third_party/WebKit/Source/platform/image-decoders/FastSharedBufferReader.h

   1 /*
   2  * Copyright (C) 2015 Google Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
   6  * met:
   7  *
   8  *     * Redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer.
  10  *     * Redistributions in binary form must reproduce the above
  11  * copyright notice, this list of conditions and the following disclaimer
  12  * in the documentation and/or other materials provided with the
  13  * distribution.
  14  *     * Neither the name of Google Inc. nor the names of its
  15  * contributors may be used to endorse or promote products derived from
  16  * this software without specific prior written permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  19  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  20  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  21  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  22  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  23  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  24  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  26  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  27  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  28  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  29  */
  30
  31 #ifndef FastSharedBufferReader_h
  32 #define FastSharedBufferReader_h
  33
  34 #include "platform/PlatformExport.h"
  35 #include "platform/SharedBuffer.h"
  36 #include "wtf/PassRefPtr.h"
  37 #include "wtf/RefPtr.h"
  38
  39 namespace blink {
  40
  41 // This class is used by image decoders to avoid memory consolidation and
  42 // therefore minimizes the cost of memory copying when the decoders
  43 // repeatedly read from a buffer that is continually growing due to network
  44 // traffic.
  45 class PLATFORM_EXPORT FastSharedBufferReader {
  46 public:
  47     FastSharedBufferReader(PassRefPtr<SharedBuffer> data);
  48
  49     // Returns a consecutive buffer that carries the data starting
  50     // at |dataPosition| with |length| bytes.
  51     // This method returns a pointer to a memory segment stored in
  52     // |m_data| if such a consecutive buffer can be found.
  53     // Otherwise copies into |buffer| and returns it.
  54     // Caller must ensure there are enough bytes in |m_data| and |buffer|.
  55     const char* getConsecutiveData(size_t dataPosition, size_t length, char* buffer) const;
  56
  57     // Wraps SharedBuffer::getSomeData().
  58     size_t getSomeData(const char*& someData, size_t dataPosition) const;
  59
  60     // Returns a byte at |dataPosition|.
  61     // Caller must ensure there are enough bytes in |m_data|.
  62     inline char getOneByte(size_t dataPosition) const
  63     {
  64         return *getConsecutiveData(dataPosition, 1, 0);
  65     }
  66
  67     size_t size() const
  68     {
  69         return m_data->size();
  70     }
  71
  72 private:
  73     void getSomeDataInternal(unsigned dataPosition) const;
  74
  75     RefPtr<SharedBuffer> m_data;
  76
  77     // Caches the last segment of |m_data| accessed, since subsequent reads are
  78     // likely to re-access it.
  79     mutable const char* m_segment;
  80     mutable size_t m_segmentLength;
  81
  82     // Data position in |m_data| pointed to by |m_segment|.
  83     mutable size_t m_dataPosition;
  84 };
  85
  86 } // namespace blink
  87
  88 #endif