Cap the duration of EventLoop::run in the main thread

https://bugs.webkit.org/show_bug.cgi?id=260112 Reviewed by Yusuke Suzuki. Cap the duration of EventLoop::run in the main thread using the same time limit ThreadTimers::sharedTimerFiredInternal() uses. * LayoutTests/fast/eventloop/queue-task-event-loop-starvation-expected.txt: Added. * LayoutTests/fast/eventloop/queue-task-event-loop-starvation.html: Added. * Source/WebCore/dom/EventLoop.cpp: (WebCore::EventLoop::run): * Source/WebCore/dom/EventLoop.h: * Source/WebCore/dom/WindowEventLoop.cpp: (WebCore::WindowEventLoop::didReachTimeToRun): * Source/WebCore/platform/ThreadTimers.cpp: * Source/WebCore/platform/ThreadTimers.h: Canonical link: https://commits.webkit.org/266896@main
WebKit · Aug 15, 2023 · 9c58823 · 9c58823
1 parent f8811c9
commit 9c58823
Show file tree

Hide file tree

Showing 7 changed files with 71 additions and 7 deletions.
diff --git a/LayoutTests/fast/eventloop/queue-task-event-loop-starvation-expected.txt b/LayoutTests/fast/eventloop/queue-task-event-loop-starvation-expected.txt
@@ -0,0 +1,10 @@
+This tests repeated queueing of event loop tasks. Event loop should eventually yield to the run loop.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS executedTaskCount < 100 is true
+PASS successfullyParsed is true
+
+TEST COMPLETE
+
diff --git a/LayoutTests/fast/eventloop/queue-task-event-loop-starvation.html b/LayoutTests/fast/eventloop/queue-task-event-loop-starvation.html
@@ -0,0 +1,45 @@
+<!DOCTYPE html>
+<html>
+<body>
+<script src="../../resources/js-test.js"></script>
+<script>
+
+description('This tests repeated queueing of event loop tasks. Event loop should eventually yield to the run loop.');
+
+if (!window.internals)
+    testFailed('This test relies on window.internals');
+else {
+    jsTestIsAsync = true;
+    logs = [];
+}
+
+function slowFunction(duration)
+{
+    const startTime = performance.now();
+    while (performance.now() < startTime + duration);
+}
+
+let executedTaskCount = 0;
+function scheduleSlowTask()
+{
+    internals.queueTask("DOMManipulation", () => {
+        slowFunction(10);
+        ++executedTaskCount;
+    });
+}
+
+function runTest()
+{
+    setTimeout(() => {
+        shouldBeTrue('executedTaskCount < 100');
+        finishJSTest();
+    }, 100);
+    for (let i = 0; i < 100; ++i)
+        scheduleSlowTask();
+}
+
+onload = runTest;
+
+</script>
+</body>
+</html>
diff --git a/Source/WebCore/dom/EventLoop.cpp b/Source/WebCore/dom/EventLoop.cpp
@@ -295,7 +295,7 @@ void EventLoop::scheduleToRunIfNeeded()
     scheduleToRun();
 }
 
-void EventLoop::run()
+void EventLoop::run(std::optional<ApproximateTime> deadline)
 {
     m_isScheduledToRun = false;
     bool didPerformMicrotaskCheckpoint = false;
@@ -304,12 +304,14 @@ void EventLoop::run()
         auto tasks = std::exchange(m_tasks, { });
         m_groupsWithSuspendedTasks.clear();
         Vector<std::unique_ptr<EventLoopTask>> remainingTasks;
+        bool hasReachedDeadline = false;
         for (auto& task : tasks) {
             auto* group = task->group();
             if (!group || group->isStoppedPermanently())
                 continue;
 
-            if (group->isSuspended()) {
+            hasReachedDeadline = hasReachedDeadline || (deadline && ApproximateTime::now() > *deadline);
+            if (group->isSuspended() || hasReachedDeadline) {
                 m_groupsWithSuspendedTasks.add(*group);
                 remainingTasks.append(WTFMove(task));
                 continue;
@@ -322,6 +324,9 @@ void EventLoop::run()
         for (auto& task : m_tasks)
             remainingTasks.append(WTFMove(task));
         m_tasks = WTFMove(remainingTasks);
+
+        if (!m_tasks.isEmpty() && hasReachedDeadline)
+            scheduleToRunIfNeeded();
     }
 
     // FIXME: Remove this once everything is integrated with the event loop.

diff --git a/Source/WebCore/dom/EventLoop.h b/Source/WebCore/dom/EventLoop.h
@@ -26,6 +26,8 @@
 #pragma once
 
 #include "TaskSource.h"
+#include <optional>
+#include <wtf/ApproximateTime.h>
 #include <wtf/Function.h>
 #include <wtf/Markable.h>
 #include <wtf/MonotonicTime.h>
@@ -128,7 +130,7 @@ class EventLoop : public RefCounted<EventLoop>, public CanMakeWeakPtr<EventLoop>
 protected:
     EventLoop();
     void scheduleToRunIfNeeded();
-    void run();
+    void run(std::optional<ApproximateTime> deadline = std::nullopt);
     void clearAllTasks();
 
     // FIXME: Account for fully-activeness of each document.

diff --git a/Source/WebCore/dom/WindowEventLoop.cpp b/Source/WebCore/dom/WindowEventLoop.cpp
@@ -36,6 +36,7 @@
 #include "Page.h"
 #include "SecurityOrigin.h"
 #include "ThreadGlobalData.h"
+#include "ThreadTimers.h"
 #include <wtf/RobinHoodHashMap.h>
 #include <wtf/RunLoop.h>
 
@@ -179,7 +180,8 @@ MonotonicTime WindowEventLoop::computeIdleDeadline()
 void WindowEventLoop::didReachTimeToRun()
 {
     Ref protectedThis { *this }; // Executing tasks may remove the last reference to this WindowEventLoop.
-    run();
+    auto deadline = ApproximateTime::now() + ThreadTimers::maxDurationOfFiringTimers;
+    run(deadline);
 
     if (hasTasksForFullyActiveDocument() || !microtaskQueue().isEmpty())
         return;

diff --git a/Source/WebCore/platform/ThreadTimers.cpp b/Source/WebCore/platform/ThreadTimers.cpp
@@ -39,9 +39,6 @@
 
 namespace WebCore {
 
-// Fire timers for this length of time, and then quit to let the run loop process user input events.
-static constexpr auto maxDurationOfFiringTimers { 16_ms };
-
 // Timers are created, started and fired on the same thread, and each thread has its own ThreadTimers
 // copy to keep the heap and a set of currently firing timers.
 

diff --git a/Source/WebCore/platform/ThreadTimers.h b/Source/WebCore/platform/ThreadTimers.h
@@ -48,6 +48,9 @@ class ThreadTimers {
 public:
     ThreadTimers();
 
+    // Fire timers for this length of time, and then quit to let the run loop process user input events.
+    static constexpr auto maxDurationOfFiringTimers { 16_ms };
+
     // On a thread different then main, we should set the thread's instance of the SharedTimer.
     void setSharedTimer(SharedTimer*);