'Re: Review Request 111718: Prevent EntityListCache from causing endless loop'

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List:       kde-release-team
Subject:    Re: Review Request 111718: Prevent EntityListCache from causing endless loop
From:       "Commit Hook" <null () kde ! org>
Date:       2013-07-27 12:04:23
Message-ID: 20130727120423.4847.22843 () vidsolbach ! de
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(Updated July 27, 2013, 12:04 p.m.)

Status
------

This change has been marked as submitted.

Review request for KDEPIM-Libraries and Release Team.

Description
-------

Calling ensureCached() can cause the cache and Monitor to end up in an \
endless loop.

In situation, that there are items 1,2,4,5 and 6 in the cache, calling \
ensureCached(1,2,3,4,5) will call request(3) and return false. request() \
internally calls shrinkCache() which removes all fetched items to make sure \
the cache does not grow indefinitely. After the item 3 is fetched, we end \
up with cache with only item 3. Monitor will then again call \
ensureCached(1,2,3,4,5), which will call request(1,2,4,5) which in return \
calls shrinkCache(), which will remove the item 3 and after fetched is \
finished the cache only contains items 1,2,4 and 5. This way the cache ends \
up in an endless loop because it will never contain all items that Monitor \
requested.

This patch prevents shrinkCache() from removing items that are part of the \
ensureCached() request.

I would like to get this patch to 4.11, because it's not that difficult to \
trigger this bug and in such case you end up with Akonadi resource going \
nuts (and not processing any further requests)

This implementation is still not optimal, because meanwhile the Monitor can \
call ensureCached(7,8,9), which will cause (1,2,4,5) to be removed from \
cache anyway, so it can take several tries for EntityListCache to retrieve \
the entire set (1,2,3,4,5). However now it's guaranteed that at some point \
the cache will succeed. We can rethink (and maybe remove) the cache when \
server-side recording is implemented.

Diffs
-----

  akonadi/entitycache_p.h 5f00917 

Diff: http://git.reviewboard.kde.org/r/111718/diff/

Testing
-------

Thanks,

Dan Vrátil

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      This is an automatically generated e-mail. To reply, visit:
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<div>Review request for KDEPIM-Libraries and Release Team.</div>
<div>By Dan Vrátil.</div>

<p style="color: grey;"><i>Updated July 27, 2013, 12:04 p.m.</i></p>

<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description \
</h1>  <table width="100%" bgcolor="#ffffff" cellspacing="0" \
cellpadding="10" style="border: 1px solid #b8b5a0">  <tr>
  <td>
   <pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;">Calling ensureCached() can cause the cache and Monitor to end \
up in an endless loop.

In situation, that there are items 1,2,4,5 and 6 in the cache, calling \
ensureCached(1,2,3,4,5) will call request(3) and return false. request() \
internally calls shrinkCache() which removes all fetched items to make sure \
the cache does not grow indefinitely. After the item 3 is fetched, we end \
up with cache with only item 3. Monitor will then again call \
ensureCached(1,2,3,4,5), which will call request(1,2,4,5) which in return \
calls shrinkCache(), which will remove the item 3 and after fetched is \
finished the cache only contains items 1,2,4 and 5. This way the cache ends \
up in an endless loop because it will never contain all items that Monitor \
requested.

This patch prevents shrinkCache() from removing items that are part of the \
ensureCached() request.

I would like to get this patch to 4.11, because it&#39;s not that difficult \
to trigger this bug and in such case you end up with Akonadi resource going \
nuts (and not processing any further requests)

This implementation is still not optimal, because meanwhile the Monitor can \
call ensureCached(7,8,9), which will cause (1,2,4,5) to be removed from \
cache anyway, so it can take several tries for EntityListCache to retrieve \
the entire set (1,2,3,4,5). However now it&#39;s guaranteed that at some \
point the cache will succeed. We can rethink (and maybe remove) the cache \
when server-side recording is implemented.</pre>  </td>
 </tr>
</table>

<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> \
</h1> <ul style="margin-left: 3em; padding-left: 0;">

 <li>akonadi/entitycache_p.h <span style="color: \
grey">(5f00917)</span></li>

</ul>

<p><a href="http://git.reviewboard.kde.org/r/111718/diff/" \
style="margin-left: 3em;">View Diff</a></p>

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