[wpiutil] Add WPICleaner and an example how to use it (#4850)

wpinet/src/main/java/edu/wpi/first/net/MulticastServiceAnnouncer.java

@@ -4,11 +4,18 @@
 
 package edu.wpi.first.net;
 
+import edu.wpi.first.util.WPICleaner;
+import java.lang.ref.Cleaner.Cleanable;
 import java.util.Map;
 
 /** Class to announce over mDNS that a service is available. */
 public class MulticastServiceAnnouncer implements AutoCloseable {
   private final int m_handle;
+  private final Cleanable m_cleanable;
+
+  private static Runnable cleanupAction(int handle) {
+    return () -> WPINetJNI.freeMulticastServiceAnnouncer(handle);
+  }
 
   /**
    * Creates a MulticastServiceAnnouncer.
@@ -24,6 +31,7 @@ public class MulticastServiceAnnouncer implements AutoCloseable {
     String[] values = txt.values().toArray(String[]::new);
     m_handle =
         WPINetJNI.createMulticastServiceAnnouncer(serviceName, serviceType, port, keys, values);
+    m_cleanable = WPICleaner.register(this, cleanupAction(m_handle));
   }
 
   /**
@@ -36,11 +44,12 @@ public class MulticastServiceAnnouncer implements AutoCloseable {
   public MulticastServiceAnnouncer(String serviceName, String serviceType, int port) {
     m_handle =
         WPINetJNI.createMulticastServiceAnnouncer(serviceName, serviceType, port, null, null);
+    m_cleanable = WPICleaner.register(this, cleanupAction(m_handle));
   }
 
   @Override
   public void close() {
-    WPINetJNI.freeMulticastServiceAnnouncer(m_handle);
+    m_cleanable.clean();
   }
 
   public void start() {

wpinet/src/main/java/edu/wpi/first/net/MulticastServiceResolver.java

@@ -4,9 +4,17 @@
 
 package edu.wpi.first.net;
 
+import edu.wpi.first.util.WPICleaner;
+import java.lang.ref.Cleaner.Cleanable;
+
 /** Class to resolve a service over mDNS. */
 public class MulticastServiceResolver implements AutoCloseable {
   private final int m_handle;
+  private final Cleanable m_cleanable;
+
+  private static Runnable cleanupAction(int handle) {
+    return () -> WPINetJNI.freeMulticastServiceResolver(handle);
+  }
 
   /**
    * Creates a MulticastServiceResolver.
@@ -15,11 +23,12 @@ public class MulticastServiceResolver implements AutoCloseable {
    */
   public MulticastServiceResolver(String serviceType) {
     m_handle = WPINetJNI.createMulticastServiceResolver(serviceType);
+    m_cleanable = WPICleaner.register(this, cleanupAction(m_handle));
   }
 
   @Override
   public void close() {
-    WPINetJNI.freeMulticastServiceResolver(m_handle);
+    m_cleanable.clean();
   }
 
   public void start() {

wpiutil/src/main/java/edu/wpi/first/util/WPICleaner.java

@@ -0,0 +1,28 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package edu.wpi.first.util;
+
+import java.lang.ref.Cleaner;
+import java.lang.ref.Cleaner.Cleanable;
+
+/** Cleaner object for WPILib objects. */
+public final class WPICleaner {
+  private WPICleaner() {
+    throw new UnsupportedOperationException("This is a utility class!");
+  }
+
+  private static final Cleaner instance = Cleaner.create();
+
+  /**
+   * Register an object with the cleaner.
+   *
+   * @param object The object to register.
+   * @param runnable The runnable to call on cleanup.
+   * @return The registered Cleanable.
+   */
+  public static Cleanable register(Object object, Runnable runnable) {
+    return instance.register(object, runnable);
+  }
+}