Add extensions package to V2.

- Not doing any renaming for now. It'll be easier to wait
  until after the extensions themselves are brought across.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=117438338

library/src/main/java/com/google/android/exoplayer/util/extensions/Buffer.java

+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer.util.extensions;
+
+/**
+ * Base class for {@link Decoder} buffers with flags.
+ */
+public abstract class Buffer {
+
+  /**
+   * Flag for empty input/output buffers that signal that the end of the stream was reached.
+   */
+  public static final int FLAG_END_OF_STREAM = 1;
+  /**
+   * Flag for non-empty input buffers which signals that the decoder must be reset before decoding.
+   */
+  public static final int FLAG_RESET = 2;
+  /**
+   * Flag for non-empty input/output buffers that should only be decoded (not rendered).
+   */
+  public static final int FLAG_DECODE_ONLY = 4;
+
+  private int flags;
+
+  public void reset() {
+    flags = 0;
+  }
+
+  public final void setFlag(int flag) {
+    flags |= flag;
+  }
+
+  public final boolean getFlag(int flag) {
+    return (flags & flag) == flag;
+  }
+
+}

library/src/main/java/com/google/android/exoplayer/util/extensions/Decoder.java

+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer.util.extensions;
+
+/**
+ * A media decoder.
+ *
+ * @param <I> The type of buffer input to the decoder.
+ * @param <O> The type of buffer output from the decoder.
+ * @param <E> The type of exception thrown from the decoder.
+ */
+public interface Decoder<I, O, E extends Exception> {
+
+  /**
+   * Dequeues the next input buffer to be filled and queued to the decoder.
+   *
+   * @return The input buffer, or null if an input buffer isn't available.
+   * @throws E If a decoder error has occurred.
+   */
+  I dequeueInputBuffer() throws E;
+
+  /**
+   * Queues an input buffer to the decoder.
+   *
+   * @param inputBuffer The input buffer.
+   * @throws E If a decoder error has occurred.
+   */
+  void queueInputBuffer(I inputBuffer) throws E;
+
+  /**
+   * Dequeues the next output buffer from the decoder.
+   *
+   * @return The output buffer, or null if an output buffer isn't available.
+   * @throws E If a decoder error has occurred.
+   */
+  O dequeueOutputBuffer() throws E;
+
+  /**
+   * Flushes input/output buffers that have not been dequeued yet and returns ownership of any
+   * dequeued input buffer to the decoder. Flushes any pending output currently in the decoder. The
+   * caller is still responsible for releasing any dequeued output buffers.
+   */
+  void flush();
+
+  /**
+   * Releases the decoder. Must be called when the decoder is no longer needed.
+   */
+  void release();
+
+}

library/src/main/java/com/google/android/exoplayer/util/extensions/InputBuffer.java

+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer.util.extensions;
+
+import com.google.android.exoplayer.SampleHolder;
+
+/**
+ * Input buffer to be decoded by a {@link Decoder}.
+ */
+public class InputBuffer extends Buffer {
+
+  public final SampleHolder sampleHolder;
+
+  public InputBuffer() {
+    sampleHolder = new SampleHolder(SampleHolder.BUFFER_REPLACEMENT_MODE_DIRECT);
+  }
+
+  @Override
+  public void reset() {
+    super.reset();
+    sampleHolder.clearData();
+  }
+
+}

library/src/main/java/com/google/android/exoplayer/util/extensions/OutputBuffer.java

+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer.util.extensions;
+
+/**
+ * Output buffer decoded by a {@link Decoder}.
+ */
+public abstract class OutputBuffer extends Buffer {
+
+  /**
+   * The presentation timestamp for the buffer, in microseconds.
+   */
+  public long timestampUs;
+
+  /**
+   * Releases the output buffer for reuse. Must be called when the buffer is no longer needed.
+   */
+  public abstract void release();
+
+}

library/src/main/java/com/google/android/exoplayer/util/extensions/SimpleDecoder.java

+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer.util.extensions;
+
+import com.google.android.exoplayer.util.Assertions;
+
+import java.util.LinkedList;
+
+/**
+ * Base class for {@link Decoder}s that use their own decode thread.
+ */
+public abstract class SimpleDecoder<I extends InputBuffer, O extends OutputBuffer,
+    E extends Exception> extends Thread implements Decoder<I, O, E> {
+
+  /**
+   * Listener for {@link SimpleDecoder} events.
+   */
+  public interface EventListener<E> {
+
+    /**
+     * Invoked when the decoder encounters an error.
+     *
+     * @param e The corresponding exception.
+     */
+    void onDecoderError(E e);
+
+  }
+
+  private final Object lock;
+  private final LinkedList<I> queuedInputBuffers;
+  private final LinkedList<O> queuedOutputBuffers;
+  private final I[] availableInputBuffers;
+  private final O[] availableOutputBuffers;
+
+  private int availableInputBufferCount;
+  private int availableOutputBufferCount;
+  private I dequeuedInputBuffer;
+
+  private E exception;
+  private boolean flushDecodedOutputBuffer;
+  private boolean released;
+
+  /**
+   * @param inputBuffers An array of nulls that will be used to store references to input buffers.
+   * @param outputBuffers An array of nulls that will be used to store references to output buffers.
+   */
+  protected SimpleDecoder(I[] inputBuffers, O[] outputBuffers) {
+    lock = new Object();
+    queuedInputBuffers = new LinkedList<>();
+    queuedOutputBuffers = new LinkedList<>();
+    availableInputBuffers = inputBuffers;
+    availableInputBufferCount = inputBuffers.length;
+    for (int i = 0; i < availableInputBufferCount; i++) {
+      availableInputBuffers[i] = createInputBuffer();
+    }
+    availableOutputBuffers = outputBuffers;
+    availableOutputBufferCount = outputBuffers.length;
+    for (int i = 0; i < availableOutputBufferCount; i++) {
+      availableOutputBuffers[i] = createOutputBuffer();
+    }
+  }
+
+  /**
+   * Sets the initial size of each input buffer.
+   * <p>
+   * This method should only be called before the decoder is used (i.e. before the first call to
+   * {@link #dequeueInputBuffer()}.
+   *
+   * @param size The required input buffer size.
+   */
+  protected final void setInitialInputBufferSize(int size) {
+    Assertions.checkState(availableInputBufferCount == availableInputBuffers.length);
+    for (int i = 0; i < availableInputBuffers.length; i++) {
+      availableInputBuffers[i].sampleHolder.ensureSpaceForWrite(size);
+    }
+  }
+
+  @Override
+  public final I dequeueInputBuffer() throws E {
+    synchronized (lock) {
+      maybeThrowException();
+      Assertions.checkState(dequeuedInputBuffer == null);
+      if (availableInputBufferCount == 0) {
+        return null;
+      }
+      I inputBuffer = availableInputBuffers[--availableInputBufferCount];
+      inputBuffer.reset();
+      dequeuedInputBuffer = inputBuffer;
+      return inputBuffer;
+    }
+  }
+
+  @Override
+  public final void queueInputBuffer(I inputBuffer) throws E {
+    synchronized (lock) {
+      maybeThrowException();
+      Assertions.checkArgument(inputBuffer == dequeuedInputBuffer);
+      queuedInputBuffers.addLast(inputBuffer);
+      maybeNotifyDecodeLoop();
+      dequeuedInputBuffer = null;
+    }
+  }
+
+  @Override
+  public final O dequeueOutputBuffer() throws E {
+    synchronized (lock) {
+      maybeThrowException();
+      if (queuedOutputBuffers.isEmpty()) {
+        return null;
+      }
+      return queuedOutputBuffers.removeFirst();
+    }
+  }
+
+  /**
+   * Releases an output buffer back to the decoder.
+   *
+   * @param outputBuffer The output buffer being released.
+   */
+  protected void releaseOutputBuffer(O outputBuffer) {
+    synchronized (lock) {
+      availableOutputBuffers[availableOutputBufferCount++] = outputBuffer;
+      maybeNotifyDecodeLoop();
+    }
+  }
+
+  @Override
+  public final void flush() {
+    synchronized (lock) {
+      flushDecodedOutputBuffer = true;
+      if (dequeuedInputBuffer != null) {
+        availableInputBuffers[availableInputBufferCount++] = dequeuedInputBuffer;
+        dequeuedInputBuffer = null;
+      }
+      while (!queuedInputBuffers.isEmpty()) {
+        availableInputBuffers[availableInputBufferCount++] = queuedInputBuffers.removeFirst();
+      }
+      while (!queuedOutputBuffers.isEmpty()) {
+        availableOutputBuffers[availableOutputBufferCount++] = queuedOutputBuffers.removeFirst();
+      }
+    }
+  }
+
+  @Override
+  public void release() {
+    synchronized (lock) {
+      released = true;
+      lock.notify();
+    }
+    try {
+      join();
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+    }
+  }
+
+  /**
+   * Throws a decode exception, if there is one.
+   *
+   * @throws E The decode exception.
+   */
+  private void maybeThrowException() throws E {
+    if (exception != null) {
+      throw exception;
+    }
+  }
+
+  /**
+   * Notifies the decode loop if there exists a queued input buffer and an available output buffer
+   * to decode into.
+   * <p>
+   * Should only be called whilst synchronized on the lock object.
+   */
+  private void maybeNotifyDecodeLoop() {
+    if (canDecodeBuffer()) {
+      lock.notify();
+    }
+  }
+
+  @Override
+  public final void run() {
+    try {
+      while (decode()) {
+        // Do nothing.
+      }
+    } catch (InterruptedException e) {
+      // Not expected.
+      throw new IllegalStateException(e);
+    }
+  }
+
+  private boolean decode() throws InterruptedException {
+    I inputBuffer;
+    O outputBuffer;
+
+    // Wait until we have an input buffer to decode, and an output buffer to decode into.
+    synchronized (lock) {
+      while (!released && !canDecodeBuffer()) {
+        lock.wait();
+      }
+      if (released) {
+        return false;
+      }
+      inputBuffer = queuedInputBuffers.removeFirst();
+      outputBuffer = availableOutputBuffers[--availableOutputBufferCount];
+      flushDecodedOutputBuffer = false;
+    }
+
+    exception = decode(inputBuffer, outputBuffer);
+    if (exception != null) {
+      // Memory barrier to ensure that the decoder exception is visible from the playback thread.
+      synchronized (lock) {}
+      return false;
+    }
+
+    boolean decodeOnly = outputBuffer.getFlag(Buffer.FLAG_DECODE_ONLY);
+    synchronized (lock) {
+      if (flushDecodedOutputBuffer || decodeOnly) {
+        // If a flush occurred while decoding or the buffer was only for decoding (not presentation)
+        // then make the output buffer available again rather than queueing it to be consumed.
+        availableOutputBuffers[availableOutputBufferCount++] = outputBuffer;
+      } else {
+        // Queue the decoded output buffer to be consumed.
+        queuedOutputBuffers.addLast(outputBuffer);
+      }
+      // Make the input buffer available again.
+      availableInputBuffers[availableInputBufferCount++] = inputBuffer;
+    }
+
+    return true;
+  }
+
+  private boolean canDecodeBuffer() {
+    return !queuedInputBuffers.isEmpty() && availableOutputBufferCount > 0;
+  }
+
+  /**
+   * Creates a new input buffer.
+   */
+  protected abstract I createInputBuffer();
+
+  /**
+   * Creates a new output buffer.
+   */
+  protected abstract O createOutputBuffer();
+
+  /**
+   * Decodes the {@code inputBuffer} and stores any decoded output in {@code outputBuffer}.
+   *
+   * @param inputBuffer The buffer to decode.
+   * @param outputBuffer The output buffer to store decoded data. If the flag
+   *     {@link Buffer#FLAG_DECODE_ONLY} is set after this method returns, any output should not be
+   *     presented.
+   * @return A decode exception if an error occurred, or null if the decode was successful.
+   */
+  protected abstract E decode(I inputBuffer, O outputBuffer);
+
+}