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https://issues.apache.org/jira/browse/CONFIGURATION-390?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12759947#action_12759947
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Ralph Goers commented on CONFIGURATION-390:
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I don't understand the Accessor thing. The issue is that various operations
have to be synchronized since the underlying structure might change while the
operation is being performed. I'm not sure how this construct helps.
With CombinedConfiguration I also have focused on that bit of code and
syncrhonized there pretty much the way you have suggested but the use case I
posted above still fails. From what I can tell this is because in an
XMLConfiguration the root node is cleared and then reloaded. Apparently
getTransformedRoot() adds the nodes from the actual HierarchicalConfiguration
into the CombinedConfiguration instead of making copies of them. This means
that once the reloadLock is released the CombinedConfiguration can be modified
asynchronously.
The above shouldn't be a problem if it simply isn't allowed to use a
Configuration object directly once it is incorporated into a combined
configuration.
> AbstractHierarchicalFileConfiguration is not thread safe
> --------------------------------------------------------
>
> Key: CONFIGURATION-390
> URL: https://issues.apache.org/jira/browse/CONFIGURATION-390
> Project: Commons Configuration
> Issue Type: Bug
> Components: File reloading
> Affects Versions: 1.6
> Reporter: Emmanuel Bourg
> Fix For: 1.7
>
> Attachments: commons-configuration-390.patch, configtest.tar.gz,
> TestSuite.txt
>
>
> AbstractHierarchicalFileConfiguration doesn't implement the same locking
> mechanism found in AbstractFileConfiguration. The consequence is that getting
> a property while the configuration is being reloaded by another thread can
> return an invalid result.
> This can be demonstrated by changing testDeadlockWithReload() in
> TestCombinedConfiguration to use an XMLConfiguration instead of a
> PropertiesConfiguration.
> Here is a reduced test case:
> {code:java}
> public void testConcurrentGetAndReload() throws Exception
> {
> //final FileConfiguration config = new
> PropertiesConfiguration("test.properties");
> final FileConfiguration config = new XMLConfiguration("test.xml");
> config.setReloadingStrategy(new FileAlwaysReloadingStrategy());
> assertTrue("Property not found", config.getProperty("test.short") !=
> null);
> new Thread()
> {
> public void run()
> {
> for (int i = 0; i < 1000; i++)
> {
> config.reload();
> }
> }
> }.start();
>
> for (int i = 0; i < 1000; i++)
> {
> assertTrue("Property not found", config.getProperty("test.short") !=
> null); // failure here
> }
> }
> {code}
> The test doesn't always fail. It does about 50% of the time.
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