Mercurial > my-ubiquity-commands

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  <title>Pseudo Weak References for Web Content</title>
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<h1>Pseudo Weak References for Web Content</h1>
<p>This Ubiquity feed provides pseudo weak reference functionality to
web content, for the purpose of making it easier to debug memory
management issues. Specifically, it adds two new functions to
the global <tt>window</tt> object of all web pages:</p>
<ul>
  <li><tt>PseudoWeakRef(object)</tt> is a constructor that makes a
    pseudo-weak reference for the object.  The returned object has one
    method, <tt>exists()</tt>, which returns whether or not the
    referent still exists.</li>
  <li><tt>forceGC()</tt> forces garbage collection.</li>
</ul>
<p>Here's some example code:</p>
<script id="tests">
function testExistsReturnsFalse() {
  var object = new Object();
  var weak = new PseudoWeakRef(object);

  // Destroy our one strong reference to the object, leaving it available
  // for garbage collection.
  object = null;

  forceGC();
  if (weak.exists())
    throw new Error("weak referent should not exist");
}
</script>
<p>The above source code is actually part of the test suite for this
feed.  <span id="test-result">If this feed were installed, the suite would
run now.</span></p>
<p>The source code for this feed can be viewed
at <a href="pseudo-weak-refs.js">pseudo-weak-refs.js</a>.</p>
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<div id="messages">
<span id="tests-failed">The suite was run, but some tests failed.</span>
<span id="tests-passed">The suite was run, and all tests passed.</span>
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<script>
function testExistsReturnsTrue() {
  var object = new Object();
  var weak = new PseudoWeakRef(object);
  forceGC();
  if (!weak.exists())
    throw new Error("weak referent should exist");
}

function onLoad() {
  function $(id) { return document.getElementById(id); }

  $("tests").innerHTML = $("tests").innerHTML.slice(1);
  if (window.PseudoWeakRef && window.forceGC) {
    try {
      testExistsReturnsFalse();
      testExistsReturnsTrue();
    } catch (e) {
      $("test-result").innerHTML = $("tests-failed").innerHTML;
      throw e;
    }
    $("test-result").innerHTML = $("tests-passed").innerHTML;
  }
}

window.addEventListener("load", onLoad, false);
</script>
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author	Atul Varma <varmaa@toolness.com>
date	Mon, 18 May 2009 22:51:37 -0700
parents	08bddf757ed8
children