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https://issues.apache.org/jira/browse/SLING-10133?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Christian Schneider updated SLING-10133:
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Fix Version/s: (was: Content Distribution Core 0.4.4)
Content Distribution Core 0.4.6
> Memory leak in MonitoringDistributionPackageBuilder
> ---------------------------------------------------
>
> Key: SLING-10133
> URL: https://issues.apache.org/jira/browse/SLING-10133
> Project: Sling
> Issue Type: Bug
> Components: Content Distribution
> Affects Versions: Content Distribution Core 0.4.0
> Reporter: Timothee Maret
> Priority: Major
> Fix For: Content Distribution Core 0.4.6
>
>
> The MonitoringDistributionPackageBuilder maintain a list of MBean for the
> latest packages. The number of packages to be monitored is passed as the
> [queueCapacity|https://github.com/apache/sling-org-apache-sling-distribution-core/blob/b80cd8f3bae6b7875387ee7caaea271b7e9baec6/src/main/java/org/apache/sling/distribution/monitor/impl/MonitoringDistributionPackageBuilder.java#L49]
> via the constructor. When the queueCapacity is 0, the monitoring is disabled.
> [VaultDistributionPackageBuilderFactory|https://github.com/apache/sling-org-apache-sling-distribution-core/blob/b80cd8f3bae6b7875387ee7caaea271b7e9baec6/src/main/java/org/apache/sling/distribution/serialization/impl/vlt/VaultDistributionPackageBuilderFactory.java#L201]
> and
> [DistributionPackageBuilderFactory|https://github.com/apache/sling-org-apache-sling-distribution-core/blob/b80cd8f3bae6b7875387ee7caaea271b7e9baec6/src/main/java/org/apache/sling/distribution/serialization/impl/DistributionPackageBuilderFactory.java]
> disable this feature by default. An environment that runs for multiple weeks
> without restart and with the default configuration will experience a memory
> leak that leads to the JVM running out of memory.
> The implementation has two flaws that explain the memory leak.
>
> h2. #1 - Registering a MBean when the queueCapacity is 0
> The code [unconditionally registers a
> MBean|https://github.com/apache/sling-org-apache-sling-distribution-core/blob/b80cd8f3bae6b7875387ee7caaea271b7e9baec6/src/main/java/org/apache/sling/distribution/monitor/impl/MonitoringDistributionPackageBuilder.java#L106]
> even if the queueCapacity is 0. We need to only register a MBean when the
> capacity is > 0.
> h2. #2 - Concurrency issue when un-registering MBean
> The code [attempts to
> remove|https://github.com/apache/sling-org-apache-sling-distribution-core/blob/b80cd8f3bae6b7875387ee7caaea271b7e9baec6/src/main/java/org/apache/sling/distribution/monitor/impl/MonitoringDistributionPackageBuilder.java#L108]
> by checking if the queueCapacity equals the list of MBeans. This check works
> in a single threaded context but it falls short when
> registerDistributionPackageMBean is invoked concurrently. In the latter case,
> it can happen that the check never holds true leading the mBeans queue to
> grow indefinitely. One solution is to leverage the features of the
> LinkedBlockingDeque. Create a LinkedBlockingDeque with bounded capacity and
> rely on the returned status from the offer method to decide if an item needs
> to be removed.
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