Replace FFmpegDemuxer thread per element with base::TaskScheduler.

media/filters/blocking_url_protocol.h

 // Copyright (c) 2012 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.
 
 #ifndef MEDIA_FILTERS_BLOCKING_URL_PROTOCOL_H_
 #define MEDIA_FILTERS_BLOCKING_URL_PROTOCOL_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
 #include "base/macros.h"
+#include "base/synchronization/lock.h"
 #include "base/synchronization/waitable_event.h"
 #include "media/filters/ffmpeg_glue.h"
 
 namespace media {
 
 class DataSource;
 
 // An implementation of FFmpegURLProtocol that blocks until the underlying
-// asynchronous DataSource::Read() operation completes.
+// asynchronous DataSource::Read() operation completes. Generally constructed on
+// the media thread and used by ffmpeg through the AVIO interface from a
+// sequenced blocking pool.
 class MEDIA_EXPORT BlockingUrlProtocol : public FFmpegURLProtocol {
  public:
   // Implements FFmpegURLProtocol using the given |data_source|. |error_cb| is
   // fired any time DataSource::Read() returns an error.
-  //
-  // TODO(scherkus): After all blocking operations are isolated on a separate
-  // thread we should be able to eliminate |error_cb|.
   BlockingUrlProtocol(DataSource* data_source, const base::Closure& error_cb);
   virtual ~BlockingUrlProtocol();
 
   // Aborts any pending reads by returning a read error. After this method
-  // returns all subsequent calls to Read() will immediately fail.
+  // returns all subsequent calls to Read() will immediately fail. May be called
+  // from any thread and upon return ensures no further use of |data_source_|.
   void Abort();
 
   // FFmpegURLProtocol implementation.
   int Read(int size, uint8_t* data) override;
   bool GetPosition(int64_t* position_out) override;
   bool SetPosition(int64_t position) override;
   bool GetSize(int64_t* size_out) override;
   bool IsStreaming() override;
 
  private:
   // Sets |last_read_bytes_| and signals the blocked thread that the read
   // has completed.
   void SignalReadCompleted(int size);
 
+  // |data_source_lock_| allows Abort() to be called from any thread and stop
+  // all outstanding access to |data_source_|. Typically Abort() is called from
+  // the media thread while ffmpeg is operating on another thread.
+  base::Lock data_source_lock_;
   DataSource* data_source_;
+
   base::Closure error_cb_;
+  const bool is_streaming_;
 
   // Used to unblock the thread during shutdown and when reads complete.
   base::WaitableEvent aborted_;
   base::WaitableEvent read_complete_;
 
   // Cached number of bytes last read from the data source.
   int last_read_bytes_;
 
   // Cached position within the data source.
   int64_t read_position_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(BlockingUrlProtocol);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_BLOCKING_URL_PROTOCOL_H_