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/*
* Copyright (C) 2015 Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef FastSharedBufferReader_h
#define FastSharedBufferReader_h
#include "platform/PlatformExport.h"
#include "platform/SharedBuffer.h"
#include "wtf/Allocator.h"
#include "wtf/Noncopyable.h"
#include "wtf/PassRefPtr.h"
#include "wtf/RefPtr.h"
namespace blink {
// This class is used by image decoders to avoid memory consolidation and
// therefore minimizes the cost of memory copying when the decoders
// repeatedly read from a buffer that is continually growing due to network
// traffic.
class PLATFORM_EXPORT FastSharedBufferReader final {
DISALLOW_NEW();
WTF_MAKE_NONCOPYABLE(FastSharedBufferReader);
public:
FastSharedBufferReader(PassRefPtr<SharedBuffer> data);
void setData(PassRefPtr<SharedBuffer>);
// Returns a consecutive buffer that carries the data starting
// at |dataPosition| with |length| bytes.
// This method returns a pointer to a memory segment stored in
// |m_data| if such a consecutive buffer can be found.
// Otherwise copies into |buffer| and returns it.
// Caller must ensure there are enough bytes in |m_data| and |buffer|.
const char* getConsecutiveData(size_t dataPosition, size_t length, char* buffer) const;
// Wraps SharedBuffer::getSomeData().
size_t getSomeData(const char*& someData, size_t dataPosition) const;
// Returns a byte at |dataPosition|.
// Caller must ensure there are enough bytes in |m_data|.
inline char getOneByte(size_t dataPosition) const
{
return *getConsecutiveData(dataPosition, 1, 0);
}
size_t size() const
{
return m_data->size();
}
// This class caches the last access for faster subsequent reads. This
// method clears that cache in case the SharedBuffer has been modified
// (i.e. with mergeSegmentsIntoBuffer).
void clearCache();
private:
void getSomeDataInternal(size_t dataPosition) const;
RefPtr<SharedBuffer> m_data;
// Caches the last segment of |m_data| accessed, since subsequent reads are
// likely to re-access it.
mutable const char* m_segment;
mutable size_t m_segmentLength;
// Data position in |m_data| pointed to by |m_segment|.
mutable size_t m_dataPosition;
};
} // namespace blink
#endif
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