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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/281188">281188</a></dd>
<dt>Author</dt> <dd>cdumez@apple.com</dd>
<dt>Date</dt> <dd>2021-08-18 08:25:04 -0700 (Wed, 18 Aug 2021)</dd>
</dl>

<h3>Log Message</h3>
<pre>Crash under JSIntersectionObserverCallback::handleEvent()
https://bugs.webkit.org/show_bug.cgi?id=229196
<rdar://82016054>

Reviewed by Geoffrey Garen.

Early return in IntersectionObserver::notify() if the callback has already been destroyed.
This is not supposed to happen as we're supposed to be keeping the JSIntersectionObserver
wrapper alive as long as the IntersectionObserver may fire events, which should keep the
callback alive too. However, despite Ryosuke's fix in <a href="http://trac.webkit.org/projects/webkit/changeset/280549">r280549</a>, the crash is still happening
in the wild. To address the crash, I am simply doing an early return for now, similarly to
what we already do in MutationObserver::deliver(), while keeping a debug assertion around
in hope of finding the root cause at some point.

No new tests, we do not not how this is happening yet.

* page/IntersectionObserver.cpp:
(WebCore::IntersectionObserver::notify):</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCorehtmlLazyLoadFrameObservercpp">trunk/Source/WebCore/html/LazyLoadFrameObserver.cpp</a></li>
<li><a href="#trunkSourceWebCorehtmlLazyLoadImageObservercpp">trunk/Source/WebCore/html/LazyLoadImageObserver.cpp</a></li>
<li><a href="#trunkSourceWebCorepageIntersectionObservercpp">trunk/Source/WebCore/page/IntersectionObserver.cpp</a></li>
<li><a href="#trunkSourceWebCorepageIntersectionObserverCallbackh">trunk/Source/WebCore/page/IntersectionObserverCallback.h</a></li>
<li><a href="#trunkSourceWebCorepageResizeObservercpp">trunk/Source/WebCore/page/ResizeObserver.cpp</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (281187 => 281188)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog   2021-08-18 15:10:54 UTC (rev 281187)
+++ trunk/Source/WebCore/ChangeLog      2021-08-18 15:25:04 UTC (rev 281188)
</span><span class="lines">@@ -1,3 +1,24 @@
</span><ins>+2021-08-18  Chris Dumez  <cdumez@apple.com>
+
+        Crash under JSIntersectionObserverCallback::handleEvent()
+        https://bugs.webkit.org/show_bug.cgi?id=229196
+        <rdar://82016054>
+
+        Reviewed by Geoffrey Garen.
+
+        Early return in IntersectionObserver::notify() if the callback has already been destroyed.
+        This is not supposed to happen as we're supposed to be keeping the JSIntersectionObserver
+        wrapper alive as long as the IntersectionObserver may fire events, which should keep the
+        callback alive too. However, despite Ryosuke's fix in r280549, the crash is still happening
+        in the wild. To address the crash, I am simply doing an early return for now, similarly to
+        what we already do in MutationObserver::deliver(), while keeping a debug assertion around
+        in hope of finding the root cause at some point.
+
+        No new tests, we do not not how this is happening yet.
+
+        * page/IntersectionObserver.cpp:
+        (WebCore::IntersectionObserver::notify):
+
</ins><span class="cx"> 2021-08-18  Martin Robinson  <mrobinson@webkit.org>
</span><span class="cx"> 
</span><span class="cx">         position: sticky with display: inline-block
</span></span></pre></div>
<a id="trunkSourceWebCorehtmlLazyLoadFrameObservercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/html/LazyLoadFrameObserver.cpp (281187 => 281188)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/html/LazyLoadFrameObserver.cpp      2021-08-18 15:10:54 UTC (rev 281187)
+++ trunk/Source/WebCore/html/LazyLoadFrameObserver.cpp 2021-08-18 15:25:04 UTC (rev 281188)
</span><span class="lines">@@ -43,6 +43,8 @@
</span><span class="cx">     }
</span><span class="cx"> 
</span><span class="cx"> private:
</span><ins>+    bool hasCallback() const final { return true; }
+
</ins><span class="cx">     CallbackResult<void> handleEvent(IntersectionObserver&, const Vector<Ref<IntersectionObserverEntry>>& entries, IntersectionObserver&) final
</span><span class="cx">     {
</span><span class="cx">         ASSERT(!entries.isEmpty());
</span></span></pre></div>
<a id="trunkSourceWebCorehtmlLazyLoadImageObservercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/html/LazyLoadImageObserver.cpp (281187 => 281188)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/html/LazyLoadImageObserver.cpp      2021-08-18 15:10:54 UTC (rev 281187)
+++ trunk/Source/WebCore/html/LazyLoadImageObserver.cpp 2021-08-18 15:25:04 UTC (rev 281188)
</span><span class="lines">@@ -43,6 +43,8 @@
</span><span class="cx">     }
</span><span class="cx"> 
</span><span class="cx"> private:
</span><ins>+    bool hasCallback() const final { return true; }
+
</ins><span class="cx">     CallbackResult<void> handleEvent(IntersectionObserver&, const Vector<Ref<IntersectionObserverEntry>>& entries, IntersectionObserver&) final
</span><span class="cx">     {
</span><span class="cx">         ASSERT(!entries.isEmpty());
</span></span></pre></div>
<a id="trunkSourceWebCorepageIntersectionObservercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/page/IntersectionObserver.cpp (281187 => 281188)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/page/IntersectionObserver.cpp       2021-08-18 15:10:54 UTC (rev 281187)
+++ trunk/Source/WebCore/page/IntersectionObserver.cpp  2021-08-18 15:25:04 UTC (rev 281188)
</span><span class="lines">@@ -273,12 +273,17 @@
</span><span class="cx">         return;
</span><span class="cx">     }
</span><span class="cx"> 
</span><ins>+    auto takenRecords = takeRecords();
+
+    // FIXME: The JSIntersectionObserver wrapper should be kept alive as long as the intersection observer can fire events.
+    ASSERT(m_callback->hasCallback());
+    if (!m_callback->hasCallback())
+        return;
+
</ins><span class="cx">     auto* context = m_callback->scriptExecutionContext();
</span><span class="cx">     if (!context)
</span><span class="cx">         return;
</span><span class="cx"> 
</span><del>-    auto takenRecords = takeRecords();
-
</del><span class="cx">     InspectorInstrumentation::willFireObserverCallback(*context, "IntersectionObserver"_s);
</span><span class="cx">     m_callback->handleEvent(*this, WTFMove(takenRecords.records), *this);
</span><span class="cx">     InspectorInstrumentation::didFireObserverCallback(*context);
</span></span></pre></div>
<a id="trunkSourceWebCorepageIntersectionObserverCallbackh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/page/IntersectionObserverCallback.h (281187 => 281188)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/page/IntersectionObserverCallback.h 2021-08-18 15:10:54 UTC (rev 281187)
+++ trunk/Source/WebCore/page/IntersectionObserverCallback.h    2021-08-18 15:25:04 UTC (rev 281188)
</span><span class="lines">@@ -41,7 +41,7 @@
</span><span class="cx"> public:
</span><span class="cx">     using ActiveDOMCallback::ActiveDOMCallback;
</span><span class="cx"> 
</span><del>-    virtual bool hasCallback() const { return false; }
</del><ins>+    virtual bool hasCallback() const = 0;
</ins><span class="cx"> 
</span><span class="cx">     virtual CallbackResult<void> handleEvent(IntersectionObserver&, const Vector<Ref<IntersectionObserverEntry>>&, IntersectionObserver&) = 0;
</span><span class="cx"> };
</span></span></pre></div>
<a id="trunkSourceWebCorepageResizeObservercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/page/ResizeObserver.cpp (281187 => 281188)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/page/ResizeObserver.cpp     2021-08-18 15:10:54 UTC (rev 281187)
+++ trunk/Source/WebCore/page/ResizeObserver.cpp        2021-08-18 15:25:04 UTC (rev 281188)
</span><span class="lines">@@ -124,6 +124,11 @@
</span><span class="cx">     m_activeObservations.clear();
</span><span class="cx">     auto activeObservationTargets = std::exchange(m_activeObservationTargets, { });
</span><span class="cx"> 
</span><ins>+    // FIXME: The JSResizeObserver wrapper should be kept alive as long as the resize observer can fire events.
+    ASSERT(m_callback->hasCallback());
+    if (!m_callback->hasCallback())
+        return;
+
</ins><span class="cx">     auto* context = m_callback->scriptExecutionContext();
</span><span class="cx">     if (!context)
</span><span class="cx">         return;
</span></span></pre>
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