DOMTimer.cpp   [plain text]

/*
 * Copyright (C) 2008, 2014 Apple Inc. All Rights Reserved.
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#include "config.h"
#include "DOMTimer.h"

#include "HTMLPlugInElement.h"
#include "InspectorInstrumentation.h"
#include "Logging.h"
#include "Page.h"
#include "PluginViewBase.h"
#include "ScheduledAction.h"
#include "ScriptExecutionContext.h"
#include "Settings.h"
#include <wtf/HashMap.h>
#include <wtf/MathExtras.h>
#include <wtf/NeverDestroyed.h>
#include <wtf/RandomNumber.h>
#include <wtf/StdLibExtras.h>

#if PLATFORM(IOS_FAMILY)
#include "Chrome.h"
#include "ChromeClient.h"
#include "Frame.h"
#include "WKContentObservation.h"
#include "WKContentObservationInternal.h"
#endif

namespace WebCore {

static const Seconds maxIntervalForUserGestureForwarding { 1_s }; // One second matches Gecko.
static const Seconds minIntervalForNonUserObservableChangeTimers { 1_s }; // Empirically determined to maximize battery life.
static const int maxTimerNestingLevel = 5;

class DOMTimerFireState {
public:
    DOMTimerFireState(ScriptExecutionContext& context, int nestingLevel, const Seconds& nestedTimerInterval)
        : m_context(context)
        , m_nestedTimerInterval(nestedTimerInterval)
        , m_contextIsDocument(is<Document>(m_context))
    {
        // For worker threads, don't update the current DOMTimerFireState.
        // Setting this from workers would not be thread-safe, and its not relevant to current uses.
        if (m_contextIsDocument) {
            m_initialDOMTreeVersion = downcast<Document>(context).domTreeVersion();
            m_previous = current;
            current = this;
        }

        m_context.setTimerNestingLevel(nestingLevel);
    }

    ~DOMTimerFireState()
    {
        if (m_contextIsDocument)
            current = m_previous;
        m_context.setTimerNestingLevel(0);
    }

    Document* contextDocument() const { return m_contextIsDocument ? &downcast<Document>(m_context) : nullptr; }

    const Seconds& nestedTimerInterval() const { return m_nestedTimerInterval; }

    void setScriptMadeUserObservableChanges() { m_scriptMadeUserObservableChanges = true; }
    void setScriptMadeNonUserObservableChanges() { m_scriptMadeNonUserObservableChanges = true; }

    bool scriptMadeNonUserObservableChanges() const { return m_scriptMadeNonUserObservableChanges; }
    bool scriptMadeUserObservableChanges() const
    {
        if (m_scriptMadeUserObservableChanges)
            return true;

        Document* document = contextDocument();
        // To be conservative, we also consider any DOM Tree change to be user observable.
        return document && document->domTreeVersion() != m_initialDOMTreeVersion;
    }

    static DOMTimerFireState* current;

private:
    ScriptExecutionContext& m_context;
    Seconds m_nestedTimerInterval;
    uint64_t m_initialDOMTreeVersion;
    DOMTimerFireState* m_previous;
    bool m_contextIsDocument;
    bool m_scriptMadeNonUserObservableChanges { false };
    bool m_scriptMadeUserObservableChanges { false };
};

DOMTimerFireState* DOMTimerFireState::current = nullptr;

struct NestedTimersMap {
    typedef HashMap<int, Ref<DOMTimer>>::const_iterator const_iterator;

    static NestedTimersMap* instanceForContext(ScriptExecutionContext& context)
    {
        // For worker threads, we don't use NestedTimersMap as doing so would not
        // be thread safe.
        if (is<Document>(context))
            return &instance();
        return nullptr;
    }

    void startTracking()
    {
        // Make sure we start with an empty HashMap. In theory, it is possible the HashMap is not
        // empty if a timer fires during the execution of another timer (may happen with the
        // in-process Web Inspector).
        nestedTimers.clear();
        isTrackingNestedTimers = true;
    }

    void stopTracking()
    {
        isTrackingNestedTimers = false;
        nestedTimers.clear();
    }

    void add(int timeoutId, Ref<DOMTimer>&& timer)
    {
        if (isTrackingNestedTimers)
            nestedTimers.add(timeoutId, WTFMove(timer));
    }

    void remove(int timeoutId)
    {
        if (isTrackingNestedTimers)
            nestedTimers.remove(timeoutId);
    }

    const_iterator begin() const { return nestedTimers.begin(); }
    const_iterator end() const { return nestedTimers.end(); }

private:
    static NestedTimersMap& instance()
    {
        static NeverDestroyed<NestedTimersMap> map;
        return map;
    }

    static bool isTrackingNestedTimers;
    HashMap<int /* timeoutId */, Ref<DOMTimer>> nestedTimers;
};

bool NestedTimersMap::isTrackingNestedTimers = false;

static inline bool shouldForwardUserGesture(Seconds interval)
{
    return UserGestureIndicator::processingUserGesture()
        && interval <= maxIntervalForUserGestureForwarding;
}

static inline RefPtr<UserGestureToken> userGestureTokenToForward(Seconds interval)
{
    if (!shouldForwardUserGesture(interval))
        return nullptr;

    return UserGestureIndicator::currentUserGesture();
}

static inline Seconds currentNestedTimerInterval()
{
    if (DOMTimerFireState::current)
        return DOMTimerFireState::current->nestedTimerInterval();
    return { };
}

DOMTimer::DOMTimer(ScriptExecutionContext& context, std::unique_ptr<ScheduledAction> action, Seconds interval, bool singleShot)
    : SuspendableTimer(context)
    , m_nestingLevel(context.timerNestingLevel())
    , m_action(WTFMove(action))
    , m_originalInterval(interval)
    , m_throttleState(Undetermined)
    , m_currentTimerInterval(intervalClampedToMinimum())
    , m_nestedTimerInterval(currentNestedTimerInterval())
    , m_userGestureTokenToForward(userGestureTokenToForward(m_nestedTimerInterval + m_currentTimerInterval))
{
    RefPtr<DOMTimer> reference = adoptRef(this);

    // Keep asking for the next id until we're given one that we don't already have.
    do {
        m_timeoutId = context.circularSequentialID();
    } while (!context.addTimeout(m_timeoutId, *this));

    if (singleShot)
        startOneShot(m_currentTimerInterval);
    else
        startRepeating(m_currentTimerInterval);
}

DOMTimer::~DOMTimer() = default;

int DOMTimer::install(ScriptExecutionContext& context, std::unique_ptr<ScheduledAction> action, Seconds timeout, bool singleShot)
{
    // DOMTimer constructor passes ownership of the initial ref on the object to the constructor.
    // This reference will be released automatically when a one-shot timer fires, when the context
    // is destroyed, or if explicitly cancelled by removeById. 
    DOMTimer* timer = new DOMTimer(context, WTFMove(action), timeout, singleShot);
#if PLATFORM(IOS_FAMILY)
    if (WKIsObservingDOMTimerScheduling() && is<Document>(context)) {
        bool didDeferTimeout = context.activeDOMObjectsAreSuspended();
        if (!didDeferTimeout && timeout <= 250_ms && singleShot) {
            WKSetObservedContentChange(WKContentIndeterminateChange);
            WebThreadAddObservedDOMTimer(timer);
            LOG_WITH_STREAM(ContentObservation, stream << "DOMTimer::install: registed this timer: (" << timer << ") and observe when it fires.");
        }
    }
#endif

    timer->suspendIfNeeded();
    InspectorInstrumentation::didInstallTimer(context, timer->m_timeoutId, timeout, singleShot);

    // Keep track of nested timer installs.
    if (NestedTimersMap* nestedTimers = NestedTimersMap::instanceForContext(context))
        nestedTimers->add(timer->m_timeoutId, *timer);

    return timer->m_timeoutId;
}

void DOMTimer::removeById(ScriptExecutionContext& context, int timeoutId)
{
    // timeout IDs have to be positive, and 0 and -1 are unsafe to
    // even look up since they are the empty and deleted value
    // respectively
    if (timeoutId <= 0)
        return;

    if (NestedTimersMap* nestedTimers = NestedTimersMap::instanceForContext(context))
        nestedTimers->remove(timeoutId);

    InspectorInstrumentation::didRemoveTimer(context, timeoutId);
    context.removeTimeout(timeoutId);
}

inline bool DOMTimer::isDOMTimersThrottlingEnabled(Document& document) const
{
    auto* page = document.page();
    if (!page)
        return true;
    return page->settings().domTimersThrottlingEnabled();
}

void DOMTimer::updateThrottlingStateIfNecessary(const DOMTimerFireState& fireState)
{
    Document* contextDocument = fireState.contextDocument();
    // We don't throttle timers in worker threads.
    if (!contextDocument)
        return;

    if (UNLIKELY(!isDOMTimersThrottlingEnabled(*contextDocument))) {
        if (m_throttleState == ShouldThrottle) {
            // Unthrottle the timer in case it was throttled before the setting was updated.
            LOG(DOMTimers, "%p - Unthrottling DOM timer because throttling was disabled via settings.", this);
            m_throttleState = ShouldNotThrottle;
            updateTimerIntervalIfNecessary();
        }
        return;
    }

    if (fireState.scriptMadeUserObservableChanges()) {
        if (m_throttleState != ShouldNotThrottle) {
            m_throttleState = ShouldNotThrottle;
            updateTimerIntervalIfNecessary();
        }
    } else if (fireState.scriptMadeNonUserObservableChanges()) {
        if (m_throttleState != ShouldThrottle) {
            m_throttleState = ShouldThrottle;
            updateTimerIntervalIfNecessary();
        }
    }
}

void DOMTimer::scriptDidInteractWithPlugin(HTMLPlugInElement& pluginElement)
{
    if (!DOMTimerFireState::current)
        return;

    if (pluginElement.isUserObservable())
        DOMTimerFireState::current->setScriptMadeUserObservableChanges();
    else
        DOMTimerFireState::current->setScriptMadeNonUserObservableChanges();
}

void DOMTimer::fired()
{
    // Retain this - if the timer is cancelled while this function is on the stack (implicitly and always
    // for one-shot timers, or if removeById is called on itself from within an interval timer fire) then
    // wait unit the end of this function to delete DOMTimer.
    RefPtr<DOMTimer> reference = this;

    ASSERT(scriptExecutionContext());
    ScriptExecutionContext& context = *scriptExecutionContext();

    DOMTimerFireState fireState(context, std::min(m_nestingLevel + 1, maxTimerNestingLevel), m_nestedTimerInterval + m_currentTimerInterval);

    ASSERT(!isSuspended());
    ASSERT(!context.activeDOMObjectsAreSuspended());
    UserGestureIndicator gestureIndicator(m_userGestureTokenToForward);
    // Only the first execution of a multi-shot timer should get an affirmative user gesture indicator.
    m_userGestureTokenToForward = nullptr;

    InspectorInstrumentationCookie cookie = InspectorInstrumentation::willFireTimer(context, m_timeoutId, !repeatInterval());

    // Simple case for non-one-shot timers.
    if (isActive()) {
        if (m_nestingLevel < maxTimerNestingLevel) {
            m_nestingLevel++;
            updateTimerIntervalIfNecessary();
        }

        m_action->execute(context);

        InspectorInstrumentation::didFireTimer(cookie);
        updateThrottlingStateIfNecessary(fireState);

        return;
    }

    context.removeTimeout(m_timeoutId);

#if PLATFORM(IOS_FAMILY)
    auto isObversingLastTimer = false;
    auto shouldBeginObservingChanges = false;
    if (is<Document>(context)) {
        isObversingLastTimer = WebThreadCountOfObservedDOMTimers() == 1;
        shouldBeginObservingChanges = WebThreadContainsObservedDOMTimer(this);
    }

    if (shouldBeginObservingChanges) {
        LOG_WITH_STREAM(ContentObservation, stream << "DOMTimer::fired: start observing (" << this << ") timer callback.");
        WKStartObservingContentChanges();
        WKStartObservingStyleRecalcScheduling();
        WebThreadRemoveObservedDOMTimer(this);
    }
#endif

    // Keep track nested timer installs.
    NestedTimersMap* nestedTimers = NestedTimersMap::instanceForContext(context);
    if (nestedTimers)
        nestedTimers->startTracking();

    m_action->execute(context);

#if PLATFORM(IOS_FAMILY)
    if (shouldBeginObservingChanges) {
        LOG_WITH_STREAM(ContentObservation, stream << "DOMTimer::fired: stop observing (" << this << ") timer callback.");
        WKStopObservingStyleRecalcScheduling();
        WKStopObservingContentChanges();

        auto observedContentChange = WKObservedContentChange();
        // Check if the timer callback triggered either a sync or async style update.
        auto inDeterminedState = observedContentChange == WKContentVisibilityChange || (isObversingLastTimer && observedContentChange == WKContentNoChange);  
        if (inDeterminedState) {
            LOG(ContentObservation, "DOMTimer::fired: in determined state.");
            auto& document = downcast<Document>(context);
            if (auto* page = document.page())
                page->chrome().client().observedContentChange(*document.frame());
        } else if (observedContentChange == WKContentIndeterminateChange) {
            // An async style recalc has been scheduled. Let's observe it.
            LOG(ContentObservation, "DOMTimer::fired: wait until next style recalc fires.");
            WKSetShouldObserveNextStyleRecalc(true);
        }
    }
#endif

    InspectorInstrumentation::didFireTimer(cookie);

    // Check if we should throttle nested single-shot timers.
    if (nestedTimers) {
        for (auto& idAndTimer : *nestedTimers) {
            auto& timer = idAndTimer.value;
            if (timer->isActive() && !timer->repeatInterval())
                timer->updateThrottlingStateIfNecessary(fireState);
        }
        nestedTimers->stopTracking();
    }
}

void DOMTimer::didStop()
{
    // Need to release JS objects potentially protected by ScheduledAction
    // because they can form circular references back to the ScriptExecutionContext
    // which will cause a memory leak.
    m_action = nullptr;
}

void DOMTimer::updateTimerIntervalIfNecessary()
{
    ASSERT(m_nestingLevel <= maxTimerNestingLevel);

    auto previousInterval = m_currentTimerInterval;
    m_currentTimerInterval = intervalClampedToMinimum();
    if (previousInterval == m_currentTimerInterval)
        return;

    if (repeatInterval()) {
        ASSERT(repeatInterval() == previousInterval);
        LOG(DOMTimers, "%p - Updating DOMTimer's repeat interval from %.2f ms to %.2f ms due to throttling.", this, previousInterval.milliseconds(), m_currentTimerInterval.milliseconds());
        augmentRepeatInterval(m_currentTimerInterval - previousInterval);
    } else {
        LOG(DOMTimers, "%p - Updating DOMTimer's fire interval from %.2f ms to %.2f ms due to throttling.", this, previousInterval.milliseconds(), m_currentTimerInterval.milliseconds());
        augmentFireInterval(m_currentTimerInterval - previousInterval);
    }
}

Seconds DOMTimer::intervalClampedToMinimum() const
{
    ASSERT(scriptExecutionContext());
    ASSERT(m_nestingLevel <= maxTimerNestingLevel);

    Seconds interval = std::max(1_ms, m_originalInterval);

    // Only apply throttling to repeating timers.
    if (m_nestingLevel < maxTimerNestingLevel)
        return interval;

    // Apply two throttles - the global (per Page) minimum, and also a per-timer throttle.
    interval = std::max(interval, scriptExecutionContext()->minimumDOMTimerInterval());
    if (m_throttleState == ShouldThrottle)
        interval = std::max(interval, minIntervalForNonUserObservableChangeTimers);
    return interval;
}

Optional<MonotonicTime> DOMTimer::alignedFireTime(MonotonicTime fireTime) const
{
    Seconds alignmentInterval = scriptExecutionContext()->domTimerAlignmentInterval(m_nestingLevel >= maxTimerNestingLevel);
    if (!alignmentInterval)
        return WTF::nullopt;
    
    static const double randomizedProportion = randomNumber();

    // Force alignment to randomizedAlignment fraction of the way between alignemntIntervals, e.g.
    // if alignmentInterval is 10_ms and randomizedAlignment is 0.3 this will align to 3, 13, 23, ...
    Seconds randomizedOffset = alignmentInterval * randomizedProportion;
    MonotonicTime adjustedFireTime = fireTime - randomizedOffset;
    return adjustedFireTime - (adjustedFireTime % alignmentInterval) + alignmentInterval + randomizedOffset;
}

const char* DOMTimer::activeDOMObjectName() const
{
    return "DOMTimer";
}

} // namespace WebCore