<html>
    <head>
      <base href="https://bugs.webkit.org/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - REGRESSION: Assertion failed: (!&quot;initialized()&quot;), function operator() in com.apple.JavaScriptCore: std::optional&lt;unsigned int&gt;::operator* const + 46"
   href="https://bugs.webkit.org/show_bug.cgi?id=169042">169042</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>REGRESSION: Assertion failed: (!&quot;initialized()&quot;), function operator() in com.apple.JavaScriptCore: std::optional&lt;unsigned int&gt;::operator* const + 46
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>WebKit
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>WebKit Nightly Build
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>Unspecified
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Unspecified
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>Normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P2
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>New Bugs
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>webkit-unassigned&#64;lists.webkit.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>ryanhaddad&#64;apple.com
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Thread 19 Crashed:: WTF::AutomaticThread
0   libsystem_kernel.dylib            0x00007fff84e6df06 __pthread_kill + 10
1   libsystem_pthread.dylib           0x00007fff83f7b4ec pthread_kill + 90
2   libsystem_c.dylib                 0x00007fff903366df abort + 129
3   libsystem_c.dylib                 0x00007fff902fddd8 __assert_rtn + 321
4   com.apple.JavaScriptCore          0x0000000105e3a41e std::optional&lt;unsigned int&gt;::operator*() const::'lambda'()::operator()() const + 46
5   com.apple.JavaScriptCore          0x0000000105e3a3b1 std::optional&lt;unsigned int&gt;::operator*() const + 65 (Optional.h:595)
6   com.apple.JavaScriptCore          0x0000000105e3a31f bool std::operator==&lt;unsigned int&gt;(std::optional&lt;unsigned int&gt; const&amp;, unsigned int const&amp;) + 47 (Optional.h:863)
7   com.apple.JavaScriptCore          0x0000000105e3a2e0 JSC::JSLock::currentThreadIsHoldingLock() + 48 (JSLock.h:97)
8   com.apple.JavaScriptCore          0x0000000105e3a284 JSC::VM::currentThreadIsHoldingAPILock() const + 36 (VM.h:629)
9   com.apple.JavaScriptCore          0x0000000105e39dde JSC::JSCell::classInfo(JSC::VM&amp;) const + 62 (JSCellInlines.h:283)
10  com.apple.JavaScriptCore          0x0000000106fd0845 JSC::validate(JSC::JSCell*) + 181 (SlotVisitor.cpp:61)
11  com.apple.JavaScriptCore          0x0000000106fd06aa JSC::SlotVisitor::setMarkedAndAppendToMarkStack(JSC::JSCell*) + 138 (SlotVisitor.cpp:256)
12  com.apple.JavaScriptCore          0x0000000106fd0615 JSC::SlotVisitor::appendUnbarriered(JSC::JSValue) + 181 (SlotVisitor.cpp:234)
13  com.apple.JavaScriptCore          0x0000000105e4e985 JSC::SlotVisitor::appendUnbarriered(JSC::JSCell*) + 53 (SlotVisitorInlines.h:43)
14  com.apple.JavaScriptCore          0x00000001070056f0 void JSC::SlotVisitor::append&lt;JSC::PropertyTable&gt;(JSC::WriteBarrierBase&lt;JSC::PropertyTable&gt; const&amp;) + 48 (SlotVisitorInlines.h:55)
15  com.apple.JavaScriptCore          0x0000000106ffe468 JSC::Structure::visitChildren(JSC::JSCell*, JSC::SlotVisitor&amp;) + 552 (Structure.cpp:1095)
16  com.apple.JavaScriptCore          0x0000000106fd37f4 JSC::SlotVisitor::visitChildren(JSC::JSCell const*) + 292 (SlotVisitor.cpp:400)
17  com.apple.JavaScriptCore          0x0000000106fd2e0e JSC::SlotVisitor::drain(WTF::MonotonicTime)::$_3::operator()(JSC::MarkStackArray&amp;) const + 206 (SlotVisitor.cpp:494)
18  com.apple.JavaScriptCore          0x0000000106fd0f51 JSC::IterationStatus JSC::SlotVisitor::forEachMarkStack&lt;JSC::SlotVisitor::drain(WTF::MonotonicTime)::$_3&gt;(JSC::SlotVisitor::drain(WTF::MonotonicTime)::$_3 const&amp;) + 33 (SlotVisitorInlines.h:116)
19  com.apple.JavaScriptCore          0x0000000106fd0edb JSC::SlotVisitor::drain(WTF::MonotonicTime) + 187 (SlotVisitor.cpp:485)
20  com.apple.JavaScriptCore          0x0000000106fd1a21 JSC::SlotVisitor::drainFromShared(JSC::SlotVisitor::SharedDrainMode, WTF::MonotonicTime) + 1153 (SlotVisitor.cpp:665)
21  com.apple.JavaScriptCore          0x00000001069eb610 JSC::Heap::runBeginPhase(JSC::GCConductor)::$_11::operator()() const + 1056 (Heap.cpp:1152)
22  com.apple.JavaScriptCore          0x00000001069eb1bc WTF::SharedTaskFunctor&lt;void (), JSC::Heap::runBeginPhase(JSC::GCConductor)::$_11&gt;::run() + 28 (SharedTask.h:90)
23  com.apple.JavaScriptCore          0x0000000107394390 WTF::ParallelHelperClient::runTask(WTF::RefPtr&lt;WTF::SharedTask&lt;void ()&gt; &gt;) + 176 (ParallelHelperPool.cpp:115)
24  com.apple.JavaScriptCore          0x00000001073953b2 WTF::ParallelHelperPool::Thread::work() + 66 (ParallelHelperPool.cpp:194)
25  com.apple.JavaScriptCore          0x000000010735b6ee WTF::AutomaticThread::start(WTF::AbstractLocker const&amp;)::$_0::operator()() const + 606 (AutomaticThread.cpp:215)
26  com.apple.JavaScriptCore          0x000000010735b47d void std::__1::__invoke_void_return_wrapper&lt;void&gt;::__call&lt;WTF::AutomaticThread::start(WTF::AbstractLocker const&amp;)::$_0&amp;&gt;(WTF::AutomaticThread::start(WTF::AbstractLocker const&amp;)::$_0&amp;&amp;&amp;) + 45 (__functional_base:441)
27  com.apple.JavaScriptCore          0x000000010735b26c std::__1::__function::__func&lt;WTF::AutomaticThread::start(WTF::AbstractLocker const&amp;)::$_0, std::__1::allocator&lt;WTF::AutomaticThread::start(WTF::AbstractLocker const&amp;)::$_0&gt;, void ()&gt;::operator()() + 44 (functional:1407)
28  com.apple.JavaScriptCore          0x000000010677b67a std::__1::function&lt;void ()&gt;::operator()() const + 26 (functional:1793)
29  com.apple.JavaScriptCore          0x00000001073cc60e WTF::threadEntryPoint(void*) + 158 (Threading.cpp:92)
30  com.apple.JavaScriptCore          0x00000001073ce2c1 WTF::wtfThreadEntryPoint(void*) + 289 (ThreadingPthreads.cpp:168)
31  libsystem_pthread.dylib           0x00007fff83f7899d _pthread_body + 131
32  libsystem_pthread.dylib           0x00007fff83f7891a _pthread_start + 168
33  libsystem_pthread.dylib           0x00007fff83f76351 thread_start + 13

Seen here with imported/w3c/web-platform-tests/dom/nodes/Document-constructor.html and imported/w3c/web-platform-tests/streams/readable-streams/bad-underlying-sources.dedicatedworker.html

<a href="https://build.webkit.org/results/Apple%20El%20Capitan%20Debug%20WK2%20(Tests)/r213221%20(11340)/results.html">https://build.webkit.org/results/Apple%20El%20Capitan%20Debug%20WK2%20(Tests)/r213221%20(11340)/results.html</a></pre>
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