= What is an abandoned document? = Abandoned documents are effectively leaked: they are Document objects which have never been destroyed, and persist after loading about:blank, running a garbage collection and clearing caches. This is probably because there's some object that is holding a reference to the Document object, possibly in the GC heap, or via a retain cycle (often involving Nodes in the document). All documents are referenced by Document::allDocumentsMap(), so they are not leaked in the sense that the 'leaks' tool doesn't show them. = Why are layout test results showing me a list of abandoned documents? = Leaked documents usually entrain a lot of other objects, which can use lots of memory (e.g. via entries in the memory cache). Leaking documents is bad because it will cause ever-increasing memory use as the user browses. See [https://bugs.webkit.org/show_bug.cgi?id=186214] = What should I do if see a new case of document abandonment? = If you made a code change that is causing a test to newly show that a document is leaked, it probably means you have a coding bug that is triggered a leak or (more likely) a reference cycle. You need to resolve this before committing. = How do I debug document abandonment? = Let's take an example [https://bugs.webkit.org/show_bug.cgi?id=188722]. We run tests, checking for abandonment: {{{ run-webkit-tests fast/forms/ --check-for-abandoned-documents }}} The results say that {{{fast/forms/textarea-paste-newline.html}}} was abandoned. Now you have to figure out why this Document object is not going away. A bit of testing in MiniBrowser can be useful, and if you're lucky, the abandonment will reproduce there. To test this, do these steps: 1. Run MiniBrowser 2. Load a simple HTML file (not the test!) 3. Load the test file 4. Go back to the simple HTML file 5. Simulate a memory warning (on macOS, you can do this by running {{{notifyutil -p "org.WebKit.lowMemory"}}} in the Terminal). 6. Now dump the list of live documents: {{{notifyutil -p "com.apple.WebKit.showAllDocuments"}}}. This will show something like: {{{ 2 live documents: Document 0x630002400 (refCount 5, referencingNodeCount 1) file:///Volumes/Data/webkit/LayoutTests/fast/forms/textarea-paste-newline.html Document 0x630024400 (refCount 2, referencingNodeCount 4) file:///Volumes/Data/simple.html }}} 7. That confirms that after a memory warning (which clears caches and does a GC) that the document is still alive. So something is holding a reference to it. 8. Now you could start doing manual debugging of ref() and deref() to try to figure out where the extra ref() is happening. But there's a better way. 1. Apply the most recent patch from [https://bugs.webkit.org/show_bug.cgi?id=186269] (if this has not been checked in yet) and build. 2. Repeat the above steps. Now the output will be something like: {{{ 2 live documents: Document 0x630002400 (refCount 5, referencingNodeCount 1) file:///Volumes/Data/Development/apple/webkit/OpenSource/LayoutTests/fast/forms/textarea-paste-newline.html Document 0x630002400 reference stacks: Backtrace for token 6074 1 0x6179baa97 WebCore::Node::ref() 2 0x615af576e unsigned int WTF::refIfNotNull(WebCore::Node*) 3 0x615af5728 WTF::RefPtr >::RefPtr(WebCore::Node*) 4 0x615af4add WTF::RefPtr >::RefPtr(WebCore::Node*) 5 0x615af4b73 WTF::RefPtr >::operator=(WebCore::Node*) 6 0x61788ccb2 WebCore::Document::removeFocusNavigationNodeOfSubtree(WebCore::Node&, bool) 7 0x61788c82a WebCore::Document::nodeChildrenWillBeRemoved(WebCore::ContainerNode&) 8 0x6178252de WebCore::ContainerNode::removeAllChildrenWithScriptAssertion(WebCore::ContainerNode::ChildChangeSource, WebCore::ContainerNode::DeferChildrenChanged) 9 0x617828d49 WebCore::ContainerNode::removeChildren() 10 0x617882aef WebCore::Document::implicitOpen() 11 0x617878043 WebCore::Document::open(WebCore::Document*) 12 0x617884062 WebCore::Document::write(WebCore::Document*, WebCore::SegmentedString&&) 13 0x61788432b WebCore::Document::write(WebCore::Document*, WTF::Vector&&) 14 0x61609d242 WebCore::jsDocumentPrototypeFunctionWriteBody(JSC::ExecState*, WebCore::JSDocument*, JSC::ThrowScope&) 15 0x61608046e long long WebCore::IDLOperation::call<&(WebCore::jsDocumentPrototypeFunctionWriteBody(JSC::ExecState*, WebCore::JSDocument*, JSC::ThrowScope&)), (WebCore::CastedThisErrorBehavior)0>(JSC::ExecState&, char const*) 16 0x61608016c WebCore::jsDocumentPrototypeFunctionWrite(JSC::ExecState*) 17 0xeef1324177 18 0x62650d44b llint_entry 19 0x62650d44b llint_entry 20 0x626504e37 vmEntryToJavaScript 21 0x6270a7c7a JSC::JITCode::execute(JSC::VM*, JSC::ProtoCallFrame*) 22 0x6270a8303 JSC::Interpreter::executeCall(JSC::ExecState*, JSC::JSObject*, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&) 23 0x627356dce JSC::call(JSC::ExecState*, JSC::JSValue, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&) 24 0x627356eac JSC::call(JSC::ExecState*, JSC::JSValue, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&, WTF::NakedPtr&) 25 0x62735717d JSC::profiledCall(JSC::ExecState*, JSC::ProfilingReason, JSC::JSValue, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&, WTF::NakedPtr&) 26 0x617351ffb WebCore::JSExecState::profiledCall(JSC::ExecState*, JSC::ProfilingReason, JSC::JSValue, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&, WTF::NakedPtr&) 27 0x617398407 WebCore::JSEventListener::handleEvent(WebCore::ScriptExecutionContext&, WebCore::Event&) 28 0x617960d3e WebCore::EventTarget::fireEventListeners(WebCore::Event&, WTF::Vector >, 1ul, WTF::CrashOnOverflow, 16ul>) 29 0x61795c7a0 WebCore::EventTarget::fireEventListeners(WebCore::Event&) 30 0x61824752d WebCore::DOMWindow::dispatchEvent(WebCore::Event&, WebCore::EventTarget*) 31 0x6182523de WebCore::DOMWindow::dispatchLoadEvent() 32 0x6178839fa WebCore::Document::dispatchWindowLoadEvent() 33 0x61787bff3 WebCore::Document::implicitClose() 34 0x6180d6f2b WebCore::FrameLoader::checkCallImplicitClose() 35 0x6180d69c8 WebCore::FrameLoader::checkCompleted() 36 0x6180d58f5 WebCore::FrameLoader::finishedParsing() 37 0x617895ca9 WebCore::Document::finishedParsing() 38 0x617e3df58 WebCore::HTMLConstructionSite::finishedParsing() 39 0x617e8c969 WebCore::HTMLTreeBuilder::finished() 40 0x617e4708c WebCore::HTMLDocumentParser::end() 41 0x617e440e9 WebCore::HTMLDocumentParser::attemptToRunDeferredScriptsAndEnd() 42 0x617e43de3 WebCore::HTMLDocumentParser::prepareToStopParsing() 43 0x617e470ff WebCore::HTMLDocumentParser::attemptToEnd() 44 0x617e471d8 WebCore::HTMLDocumentParser::finish() 45 0x6180c55fe WebCore::DocumentWriter::end() 46 0x618084a1f WebCore::DocumentLoader::finishedLoading() 47 0x6180847bf WebCore::DocumentLoader::notifyFinished(WebCore::CachedResource&) 48 0x6181c7fdf WebCore::CachedResource::checkNotify() 49 0x6181ba091 WebCore::CachedResource::finishLoading(WebCore::SharedBuffer*) 50 0x6181c4ec2 WebCore::CachedRawResource::finishLoading(WebCore::SharedBuffer*) 51 0x618155a58 WebCore::SubresourceLoader::didFinishLoading(WebCore::NetworkLoadMetrics const&) 52 0x610f6d50b WebKit::WebResourceLoader::didFinishResourceLoad(WebCore::NetworkLoadMetrics const&) 53 0x610f71b8a void IPC::callMemberFunctionImpl, 0ul>(WebKit::WebResourceLoader*, void (WebKit::WebResourceLoader::*)(WebCore::NetworkLoadMetrics const&), std::__1::tuple&&, std::__1::integer_sequence) 54 0x610f71a10 void IPC::callMemberFunction, std::__1::integer_sequence >(std::__1::tuple&&, WebKit::WebResourceLoader*, void (WebKit::WebResourceLoader::*)(WebCore::NetworkLoadMetrics const&)) 55 0x610f70bea void IPC::handleMessage(IPC::Decoder&, WebKit::WebResourceLoader*, void (WebKit::WebResourceLoader::*)(WebCore::NetworkLoadMetrics const&)) 56 0x610f701fc WebKit::WebResourceLoader::didReceiveWebResourceLoaderMessage(IPC::Connection&, IPC::Decoder&) 57 0x6103c73a9 WebKit::NetworkProcessConnection::didReceiveMessage(IPC::Connection&, IPC::Decoder&) 58 0x610774e3c IPC::Connection::dispatchMessage(IPC::Decoder&) 59 0x6107679ad IPC::Connection::dispatchMessage(std::__1::unique_ptr >) 60 0x6107759f7 IPC::Connection::dispatchOneIncomingMessage() 61 0x610793bc8 IPC::Connection::enqueueIncomingMessage(std::__1::unique_ptr >)::$_14::operator()() 62 0x610793ad9 WTF::Function::CallableWrapper >)::$_14>::call() 63 0x62609018f WTF::Function::operator()() const 64 0x6260e8f83 WTF::RunLoop::performWork() 65 0x6260e9934 WTF::RunLoop::performWork(void*) 66 0x7fff2e435a11 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ 67 0x7fff2e4ef42c __CFRunLoopDoSource0 68 0x7fff2e418470 __CFRunLoopDoSources0 69 0x7fff2e4178ed __CFRunLoopRun 70 0x7fff2e417153 CFRunLoopRunSpecific 71 0x7fff2d701d96 RunCurrentEventLoopInMode 72 0x7fff2d701b06 ReceiveNextEventCommon 73 0x7fff2d701884 _BlockUntilNextEventMatchingListInModeWithFilter 74 0x7fff2b9b2a73 _DPSNextEvent 75 0x7fff2c148e34 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] 76 0x7fff2b9a7885 -[NSApplication run] 77 0x7fff2b976a72 NSApplicationMain 78 0x7fff56619d77 _xpc_objc_main 79 0x7fff566189ca xpc_main 80 0x1091cd077 WebKit::XPCServiceMain() 81 0x1091cd36b main 82 0x7fff562bf015 start 83 0x1 Backtrace for token 5651 1 0x6179baa97 WebCore::Node::ref() 2 0x615d77d88 WTF::Ref >::Ref(WebCore::Document&) 3 0x615d77d4d WTF::Ref >::Ref(WebCore::Document&) 4 0x617396d29 WebCore::toJS(JSC::ExecState*, WebCore::JSDOMGlobalObject*, WebCore::Document&) 5 0x6173ad378 WebCore::createWrapperInline(JSC::ExecState*, WebCore::JSDOMGlobalObject*, WTF::Ref >&&) 6 0x6173ad0a0 WebCore::createWrapper(JSC::ExecState*, WebCore::JSDOMGlobalObject*, WTF::Ref >&&) 7 0x615c363de WebCore::toJS(JSC::ExecState*, WebCore::JSDOMGlobalObject*, WebCore::Node&) 8 0x615c8fbb0 WebCore::toJS(JSC::ExecState*, WebCore::JSDOMGlobalObject*, WebCore::Node*) 9 0x617384fd3 WebCore::JSDOMWindowBase::updateDocument() 10 0x6173d677e WebCore::ScriptController::initScriptForWindowProxy(WebCore::JSWindowProxy&) 11 0x617457455 WebCore::WindowProxy::createJSWindowProxyWithInitializedScript(WebCore::DOMWrapperWorld&) 12 0x6173c70d6 WebCore::WindowProxy::jsWindowProxy(WebCore::DOMWrapperWorld&) 13 0x6173d556b WebCore::ScriptController::jsWindowProxy(WebCore::DOMWrapperWorld&) 14 0x6173d5355 WebCore::ScriptController::evaluateInWorld(WebCore::ScriptSourceCode const&, WebCore::DOMWrapperWorld&, WebCore::ExceptionDetails*) 15 0x6173d57bd WebCore::ScriptController::evaluate(WebCore::ScriptSourceCode const&, WebCore::ExceptionDetails*) 16 0x617a04d37 WebCore::ScriptElement::executeClassicScript(WebCore::ScriptSourceCode const&) 17 0x617a03084 WebCore::ScriptElement::prepareScript(WTF::TextPosition const&, WebCore::ScriptElement::LegacyTypeSupport) 18 0x617e64798 WebCore::HTMLScriptRunner::runScript(WebCore::ScriptElement&, WTF::TextPosition const&) 19 0x617e645bf WebCore::HTMLScriptRunner::execute(WTF::Ref >&&, WTF::TextPosition const&) 20 0x617e455a3 WebCore::HTMLDocumentParser::runScriptsForPausedTreeBuilder() 21 0x617e45b63 WebCore::HTMLDocumentParser::pumpTokenizerLoop(WebCore::HTMLDocumentParser::SynchronousMode, bool, WebCore::PumpSession&) 22 0x617e44684 WebCore::HTMLDocumentParser::pumpTokenizer(WebCore::HTMLDocumentParser::SynchronousMode) 23 0x617e43f8f WebCore::HTMLDocumentParser::pumpTokenizerIfPossible(WebCore::HTMLDocumentParser::SynchronousMode) 24 0x617e46e9a WebCore::HTMLDocumentParser::append(WTF::RefPtr >&&) 25 0x61785fe62 WebCore::DecodedDataDocumentParser::flush(WebCore::DocumentWriter&) 26 0x6180c55b4 WebCore::DocumentWriter::end() 27 0x618084a1f WebCore::DocumentLoader::finishedLoading() 28 0x6180847bf WebCore::DocumentLoader::notifyFinished(WebCore::CachedResource&) 29 0x6181c7fdf WebCore::CachedResource::checkNotify() 30 0x6181ba091 WebCore::CachedResource::finishLoading(WebCore::SharedBuffer*) 31 0x6181c4ec2 WebCore::CachedRawResource::finishLoading(WebCore::SharedBuffer*) 32 0x618155a58 WebCore::SubresourceLoader::didFinishLoading(WebCore::NetworkLoadMetrics const&) 33 0x610f6d50b WebKit::WebResourceLoader::didFinishResourceLoad(WebCore::NetworkLoadMetrics const&) 34 0x610f71b8a void IPC::callMemberFunctionImpl, 0ul>(WebKit::WebResourceLoader*, void (WebKit::WebResourceLoader::*)(WebCore::NetworkLoadMetrics const&), std::__1::tuple&&, std::__1::integer_sequence) 35 0x610f71a10 void IPC::callMemberFunction, std::__1::integer_sequence >(std::__1::tuple&&, WebKit::WebResourceLoader*, void (WebKit::WebResourceLoader::*)(WebCore::NetworkLoadMetrics const&)) 36 0x610f70bea void IPC::handleMessage(IPC::Decoder&, WebKit::WebResourceLoader*, void (WebKit::WebResourceLoader::*)(WebCore::NetworkLoadMetrics const&)) 37 0x610f701fc WebKit::WebResourceLoader::didReceiveWebResourceLoaderMessage(IPC::Connection&, IPC::Decoder&) 38 0x6103c73a9 WebKit::NetworkProcessConnection::didReceiveMessage(IPC::Connection&, IPC::Decoder&) 39 0x610774e3c IPC::Connection::dispatchMessage(IPC::Decoder&) 40 0x6107679ad IPC::Connection::dispatchMessage(std::__1::unique_ptr >) 41 0x6107759f7 IPC::Connection::dispatchOneIncomingMessage() 42 0x610793bc8 IPC::Connection::enqueueIncomingMessage(std::__1::unique_ptr >)::$_14::operator()() 43 0x610793ad9 WTF::Function::CallableWrapper >)::$_14>::call() 44 0x62609018f WTF::Function::operator()() const 45 0x6260e8f83 WTF::RunLoop::performWork() 46 0x6260e9934 WTF::RunLoop::performWork(void*) 47 0x7fff2e435a11 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ 48 0x7fff2e4ef42c __CFRunLoopDoSource0 49 0x7fff2e418470 __CFRunLoopDoSources0 50 0x7fff2e4178ed __CFRunLoopRun 51 0x7fff2e417153 CFRunLoopRunSpecific 52 0x7fff2d701d96 RunCurrentEventLoopInMode 53 0x7fff2d701b06 ReceiveNextEventCommon 54 0x7fff2d701884 _BlockUntilNextEventMatchingListInModeWithFilter 55 0x7fff2b9b2a73 _DPSNextEvent 56 0x7fff2c148e34 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] 57 0x7fff2b9a7885 -[NSApplication run] 58 0x7fff2b976a72 NSApplicationMain 59 0x7fff56619d77 _xpc_objc_main 60 0x7fff566189ca xpc_main 61 0x1091cd077 WebKit::XPCServiceMain() 62 0x1091cd36b main 63 0x7fff562bf015 start 64 0x1 }}}