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https://issues.apache.org/jira/browse/UIMA-6413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17479926#comment-17479926
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Richard Eckart de Castilho edited comment on UIMA-6413 at 1/21/22, 9:12 AM:
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When a resource manager is copied using the {{ResourceManager_impl.copy()}}
method, the {{UIMAClassLoader}} is copied along. If the copy of the resource
manager is destroyed, then the {{UIMAClassLoader}} is currently closed - that
means that the original resource manager can also no longer use the class
loader. This seems to happen only in
{{PearAnalysisEngineWrapper.createRM(StringPair, PackageBrowser,
ResourceManager)}}.
{code}
if (null == parentResourceManager) {
// could be null for top level Pear not in an aggregate
rsrcMgr = UIMAFramework.newDefaultResourceManager();
} else {
rsrcMgr = ((ResourceManager_impl) parentResourceManager).copy();
}
rsrcMgr.setExtensionClassPath(sp.classPath, true);
{code}
However, the call to {{rsrcMgr.setExtensionClassPath}} following the copy
immediately in fact currently installs a new {{UIMAClassLoader}} in the copied
resource manager.
was (Author: rec):
When a resource manager is copied using the {{ResourceManager_impl.copy()}}
method, the {{UIMAClassLoader}} is copied along. If the copy of the resource
manager is destroyed, then the {{UIMAClassLoader}} is currently closed - that
means that the original resource manager can also no longer use the class
loader. This seems to happen only in
{{PearAnalysisEngineWrapper.createRM(StringPair, PackageBrowser,
ResourceManager)}}.
{code}
if (null == parentResourceManager) {
// could be null for top level Pear not in an aggregate
rsrcMgr = UIMAFramework.newDefaultResourceManager();
} else {
rsrcMgr = ((ResourceManager_impl) parentResourceManager).copy();
// newPearsParent.set((ResourceManager_impl) parentResourceManager);
// rsrcMgr = UIMAFramework.newDefaultResourceManagerPearWrapper();
// newPearsParent.remove();
//
((ResourceManagerPearWrapper)rsrcMgr).initializeFromParentResourceManager(parentResourceManager);
}
rsrcMgr.setExtensionClassPath(sp.classPath, true);
{code}
However, the call to {{rsrcMgr.setExtensionClassPath}} following the copy
immediately in fact currently installs a new {{UIMAClassLoader}} in the copied
resource manager.
> Memory leak in FSClassRegistry
> ------------------------------
>
> Key: UIMA-6413
> URL: https://issues.apache.org/jira/browse/UIMA-6413
> Project: UIMA
> Issue Type: Improvement
> Components: Core Java Framework
> Reporter: Richard Eckart de Castilho
> Assignee: Richard Eckart de Castilho
> Priority: Major
> Fix For: 3.3.0SDK
>
>
> This is essentially a follow-up issue to UIMA-6276.
> So, when a CAS is created, then a cache is filled in
> {{FSClassRegistry.cl_to_type2JCas}} which maintains information about the
> JCas representation of the different types. This is a per-classloader cache -
> so for every classloader which is involved in the creation of a (J)CAS, an
> entry is added. Now normally, classloaders are pretty long-lived objects and
> you only have so many during the runtime of a program. But there are cases
> where classloaders are created in volumes and in this case we run into
> trouble. Now, UIMA-6276 has turned the cache into a weak map hoping that once
> a classloader is garbarge-collected, the cache would get cleaned up
> automatically. However, that idea was not thought through entirely because
> one of the pieces of information stored in the map is a {{FsGenerator3}} and
> that generator is actually generated via the particular classloader that is
> the key in the map. Thus, a value in the map has a strong reference to the
> weak key causing the key never to get garbage collected... and there might be
> other fields as well contributing to that cycle.
> In particular, a new classloader is generated whenever a new
> {{ResourceManager}} with a custom extension path. A typical case for this to
> happen is when a PEAR is used. But there can be other reasons why somebody
> would create new custom resource managers.
> Limiting the number of {{ResourceManager}}s in a system may not be feasible
> because typically there should be one per pipeline (to allow for shared
> resources), so if you are in a situation where pipelines are instantiated and
> destroyed repeatedly, it makes sense to create {{ResourceManager}}s alongside.
> However, typically the number of classloaders in a system is pretty set. The
> {{ResourceManager}} internally wraps these classloaders with an
> {{UimaClassLoader}} (only if a specific classloader or a extension path is
> passed to the resource manager). So assuming that essentially always the same
> set of classloaders is provided (any maybe only a limited set of extension
> paths), it should be ok to introduce another cache of {{[classloader,
> extension path] -> UimaClassLoader}} to limit the number of
> {{UimaClassLoader}} instances and therefore limit the size of
> {{FSClassRegistry.cl_to_type2JCas}}.
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