Bug 148951 – fast/dom/rtl-scroll-to-leftmost-and-resize.html is a flaky timeout - IPC drops messages

• Component: WebKit2
• Status: RESOLVED FIXED

[Alexey Proskuryakov]

fast/dom/rtl-scroll-to-leftmost-and-resize.html frequently times out on Mac.

This usually reproduces the problem on my MacBook Pro:

run-webkit-tests fast/dom/rtl-scroll-to-leftmost-and-resize.html --repeat 100 --no-build --no-retry -f

Via printf debugging, I found that WebContent sends DrawingAreaProxy::DidUpdateGeometry, but the message never reaches Connection::dispatchMessage in UI process.

[Alexey Proskuryakov]

The message doesn't even reach Connection::enqueueIncomingMessage in UI process...

[Alexey Proskuryakov]

Okay, a little less mysterious. We do get the message in Connection::processIncomingMessage in UI process, but in the failing case, it gets processed by this block:

    // Check if we're waiting for this message.
    {
        std::lock_guard<Lock> lock(m_waitForMessageMutex);

        if (m_waitingForMessage && m_waitingForMessage->messageReceiverName == message->messageReceiverName() && m_waitingForMessage->messageName == message->messageName() && m_waitingForMessage->destinationID == message->destinationID()) {
            m_waitingForMessage->decoder = WTF::move(message);
            ASSERT(m_waitingForMessage->decoder);
            m_waitForMessageCondition.notifyOne();
            return;
        }
...

So, Connection::waitForAndDispatchImmediately must be buggy, the message that it's waiting for can get dropped altogether.

Once a DidUpdateGeometry message gets dropped, that makes UI process never again send any DrawingArea::UpdateGeometry messages for this drawing area.

[Alexey Proskuryakov]

Added a test expectation in r189491. But this likely affects more tests.

[Alexey Proskuryakov]

Created attachment 260838 [details]
proposed fix

[Alexey Proskuryakov]

Created attachment 260841 [details]
proposed fix

Actually, let's also make sure that we don't overwrite m_waitingForMessage->decoder when two messages come in quickly.

[WebKit Commit Bot]

Comment on attachment 260841 [details]
proposed fix

Clearing flags on attachment: 260841

Committed r189546: <http://trac.webkit.org/changeset/189546>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.