media/formats/common/offset_byte_queue.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MEDIA_FORMATS_COMMON_OFFSET_BYTE_QUEUE_H_
   6 #define MEDIA_FORMATS_COMMON_OFFSET_BYTE_QUEUE_H_
   7
   8 #include "base/basictypes.h"
   9 #include "media/base/byte_queue.h"
  10 #include "media/base/media_export.h"
  11
  12 namespace media {
  13
  14 // A wrapper around a ByteQueue which maintains a notion of a
  15 // monotonically-increasing offset. All buffer access is done by passing these
  16 // offsets into this class, going some way towards preventing the proliferation
  17 // of many different meanings of "offset", "head", etc.
  18 class MEDIA_EXPORT OffsetByteQueue {
  19  public:
  20   OffsetByteQueue();
  21   ~OffsetByteQueue();
  22
  23   // These work like their underlying ByteQueue counterparts.
  24   void Reset();
  25   void Push(const uint8* buf, int size);
  26   void Peek(const uint8** buf, int* size);
  27   void Pop(int count);
  28
  29   // Sets |buf| to point at the first buffered byte corresponding to |offset|,
  30   // and |size| to the number of bytes available starting from that offset.
  31   //
  32   // It is an error if the offset is before the current head. It's not an error
  33   // if the current offset is beyond tail(), but you will of course get back
  34   // a null |buf| and a |size| of zero.
  35   void PeekAt(int64 offset, const uint8** buf, int* size);
  36
  37   // Marks the bytes up to (but not including) |max_offset| as ready for
  38   // deletion. This is relatively inexpensive, but will not necessarily reduce
  39   // the resident buffer size right away (or ever).
  40   //
  41   // Returns true if the full range of bytes were successfully trimmed,
  42   // including the case where |max_offset| is less than the current head.
  43   // Returns false if |max_offset| > tail() (although all bytes currently
  44   // buffered are still cleared).
  45   bool Trim(int64 max_offset);
  46
  47   // The head and tail positions, in terms of the file's absolute offsets.
  48   // tail() is an exclusive bound.
  49   int64 head() { return head_; }
  50   int64 tail() { return head_ + size_; }
  51
  52  private:
  53   // Synchronize |buf_| and |size_| with |queue_|.
  54   void Sync();
  55
  56   ByteQueue queue_;
  57   const uint8* buf_;
  58   int size_;
  59   int64 head_;
  60
  61   DISALLOW_COPY_AND_ASSIGN(OffsetByteQueue);
  62 };
  63
  64 }  // namespace media
  65
  66 #endif  // MEDIA_FORMATS_COMMON_OFFSET_BYTE_QUEUE_H_