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// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_IMAGE_DECODERS_FAST_SHARED_BUFFER_READER_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_IMAGE_DECODERS_FAST_SHARED_BUFFER_READER_H_
#include "base/memory/scoped_refptr.h"
#include "third_party/blink/renderer/platform/image-decoders/segment_reader.h"
#include "third_party/blink/renderer/platform/platform_export.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.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();
public:
explicit FastSharedBufferReader(scoped_refptr<SegmentReader> data);
FastSharedBufferReader(const FastSharedBufferReader&) = delete;
FastSharedBufferReader& operator=(const FastSharedBufferReader&) = delete;
~FastSharedBufferReader();
void SetData(scoped_refptr<SegmentReader>);
// Returns a consecutive buffer that carries the data starting
// at |data_position| with |length| bytes.
// This method returns a pointer to a memory segment stored in
// |data_| if such a consecutive buffer can be found.
// Otherwise copies into |buffer| and returns it.
// Caller must ensure there are enough bytes in |data_| and |buffer|.
const char* GetConsecutiveData(size_t data_position,
size_t length,
char* buffer) const;
// Wraps SegmentReader::GetSomeData().
size_t GetSomeData(const char*& some_data, size_t data_position) const;
// Returns a byte at |data_position|.
// Caller must ensure there are enough bytes in |data_|.
inline char GetOneByte(size_t data_position) const {
return *GetConsecutiveData(data_position, 1, nullptr);
}
size_t size() const { return data_->size(); }
// This class caches the last access for faster subsequent reads. This
// method clears that cache in case the SegmentReader has been modified
// (e.g. with MergeSegmentsIntoBuffer on a wrapped SharedBuffer).
void ClearCache();
private:
void GetSomeDataInternal(size_t data_position) const;
scoped_refptr<SegmentReader> data_;
// Caches the last segment of |data_| accessed, since subsequent reads are
// likely to re-access it.
mutable const char* segment_;
mutable size_t segment_length_;
// Data position in |data_| pointed to by |segment_|.
mutable size_t data_position_;
};
} // namespace blink
#endif // THIRD_PARTY_BLINK_RENDERER_PLATFORM_IMAGE_DECODERS_FAST_SHARED_BUFFER_READER_H_
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