Source/platform/graphics/DiscardablePixelRef.cpp

/*
 * Copyright (C) 2013 Google Inc. All rights reserved.
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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#include "config.h"
#include "platform/graphics/DiscardablePixelRef.h"

#include "public/platform/Platform.h"
#include "wtf/StdLibExtras.h"

namespace WebCore {

namespace {

// URI label for a discardable SkPixelRef.
const char labelDiscardable[] = "discardable";

} // namespace


bool DiscardablePixelRefAllocator::allocPixelRef(SkBitmap* dst, SkColorTable* ctable)
{
    // It should not be possible to have a non-null color table in Blink.
    ASSERT(!ctable);

    Sk64 size = dst->getSize64();
    if (size.isNeg() || !size.is32())
        return false;

    SkAutoTUnref<DiscardablePixelRef> pixelRef(new DiscardablePixelRef(adoptPtr(new SkMutex())));
    if (pixelRef->allocAndLockDiscardableMemory(size.get32())) {
        pixelRef->setURI(labelDiscardable);
        dst->setPixelRef(pixelRef.get());
        // This method is only called when a DiscardablePixelRef is created to back a SkBitmap.
        // It is necessary to lock this SkBitmap to have a valid pointer to pixels. Otherwise,
        // this SkBitmap could be assigned to another SkBitmap and locking/unlocking the other
        // SkBitmap will make this one losing its pixels.
        dst->lockPixels();
        return true;
    }

    // Fallback to heap allocator if discardable memory is not available.
    return dst->allocPixels();
}

DiscardablePixelRef::DiscardablePixelRef(PassOwnPtr<SkMutex> mutex)
    : SkPixelRef(mutex.get())
    , m_lockedMemory(0)
    , m_mutex(mutex)
{
}

DiscardablePixelRef::~DiscardablePixelRef()
{
}

bool DiscardablePixelRef::allocAndLockDiscardableMemory(size_t bytes)
{
    m_discardable = adoptPtr(blink::Platform::current()->allocateAndLockDiscardableMemory(bytes));
    if (m_discardable) {
        m_lockedMemory = m_discardable->data();
        return true;
    }
    return false;
}

void* DiscardablePixelRef::onLockPixels(SkColorTable** ctable)
{
    if (!m_lockedMemory && m_discardable->lock())
        m_lockedMemory = m_discardable->data();

    *ctable = 0;
    return m_lockedMemory;
}

void DiscardablePixelRef::onUnlockPixels()
{
    if (m_lockedMemory)
        m_discardable->unlock();
    m_lockedMemory = 0;
}

bool DiscardablePixelRef::isDiscardable(SkPixelRef* pixelRef)
{
    // FIXME: DEFINE_STATIC_LOCAL is not thread safe.
    // ImageDecodingStore provides the synchronization for this.
    DEFINE_STATIC_LOCAL(const SkString, discardable, (labelDiscardable));
    return pixelRef && pixelRef->getURI() && discardable.equals(pixelRef->getURI());
}

} // namespace WebCore