[jira] [Commented] (OFBIZ-5204) Concurrent access to GenericEngineFactory causes exceptions

["Adrian Crum (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OFBIZ-5204?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13672320#comment-13672320 ] 

Adrian Crum commented on OFBIZ-5204:
------------------------------------

The new models are committed to the trunk in rev 1488643.

Since the models validate the configuration, client code can be simplified. In other words, feel free to remove configuration validation code from the classes that use the service engine.


                
> Concurrent access to GenericEngineFactory causes exceptions
> -----------------------------------------------------------
>
>                 Key: OFBIZ-5204
>                 URL: https://issues.apache.org/jira/browse/OFBIZ-5204
>             Project: OFBiz
>          Issue Type: Bug
>          Components: framework
>    Affects Versions: SVN trunk
>            Reporter: Christoph Neuroth
>            Priority: Critical
>         Attachments: GenericEngineFactoryTests.java, OFBIZ-5204-2013-05-31.patch, OFBIZ-5204-2013-05-31.patch, ofbiz-serviceengine.patch
>
>
> Several users (see e.g. OFBIZ-2807, OFBIZ-2793) have reported sometimes getting the following exception, especially during startup or after clearing the cache:
> {quote}Cannot find a service engine definition for the engine name [" + engineName + "] in the serviceengine.xml file{quote}
> By including some debug logging we found that when this happens, one or more of the nodes in the DOM lose attribute values, so for example this node from the serviceengine.xml file:
> {code}<engine name="java" class="org.ofbiz.service.engine.StandardJavaEngine"/>{code}
> might look like this to the calling code:
> {code}<engine name="java" class=""/>{code}
> As usual with multi-threading problems this occurs very randomly and depends on a lot of factors out of control, so to test the behavior we included a test case which emulates lots of concurrent accesses and fails most of the time, see GenericEngineFactoryTests.java.
> The reason for this bug is that OFBiz reuses and concurrently accesses Xerces DOM objects which are not thread-safe (not even for read access).
> ResourceLoader.java#getXmlDocument also states that:
> {quote}
>     // This method should be avoided. DOM object trees take a lot of memory, so they should
>     // not be cached.
> {quote}
> Therefore we would like to propose to refactor ServiceConfigUtil (and other places) so that it never returns Xerces dom objects and instead internally binds the XML to POJOs.
> We implemented an example which fixes this particular issue.
> Apply the attached patch and generate the POJOs:
> {code}
> $ patch < ofbiz-serviceengine.patch
> $ xjc ./framework/service/dtd/service-config.xsd -p org.ofbiz.service.config.generated -d framework/service/src
> {code}
> This fixed this particular issue for us, but we think there might be others issues like this wherever Document/Element objects are passed around.
> If you are okay with this implementation we could do some more work on this, implementing the xjc stuff in the ant build and potentially fix other places where the DOM objects are used as well, but we wanted to get your opinion first.

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