ASSERTION FAILED: Unsafe to ref/deref from different threads m_isOwnedByMainThread == isMainThread() /Users/yurys/WebKit/WebKitBuild/Debug/usr/local/include/wtf/RefCounted.h(115) : void WTF::RefCountedBase::applyRefDerefThreadingCheck() const 1 0x107e117f9 WTFCrash 2 0x11a85b7da WTF::RefCountedBase::applyRefDerefThreadingCheck() const 3 0x11a86ded9 WTF::RefCountedBase::ref() const 4 0x11d91b867 WTF::Ref<WTF::Stopwatch, WTF::DumbPtrTraits<WTF::Stopwatch> >::Ref(WTF::Stopwatch&) 5 0x11d91b82d WTF::Ref<WTF::Stopwatch, WTF::DumbPtrTraits<WTF::Stopwatch> >::Ref(WTF::Stopwatch&) 6 0x11d90928f WTF::Ref<WTF::Stopwatch, WTF::DumbPtrTraits<WTF::Stopwatch> >::copyRef() const & 7 0x11d909260 WebCore::InspectorController::executionStopwatch() 8 0x10903fbfc Inspector::InspectorHeapAgent::didGarbageCollect(JSC::CollectionScope) 9 0x108ec14ef JSC::Heap::didFinishCollection() 10 0x108ebf948 JSC::Heap::runEndPhase(JSC::GCConductor) 11 0x108ebe020 JSC::Heap::runCurrentPhase(JSC::GCConductor, JSC::CurrentThreadState*) 12 0x108ebde26 JSC::Heap::collectInCollectorThread() 13 0x108ec9039 JSC::Heap::HeapThread::work() 14 0x107e29d59 WTF::AutomaticThread::start(WTF::AbstractLocker const&)::$_0::operator()() const 15 0x107e29949 WTF::Detail::CallableWrapper<WTF::AutomaticThread::start(WTF::AbstractLocker const&)::$_0, void>::call() 16 0x107e3e10a WTF::Function<void ()>::operator()() const 17 0x107ee9920 WTF::Thread::entryPoint(WTF::Thread::NewThreadContext*) 18 0x107ef56d5 WTF::wtfThreadEntryPoint(void*) 19 0x7fff7ecc72eb _pthread_body 20 0x7fff7ecca249 _pthread_start 21 0x7fff7ecc640d thread_start This happens every once in a while on WK1 Mac Debug when running inspector/timeline/timeline-recording.html