Fix thread leak (#16)

Author: tomwmth

src/main/java/de/labystudio/spotifyapi/SpotifyAPI.java

@@ -36,7 +36,6 @@ default SpotifyAPI initialize() {
      */
     SpotifyAPI initialize(SpotifyConfiguration configuration);
 
-
     /**
      * Initialize the SpotifyAPI and connect to the Spotify process asynchronously.
      *
@@ -47,7 +46,6 @@ default CompletableFuture<SpotifyAPI> initializeAsync(SpotifyConfiguration confi
         return CompletableFuture.supplyAsync(() -> this.initialize(configuration));
     }
 
-
     /**
      * Initialize the SpotifyAPI and connect to the Spotify process asynchronously.
      * It will use a default configuration.
@@ -119,7 +117,6 @@ default boolean hasTrack() {
      */
     boolean isConnected();
 
-
     /**
      * Returns true if the background process is running.
      *
@@ -154,4 +151,11 @@ default boolean hasTrack() {
      * Disconnect from the Spotify application and stop all background tasks.
      */
     void stop();
+
+    /**
+     * Similar to {@link SpotifyAPI#stop()} but releases any held resources.
+     * <p>
+     * Should only be called if there is no intent to reuse this instance.
+     */
+    void shutdown();
 }

src/main/java/de/labystudio/spotifyapi/platform/AbstractTickSpotifyAPI.java

@@ -8,6 +8,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 
@@ -27,33 +28,34 @@ public abstract class AbstractTickSpotifyAPI implements SpotifyAPI {
 
     private SpotifyConfiguration configuration;
 
+    private final ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor();
+
     private ScheduledFuture<?> task;
+
     private long timeLastException = -1;
 
     /**
      * Initialize the SpotifyAPI abstract tick implementation.
      * It will create a task that will update the current track and position every second.
      *
      * @return the initialized SpotifyAPI
-     * @throws IllegalStateException if the API is already initialized
+     * @throws IllegalStateException if the API is already initialized or has been shutdown
      */
     @Override
     public SpotifyAPI initialize(SpotifyConfiguration configuration) {
         synchronized (this) {
             this.configuration = configuration;
 
+            if (this.executor.isShutdown()) {
+                throw new IllegalStateException("This SpotifyAPI has been shutdown and cannot be reused");
+            }
+
             if (this.isInitialized()) {
-                throw new IllegalStateException("The SpotifyAPI is already initialized");
+                throw new IllegalStateException("This SpotifyAPI is already initialized");
             }
 
             // Start task to update every second
-            this.task = Executors.newScheduledThreadPool(1)
-                    .scheduleWithFixedDelay(
-                            this::onInternalTick,
-                            0,
-                            1,
-                            TimeUnit.SECONDS
-                    );
+            this.task = this.executor.scheduleWithFixedDelay(this::onInternalTick, 0L, 1L, TimeUnit.SECONDS);
         }
         return this;
     }
@@ -120,4 +122,10 @@ public void stop() {
             }
         }
     }
+
+    @Override
+    public void shutdown() {
+        this.stop();
+        this.executor.shutdownNow();
+    }
 }