<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head><meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title>[202736] trunk/Source/WTF</title>
</head>
<body>
<style type="text/css"><!--
#msg dl.meta { border: 1px #006 solid; background: #369; padding: 6px; color: #fff; }
#msg dl.meta dt { float: left; width: 6em; font-weight: bold; }
#msg dt:after { content:':';}
#msg dl, #msg dt, #msg ul, #msg li, #header, #footer, #logmsg { font-family: verdana,arial,helvetica,sans-serif; font-size: 10pt; }
#msg dl a { font-weight: bold}
#msg dl a:link { color:#fc3; }
#msg dl a:active { color:#ff0; }
#msg dl a:visited { color:#cc6; }
h3 { font-family: verdana,arial,helvetica,sans-serif; font-size: 10pt; font-weight: bold; }
#msg pre { overflow: auto; background: #ffc; border: 1px #fa0 solid; padding: 6px; }
#logmsg { background: #ffc; border: 1px #fa0 solid; padding: 1em 1em 0 1em; }
#logmsg p, #logmsg pre, #logmsg blockquote { margin: 0 0 1em 0; }
#logmsg p, #logmsg li, #logmsg dt, #logmsg dd { line-height: 14pt; }
#logmsg h1, #logmsg h2, #logmsg h3, #logmsg h4, #logmsg h5, #logmsg h6 { margin: .5em 0; }
#logmsg h1:first-child, #logmsg h2:first-child, #logmsg h3:first-child, #logmsg h4:first-child, #logmsg h5:first-child, #logmsg h6:first-child { margin-top: 0; }
#logmsg ul, #logmsg ol { padding: 0; list-style-position: inside; margin: 0 0 0 1em; }
#logmsg ul { text-indent: -1em; padding-left: 1em; }#logmsg ol { text-indent: -1.5em; padding-left: 1.5em; }
#logmsg > ul, #logmsg > ol { margin: 0 0 1em 0; }
#logmsg pre { background: #eee; padding: 1em; }
#logmsg blockquote { border: 1px solid #fa0; border-left-width: 10px; padding: 1em 1em 0 1em; background: white;}
#logmsg dl { margin: 0; }
#logmsg dt { font-weight: bold; }
#logmsg dd { margin: 0; padding: 0 0 0.5em 0; }
#logmsg dd:before { content:'\00bb';}
#logmsg table { border-spacing: 0px; border-collapse: collapse; border-top: 4px solid #fa0; border-bottom: 1px solid #fa0; background: #fff; }
#logmsg table th { text-align: left; font-weight: normal; padding: 0.2em 0.5em; border-top: 1px dotted #fa0; }
#logmsg table td { text-align: right; border-top: 1px dotted #fa0; padding: 0.2em 0.5em; }
#logmsg table thead th { text-align: center; border-bottom: 1px solid #fa0; }
#logmsg table th.Corner { text-align: left; }
#logmsg hr { border: none 0; border-top: 2px dashed #fa0; height: 1px; }
#header, #footer { color: #fff; background: #636; border: 1px #300 solid; padding: 6px; }
#patch { width: 100%; }
#patch h4 {font-family: verdana,arial,helvetica,sans-serif;font-size:10pt;padding:8px;background:#369;color:#fff;margin:0;}
#patch .propset h4, #patch .binary h4 {margin:0;}
#patch pre {padding:0;line-height:1.2em;margin:0;}
#patch .diff {width:100%;background:#eee;padding: 0 0 10px 0;overflow:auto;}
#patch .propset .diff, #patch .binary .diff {padding:10px 0;}
#patch span {display:block;padding:0 10px;}
#patch .modfile, #patch .addfile, #patch .delfile, #patch .propset, #patch .binary, #patch .copfile {border:1px solid #ccc;margin:10px 0;}
#patch ins {background:#dfd;text-decoration:none;display:block;padding:0 10px;}
#patch del {background:#fdd;text-decoration:none;display:block;padding:0 10px;}
#patch .lines, .info {color:#888;background:#fff;}
--></style>
<div id="msg">
<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/202736">202736</a></dd>
<dt>Author</dt> <dd>jer.noble@apple.com</dd>
<dt>Date</dt> <dd>2016-07-01 08:40:39 -0700 (Fri, 01 Jul 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>Deadlock inside -[WebCoreNSURLSession dealloc]
https://bugs.webkit.org/show_bug.cgi?id=159331
<rdar://problem/27122716>
Reviewed by Alex Christensen.
A Function<> object can wrap any callable type, including a C++ lambda.
dispatchFunctionsFromMainThread() holds a lock while iterating over the functions in
functionQueue(), and during ths iteration, the previous callable object is destroyed by
assigning the result of functionQueue().takeFirst(). Because lambdas (and other callables,
like functors) can own objects, destroying this callable can have side effects, and if one
of those side effects is to call callOnMainThread(), this can deadlock.
Move this side-effect-having call outside the locked block by clearing the function object
immediately after calling it.
* wtf/MainThread.cpp:
(WTF::dispatchFunctionsFromMainThread):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWTFChangeLog">trunk/Source/WTF/ChangeLog</a></li>
<li><a href="#trunkSourceWTFwtfMainThreadcpp">trunk/Source/WTF/wtf/MainThread.cpp</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWTFChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/ChangeLog (202735 => 202736)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/ChangeLog 2016-07-01 15:29:09 UTC (rev 202735)
+++ trunk/Source/WTF/ChangeLog 2016-07-01 15:40:39 UTC (rev 202736)
</span><span class="lines">@@ -1,3 +1,25 @@
</span><ins>+2016-07-01 Jer Noble <jer.noble@apple.com>
+
+ Deadlock inside -[WebCoreNSURLSession dealloc]
+ https://bugs.webkit.org/show_bug.cgi?id=159331
+ <rdar://problem/27122716>
+
+ Reviewed by Alex Christensen.
+
+ A Function<> object can wrap any callable type, including a C++ lambda.
+
+ dispatchFunctionsFromMainThread() holds a lock while iterating over the functions in
+ functionQueue(), and during ths iteration, the previous callable object is destroyed by
+ assigning the result of functionQueue().takeFirst(). Because lambdas (and other callables,
+ like functors) can own objects, destroying this callable can have side effects, and if one
+ of those side effects is to call callOnMainThread(), this can deadlock.
+
+ Move this side-effect-having call outside the locked block by clearing the function object
+ immediately after calling it.
+
+ * wtf/MainThread.cpp:
+ (WTF::dispatchFunctionsFromMainThread):
+
</ins><span class="cx"> 2016-06-29 Jer Noble <jer.noble@apple.com>
</span><span class="cx">
</span><span class="cx"> Adopt MediaRemote.
</span></span></pre></div>
<a id="trunkSourceWTFwtfMainThreadcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/wtf/MainThread.cpp (202735 => 202736)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/wtf/MainThread.cpp 2016-07-01 15:29:09 UTC (rev 202735)
+++ trunk/Source/WTF/wtf/MainThread.cpp 2016-07-01 15:40:39 UTC (rev 202736)
</span><span class="lines">@@ -133,6 +133,9 @@
</span><span class="cx">
</span><span class="cx"> function();
</span><span class="cx">
</span><ins>+ // Clearing the function can have side effects, so do so outside of the lock above.
+ function = nullptr;
+
</ins><span class="cx"> // If we are running accumulated functions for too long so UI may become unresponsive, we need to
</span><span class="cx"> // yield so the user input can be processed. Otherwise user may not be able to even close the window.
</span><span class="cx"> // This code has effect only in case the scheduleDispatchFunctionsOnMainThread() is implemented in a way that
</span></span></pre>
</div>
</div>
</body>
</html>