Source/platform/graphics/Canvas2DLayerManager.cpp

/*
Copyright (C) 2012 Google Inc. All rights reserved.

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    documentation and/or other materials provided with the distribution.

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DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
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(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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*/
#include "config.h"

#include "platform/graphics/Canvas2DLayerManager.h"

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

namespace {

enum {
    DefaultMaxBytesAllocated = 64*1024*1024,
    DefaultTargetBytesAllocated = 16*1024*1024,
};

} // unnamed namespace

namespace blink {

Canvas2DLayerManager::Canvas2DLayerManager()
    : m_bytesAllocated(0)
    , m_maxBytesAllocated(DefaultMaxBytesAllocated)
    , m_targetBytesAllocated(DefaultTargetBytesAllocated)
    , m_taskObserverActive(false)
{
}

Canvas2DLayerManager::~Canvas2DLayerManager()
{
    ASSERT(!m_bytesAllocated);
    ASSERT(!m_layerList.head());
    ASSERT(!m_taskObserverActive);
}

void Canvas2DLayerManager::init(size_t maxBytesAllocated, size_t targetBytesAllocated)
{
    ASSERT(maxBytesAllocated >= targetBytesAllocated);
    m_maxBytesAllocated = maxBytesAllocated;
    m_targetBytesAllocated = targetBytesAllocated;
    if (m_taskObserverActive) {
        Platform::current()->currentThread()->removeTaskObserver(this);
        m_taskObserverActive = false;
    }
}

Canvas2DLayerManager& Canvas2DLayerManager::get()
{
    DEFINE_STATIC_LOCAL(Canvas2DLayerManager, manager, ());
    return manager;
}

void Canvas2DLayerManager::willProcessTask()
{
}

void Canvas2DLayerManager::didProcessTask()
{
    // Called after the script action for the current frame has been processed.
    ASSERT(m_taskObserverActive);
    Platform::current()->currentThread()->removeTaskObserver(this);
    m_taskObserverActive = false;
    Canvas2DLayerBridge* layer = m_layerList.head();
    while (layer) {
        Canvas2DLayerBridge* currentLayer = layer;
        // must increment iterator before calling limitPendingFrames, which
        // may result in the layer being removed from the list.
        layer = layer->next();
        currentLayer->limitPendingFrames();
    }
}

void Canvas2DLayerManager::layerDidDraw(Canvas2DLayerBridge* layer)
{
    if (isInList(layer)) {
        if (layer != m_layerList.head()) {
            m_layerList.remove(layer);
            m_layerList.push(layer); // Set as MRU
        }
    }

    if (!m_taskObserverActive) {
        m_taskObserverActive = true;
        // Schedule a call to didProcessTask() after completion of the current script task.
        Platform::current()->currentThread()->addTaskObserver(this);
    }
}

void Canvas2DLayerManager::layerTransientResourceAllocationChanged(Canvas2DLayerBridge* layer, intptr_t deltaBytes)
{
    ASSERT((intptr_t)m_bytesAllocated + deltaBytes >= 0);
    m_bytesAllocated = (intptr_t)m_bytesAllocated + deltaBytes;
    if (!isInList(layer) && layer->hasTransientResources()) {
        m_layerList.push(layer);
    } else if (isInList(layer) && !layer->hasTransientResources()) {
        m_layerList.remove(layer);
        layer->setNext(0);
        layer->setPrev(0);
    }

    if (deltaBytes > 0)
        freeMemoryIfNecessary();
}

void Canvas2DLayerManager::freeMemoryIfNecessary()
{
    if (m_bytesAllocated >= m_maxBytesAllocated) {
        // Pass 1: Free memory from caches
        Canvas2DLayerBridge* layer = m_layerList.tail(); // LRU
        while (layer && m_bytesAllocated > m_targetBytesAllocated) {
            Canvas2DLayerBridge* currentLayer = layer;
            layer = layer->prev();
            currentLayer->freeMemoryIfPossible(m_bytesAllocated - m_targetBytesAllocated);
            ASSERT(isInList(currentLayer) == currentLayer->hasTransientResources());
        }

        // Pass 2: Flush canvases
        layer = m_layerList.tail();
        while (m_bytesAllocated > m_targetBytesAllocated && layer) {
            Canvas2DLayerBridge* currentLayer = layer;
            layer = layer->prev();
            currentLayer->flush();
            currentLayer->freeMemoryIfPossible(m_bytesAllocated - m_targetBytesAllocated);
            ASSERT(isInList(currentLayer) == currentLayer->hasTransientResources());
        }
    }
}

bool Canvas2DLayerManager::isInList(Canvas2DLayerBridge* layer) const
{
    return layer->prev() || m_layerList.head() == layer;
}

} // namespace blink