Source/core/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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*/
#include "config.h"

#include "core/platform/graphics/Canvas2DLayerManager.h"

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

using blink::WebThread;

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

namespace WebCore {

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) {
        blink::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);
    blink::Platform::current()->currentThread()->removeTaskObserver(this);
    m_taskObserverActive = false;
    for (Canvas2DLayerBridge* layer = m_layerList.head(); layer; layer = layer->next())
        layer->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
        }
    } else
        addLayerToList(layer);

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

void Canvas2DLayerManager::addLayerToList(Canvas2DLayerBridge* layer)
{
    ASSERT(!isInList(layer));
    m_bytesAllocated += layer->bytesAllocated();
    m_layerList.push(layer); // Set as MRU
}

void Canvas2DLayerManager::layerAllocatedStorageChanged(Canvas2DLayerBridge* layer, intptr_t deltaBytes)
{
    if (!isInList(layer))
        addLayerToList(layer);
    else {
        ASSERT((intptr_t)m_bytesAllocated + deltaBytes >= 0);
        m_bytesAllocated = (intptr_t)m_bytesAllocated + deltaBytes;
    }
    if (deltaBytes > 0)
        freeMemoryIfNecessary();
}

void Canvas2DLayerManager::layerToBeDestroyed(Canvas2DLayerBridge* layer)
{
    if (isInList(layer))
        removeLayerFromList(layer);
}

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

        // Pass 2: Flush canvases
        Canvas2DLayerBridge* leastRecentlyUsedLayer = m_layerList.tail();
        while (m_bytesAllocated > m_targetBytesAllocated && leastRecentlyUsedLayer) {
            leastRecentlyUsedLayer->flush();
            leastRecentlyUsedLayer->freeMemoryIfPossible(~0);
            removeLayerFromList(leastRecentlyUsedLayer);
            leastRecentlyUsedLayer = m_layerList.tail();
        }
    }
}

void Canvas2DLayerManager::removeLayerFromList(Canvas2DLayerBridge* layer)
{
    ASSERT(isInList(layer));
    m_bytesAllocated -= layer->bytesAllocated();
    m_layerList.remove(layer);
    layer->setNext(0);
    layer->setPrev(0);
}

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

}