Splitting media filter's Initialize() into Create() + callback and Seek() + callback.

media/base/filters.h

 // Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Filters are connected in a strongly typed manner, with downstream filters
 // always reading data from upstream filters.  Upstream filters have no clue
 // who is actually reading from them, and return the results via callbacks.
 //
 //                         DemuxerStream(Video) <- VideoDecoder <- VideoRenderer
 // DataSource <- Demuxer <
@@ skipping 35 matching lines @@
 // knock off of MSVC's __uuidof() operator.
 enum FilterType {
   FILTER_DATA_SOURCE,
   FILTER_DEMUXER,
   FILTER_AUDIO_DECODER,
   FILTER_VIDEO_DECODER,
   FILTER_AUDIO_RENDERER,
   FILTER_VIDEO_RENDERER
 };
 
+// Used for completing asynchronous methods.
+typedef Callback0::Type FilterCallback;
 
 class MediaFilter : public base::RefCountedThreadSafe<MediaFilter> {
  public:
   MediaFilter() : host_(NULL), message_loop_(NULL) {}
 
   // Sets the private member |host_|. This is the first method called by
   // the FilterHost after a filter is created.  The host holds a strong
   // reference to the filter.  The reference held by the host is guaranteed
   // to be released before the host object is destroyed by the pipeline.
   virtual void set_host(FilterHost* host) {
@@ skipping 21 matching lines @@
   }
 
   // The pipeline is being stopped either as a result of an error or because
   // the client called Stop().
   virtual void Stop() = 0;
 
   // The pipeline playback rate has been changed.  Filters may implement this
   // method if they need to respond to this call.
   virtual void SetPlaybackRate(float playback_rate) {}
 
-  // The pipeline is seeking to the specified time.  Filters may implement
-  // this method if they need to respond to this call.
-  virtual void Seek(base::TimeDelta time) {}
+  // Carry out any actions required to seek to the given time, executing the
+  // callback upon completion.
+  virtual void Seek(base::TimeDelta time, FilterCallback* callback) {
+    scoped_ptr<FilterCallback> seek_callback(callback);
+    if (seek_callback.get()) {
+      seek_callback->Run();
+    }
+  }
 
  protected:
   // Only allow scoped_refptr<> to delete filters.
   friend class base::RefCountedThreadSafe<MediaFilter>;
   virtual ~MediaFilter() {}
 
   FilterHost* host() const { return host_; }
   MessageLoop* message_loop() const { return message_loop_; }
 
  private:
@@ skipping 11 matching lines @@
   }
 
   static bool IsMediaFormatSupported(const MediaFormat& media_format) {
     std::string mime_type;
     return (media_format.GetAsString(MediaFormat::kMimeType, &mime_type) &&
             mime_type == mime_type::kURL);
   }
 
   static const size_t kReadError = static_cast<size_t>(-1);
 
-  // Initializes this filter, returns true if successful, false otherwise.
-  virtual bool Initialize(const std::string& url) = 0;
+  // Initialize a DataSource for the given URL, executing the callback upon
+  // completion.
+  virtual void Initialize(const std::string& url, FilterCallback* callback) = 0;
 
   // Returns the MediaFormat for this filter.
   virtual const MediaFormat& media_format() = 0;
 
   // Read the given amount of bytes into data, returns the number of bytes read
   // if successful, kReadError otherwise.
   virtual size_t Read(uint8* data, size_t size) = 0;
 
   // Returns true and the current file position for this file, false if the
   // file position could not be retrieved.
@@ skipping 16 matching lines @@
   static const FilterType filter_type() {
     return FILTER_DEMUXER;
   }
 
   static bool IsMediaFormatSupported(const MediaFormat& media_format) {
     std::string mime_type;
     return (media_format.GetAsString(MediaFormat::kMimeType, &mime_type) &&
             mime_type == mime_type::kApplicationOctetStream);
   }
 
-  // Initializes this filter, returns true if successful, false otherwise.
-  virtual bool Initialize(DataSource* data_source) = 0;
+  // Initialize a Demuxer with the given DataSource, executing the callback upon
+  // completion.
+  virtual void Initialize(DataSource* data_source,
+                          FilterCallback* callback) = 0;
 
   // Returns the number of streams available
   virtual size_t GetNumberOfStreams() = 0;
 
   // Returns the stream for the given index, NULL otherwise
   virtual scoped_refptr<DemuxerStream> GetStream(int stream_id) = 0;
 };
 
 
 class DemuxerStream : public base::RefCountedThreadSafe<DemuxerStream> {
@@ skipping 35 matching lines @@
 class VideoDecoder : public MediaFilter {
  public:
   static const FilterType filter_type() {
     return FILTER_VIDEO_DECODER;
   }
 
   static const char* major_mime_type() {
     return mime_type::kMajorTypeVideo;
   }
 
-  // Initializes this filter, returns true if successful, false otherwise.
-  virtual bool Initialize(DemuxerStream* demuxer_stream) = 0;
+  // Initialize a VideoDecoder with the given DemuxerStream, executing the
+  // callback upon completion.
+  virtual void Initialize(DemuxerStream* stream, FilterCallback* callback) = 0;
 
   // Returns the MediaFormat for this filter.
   virtual const MediaFormat& media_format() = 0;
 
   // Schedules a read.  Decoder takes ownership of the callback.
   //
   // TODO(scherkus): switch Read() callback to scoped_refptr<>.
   virtual void Read(Callback1<VideoFrame*>::Type* read_callback) = 0;
 };
 
 
 class AudioDecoder : public MediaFilter {
  public:
   static const FilterType filter_type() {
     return FILTER_AUDIO_DECODER;
   }
 
   static const char* major_mime_type() {
     return mime_type::kMajorTypeAudio;
   }
 
-  // Initializes this filter, returns true if successful, false otherwise.
-  virtual bool Initialize(DemuxerStream* demuxer_stream) = 0;
+  // Initialize a AudioDecoder with the given DemuxerStream, executing the
+  // callback upon completion.
+  virtual void Initialize(DemuxerStream* stream, FilterCallback* callback) = 0;
 
   // Returns the MediaFormat for this filter.
   virtual const MediaFormat& media_format() = 0;
 
   // Schedules a read.  Decoder takes ownership of the callback.
   //
   // TODO(scherkus): switch Read() callback to scoped_refptr<>.
   virtual void Read(Callback1<Buffer*>::Type* read_callback) = 0;
 };
 
 
 class VideoRenderer : public MediaFilter {
  public:
   static const FilterType filter_type() {
     return FILTER_VIDEO_RENDERER;
   }
 
   static const char* major_mime_type() {
     return mime_type::kMajorTypeVideo;
   }
 
-  // Initializes this filter, returns true if successful, false otherwise.
-  virtual bool Initialize(VideoDecoder* decoder) = 0;
+  // Initialize a VideoRenderer with the given VideoDecoder, executing the
+  // callback upon completion.
+  virtual void Initialize(VideoDecoder* decoder, FilterCallback* callback) = 0;
 };
 
 
 class AudioRenderer : public MediaFilter {
  public:
   static const FilterType filter_type() {
     return FILTER_AUDIO_RENDERER;
   }
 
   static const char* major_mime_type() {
     return mime_type::kMajorTypeAudio;
   }
 
-  // Initializes this filter, returns true if successful, false otherwise.
-  virtual bool Initialize(AudioDecoder* decoder) = 0;
+  // Initialize a AudioRenderer with the given AudioDecoder, executing the
+  // callback upon completion.
+  virtual void Initialize(AudioDecoder* decoder, FilterCallback* callback) = 0;
 
   // Sets the output volume.
   virtual void SetVolume(float volume) = 0;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_FILTERS_H_