Regression: Pages that update their title now get suspended when back…

…grounded

https://bugs.webkit.org/show_bug.cgi?id=270813
rdar://124222280

Reviewed by Ben Nham.

Pages that update their title now get suspended when backgrounded since we've
stopped taking near-suspended assertions on both iOS and macOS. We used to
monitor pages in the background for 8 minutes to see if they update their title
while in the background, if they did, we would let them keep running in the
background.

Since we no longer take near-suspended assertions, we can no longer observe
pages in the background (since they'd get suspended as soon as backgrounded).
To address the issue, we now monitor title changes while in the foreground. If
the page updates its title, we now take a background assertion to let it keep
running after backgrounding.

This is not perfect but this addresses the regression for now. We should
revisit though because this is too permissive. Maybe we only want to consider
title changes without recent user interaction for e.g.

* Source/WebKit/UIProcess/ProcessThrottler.cpp:
(WebKit::ProcessThrottler::ProcessThrottler):
(WebKit::ProcessThrottler::dropNearSuspendedAssertionTimerFired):
(WebKit::m_shouldTakeUIBackgroundAssertion): Deleted.
(WebKit::ProcessThrottler::pageAllowedToRunInTheBackgroundToken): Deleted.
(WebKit::ProcessThrottler::numberOfPagesAllowedToRunInTheBackgroundChanged): Deleted.
* Source/WebKit/UIProcess/ProcessThrottler.h:
* Source/WebKit/UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::didCommitLoadForFrame):
(WebKit::WebPageProxy::didFailLoadForFrame):
(WebKit::WebPageProxy::didReceiveTitleForFrame):
(WebKit::WebPageProxy::resetStateAfterProcessExited):
* Source/WebKit/UIProcess/WebPageProxyInternals.h:

Canonical link: https://commits.webkit.org/275960@main

Source/WebKit/UIProcess/ProcessThrottler.cpp

@@ -123,7 +123,6 @@ ProcessThrottler::ProcessThrottler(AuxiliaryProcessProxy& process, bool shouldTa
     , m_prepareToSuspendTimeoutTimer(RunLoop::main(), this, &ProcessThrottler::prepareToSuspendTimeoutTimerFired)
     , m_dropNearSuspendedAssertionTimer(RunLoop::main(), this, &ProcessThrottler::dropNearSuspendedAssertionTimerFired)
     , m_prepareToDropLastAssertionTimeoutTimer(RunLoop::main(), this, &ProcessThrottler::prepareToDropLastAssertionTimeoutTimerFired)
-    , m_pageAllowedToRunInTheBackgroundCounter([this](RefCounterEvent) { numberOfPagesAllowedToRunInTheBackgroundChanged(); })
     , m_shouldTakeUIBackgroundAssertion(shouldTakeUIBackgroundAssertion)
 {
 }
@@ -362,10 +361,7 @@ void ProcessThrottler::dropNearSuspendedAssertionTimerFired()
     PROCESSTHROTTLER_RELEASE_LOG("dropNearSuspendedAssertionTimerFired: Removing near-suspended process assertion");
     RELEASE_ASSERT(isHoldingNearSuspendedAssertion());
     ASSERT(m_shouldDropNearSuspendedAssertionAfterDelay);
-    if (m_pageAllowedToRunInTheBackgroundCounter.value())
-        PROCESSTHROTTLER_RELEASE_LOG("dropNearSuspendedAssertionTimerFired: Not releasing near-suspended assertion because a page is allowed to run in the background");
-    else
-        clearAssertion();
+    clearAssertion();
 }
 
 void ProcessThrottler::processReadyToSuspend()
@@ -522,25 +518,6 @@ Ref<AuxiliaryProcessProxy> ProcessThrottler::protectedProcess() const
     return m_process.get();
 }
 
-PageAllowedToRunInTheBackgroundCounter::Token ProcessThrottler::pageAllowedToRunInTheBackgroundToken()
-{
-    return m_pageAllowedToRunInTheBackgroundCounter.count();
-}
-
-void ProcessThrottler::numberOfPagesAllowedToRunInTheBackgroundChanged()
-{
-    if (m_pageAllowedToRunInTheBackgroundCounter.value())
-        return;
-
-    if (m_dropNearSuspendedAssertionTimer.isActive())
-        return;
-
-    if (isHoldingNearSuspendedAssertion()) {
-        PROCESSTHROTTLER_RELEASE_LOG("numberOfPagesAllowedToRunInTheBackgroundChanged: Releasing near-suspended assertion");
-        clearAssertion();
-    }
-}
-
 bool ProcessThrottler::isSuspended() const
 {
     return m_isConnectedToProcess && !m_assertion;

Source/WebKit/UIProcess/ProcessThrottler.h

@@ -50,9 +50,6 @@ enum ProcessSuppressionDisabledCounterType { };
 using ProcessSuppressionDisabledCounter = RefCounter<ProcessSuppressionDisabledCounterType>;
 using ProcessSuppressionDisabledToken = ProcessSuppressionDisabledCounter::Token;
 
-enum PageAllowedToRunInTheBackgroundCounterType { };
-using PageAllowedToRunInTheBackgroundCounter = RefCounter<PageAllowedToRunInTheBackgroundCounterType>;
-
 enum class IsSuspensionImminent : bool { No, Yes };
 enum class ProcessThrottleState : uint8_t { Suspended, Background, Foreground };
 enum class ProcessThrottlerActivityType : bool { Background, Foreground };
@@ -124,11 +121,6 @@ class ProcessThrottler : public CanMakeWeakPtr<ProcessThrottler> {
     static bool isValidBackgroundActivity(const ActivityVariant&);
     static bool isValidForegroundActivity(const ActivityVariant&);
 
-    // If any page holds one of these tokens, we will never release the "suspended" assertion which
-    // means that the page will not be suspended when in the background, except if the application
-    // also gets backgrounded.
-    PageAllowedToRunInTheBackgroundCounter::Token pageAllowedToRunInTheBackgroundToken();
-
     using TimedActivity = ProcessThrottlerTimedActivity;
 
     void didConnectToProcess(AuxiliaryProcessProxy&);
@@ -168,7 +160,6 @@ class ProcessThrottler : public CanMakeWeakPtr<ProcessThrottler> {
     void assertionWasInvalidated();
 
     void clearPendingRequestToSuspend();
-    void numberOfPagesAllowedToRunInTheBackgroundChanged();
     void clearAssertion();
 
     class ProcessAssertionCache;
@@ -186,7 +177,6 @@ class ProcessThrottler : public CanMakeWeakPtr<ProcessThrottler> {
     WeakHashSet<Activity> m_backgroundActivities;
     std::optional<uint64_t> m_pendingRequestToSuspendID;
     ProcessThrottleState m_state { ProcessThrottleState::Suspended };
-    PageAllowedToRunInTheBackgroundCounter m_pageAllowedToRunInTheBackgroundCounter;
     bool m_shouldDropNearSuspendedAssertionAfterDelay { false };
     const bool m_shouldTakeUIBackgroundAssertion { false };
     bool m_shouldTakeNearSuspendedAssertion { true };

Source/WebKit/UIProcess/WebPageProxy.cpp

@@ -6221,7 +6221,7 @@ void WebPageProxy::didCommitLoadForFrame(FrameIdentifier frameID, FrameInfoData&
         if (auto* drawingAreaProxy = dynamicDowncast<RemoteLayerTreeDrawingAreaProxy>(*m_drawingArea))
             internals().firstLayerTreeTransactionIdAfterDidCommitLoad = drawingAreaProxy->nextLayerTreeTransactionID();
 #endif
-        internals().pageAllowedToRunInTheBackgroundToken = nullptr;
+        internals().pageAllowedToRunInTheBackgroundActivityDueToTitleChanges = nullptr;
         internals().pageAllowedToRunInTheBackgroundActivityDueToNotifications = nullptr;
     }
 
@@ -6477,7 +6477,7 @@ void WebPageProxy::didFailLoadForFrame(FrameIdentifier frameID, FrameInfoData&&
 
     if (isMainFrame) {
         internals().pageLoadState.didFailLoad(transaction);
-        internals().pageAllowedToRunInTheBackgroundToken = nullptr;
+        internals().pageAllowedToRunInTheBackgroundActivityDueToTitleChanges = nullptr;
         internals().pageAllowedToRunInTheBackgroundActivityDueToNotifications = nullptr;
     }
 
@@ -6654,12 +6654,12 @@ void WebPageProxy::didReceiveTitleForFrame(FrameIdentifier frameID, const String
 
     if (frame->isMainFrame()) {
         internals().pageLoadState.setTitle(transaction, title);
-        if (!isViewVisible() && !frame->title().isNull() && frame->title() != title) {
-            WEBPAGEPROXY_RELEASE_LOG(ViewState, "didReceiveTitleForFrame: This page changes its title in the background and is allowed to run in the background");
+        if (!frame->title().isNull() && frame->title() != title) {
+            WEBPAGEPROXY_RELEASE_LOG(ViewState, "didReceiveTitleForFrame: This page updates its title and is now allowed to run in the background");
             // This page updates its title in the background and is thus able to communicate with
             // the user while in the background. Allow it to run in the background.
-            if (!internals().pageAllowedToRunInTheBackgroundToken)
-                internals().pageAllowedToRunInTheBackgroundToken = process().throttler().pageAllowedToRunInTheBackgroundToken();
+            if (!internals().pageAllowedToRunInTheBackgroundActivityDueToTitleChanges)
+                internals().pageAllowedToRunInTheBackgroundActivityDueToTitleChanges = process().throttler().backgroundActivity("Page updates its title"_s).moveToUniquePtr();
         }
     }
 
@@ -9780,7 +9780,7 @@ void WebPageProxy::resetStateAfterProcessExited(ProcessTerminationReason termina
 
     internals().pageIsUserObservableCount = nullptr;
     internals().visiblePageToken = nullptr;
-    internals().pageAllowedToRunInTheBackgroundToken = nullptr;
+    internals().pageAllowedToRunInTheBackgroundActivityDueToTitleChanges = nullptr;
     internals().pageAllowedToRunInTheBackgroundActivityDueToNotifications = nullptr;
 
     m_hasRunningProcess = false;

Source/WebKit/UIProcess/WebPageProxyInternals.h

@@ -216,7 +216,7 @@ struct WebPageProxy::Internals final : WebPopupMenuProxy::Client
     WebCore::IntRect visibleScrollerThumbRect;
     WebCore::PageIdentifier webPageID;
     WindowKind windowKind { WindowKind::Unparented };
-    PageAllowedToRunInTheBackgroundCounter::Token pageAllowedToRunInTheBackgroundToken;
+    std::unique_ptr<ProcessThrottlerActivity> pageAllowedToRunInTheBackgroundActivityDueToTitleChanges;
     std::unique_ptr<ProcessThrottlerActivity> pageAllowedToRunInTheBackgroundActivityDueToNotifications;
 
     WebPageProxyMessageReceiverRegistration messageReceiverRegistration;