Do not spawn unecessary threads, refs #228

webcam-capture/src/example/java/WebcamViewerExample.java

@@ -9,6 +9,8 @@
 import javax.swing.SwingUtilities;
 
 import com.github.sarxos.webcam.Webcam;
+import com.github.sarxos.webcam.WebcamDiscoveryEvent;
+import com.github.sarxos.webcam.WebcamDiscoveryListener;
 import com.github.sarxos.webcam.WebcamEvent;
 import com.github.sarxos.webcam.WebcamListener;
 import com.github.sarxos.webcam.WebcamPanel;
@@ -21,7 +23,7 @@
  * 
  * @author Bartosz Firyn (SarXos)
  */
-public class WebcamViewerExample extends JFrame implements Runnable, WebcamListener, WindowListener, UncaughtExceptionHandler, ItemListener {
+public class WebcamViewerExample extends JFrame implements Runnable, WebcamListener, WindowListener, UncaughtExceptionHandler, ItemListener, WebcamDiscoveryListener {
 
 	private static final long serialVersionUID = 1L;
 
@@ -32,6 +34,8 @@ public class WebcamViewerExample extends JFrame implements Runnable, WebcamListe
 	@Override
 	public void run() {
 
+		Webcam.addDiscoveryListener(this);
+
 		setTitle("Java Webcam Capture POC");
 		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 		setLayout(new BorderLayout());
@@ -155,6 +159,7 @@ public void itemStateChanged(ItemEvent e) {
 				System.out.println("selected " + webcam.getName());
 
 				panel = new WebcamPanel(webcam, false);
+				panel.setFPSDisplayed(true);
 
 				add(panel, BorderLayout.CENTER);
 				pack();
@@ -173,4 +178,18 @@ public void run() {
 			}
 		}
 	}
+
+	@Override
+	public void webcamFound(WebcamDiscoveryEvent event) {
+		if (picker != null) {
+			picker.addItem(event.getWebcam());
+		}
+	}
+
+	@Override
+	public void webcamGone(WebcamDiscoveryEvent event) {
+		if (picker != null) {
+			picker.removeItem(event.getWebcam());
+		}
+	}
 }

webcam-capture/src/example/resources/logback.xml

@@ -4,7 +4,7 @@
 			<Pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</Pattern>
 		</layout>
 	</appender>
-	<root level="warn">
+	<root level="debug">
 		<appender-ref ref="STDOUT" />
 	</root>
 </configuration>

webcam-capture/src/main/java/com/github/sarxos/webcam/Webcam.java

@@ -9,6 +9,9 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -34,6 +37,61 @@
  */
 public class Webcam {
 
+	/**
+	 * Class used to asynchronously notify all webcam listeners about new image
+	 * available.
+	 * 
+	 * @author Bartosz Firyn (sarxos)
+	 */
+	private static final class ImageNotification implements Runnable {
+
+		/**
+		 * Camera.
+		 */
+		private final Webcam webcam;
+
+		/**
+		 * Acquired image.
+		 */
+		private final BufferedImage image;
+
+		/**
+		 * Create new notification.
+		 * 
+		 * @param webcam the webcam from which image has been acquired
+		 * @param image the acquired image
+		 */
+		public ImageNotification(Webcam webcam, BufferedImage image) {
+			this.webcam = webcam;
+			this.image = image;
+		}
+
+		@Override
+		public void run() {
+			if (image != null) {
+				WebcamEvent we = new WebcamEvent(WebcamEventType.NEW_IMAGE, webcam, image);
+				for (WebcamListener l : webcam.getWebcamListeners()) {
+					try {
+						l.webcamImageObtained(we);
+					} catch (Exception e) {
+						LOG.error(String.format("Notify image acquired, exception when calling listener %s", l.getClass()), e);
+					}
+				}
+			}
+		}
+	}
+
+	private final class NotificationThreadFactory implements ThreadFactory {
+
+		@Override
+		public Thread newThread(Runnable r) {
+			Thread t = new Thread(r, String.format("notificator-[%s]", getName()));
+			t.setUncaughtExceptionHandler(WebcamExceptionHandler.getInstance());
+			t.setDaemon(true);
+			return t;
+		}
+	}
+
 	/**
 	 * Logger instance.
 	 */
@@ -117,15 +175,24 @@ public class Webcam {
 	/**
 	 * Webcam image updater.
 	 */
-	private WebcamUpdater updater = new WebcamUpdater(this);
+	private volatile WebcamUpdater updater = null;
 
 	/**
-	 * IMage transformer.
+	 * Image transformer.
 	 */
 	private volatile WebcamImageTransformer transformer = null;
 
+	/**
+	 * Lock which denies access to the given webcam when it's already in use by
+	 * other webcam capture API process or thread.
+	 */
 	private WebcamLock lock = null;
 
+	/**
+	 * Executor service for image notifications.
+	 */
+	private ExecutorService notificator = null;
+
 	/**
 	 * Webcam class.
 	 * 
@@ -140,6 +207,21 @@ protected Webcam(WebcamDevice device) {
 		this.lock = new WebcamLock(this);
 	}
 
+	/**
+	 * Asynchronously start new thread which will notify all webcam listeners
+	 * about the new image available.
+	 */
+	protected void notifyWebcamImageAcquired(BufferedImage image) {
+
+		// notify webcam listeners of new image available, do that only if there
+		// are any webcam listeners available because there is no sense to start
+		// additional threads for no purpose
+
+		if (getWebcamListenersCount() > 0) {
+			notificator.execute(new ImageNotification(this, image));
+		}
+	}
+
 	/**
 	 * Open the webcam in blocking (synchronous) mode.
 	 * 
@@ -175,9 +257,10 @@ public boolean open(boolean async) {
 
 		if (open.compareAndSet(false, true)) {
 
-			assert updater != null;
 			assert lock != null;
 
+			notificator = Executors.newSingleThreadExecutor(new NotificationThreadFactory());
+
 			// lock webcam for other Java (only) processes
 
 			lock.lock();
@@ -195,16 +278,18 @@ public boolean open(boolean async) {
 			} catch (WebcamException e) {
 				lock.unlock();
 				open.set(false);
+				LOG.debug("Webcam exception when opening", e);
 				throw e;
 			}
 
 			LOG.debug("Webcam is now open {}", getName());
 
 			// setup non-blocking configuration
 
-			asynchronous = async;
-
-			if (async) {
+			if (asynchronous = async) {
+				if (updater == null) {
+					updater = new WebcamUpdater(this);
+				}
 				updater.start();
 			}
 
@@ -243,7 +328,6 @@ public boolean close() {
 
 			LOG.debug("Closing webcam {}", getName());
 
-			assert updater != null;
 			assert lock != null;
 
 			// close webcam
@@ -261,7 +345,9 @@ public boolean close() {
 			}
 
 			// stop updater
-			updater.stop();
+			if (asynchronous) {
+				updater.stop();
+			}
 
 			// remove shutdown hook (it's not more necessary)
 			removeShutdownHook();
@@ -284,6 +370,15 @@ public boolean close() {
 				}
 			}
 
+			notificator.shutdown();
+			while (!notificator.isTerminated()) {
+				try {
+					notificator.awaitTermination(100, TimeUnit.MILLISECONDS);
+				} catch (InterruptedException e) {
+					return false;
+				}
+			}
+
 			LOG.debug("Webcam {} has been closed", getName());
 
 		} else {
@@ -552,7 +647,7 @@ public BufferedImage getImage() {
 
 			// notify webcam listeners about new image available
 
-			updater.notifyWebcamImageObtained(this, image);
+			notifyWebcamImageAcquired(image);
 
 			return image;
 		}

webcam-capture/src/main/java/com/github/sarxos/webcam/WebcamPanel.java

@@ -480,7 +480,7 @@ public void run() {
 					// completely started (it was in "starting" timeframe)
 
 					LOG.warn("Executor rejected paint update");
-					LOG.debug("Executor rejected paint update because of", e);
+					LOG.trace("Executor rejected paint update because of", e);
 
 					return;
 				}

webcam-capture/src/main/java/com/github/sarxos/webcam/WebcamUpdater.java

@@ -1,7 +1,6 @@
 package com.github.sarxos.webcam;
 
 import java.awt.image.BufferedImage;
-import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.ScheduledExecutorService;
@@ -45,50 +44,6 @@ public Thread newThread(Runnable r) {
 
 	}
 
-	/**
-	 * Class used to asynchronously notify all webcam listeners about new image
-	 * available.
-	 * 
-	 * @author Bartosz Firyn (sarxos)
-	 */
-	private static final class ImageNotification implements Runnable {
-
-		/**
-		 * Camera.
-		 */
-		private final Webcam webcam;
-
-		/**
-		 * Acquired image.
-		 */
-		private final BufferedImage image;
-
-		/**
-		 * Create new notification.
-		 * 
-		 * @param webcam the webcam from which image has been acquired
-		 * @param image the acquired image
-		 */
-		public ImageNotification(Webcam webcam, BufferedImage image) {
-			this.webcam = webcam;
-			this.image = image;
-		}
-
-		@Override
-		public void run() {
-			if (image != null) {
-				WebcamEvent we = new WebcamEvent(WebcamEventType.NEW_IMAGE, webcam, image);
-				for (WebcamListener l : webcam.getWebcamListeners()) {
-					try {
-						l.webcamImageObtained(we);
-					} catch (Exception e) {
-						LOG.error(String.format("Notify image acquired, exception when calling listener %s", l.getClass()), e);
-					}
-				}
-			}
-		}
-	}
-
 	/**
 	 * Logger.
 	 */
@@ -106,11 +61,6 @@ public void run() {
 	 */
 	private ScheduledExecutorService executor = null;
 
-	/**
-	 * Executor service for image notifications.
-	 */
-	private final ExecutorService notificator = Executors.newSingleThreadExecutor(THREAD_FACTORY);
-
 	/**
 	 * Cached image.
 	 */
@@ -146,6 +96,7 @@ protected WebcamUpdater(Webcam webcam) {
 	 * Start updater.
 	 */
 	public void start() {
+
 		if (running.compareAndSet(false, true)) {
 
 			image.set(new WebcamReadImageTask(Webcam.getDriver(), webcam.getDevice()).getImage());
@@ -166,12 +117,10 @@ public void stop() {
 		if (running.compareAndSet(true, false)) {
 
 			executor.shutdown();
-
 			while (!executor.isTerminated()) {
 				try {
 					executor.awaitTermination(100, TimeUnit.MILLISECONDS);
 				} catch (InterruptedException e) {
-					LOG.trace(e.getMessage(), e);
 					return;
 				}
 			}
@@ -199,6 +148,10 @@ public void run() {
 
 	private void tick() {
 
+		if (!webcam.isOpen()) {
+			return;
+		}
+
 		long t1 = 0;
 		long t2 = 0;
 
@@ -245,22 +198,7 @@ private void tick() {
 
 		// notify webcam listeners about the new image available
 
-		notifyWebcamImageObtained(webcam, image.get());
-	}
-
-	/**
-	 * Asynchronously start new thread which will notify all webcam listeners
-	 * about the new image available.
-	 */
-	protected void notifyWebcamImageObtained(Webcam webcam, BufferedImage image) {
-
-		// notify webcam listeners of new image available, do that only if there
-		// are any webcam listeners available because there is no sense to start
-		// additional threads for no purpose
-
-		if (webcam.getWebcamListenersCount() > 0) {
-			notificator.execute(new ImageNotification(webcam, image));
-		}
+		webcam.notifyWebcamImageAcquired(image.get());
 	}
 
 	/**