Enable download parallelisation in demo app

- Deprecate constructors that don't take an executor, to direct
  developers toward the new ones. Callers can trivially pass
  Runnable::run to one of the new ones if they want old behaviour.
- Add comment explaining warning suppression added in the CL that
  added parallelised download support.

Issue: #5978
PiperOrigin-RevId: 318803296

RELEASENOTES.md

@@ -145,7 +145,10 @@
         ([#7078](https://github.com/google/ExoPlayer/issues/7078)).
     *   Remove generics from DRM components.
 *   Downloads and caching:
-    *   Merge downloads in `SegmentDownloader` to improve overall download speed
+    *   Support passing an `Executor` to `DefaultDownloaderFactory` on which
+        data downloads are performed.
+    *   Parallelize and merge downloads in `SegmentDownloader` to improve
+        overall download speed
         ([#5978](https://github.com/google/ExoPlayer/issues/5978)).
     *   Support multiple non-overlapping write locks for the same key in
         `SimpleCache`.

demos/main/src/main/java/com/google/android/exoplayer2/demo/DemoApplication.java

@@ -36,6 +36,7 @@ import com.google.android.exoplayer2.util.Log;
 import com.google.android.exoplayer2.util.Util;
 import java.io.File;
 import java.io.IOException;
+import java.util.concurrent.Executors;
 
 /**
  * Placeholder application to facilitate overriding Application methods for debugging and testing.
@@ -129,7 +130,11 @@ public class DemoApplication extends MultiDexApplication {
           DOWNLOAD_TRACKER_ACTION_FILE, downloadIndex, /* addNewDownloadsAsCompleted= */ true);
       downloadManager =
           new DownloadManager(
-              this, getDatabaseProvider(), getDownloadCache(), buildHttpDataSourceFactory());
+              this,
+              getDatabaseProvider(),
+              getDownloadCache(),
+              buildHttpDataSourceFactory(),
+              Executors.newFixedThreadPool(/* nThreads= */ 6));
       downloadTracker =
           new DownloadTracker(/* context= */ this, buildDataSourceFactory(), downloadManager);
     }

library/core/src/main/java/com/google/android/exoplayer2/offline/DefaultDownloaderFactory.java

@@ -79,7 +79,9 @@ public class DefaultDownloaderFactory implements DownloaderFactory {
    *
    * @param cacheDataSourceFactory A {@link CacheDataSource.Factory} for the cache into which
    *     downloads will be written.
+   * @deprecated Use {@link #DefaultDownloaderFactory(CacheDataSource.Factory, Executor)}.
    */
+  @Deprecated
   public DefaultDownloaderFactory(CacheDataSource.Factory cacheDataSourceFactory) {
     this(cacheDataSourceFactory, Runnable::run);
   }
@@ -89,9 +91,10 @@ public class DefaultDownloaderFactory implements DownloaderFactory {
    *
    * @param cacheDataSourceFactory A {@link CacheDataSource.Factory} for the cache into which
    *     downloads will be written.
-   * @param executor An {@link Executor} used to make requests for media being downloaded. Providing
-   *     an {@link Executor} that uses multiple threads will speed up download tasks that can be
-   *     split into smaller parts for parallel execution.
+   * @param executor An {@link Executor} used to download data. Passing {@code Runnable::run} will
+   *     cause each download task to download data on its own thread. Passing an {@link Executor}
+   *     that uses multiple threads will speed up download tasks that can be split into smaller
+   *     parts for parallel execution.
    */
   public DefaultDownloaderFactory(
       CacheDataSource.Factory cacheDataSourceFactory, Executor executor) {

library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java

@@ -52,6 +52,7 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.concurrent.CopyOnWriteArraySet;
+import java.util.concurrent.Executor;
 
 /**
  * Manages downloads.
@@ -197,16 +198,42 @@ public final class DownloadManager {
    *     an {@link CacheEvictor} that will not evict downloaded content, for example {@link
    *     NoOpCacheEvictor}.
    * @param upstreamFactory A {@link Factory} for creating {@link DataSource}s for downloading data.
+   * @deprecated Use {@link #DownloadManager(Context, DatabaseProvider, Cache, Factory, Executor)}.
    */
+  @Deprecated
   public DownloadManager(
       Context context, DatabaseProvider databaseProvider, Cache cache, Factory upstreamFactory) {
+    this(context, databaseProvider, cache, upstreamFactory, Runnable::run);
+  }
+
+  /**
+   * Constructs a {@link DownloadManager}.
+   *
+   * @param context Any context.
+   * @param databaseProvider Provides the SQLite database in which downloads are persisted.
+   * @param cache A cache to be used to store downloaded data. The cache should be configured with
+   *     an {@link CacheEvictor} that will not evict downloaded content, for example {@link
+   *     NoOpCacheEvictor}.
+   * @param upstreamFactory A {@link Factory} for creating {@link DataSource}s for downloading data.
+   * @param executor An {@link Executor} used to download data. Passing {@code Runnable::run} will
+   *     cause each download task to download data on its own thread. Passing an {@link Executor}
+   *     that uses multiple threads will speed up download tasks that can be split into smaller
+   *     parts for parallel execution.
+   */
+  public DownloadManager(
+      Context context,
+      DatabaseProvider databaseProvider,
+      Cache cache,
+      Factory upstreamFactory,
+      Executor executor) {
     this(
         context,
         new DefaultDownloadIndex(databaseProvider),
         new DefaultDownloaderFactory(
             new CacheDataSource.Factory()
                 .setCache(cache)
-                .setUpstreamDataSourceFactory(upstreamFactory)));
+                .setUpstreamDataSourceFactory(upstreamFactory),
+            executor));
   }
 
   /**

library/core/src/main/java/com/google/android/exoplayer2/util/RunnableFutureTask.java

@@ -159,6 +159,8 @@ public abstract class RunnableFutureTask<R, E extends Exception> implements Runn
     // Do nothing.
   }
 
+  // The return value is guaranteed to be non-null if and only if R is a non-null type, but there's
+  // no way to assert this. Suppress the warning instead.
   @SuppressWarnings("return.type.incompatible")
   @UnknownNull
   private R getResult() throws ExecutionException {