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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-7A71CD0B-84C7-5A77-B573-C61F67C382DA" xml:lang="en"><title>Summary

of cleanup rules</title><shortdesc>This document states general rules for cleanup.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>The general rules for cleanup during the lifetime of an object are:</p>

<ul>

<li id="GUID-AEE55F10-3FD5-5B09-B025-C5499DE7B312"><p>between the moment the

object is allocated, and the moment that a pointer to that object is stored

in a structure which would be accessible if a leave occurred, the object must

be pushed to the clean-up stack if a leave could possibly occur</p> </li>

<li id="GUID-B69DDE00-FE4C-582F-B5FA-0FA7684591F6"><p>when a pointer to the

object has been stored in an object which would be accessible if a leave occurred,

then the object should be popped from the cleanup stack before a leave could

possibly occur: normally, the object is popped first, and then the pointer

is stored</p> </li>

<li id="GUID-D8D6B31E-0B9F-56C6-B9B0-2197549E78FC"><p>an object is accessible

if a leave occurs, if either it is pushed to the cleanup stack, or there is

a reference to it from another object which would be accessible if a leave

occurred, or there is a reference to it from a stack frame which would not

be affected when a leave occurs (because of an appropriately-placed <codeph>TRAP</codeph>),

or there is a reference to it from a global variable</p> </li>

<li id="GUID-4F508BDB-59D1-52EA-84C2-CABE3E9339EC"><p>it should never be possible

to clean up an object more than once, if a leave occurred</p> </li>

</ul>

<p>In practice, this means that an object must be referred to either by a

cleanup stack frame, or by a reference from another object. More rarely, the

object may be referred to by a stack frame which cannot be unwound during

the lifetime of that object, because of an appropriate <codeph>TRAP</codeph>.

More rarely still, the object may be referred to by a global variable.</p>

</conbody></concept>