No subject

Tue Jan 27 15:54:36 PST 2015

        var dividerElement = this._headerElement.firstChild;
        for (var i = 0; i <= dividerCount; ++i) {
            if (!dividerElement) {
                dividerElement = document.createElement("div");
                dividerElement.className = WebInspector.TimelineRuler.DividerElementStyleClassName;
                this._headerElement.appendChild(dividerElement);

                var labelElement = document.createElement("div");
                labelElement.className = WebInspector.TimelineRuler.DividerLabelElementStyleClassName;
                dividerElement._labelElement = labelElement;
                dividerElement.appendChild(labelElement);
            }

            // ...

            var dividerTime = firstDividerTime + (sliceTime * i);

            // ...

            dividerElement._labelElement.textContent = isNaN(dividerTime) ? "" : Number.secondsToString(dividerTime - this._zeroTime, true);
            dividerElement = dividerElement.nextSibling;
        }

The exceptions happens on the second to last line in the loop. dividerElement._labelElement is undefined, but it should never be.

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--1430070566.B0Eac8.6568
Date: Sun, 26 Apr 2015 10:49:26 -0700
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<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 - Unexpected custom DOM wrapper property is undefined soon after it was assigned"
   href="https://bugs.webkit.org/show_bug.cgi?id=144227">144227</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Unexpected custom DOM wrapper property is undefined soon after it was assigned
          </td>
        </tr>

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

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

        <tr>
          <th>Version</th>
          <td>528+ (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>JavaScriptCore
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>timothy&#64;apple.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>fpizlo&#64;apple.com, ggaren&#64;apple.com, joepeck&#64;webkit.org, mark.lam&#64;apple.com, msaboff&#64;apple.com, webkit-bug-importer&#64;group.apple.com
          </td>
        </tr></table>
      <p>
        <div>
        <pre>TimelineRuler.js in the Web Inspector occasionally throws an exception and never records. The _labelElement property we add to a DOM node at the beginning of a loop body ends up being undefined at the end of the loop body. This smells like a JIT optimization bug to me since this code has always worked fine and only recently started happening. It is also very inconsistent on when it happens. Because it is so random when it happens, we haven't been able to pin point steps or make a reduction. Just resting the Inspector window, or zooming the Timeline in and out causes updateLayout to be called.