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<p class=MsoNormal align=center style='text-align:center'>Profile Registry Leak</p>
<p class=Paragraph>This document describes a proposed solution to the registryleak problem that we could not fix for Windows 2000.<span style="mso-spacerun:yes">� </span>Bugs 173929 and 435236 are partly caused by the registryleak.<span style="mso-spacerun: yes">� </span>Here is one example of theproblem.<span style="mso-spacerun: yes">� </span>When a user logs off, userenvtries to unload the user's profile.<span style="mso-spacerun: yes">�</span>Sometimes some process has a key open in the registry.<spanstyle="mso-spacerun: yes">� </span>This prevents userenv from unloading thehive.<span style="mso-spacerun: yes">� </span>The spreadsheet below lists mostof the known causes of the bug.</p>
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<p class=Paragraph>This bug has three symptoms that affect users.<spanstyle="mso-spacerun: yes">� </span>First, if userenv cannot unload the profilewhen the user logs off, userenv does not save the user's profile to theserver.<span style="mso-spacerun: yes">� </span>Second, since such profilesnever get unloaded, they end up using a lot of memory on a terminal server thathas lots of users logging in.<span style="mso-spacerun: yes">� </span>Third, ifthe profile is still loaded the next time the user logs in, any changes storedon the server are not loaded and are lost.</p>
<p class=Paragraph>I have a separate solution for each symptom.<spanstyle="mso-spacerun: yes">� </span>Currently when a user logs off, if the profileis locked we poll the profile for 60 seconds before giving up.<spanstyle="mso-spacerun: yes">� </span>I would change the code to use RegSaveKey tosave the hive at the end of the 60 second delay rather then giving up.</p>
<p class=Paragraph>To solve the second symptom, the memory leak, I proposeusing a new API that will soon be checked in.<span style="mso-spacerun: yes">�</span>With this API we can tell the registry to set an event when no one isusing the specified hive.<span style="mso-spacerun: yes">� </span>At that pointwe can unload the hive.<span style="mso-spacerun: yes">� </span>Our code wouldchange so that after waiting 60 seconds for a hive to be unlocked, we would usethe new API to receive notice when the hive was finally free.<spanstyle="mso-spacerun: yes">� </span>We would have to add a thread to wait for eachgroup of 64 hives (WaitForMultipleObjects can only wait for 64 events).<spanstyle="mso-spacerun: yes">� </span>We would have to add code to tell the helperthread which hives to wait for.<span style="mso-spacerun: yes">� </span>Wewould have to add code to synchronize the helper thread and LoadUserProfile inthe case where the user logs back in before the hive gets unloaded.<spanstyle="mso-spacerun: yes">� </span>This does not completely solve the problembecause wininet never releases some of the keys that it uses.<spanstyle="mso-spacerun: yes">� </span>However it makes sure that we behavecorrectly should wininet ever get fixed.<span style="mso-spacerun: yes">�</span>We can show the terminal server team what dlls are leaking registry keysand they can spend the time getting the dlls fixed.</p>
<p class=Code>NtUnloadKeyEx(<o:p></o:p></p>
<p class=Code><span style="mso-spacerun: yes">��� </span>IN POBJECT_ATTRIBUTESTargetKey,<o:p></o:p></p>
<p class=Code><span style="mso-spacerun: yes">��� </span>IN HANDLE EventOPTIONAL<o:p></o:p></p>
<p class=Code><span style="mso-spacerun: yes">��� </span>)<o:p></o:p></p>
<p class=Paragraph>It is unclear if we should solve the last symptom.<spanstyle="mso-spacerun: yes">� </span>Currently userenv does not handle overlappedlogon sessions well.<span style="mso-spacerun: yes">� </span>Userenv will loseone set of changes.<span style="mso-spacerun: yes">� </span>A solution to thatproblem would probably solve this problem.<span style="mso-spacerun: yes">�</span>We could solve this problem by using another new API.<spanstyle="mso-spacerun: yes">� </span>This API will let us rename a key even whenit is in use.<span style="mso-spacerun: yes">� </span>If a user logs on and hishive is loaded because the user has another logon session on the machine, we willuse the loaded hive and lose any changes on the server.<spanstyle="mso-spacerun: yes">� </span>If a user logs on and his hive is loadedbecause some program still has a key open from the last logon session (or someprogram has loaded the hive for its own use), then we will rename the key andload the profile from the server.<span style="mso-spacerun: yes">� </span>Thisrequires that we change our code as described above.<span style="mso-spacerun:yes">� </span>Unfortunately, since the name ntuser.dat is already taken, weneed to use a new name for the hive from the server and remember that when theuser logs out.<span style="mso-spacerun: yes">� </span>At that time we need tomake sure we copy the new hive and attempt to delete the old hive.<spanstyle="mso-spacerun: yes">� </span>We need to handle the case where the userhas multiple hives leaked simultaneously.</p>
<p class=Code>NTSTATUS<o:p></o:p></p>
<p class=Code>NtRenameKey(<o:p></o:p></p>
<p class=Code><span style="mso-spacerun: yes">��� </span>IN HANDLE<spanstyle="mso-spacerun: yes">���������� </span>KeyHandle,<o:p></o:p></p>
<p class=Code><span style="mso-spacerun: yes">��� </span>INPUNICODE_STRING<span style="mso-spacerun: yes">� </span>NewName<o:p></o:p></p>
<p class=Code><span style="mso-spacerun: yes">��� </span>)<o:p></o:p></p>
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