Reduce the number of cache files

- Increase the default cache file size to 5MB
- Recommended a minimum cache file size of 2MB to discourage
  applications from specifying values small enough such that
  unreasonably large numbers of cache files are generated
- Allow maxCacheFileSize=C.LENGTH_UNSET, equivalent to setting it
  to MAX_VALUE. This is just for API consistency with other APIs
  we have that accept LENGTH_UNSET

Issue: #4253
PiperOrigin-RevId: 227524233

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

@@ -23,6 +23,7 @@
 import com.google.android.exoplayer2.upstream.FileDataSourceFactory;
 import com.google.android.exoplayer2.upstream.PriorityDataSourceFactory;
 import com.google.android.exoplayer2.upstream.cache.Cache;
+import com.google.android.exoplayer2.upstream.cache.CacheDataSink;
 import com.google.android.exoplayer2.upstream.cache.CacheDataSinkFactory;
 import com.google.android.exoplayer2.upstream.cache.CacheDataSource;
 import com.google.android.exoplayer2.upstream.cache.CacheDataSourceFactory;
@@ -111,7 +112,7 @@ public DownloaderConstructorHelper(
     DataSink.Factory writeDataSinkFactory =
         cacheWriteDataSinkFactory != null
             ? cacheWriteDataSinkFactory
-            : new CacheDataSinkFactory(cache, CacheDataSource.DEFAULT_MAX_CACHE_FILE_SIZE);
+            : new CacheDataSinkFactory(cache, CacheDataSink.DEFAULT_MAX_CACHE_FILE_SIZE);
     onlineCacheDataSourceFactory =
         new CacheDataSourceFactory(
             cache,

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/CacheDataSink.java

@@ -20,6 +20,7 @@
 import com.google.android.exoplayer2.upstream.DataSpec;
 import com.google.android.exoplayer2.upstream.cache.Cache.CacheException;
 import com.google.android.exoplayer2.util.Assertions;
+import com.google.android.exoplayer2.util.Log;
 import com.google.android.exoplayer2.util.ReusableBufferedOutputStream;
 import com.google.android.exoplayer2.util.Util;
 import java.io.File;
@@ -36,8 +37,13 @@
  */
 public final class CacheDataSink implements DataSink {
 
+  /** Default {@code maxCacheFileSize} recommended for caching use cases. */
+  public static final long DEFAULT_MAX_CACHE_FILE_SIZE = 5 * 1024 * 1024;
   /** Default buffer size in bytes. */
-  public static final int DEFAULT_BUFFER_SIZE = 20480;
+  public static final int DEFAULT_BUFFER_SIZE = 20 * 1024;
+
+  private static final long MIN_RECOMMENDED_MAX_CACHE_FILE_SIZE = 2 * 1024 * 1024;
+  private static final String TAG = "CacheDataSink";
 
   private final Cache cache;
   private final long maxCacheFileSize;
@@ -64,28 +70,45 @@ public CacheDataSinkException(IOException cause) {
   }
 
   /**
-   * Constructs a CacheDataSink using the {@link #DEFAULT_BUFFER_SIZE}.
+   * Constructs an instance using {@link #DEFAULT_BUFFER_SIZE}.
    *
    * @param cache The cache into which data should be written.
-   * @param maxCacheFileSize The maximum size of a cache file, in bytes. If the sink is opened for a
-   *     {@link DataSpec} whose size exceeds this value, then the data will be fragmented into
-   *     multiple cache files.
+   * @param maxCacheFileSize The maximum size of a cache file, in bytes. If a request results in
+   *     data being written whose size exceeds this value, then the data will be fragmented into
+   *     multiple cache files. If set to {@link C#LENGTH_UNSET} then no fragmentation will occur.
+   *     Using a small value allows for finer-grained cache eviction policies, at the cost of
+   *     increased overhead both on the cache implementation and the file system. Values under
+   *     {@code (2 * 1024 * 1024)} are not recommended.
    */
   public CacheDataSink(Cache cache, long maxCacheFileSize) {
     this(cache, maxCacheFileSize, DEFAULT_BUFFER_SIZE);
   }
 
   /**
    * @param cache The cache into which data should be written.
-   * @param maxCacheFileSize The maximum size of a cache file, in bytes. If the sink is opened for a
-   *     {@link DataSpec} whose size exceeds this value, then the data will be fragmented into
-   *     multiple cache files.
+   * @param maxCacheFileSize The maximum size of a cache file, in bytes. If a request results in
+   *     data being written whose size exceeds this value, then the data will be fragmented into
+   *     multiple cache files. If set to {@link C#LENGTH_UNSET} then no fragmentation will occur.
+   *     Using a small value allows for finer-grained cache eviction policies, at the cost of
+   *     increased overhead both on the cache implementation and the file system. Values under
+   *     {@code (2 * 1024 * 1024)} are not recommended.
    * @param bufferSize The buffer size in bytes for writing to a cache file. A zero or negative
    *     value disables buffering.
    */
   public CacheDataSink(Cache cache, long maxCacheFileSize, int bufferSize) {
+    Assertions.checkState(
+        maxCacheFileSize > 0 || maxCacheFileSize == C.LENGTH_UNSET,
+        "maxCacheFileSize must be positive or C.LENGTH_UNSET.");
+    if (maxCacheFileSize != C.LENGTH_UNSET
+        && maxCacheFileSize < MIN_RECOMMENDED_MAX_CACHE_FILE_SIZE) {
+      Log.w(
+          TAG,
+          "maxCacheFileSize is below the minimum recommended value of "
+              + MIN_RECOMMENDED_MAX_CACHE_FILE_SIZE
+              + ". This may cause poor cache performance.");
+    }
     this.cache = Assertions.checkNotNull(cache);
-    this.maxCacheFileSize = maxCacheFileSize;
+    this.maxCacheFileSize = maxCacheFileSize == C.LENGTH_UNSET ? Long.MAX_VALUE : maxCacheFileSize;
     this.bufferSize = bufferSize;
     syncFileDescriptor = true;
   }

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/CacheDataSinkFactory.java

@@ -46,5 +46,4 @@ public CacheDataSinkFactory(Cache cache, long maxCacheFileSize, int bufferSize)
   public DataSink createDataSink() {
     return new CacheDataSink(cache, maxCacheFileSize, bufferSize);
   }
-
 }

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/CacheDataSource.java

@@ -45,14 +45,6 @@
  */
 public final class CacheDataSource implements DataSource {
 
-  /**
-   * Default maximum single cache file size.
-   *
-   * @see #CacheDataSource(Cache, DataSource, int)
-   * @see #CacheDataSource(Cache, DataSource, int, long)
-   */
-  public static final long DEFAULT_MAX_CACHE_FILE_SIZE = 2 * 1024 * 1024;
-
   /**
    * Flags controlling the CacheDataSource's behavior. Possible flag values are {@link
    * #FLAG_BLOCK_ON_CACHE}, {@link #FLAG_IGNORE_CACHE_ON_ERROR} and {@link
@@ -163,7 +155,7 @@ public interface EventListener {
    * @param upstream A {@link DataSource} for reading data not in the cache.
    */
   public CacheDataSource(Cache cache, DataSource upstream) {
-    this(cache, upstream, 0, DEFAULT_MAX_CACHE_FILE_SIZE);
+    this(cache, upstream, /* flags= */ 0);
   }
 
   /**
@@ -176,29 +168,11 @@ public CacheDataSource(Cache cache, DataSource upstream) {
    *     and {@link #FLAG_IGNORE_CACHE_FOR_UNSET_LENGTH_REQUESTS}, or 0.
    */
   public CacheDataSource(Cache cache, DataSource upstream, @Flags int flags) {
-    this(cache, upstream, flags, DEFAULT_MAX_CACHE_FILE_SIZE);
-  }
-
-  /**
-   * Constructs an instance with default {@link DataSource} and {@link DataSink} instances for
-   * reading and writing the cache. The sink is configured to fragment data such that no single
-   * cache file is greater than maxCacheFileSize bytes.
-   *
-   * @param cache The cache.
-   * @param upstream A {@link DataSource} for reading data not in the cache.
-   * @param flags A combination of {@link #FLAG_BLOCK_ON_CACHE}, {@link #FLAG_IGNORE_CACHE_ON_ERROR}
-   *     and {@link #FLAG_IGNORE_CACHE_FOR_UNSET_LENGTH_REQUESTS}, or 0.
-   * @param maxCacheFileSize The maximum size of a cache file, in bytes. If the cached data size
-   *     exceeds this value, then the data will be fragmented into multiple cache files. The
-   *     finer-grained this is the finer-grained the eviction policy can be.
-   */
-  public CacheDataSource(Cache cache, DataSource upstream, @Flags int flags,
-      long maxCacheFileSize) {
     this(
         cache,
         upstream,
         new FileDataSource(),
-        new CacheDataSink(cache, maxCacheFileSize),
+        new CacheDataSink(cache, CacheDataSink.DEFAULT_MAX_CACHE_FILE_SIZE),
         flags,
         /* eventListener= */ null);
   }

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/CacheDataSourceFactory.java

@@ -46,20 +46,11 @@ public CacheDataSourceFactory(Cache cache, DataSource.Factory upstreamFactory) {
   /** @see CacheDataSource#CacheDataSource(Cache, DataSource, int) */
   public CacheDataSourceFactory(
       Cache cache, DataSource.Factory upstreamFactory, @CacheDataSource.Flags int flags) {
-    this(cache, upstreamFactory, flags, CacheDataSource.DEFAULT_MAX_CACHE_FILE_SIZE);
-  }
-
-  /** @see CacheDataSource#CacheDataSource(Cache, DataSource, int, long) */
-  public CacheDataSourceFactory(
-      Cache cache,
-      DataSource.Factory upstreamFactory,
-      @CacheDataSource.Flags int flags,
-      long maxCacheFileSize) {
     this(
         cache,
         upstreamFactory,
         new FileDataSourceFactory(),
-        new CacheDataSinkFactory(cache, maxCacheFileSize),
+        new CacheDataSinkFactory(cache, CacheDataSink.DEFAULT_MAX_CACHE_FILE_SIZE),
         flags,
         /* eventListener= */ null);
   }

library/core/src/test/java/com/google/android/exoplayer2/upstream/cache/CacheUtilTest.java

@@ -27,6 +27,7 @@
 import com.google.android.exoplayer2.testutil.FakeDataSource;
 import com.google.android.exoplayer2.testutil.TestUtil;
 import com.google.android.exoplayer2.upstream.DataSpec;
+import com.google.android.exoplayer2.upstream.FileDataSource;
 import com.google.android.exoplayer2.upstream.cache.CacheUtil.CachingCounters;
 import com.google.android.exoplayer2.util.Util;
 import java.io.EOFException;
@@ -341,7 +342,13 @@ public void testRemove() throws Exception {
         cache,
         /* cacheKeyFactory= */ null,
         // Set maxCacheFileSize to 10 to make sure there are multiple spans.
-        new CacheDataSource(cache, dataSource, 0, 10),
+        new CacheDataSource(
+            cache,
+            dataSource,
+            new FileDataSource(),
+            new CacheDataSink(cache, /* maxCacheFileSize= */ 10),
+            /* flags= */ 0,
+            /* eventListener= */ null),
         new byte[CacheUtil.DEFAULT_BUFFER_SIZE_BYTES],
         /* priorityTaskManager= */ null,
         /* priority= */ 0,