Eliminate copies of encoded image data

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

+// Copyright 2016 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 SegmentReader_h
+#define SegmentReader_h
+
+#include "platform/SharedBuffer.h"
+#include "third_party/skia/include/core/SkData.h"
+#include "third_party/skia/include/core/SkRWBuffer.h"
+#include "wtf/Noncopyable.h"
+#include "wtf/PassRefPtr.h"
+#include "wtf/ThreadSafeRefCounted.h"
+
+namespace blink {
+
+// Interface that looks like SharedBuffer. Used by ImageDecoders to use various
+// sources of input including:
+// - SharedBuffer
+//   - for when the caller already has a SharedBuffer
+// - SkData
+//   - for when the caller already has an SkData
+// - SkROBuffer
+//   - for when the caller wants to read/write in different threads
+//
+// Unlike SharedBuffer, this is a read-only interface. There is no way to
+// modify the underlying data source.
+class PLATFORM_EXPORT SegmentReader : public ThreadSafeRefCounted<SegmentReader> {

[scroggo_chromium, 2016/04/05 20:43:04]

This fixed a bug where I sometimes hit an assert in
ThreadRestrictionVerifier::checkSafeToUse() [1]

[1]
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

+    WTF_MAKE_NONCOPYABLE(SegmentReader);
+public:
+    // This version is thread-safe so long as no thread is modifying the
+    // underlying SharedBuffer. This class does not modify it, so that would
+    // mean modifying it in another way.
+    static PassRefPtr<SegmentReader> createFromSharedBuffer(PassRefPtr<SharedBuffer>);
+
+    // These versions use thread-safe input, so they are always thread-safe.
+    static PassRefPtr<SegmentReader> createFromSkData(PassRefPtr<SkData>);
+    static PassRefPtr<SegmentReader> createFromSkROBuffer(PassRefPtr<SkROBuffer>);
+
+    SegmentReader() {}
+    virtual ~SegmentReader() {}
+    virtual size_t size() const = 0;
+    virtual size_t getSomeData(const char*& data, size_t position) const = 0;
+    virtual PassRefPtr<SkData> getAsSkData() const = 0;
+};
+
+} // namespace blink
+#endif // SegmentReader_h