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Short URL: http://html5.org/r/2898

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2898Define the storage mutex. Will be used in the next few checkins.2009-03-24 07:42
Index: source
===================================================================
--- source	(revision 2897)
+++ source	(revision 2898)
@@ -404,16 +404,7 @@
   imply a visual medium; they must be considered to apply to other
   media in equivalent ways.</p>
 
-  <p class="impl">Some of the algorithms in this specification, for
-  historical reasons, require the user agent to <dfn>pause</dfn> until
-  some condition has been met. While a user agent is paused, it must
-  ensure that no scripts execute (e.g. no event handlers, no timers,
-  etc). User agents should remain responsive to user input while
-  paused, however, albeit without letting the user interact with Web
-  pages where that would involve invoking any <span
-  title="concept-script">script</span>.</p>
 
-
   <h4>XML</h4>
 
   <p id="html-namespace">To ease migration from HTML to XHTML, UAs
@@ -45526,6 +45517,8 @@
 
   <h4>Event loops</h4>
 
+  <h5>Definitions</h5>
+
   <p>To coordinate events, user interaction, scripts, rendering,
   networking, and so forth, user agents must use <dfn title="event
   loop">event loops</dfn> as described in this section.</p>
@@ -45621,17 +45614,29 @@
   processing events from any one <span>task source</span> out of
   order.</p>
 
+  <p>A user agent is required to have one <dfn>storage
+  mutex</dfn>. This mutex is used to control access to shared state
+  like cookies. At any one point, the <span>storage mutex</span> is
+  either free, or owned by a particular <span>event loop</span>.</p>
+
+
+  <h5>Processing model</h5>
+
   <p>An <span>event loop</span> must continually run through the
   following steps for as long as it exists:</p>
 
   <ol>
 
-   <li><p>Run the oldest task on one of the <span>event loop</span>'s
-   <span title="task queue">task queues</span>, ignoring tasks whose
-   associated <code>Document</code>s are not <span>fully
-   active</span>. The user agent may pick any <span>task
-   queue</span>.</p></li>
+   <li><p>Run the oldest <span title="concept-task">task</span> on one
+   of the <span>event loop</span>'s <span title="task queue">task
+   queues</span>, ignoring tasks whose associated
+   <code>Document</code>s are not <span>fully active</span>. The user
+   agent may pick any <span>task queue</span>.</p></li>
 
+   <li><p>If the <span>storage mutex</span> is now owned by the
+   <span>event loop</span>, release it so that it is once again
+   free.</p>
+
    <li><p>Remove that task from its <span>task queue</span>.</p></li>
 
    <li><p>If necessary, update the rendering or user interface of any
@@ -45643,6 +45648,39 @@
 
   </ol>
 
+  <hr>
+
+  <p class="impl">Some of the algorithms in this specification, for
+  historical reasons, require the user agent to <dfn>pause</dfn> while
+  running a <span title="concept-task">task</span> until some
+  condition has been met. While a user agent has a paused <span
+  title="concept-task">task</span>, the corresponding <span>event
+  loop</span> must not run further <span
+  title="concept-task">tasks</span>, and any script in the currently
+  running <span title="concept-task">task</span> must block. User
+  agents should remain responsive to user input while paused, however,
+  albeit in a reduced capacity since the <span>event loop</span> will
+  not be doing anything.</p>
+
+  <hr>
+
+  <p>When a user agent is to <dfn>obtain the storage mutex</dfn> as
+  part of running a <span title="concept-task">task</span>, it must
+  run through the following steps:</p>
+
+  <ol>
+
+   <li><p>If the <span>storage mutex</span> is already owned by this
+   <span title="concept-task">task</span>'s <span>event loop</span>,
+   then abort these steps.</p></li>
+
+   <li><p>Otherwise, <span>pause</span> until the <span>storage
+   mutex</span> can be taken by the <span>event loop</span>.</p></li>
+
+   <li><p>Take ownership of the <span>storage mutex</span>.</p></li>
+
+  </ol>
+
   </div>
 
 

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