<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 - Windows: Cannot use HANDLE from GetCurrentThread() to get the CONTEXT of another thread"
href="https://bugs.webkit.org/show_bug.cgi?id=144924">144924</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Windows: Cannot use HANDLE from GetCurrentThread() to get the CONTEXT of another thread
</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@lists.webkit.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>mark.lam@apple.com
</td>
</tr></table>
<p>
<div>
<pre>The present stack scanning code in the Windows port is expecting that the GetCurrentThread() API will provide a unique HANDLE for each thread. The code then saves and later uses that HANDLE with GetThreadContext() to get the runtime state of the target thread from the GC thread. According to <a href="https://msdn.microsoft.com/en-us/library/windows/desktop/ms683182(v=vs.85).aspx">https://msdn.microsoft.com/en-us/library/windows/desktop/ms683182(v=vs.85).aspx</a>, GetCurrentThread() does not provide this unique HANDLE that we expect:
"The function cannot be used by one thread to create a handle that can be used by other threads to refer to the first thread. The handle is always interpreted as referring to the thread that is using it. A thread can create a "real" handle to itself that can be used by other threads, or inherited by other processes, by specifying the pseudo handle as the source handle in a call to the DuplicateHandle function.”
As a result of this, GetCurrentThread() always returns the same HANDLE value, and we end up never scanning the stacks of other threads because we wrongly think that they are all equal (in identity) to the scanning thread. This, in turn, results in crashes due objects that are incorrectly collected.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are the assignee for the bug.</li>
</ul>
</body>
</html>