Fully implements application shutdown procedure that is invoked when the

user closes the the main gui window or invokes exit from the file menu.

src/main/java/io/github/dsheirer/source/tuner/Tuner.java

@@ -98,8 +98,12 @@ public abstract class Tuner implements ISourceEventProcessor
         return mName;
     }
 
+    /**
+     * Dispose and prepare for shutdown
+     */
     public void dispose()
     {
+        getTunerController().dispose();
     }
 
     /**

src/main/java/io/github/dsheirer/source/tuner/TunerController.java

@@ -61,6 +61,11 @@ public abstract class TunerController implements Tunable, ISourceEventProcessor,
         mSourceEventListener = new SourceEventListenerToProcessorAdapter(this);
     }
 
+    /**
+     * Dispose of this tuner controller and prepare for shutdown.
+     */
+    public abstract void dispose();
+
     /**
      * Implements the ISourceEventListener interface to receive requests from sample consumers
      */

src/main/java/io/github/dsheirer/source/tuner/TunerManager.java

@@ -1,19 +1,16 @@
 /*******************************************************************************
- * sdrtrunk
- * Copyright (C) 2014-2017 Dennis Sheirer
+ * sdr-trunk
+ * Copyright (C) 2014-2018 Dennis Sheirer
  *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
+ * This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public
+ * License as published by  the Free Software Foundation, either version 3 of the License, or  (at your option) any
+ * later version.
  *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
+ * This program is distributed in the hope that it will be useful,  but WITHOUT ANY WARRANTY; without even the implied
+ * warranty of  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
  *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * You should have received a copy of the GNU General Public License  along with this program.
+ * If not, see <http://www.gnu.org/licenses/>
  *
  ******************************************************************************/
 package io.github.dsheirer.source.tuner;
@@ -74,7 +71,15 @@ public class TunerManager
      */
     public void dispose()
     {
-        LibUsb.exit(null);
+        mLog.info("Shutting down LibUsb ...");
+        try
+        {
+            LibUsb.exit(null);
+        }
+        catch(Exception e)
+        {
+            mLog.error("Error shutting down LibUsb", e);
+        }
     }
 
     /**
@@ -217,6 +222,22 @@ public class TunerManager
         return new TunerInitStatus(null, "Unknown Device");
     }
 
+    /**
+     * Releases all tuners in preparation for shutdown
+     */
+    public void releaseTuners()
+    {
+        mLog.info("Releasing [" + mTunerModel.getTuners().size() + "] tuner(s) ...");
+        Tuner tuner = mTunerModel.getTuner(0);
+
+        while(tuner != null)
+        {
+            mTunerModel.removeTuner(tuner);
+            tuner.dispose();
+            tuner = mTunerModel.getTuner(0);
+        }
+    }
+
     private TunerInitStatus initAirspyTuner(Device device,
                                             DeviceDescriptor descriptor)
     {

src/main/java/io/github/dsheirer/source/tuner/airspy/AirspyTunerController.java

@@ -180,6 +180,24 @@ public class AirspyTunerController extends USBTunerController
             USB_TRANSFER_BUFFER_SIZE);
     }
 
+    @Override
+    public void dispose()
+    {
+        if(mDeviceHandle != null)
+        {
+            mLog.info("Releasing Airspy Tuner - " + getDeviceInfo().getSerialNumber());
+            try
+            {
+                LibUsb.close(mDeviceHandle);
+            }
+            catch(Exception e)
+            {
+                mLog.error("error while closing device handle", e);
+            }
+
+            mDeviceHandle = null;
+        }
+    }
 
     @Override
     protected USBTransferProcessor getUSBTransferProcessor()

src/main/java/io/github/dsheirer/source/tuner/hackrf/HackRFTuner.java

@@ -37,10 +37,6 @@ public class HackRFTuner extends Tuner
         return (HackRFTunerController)getTunerController();
     }
 
-    public void dispose()
-    {
-    }
-
     @Override
     public TunerClass getTunerClass()
     {

src/main/java/io/github/dsheirer/source/tuner/hackrf/HackRFTunerController.java

@@ -157,6 +157,25 @@ public class HackRFTunerController extends USBTunerController
         mUSBTransferProcessor = new USBTransferProcessor(name, mDeviceHandle, mNativeBufferConverter, USB_TRANSFER_BUFFER_SIZE);
     }
 
+    @Override
+    public void dispose()
+    {
+        if(mDeviceHandle != null)
+        {
+            mLog.info("Releasing HackRF Tuner");
+            try
+            {
+                LibUsb.close(mDeviceHandle);
+            }
+            catch(Exception e)
+            {
+                mLog.error("error while closing device handle", e);
+            }
+
+            mDeviceHandle = null;
+        }
+    }
+
     @Override
     protected USBTransferProcessor getUSBTransferProcessor()
     {

src/main/java/io/github/dsheirer/source/tuner/rtl/RTL2832Tuner.java

@@ -38,10 +38,6 @@ public class RTL2832Tuner extends Tuner
         mTunerClass = tunerClass;
     }
 
-    public void dispose()
-    {
-    }
-
     public RTL2832TunerController getController()
     {
         return (RTL2832TunerController)getTunerController();

src/main/java/io/github/dsheirer/source/tuner/rtl/e4k/E4KTunerController.java

@@ -256,6 +256,26 @@ public class E4KTunerController extends RTL2832TunerController
             USB_TRANSFER_BUFFER_SIZE);
     }
 
+    @Override
+    public void dispose()
+    {
+        if(mDeviceHandle != null)
+        {
+            mLog.info("Releasing E4000 Tuner");
+
+            try
+            {
+                LibUsb.close(mDeviceHandle);
+            }
+            catch(Exception e)
+            {
+                mLog.error("error while closing device handle", e);
+            }
+
+            mDeviceHandle = null;
+        }
+    }
+
     /**
      * Sets the IF filters (mixer, channel and RC) to the correct filter setting
      * for the selected bandwidth/sample rate

src/main/java/io/github/dsheirer/source/tuner/rtl/r820t/R820TTunerController.java

@@ -30,6 +30,7 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.usb4java.Device;
 import org.usb4java.DeviceDescriptor;
+import org.usb4java.LibUsb;
 import org.usb4java.LibUsbException;
 
 import javax.swing.JPanel;
@@ -260,6 +261,26 @@ public class R820TTunerController extends RTL2832TunerController
         }
     }
 
+    @Override
+    public void dispose()
+    {
+        mLog.info("Releasing R820T Tuner");
+
+        if(mDeviceHandle != null)
+        {
+            try
+            {
+                LibUsb.close(mDeviceHandle);
+            }
+            catch(Exception e)
+            {
+                mLog.error("error while closing device handle", e);
+            }
+
+            mDeviceHandle = null;
+        }
+    }
+
     /**
      * Initializes the tuner section.
      */

src/main/java/io/github/dsheirer/source/tuner/test/TestTunerController.java

@@ -65,6 +65,12 @@ public class TestTunerController extends TunerController
         }
     }
 
+    @Override
+    public void dispose()
+    {
+        //no-op
+    }
+
     @Override
     public void addBufferListener(Listener<ReusableComplexBuffer> listener)
     {