Cap concurrent removal DownloadManager.Tasks

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/offline/DownloadManager.java

@@ -174,6 +174,7 @@ public final class DownloadManager {
   private static final int MSG_RELEASE = 12;
 
   private static final String TAG = "DownloadManager";
+  private static final int MAX_REMOVE_TASK_COUNT = 1;
 
   private final Context context;
   private final WritableDownloadIndex downloadIndex;
@@ -709,6 +710,7 @@ public final class DownloadManager {
     private int maxParallelDownloads;
     private int minRetryCount;
     private int activeDownloadTaskCount;
+    private int activeRemoveTaskCount;
 
     public InternalHandler(
         HandlerThread thread,
@@ -1060,6 +1062,10 @@ public final class DownloadManager {
         return;
       }
 
+      if (activeRemoveTaskCount >= MAX_REMOVE_TASK_COUNT) {
+        return;
+      }
+
       // We can start a remove task.
       Downloader downloader = downloaderFactory.createDownloader(download.request);
       activeTask =
@@ -1071,6 +1077,7 @@ public final class DownloadManager {
               minRetryCount,
               /* internalHandler= */ this);
       activeTasks.put(download.request.id, activeTask);
+      activeRemoveTaskCount++;
       activeTask.start();
     }
 
@@ -1100,7 +1107,9 @@ public final class DownloadManager {
       activeTasks.remove(downloadId);
 
       boolean isRemove = task.isRemove;
-      if (!isRemove && --activeDownloadTaskCount == 0) {
+      if (isRemove) {
+        activeRemoveTaskCount--;
+      } else if (--activeDownloadTaskCount == 0) {
         removeMessages(MSG_UPDATE_PROGRESS);
       }
 

libraries/exoplayer/src/test/java/androidx/media3/exoplayer/offline/DownloadManagerTest.java

@@ -713,7 +713,61 @@ public class DownloadManagerTest {
     assertEqualIgnoringUpdateTime(mergedDownload, expectedDownload);
   }
 
+  @Test
+  public void remove_tasks_run_sequentially()
+      throws Throwable {
+    DefaultDownloadIndex defaultDownloadIndex =
+        new DefaultDownloadIndex(TestUtil.getInMemoryDatabaseProvider());
+    defaultDownloadIndex.putDownload(
+        new Download(
+            new DownloadRequest.Builder(ID1, Uri.EMPTY).build(),
+            Download.STATE_REMOVING,
+            0,
+            1,
+            2,
+            Download.STOP_REASON_NONE,
+            Download.FAILURE_REASON_NONE
+        )
+    );
+    defaultDownloadIndex.putDownload(
+        new Download(
+            new DownloadRequest.Builder(ID2, Uri.EMPTY).build(),
+            Download.STATE_RESTARTING,
+            0,
+            1,
+            2,
+            Download.STOP_REASON_NONE,
+            Download.FAILURE_REASON_NONE
+        )
+    );
+    setupDownloadManager(100, defaultDownloadIndex);
+
+    // The second removal should wait and the first one should be able to complete.
+    FakeDownloader downloader0 = getDownloaderAt(0);
+    assertNoDownloaderAt(1);
+    downloader0.assertId(ID1);
+    downloader0.assertRemoveStarted();
+    downloader0.finish();
+    assertRemoved(ID1);
+
+    // The second removal can start once the first one has completed, and removes a download with
+    // state STATE_RESTARTING, so it should result in a new download being queued.
+    FakeDownloader downloader1 = getDownloaderAt(1);
+    downloader1.assertId(ID2);
+    downloader1.assertRemoveStarted();
+    downloader1.finish();
+    assertQueued(ID2);
+  }
+
   private void setupDownloadManager(int maxParallelDownloads) throws Exception {
+    setupDownloadManager(
+        maxParallelDownloads, new DefaultDownloadIndex(TestUtil.getInMemoryDatabaseProvider())
+    );
+  }
+
+  private void setupDownloadManager(
+      int maxParallelDownloads, WritableDownloadIndex writableDownloadIndex
+  ) throws Exception {
     if (downloadManager != null) {
       releaseDownloadManager();
     }
@@ -723,7 +777,7 @@ public class DownloadManagerTest {
             downloadManager =
                 new DownloadManager(
                     ApplicationProvider.getApplicationContext(),
-                    new DefaultDownloadIndex(TestUtil.getInMemoryDatabaseProvider()),
+                    writableDownloadIndex,
                     new FakeDownloaderFactory());
             downloadManager.setMaxParallelDownloads(maxParallelDownloads);
             downloadManager.setMinRetryCount(MIN_RETRY_COUNT);