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<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-D62A0234-348C-5553-B8C0-7B483AF9D50C" xml:lang="en"><title>Thread-relative
and Process-relative handles</title><shortdesc>This document describes the difference between thread-relative
and process-relative handles.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>This is the issue of handle ownership.</p>
<p>Threads and processes each maintain a list of objects to which they refer.
This list is an object index and is the way in which handle-numbers representing
these objects are generated.</p>
<p>When user code causes a Kernel object (e.g. a mutex) to be created, ownership
of the handle which is opened on that object may be vested either in the thread
or the process. If ownership is vested in the thread, the handle associated
with that object is said to be <i>thread-relative</i>, conversely, if ownership
is vested in the process, the handle associated with that object is said to
be<i>process-relative</i>.</p>
<p>The following diagram shows the case where code belonging to thread A creates
a mutex and vests ownership of the handle in the thread. </p>
<fig id="GUID-5A22F71B-C146-53A9-B8A4-51D79D4EF668">
<title>Thread-relative handle</title>
<image href="GUID-7B589949-2784-5B77-959E-99F8733A8853_d0e230612_href.png" placement="inline"/>
</fig>
<p>Compare with the following case where ownership of the mutex handle is
vested in the process.</p>
<fig id="GUID-6C60BB64-AE7B-5B46-983B-D6D65D8AB41C">
<title>Process-relative handle</title>
<image href="GUID-47511301-DFF9-52B0-9602-DD9D293D3044_d0e230623_href.png" placement="inline"/>
</fig>
<p>In both cases, the mutex object is added to the appropriate Kernel container
which can be considered as the owner of the object.</p>
<p>The significance of a process-relative handle is that any thread in the
process can use that handle to access the Kernel side object that the handle
represents. In contrast, a thread-relative handle can only be used by the
thread creating it; other threads in that process can only access the Kernel
side object by <xref href="GUID-A4799558-AF8C-5E97-9B03-7D1C04FEC243.dita">duplicating</xref> that
handle.</p>
<p>For a thread-relative handle, the associated Kernel side object is closed
if the thread dies. For a process-relative handle, the Kernel side object
is closed if the process dies. Such an object is not closed if any thread
belonging to that process dies; the object remains in existence for the lifetime
of the process, or until all references to it have been explicitly closed.</p>
<p>See also:</p>
<ul>
<li id="GUID-7355DCEE-85E8-58C6-9102-CBCE93251098"><p><xref href="GUID-A95CDFDE-285F-5DE2-AADE-29B2B9663757.dita">The
object index</xref> </p> </li>
</ul>
</conbody></concept>