Potential endless loop in jcr install
-------------------------------------
Key: SLING-2086
URL: https://issues.apache.org/jira/browse/SLING-2086
Project: Sling
Issue Type: Bug
Components: Installer
Affects Versions: JCR Installer 3.0.4
Reporter: Carsten Ziegeler
Assignee: Carsten Ziegeler
Fix For: JCR Installer 3.1.0
The log looks like the following:
....
12.05.2011 13:03:27.747 *INFO* [JcrInstaller.4]
org.apache.sling.installer.provider.jcr.impl.WatchedFolder Watching folder
/libs/mcm/install (priority 100)
12.05.2011 13:03:27.748 *INFO* [JcrInstaller.4]
org.apache.sling.installer.provider.jcr.impl.WatchedFolder Watching folder
/libs/crxde/install (priority 100)
12.05.2011 13:03:27.750 *INFO* [JcrInstaller.4]
org.apache.sling.installer.provider.jcr.impl.WatchedFolder Watching folder
/apps/geometrixx/install (priority 200)
12.05.2011 13:03:27.752 *INFO* [JcrInstaller.4]
org.apache.sling.installer.provider.jcr.impl.JcrInstaller Removing resource
from
OSGi installer (folder deleted): []
This repeats every 500ms.
The WatchedFolder.rescanTimer is set, but all WatchedFolders.needsScan() return
false. That leads to the endless loop, since in JcrInstaller.runOneCycle the
variable scanWf is always true, but for every watched folder needsScan()
returns
false. Therefore the rescanTimer is never reset, but updateFoldersList() is
called every 500ms.
Probably this is caused by the following timing (for example if you delete
/apps/geometrixx/install):
1. The background thread executes runOnCycle in JcrInstaller up to line 446
(at this time the rescanTimer of the WatchedFolders is not set, but
updateFoldersListTimer.expired() is true)
2. The event listener thread calls onEvent of the WatchedFolder for
/apps/geometrixx/install. This leads to a cal of scheduleScan() which itself
sets the rescanTimer and also sets needScan to true.
3. Back in the background thread updateFoldersList() is executed (line 453
of
JcrInstaller). In this method it detects that one of the watchedFolder have
been
removed and therefore indirectly resets the needScan of the WatchedFolder
/apps/geometrixx/install back to false (line 385). Unfortunately it doesn't
reset the rescanTimer.
4. The next time when runOneCycle is executed, the rescanTimer has exired ->
scanWF is true. Unfortunately every watchedFolder returns false for
needsScan().
Now you are in a loop, because the rescanTimer will not be reset.
The main problem is, that needsScan and rescanTimer.reset/set must always be
set
in parallel, but this is not true for the described usecase.
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