Keep downloads update thread paused when there aren't active downloads (

#3258)

app/src/common/shared/org/mozilla/vrbrowser/downloads/DownloadsManager.java

@@ -10,6 +10,7 @@
 import android.os.Environment;
 import android.os.Handler;
 import android.os.Looper;
+import android.util.Log;
 import android.webkit.URLUtil;
 
 import androidx.annotation.NonNull;
@@ -21,6 +22,7 @@
 import java.io.File;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 
@@ -41,6 +43,7 @@ default void onDownloadError(@NonNull String error, @NonNull String file) {}
     private List<DownloadsListener> mListeners;
     private DownloadManager mDownloadManager;
     private ScheduledThreadPoolExecutor mExecutor;
+    private ScheduledFuture<?> mFuture;
 
     public DownloadsManager(@NonNull Context context) {
         mMainHandler = new Handler(Looper.getMainLooper());
@@ -67,14 +70,29 @@ public void end() {
     public void addListener(@NonNull DownloadsListener listener) {
         mListeners.add(listener);
         if (mListeners.size() == 1) {
-            mExecutor.scheduleAtFixedRate(mDownloadUpdateTask, 0, REFRESH_INTERVAL, TimeUnit.MILLISECONDS);
+            scheduleUpdates();
         }
     }
 
     public void removeListener(@NonNull DownloadsListener listener) {
         mListeners.remove(listener);
         if (mListeners.size() == 0) {
-            mExecutor.remove(mDownloadUpdateTask);
+            stopUpdates();
+        }
+    }
+
+    private void scheduleUpdates() {
+        if (mFuture != null) {
+            // Already scheduled
+            return;
+        }
+        mFuture = mExecutor.scheduleAtFixedRate(mDownloadUpdateTask, 0, REFRESH_INTERVAL, TimeUnit.MILLISECONDS);
+    }
+
+    private void stopUpdates() {
+        if (mFuture != null) {
+            mFuture.cancel(true);
+            mFuture = null;
         }
     }
 
@@ -104,6 +122,7 @@ public void startDownload(@NonNull DownloadJob job) {
         }
 
         mDownloadManager.enqueue(request);
+        scheduleUpdates();
     }
 
     @Nullable
@@ -192,7 +211,12 @@ public void onReceive(Context context, Intent intent) {
 
     private void notifyDownloadsUpdate() {
         List<Download> downloads = getDownloads();
+        int filter = Download.RUNNING | Download.PAUSED | Download.PENDING;
+        boolean activeDownloads = downloads.stream().filter(d -> (d.getStatus() & filter) != 0).count()  > 0;
         mListeners.forEach(listener -> listener.onDownloadsUpdate(downloads));
+        if (!activeDownloads) {
+            stopUpdates();
+        }
     }
 
     private void notifyDownloadCompleted(@NonNull Download download) {