refactoring decoder interface

media/filters/decoder_base.h

 // Copyright (c) 2010 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.
 
 // A base class that provides the plumbing for a decoder filters.
 
 #ifndef MEDIA_FILTERS_DECODER_BASE_H_
 #define MEDIA_FILTERS_DECODER_BASE_H_
 
 #include <deque>
@@ skipping 34 matching lines @@
   virtual void Initialize(DemuxerStream* demuxer_stream,
                           FilterCallback* callback) {
     this->message_loop()->PostTask(FROM_HERE,
         NewRunnableMethod(this, &DecoderBase::InitializeTask, demuxer_stream,
                           callback));
   }
 
   virtual const MediaFormat& media_format() { return media_format_; }
 
   // Audio or video decoder.
-  virtual void Read(ReadCallback* read_callback) {
+  virtual void FillThisBuffer(scoped_refptr<Output> output) {
     this->message_loop()->PostTask(FROM_HERE,
-        NewRunnableMethod(this, &DecoderBase::ReadTask, read_callback));
+        NewRunnableMethod(this, &DecoderBase::ReadTask, output));
   }
 
  protected:
   DecoderBase()
       : pending_reads_(0),
+        pending_requests_(0),
         expecting_discontinuous_(false),
         state_(kUninitialized) {
   }
 
   virtual ~DecoderBase() {
     DCHECK(state_ == kUninitialized || state_ == kStopped);
     DCHECK(result_queue_.empty());
-    DCHECK(read_queue_.empty());
   }
 
   // This method is called by the derived class from within the OnDecode method.
   // It places an output buffer in the result queue.  It must be called from
   // within the OnDecode method.
   void EnqueueResult(Output* output) {
     DCHECK_EQ(MessageLoop::current(), this->message_loop());
     if (!IsStopped()) {
       result_queue_.push_back(output);
     }
@@ skipping 36 matching lines @@
   void OnDecodeComplete() {
     // Attempt to fulfill a pending read callback and schedule additional reads
     // if necessary.
     bool fulfilled = FulfillPendingRead();
 
     // Issue reads as necessary.
     //
     // Note that it's possible for us to decode but not produce a frame, in
     // which case |pending_reads_| will remain less than |read_queue_| so we
     // need to schedule an additional read.
-    DCHECK_LE(pending_reads_, read_queue_.size());
+    DCHECK_LE(pending_reads_, pending_requests_);
     if (!fulfilled) {
-      DCHECK_LT(pending_reads_, read_queue_.size());
+      DCHECK_LT(pending_reads_, pending_requests_);
       demuxer_stream_->Read(NewCallback(this, &DecoderBase::OnReadComplete));
       ++pending_reads_;
     }
   }
 
  private:
   bool IsStopped() { return state_ == kStopped; }
 
   void OnReadComplete(Buffer* buffer) {
     // Little bit of magic here to get NewRunnableMethod() to generate a Task
     // that holds onto a reference via scoped_refptr<>.
     //
     // TODO(scherkus): change the callback format to pass a scoped_refptr<> or
     // better yet see if we can get away with not using reference counting.
     scoped_refptr<Buffer> buffer_ref = buffer;
     this->message_loop()->PostTask(FROM_HERE,
         NewRunnableMethod(this, &DecoderBase::ReadCompleteTask, buffer_ref));
   }
 
   void StopTask() {
     DCHECK_EQ(MessageLoop::current(), this->message_loop());
 
     // Delegate to the subclass first.
     DoStop();
 
     // Throw away all buffers in all queues.
     result_queue_.clear();
-    STLDeleteElements(&read_queue_);
     state_ = kStopped;
   }
 
   void SeekTask(base::TimeDelta time, FilterCallback* callback) {
     DCHECK_EQ(MessageLoop::current(), this->message_loop());
     DCHECK_EQ(0u, pending_reads_) << "Pending reads should have completed";
-    DCHECK(read_queue_.empty()) << "Read requests should be empty";
+    DCHECK_EQ(0u, pending_requests_) << "Pending requests should be empty";
 
     // Delegate to the subclass first.
     //
     // TODO(scherkus): if we have the strong assertion that there are no pending
     // reads in the entire pipeline when we receive Seek(), subclasses could
     // either flush their buffers here or wait for IsDiscontinuous().  I'm
     // inclined to say that they should still wait for IsDiscontinuous() so they
     // don't have duplicated logic for Seek() and actual discontinuous frames.
     DoSeek(time,
            NewRunnableMethod(this, &DecoderBase::OnSeekComplete, callback));
@@ skipping 33 matching lines @@
     // Delegate to subclass first.
     if (!*success) {
       this->host()->SetError(PIPELINE_ERROR_DECODE);
     } else {
       // TODO(scherkus): subclass shouldn't mutate superclass media format.
       DCHECK(!media_format_.empty()) << "Subclass did not set media_format_";
       state_ = kInitialized;
     }
   }
 
-  void ReadTask(ReadCallback* read_callback) {
+  void ReadTask(scoped_refptr<Output> output) {
     DCHECK_EQ(MessageLoop::current(), this->message_loop());
 
     // TODO(scherkus): should reply with a null operation (empty buffer).
-    if (IsStopped()) {
-      delete read_callback;
+    if (IsStopped())
       return;
-    }
 
-    // Enqueue the callback and attempt to fulfill it immediately.
-    read_queue_.push_back(read_callback);
+    ++pending_requests_;
+
+    // Try to fulfill it immediately.
     if (FulfillPendingRead())
       return;
 
     // Since we can't fulfill a read request now then submit a read
     // request to the demuxer stream.
     demuxer_stream_->Read(NewCallback(this, &DecoderBase::OnReadComplete));
     ++pending_reads_;
   }
 
   void ReadCompleteTask(scoped_refptr<Buffer> buffer) {
@@ skipping 14 matching lines @@
     // Decode the frame right away.
     DoDecode(buffer);
   }
 
   // Attempts to fulfill a single pending read by dequeuing a buffer and read
   // callback pair and executing the callback.
   //
   // Return true if one read request is fulfilled.
   bool FulfillPendingRead() {
     DCHECK_EQ(MessageLoop::current(), this->message_loop());
-    if (read_queue_.empty() || result_queue_.empty()) {
+    if (!pending_requests_ || result_queue_.empty()) {
       return false;
     }
 
     // Dequeue a frame and read callback pair.
     scoped_refptr<Output> output = result_queue_.front();
-    scoped_ptr<ReadCallback> read_callback(read_queue_.front());
     result_queue_.pop_front();
-    read_queue_.pop_front();
 
     // Execute the callback!
-    read_callback->Run(output);
+    --pending_requests_;
+    Decoder::fill_buffer_done_callback()->Run(output);
     return true;
   }
 
   // Tracks the number of asynchronous reads issued to |demuxer_stream_|.
   // Using size_t since it is always compared against deque::size().
   size_t pending_reads_;
+  // Tracks the number of asynchronous reads issued from renderer.
+  size_t pending_requests_;
 
   // A flag used for debugging that we expect our next read to be discontinuous.
   bool expecting_discontinuous_;
 
   // Pointer to the demuxer stream that will feed us compressed buffers.
   scoped_refptr<DemuxerStream> demuxer_stream_;
 
   // Queue of decoded samples produced in the OnDecode() method of the decoder.
   // Any samples placed in this queue will be assigned to the OutputQueue
   // buffers once the OnDecode() method returns.
   //
   // TODO(ralphl): Eventually we want to have decoders get their destination
   // buffer from the OutputQueue and write to it directly.  Until we change
   // from the Assignable buffer to callbacks and renderer-allocated buffers,
   // we need this extra queue.
   typedef std::deque<scoped_refptr<Output> > ResultQueue;
   ResultQueue result_queue_;
 
-  // Queue of callbacks supplied by the renderer through the Read() method.
-  typedef std::deque<ReadCallback*> ReadQueue;
-  ReadQueue read_queue_;
-
   // Pause callback.
   scoped_ptr<FilterCallback> pause_callback_;
 
   // Simple state tracking variable.
   enum State {
     kUninitialized,
     kInitialized,
     kStopped,
   };
   State state_;
 
   DISALLOW_COPY_AND_ASSIGN(DecoderBase);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_DECODER_BASE_H_