MTP Streaming: Readahead Buffer

chrome/browser/media_galleries/fileapi/readahead_file_stream_reader.h

+// Copyright 2014 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 CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_READAHEAD_FILE_STREAM_READER_H_
+#define CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_READAHEAD_FILE_STREAM_READER_H_
+
+#include <queue>
+
+#include "base/memory/weak_ptr.h"
+#include "net/base/io_buffer.h"
+#include "webkit/browser/blob/file_stream_reader.h"
+
+// Wraps an underlying FileStreamReader with a readahead buffer.
+class ReadaheadFileStreamReader
+    : public NON_EXPORTED_BASE(webkit_blob::FileStreamReader) {
+ public:
+  // Takes ownership of |underlying|.
+  ReadaheadFileStreamReader(webkit_blob::FileStreamReader* underlying);

[vandebo (ex-Chrome), 2014/03/03 22:24:54]

explicit

[vandebo (ex-Chrome), 2014/03/03 22:24:54]

nit: underlying -> source ? (throughout)

[tommycli, 2014/03/04 00:39:40]

Done.

[tommycli, 2014/03/04 00:39:40]

Done.

+
+  virtual ~ReadaheadFileStreamReader();
+
+  // FileStreamReader overrides.
+  virtual int Read(net::IOBuffer* buf, int buf_len,
+                   const net::CompletionCallback& callback) OVERRIDE;
+  virtual int64 GetLength(
+      const net::Int64CompletionCallback& callback) OVERRIDE;
+
+ private:
+  // Represents an outstanding read request, waiting for the buffer to be filled
+  // from the underlying FileStreamReader.
+  struct Request {
+    Request(net::IOBuffer* buf, int buf_len,
+            const net::CompletionCallback& callback);
+    ~Request();
+
+    scoped_refptr<net::IOBuffer> buf;
+    const int buf_len;
+    const net::CompletionCallback callback;
+  };
+
+  // Returns the number of bytes consumed from the interal buffer into |buf|.
+  int ConsumeFromBuffer(net::IOBuffer* buf, int buf_len);
+
+  // Reads into a new buffer from the underlying reader. This calls
+  // OnFinishReadFromUnderlying when it completes (either synchronously or
+  // asynchronously).
+  void ReadFromUnderlying();
+  void OnFinishReadFromUnderlying(net::IOBuffer* buffer, int result);
+
+  // This is reset to NULL upon encountering a read error or EOF.
+  scoped_ptr<webkit_blob::FileStreamReader> underlying_;
+
+  // This stores the error or EOF from the underlying FileStreamReader. Its
+  // value is undefined if |underlying_| is non-NULL.
+  int underlying_error_;
+
+  int64 current_offset_;
+
+  // This contains a queue of buffers filled from |underlying_|, waiting to be
+  // consumed.
+  std::queue<scoped_refptr<net::DrainableIOBuffer>> buffers_;
+
+  // The read request waiting for the underlying FileStreamReader to finish
+  // reading and fill a buffer.
+  scoped_ptr<Request> pending_read_;

[vandebo (ex-Chrome), 2014/03/03 22:24:54]

Since you only have a pointer to Request, can you just declare it (class
Request;) or does the templatization require the full declaration?

[tommycli, 2014/03/04 00:39:40]

Done.

+
+  bool underlying_has_pending_read_;
+
+  base::WeakPtrFactory<ReadaheadFileStreamReader> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ReadaheadFileStreamReader);
+};
+
+#endif  // CHROME_BROWSER_MEDIA_GALLERIES_FILEAPI_READAHEAD_FILE_STREAM_READER_H_