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https://issues.apache.org/jira/browse/SHIRO-452?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14615311#comment-14615311
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Andreas Kohn commented on SHIRO-452:
------------------------------------
FWIW: We fixed our OptionalDataExceptions by configuring ehcache to use
{{copyonwrite}} for the shiro-activeSessionCache. In our case the issue seems
to have to been caused by shiro's logic to update the session last access time.
Unfortunately I do not have the original exception anymore, only the commit
message for the change of the configuration :/
> SimpleSession serialization failing
> -----------------------------------
>
> Key: SHIRO-452
> URL: https://issues.apache.org/jira/browse/SHIRO-452
> Project: Shiro
> Issue Type: Bug
> Components: Caching , Session Management
> Affects Versions: 1.2.1
> Environment: Java 6 - EhCache 2.6.2
> Reporter: Bruno GRIEDER
>
> We cache SimpleSession in EhCache which is configured with Overflow to Disk
> and an LRU eviction policy.
> When the cache is full, EhCache will attempt to evict a session from the Disk
> Storage to reclaim space.
> To evict the `SimpleSession`, EhCache will attempt to deserialize the
> eveicted session first. From time to time, the deserialization of the
> `SimpleSession` fails. When that happens the system is locked, since no
> additional session can be created.
> `SimpleSession` has a custom serialization mechanism that calculates a bit
> mask which indicates which fields of the `SimpleSession` contain values. This
> bitMask is serialized first (as a Short) then the fields containing values.
> When deserialization is failing, the bitMask indicates that the `attributes`
> Map contains data, however no `attributes` have actually been serialized and
> the deserialization fails with a `java.io.OptionalDataException`.
> The discrepancy is very likely due to `attributes` being a non synchronized
> Map: the SimpleSession is created on a Servlet thread, however the
> serialization to Disk is performed by EhCache on one of its cache management
> threads.
> SimpleSession fields should likely be marked as volatile and the Map should
> be a Synchronized Map or SimpleSession should be made immutable.
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