Changes notifier to be closable. (#1090)

Fixes #1089

wpilibj/src/main/java/edu/wpi/first/wpilibj/Notifier.java

@@ -12,9 +12,9 @@ import java.util.concurrent.locks.ReentrantLock;
 
 import edu.wpi.first.wpilibj.hal.NotifierJNI;
 
-public class Notifier {
+public class Notifier implements AutoCloseable {
   // The thread waiting on the HAL alarm.
-  private final Thread m_thread;
+  private Thread m_thread;
   // The lock for the process information.
   private final ReentrantLock m_processLock = new ReentrantLock();
   // The C pointer to the notifier object. We don't use it directly, it is
@@ -35,7 +35,15 @@ public class Notifier {
   @Override
   @SuppressWarnings("NoFinalizer")
   protected void finalize() {
+    close();
+  }
+
+  @Override
+  public void close() {
     int handle = m_notifier.getAndSet(0);
+    if (handle == 0) {
+      return;
+    }
     NotifierJNI.stopNotifier(handle);
     // Join the thread to ensure the handler has exited.
     if (m_thread.isAlive()) {
@@ -47,6 +55,7 @@ public class Notifier {
       }
     }
     NotifierJNI.cleanNotifier(handle);
+    m_thread = null;
   }
 
   /**
@@ -63,8 +72,8 @@ public class Notifier {
   /**
    * Create a Notifier for timer event notification.
    *
-   * @param run The handler that is called at the notification time which is set using StartSingle
-   *            or StartPeriodic.
+   * @param run The handler that is called at the notification time which is set
+   *            using StartSingle or StartPeriodic.
    */
   public Notifier(Runnable run) {
     m_handler = run;
@@ -98,6 +107,7 @@ public class Notifier {
         }
       }
     });
+    m_thread.setName("Notifier");
     m_thread.setDaemon(true);
     m_thread.setUncaughtExceptionHandler((thread, error) -> {
       Throwable cause = error.getCause();
@@ -127,8 +137,8 @@ public class Notifier {
   }
 
   /**
-   * Register for single event notification. A timer event is queued for a single event after the
-   * specified delay.
+   * Register for single event notification. A timer event is queued for a single
+   * event after the specified delay.
    *
    * @param delay Seconds to wait before the handler is called.
    */
@@ -145,12 +155,12 @@ public class Notifier {
   }
 
   /**
-   * Register for periodic event notification. A timer event is queued for periodic event
-   * notification. Each time the interrupt occurs, the event will be immediately requeued for the
-   * same time interval.
+   * Register for periodic event notification. A timer event is queued for
+   * periodic event notification. Each time the interrupt occurs, the event will
+   * be immediately requeued for the same time interval.
    *
-   * @param period Period in seconds to call the handler starting one period after the call to this
-   *               method.
+   * @param period Period in seconds to call the handler starting one period after
+   *               the call to this method.
    */
   public void startPeriodic(double period) {
     m_processLock.lock();
@@ -165,9 +175,10 @@ public class Notifier {
   }
 
   /**
-   * Stop timer events from occurring. Stop any repeating timer events from occurring. This will
-   * also remove any single notification events from the queue. If a timer-based call to the
-   * registered handler is in progress, this function will block until the handler call is complete.
+   * Stop timer events from occurring. Stop any repeating timer events from
+   * occurring. This will also remove any single notification events from the
+   * queue. If a timer-based call to the registered handler is in progress, this
+   * function will block until the handler call is complete.
    */
   public void stop() {
     NotifierJNI.cancelNotifierAlarm(m_notifier.get());

wpilibj/src/main/java/edu/wpi/first/wpilibj/PIDController.java

@@ -91,7 +91,7 @@ public class PIDController extends PIDBase implements Controller {
   @Override
   public void close() {
     super.close();
-    m_controlLoop.stop();
+    m_controlLoop.close();
     m_thisMutex.lock();
     try {
       m_pidOutput = null;

wpilibj/src/main/java/edu/wpi/first/wpilibj/SPI.java

@@ -438,7 +438,7 @@ public class SPI implements AutoCloseable {
 
     @Override
     public void close() {
-      m_notifier.stop();
+      m_notifier.close();
     }
 
     final Notifier m_notifier;