
                             } else {
-                                break;
+                                lock.writeLock().lock();
+                                try {
+                                    if (taskQueue.isEmpty()) {
+                                        queueThread = null;
+                                        break;
+                                    }
+                                } finally {
+                                    lock.writeLock().unlock();
+                                }
                             }
                         } catch (InterruptedException e) {
                         }