Ryan Heinen created MPMD-159:
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Summary: Threadsafety issue when used in parallel builds
Key: MPMD-159
URL: https://jira.codehaus.org/browse/MPMD-159
Project: Maven 2.x PMD Plugin
Issue Type: Bug
Affects Versions: 2.7.1, 2.8
Reporter: Ryan Heinen
Attachments: doxia-1.3-upgrade.patch
Using the maven-pmd-plugin during a parallel maven build can produce the
following error:
{code}
[ERROR] Failed to execute goal
org.apache.maven.plugins:maven-pmd-plugin:2.8-SNAPSHOT:pmd (pmd) on project
<projectname>: An error has occurred in PMD Report report generation. Could not
find the template
'org/apache/maven/doxia/siterenderer/resources/default-site.vm:
NullPointerException -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e
switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please
read the following articles:
[ERROR] [Help 1]
http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
{code}
Reproducibility of this problem appears to be based on the reactor structure
and how parallelizable it is. I will try to create a test case that reproduces
this problem consistently. At times it is 100% reproducible, but then a small
change to the reactor configuration (eg. add a project) will cause the error to
disappear.
I believe that this bug is caused by thread safety issues in the velocity
library that is used by doxia.
Upgrading doxia dependencies to version 1.3 appears to resolve this bug.
Although the version of velocity used by doxia 1.3 is still the same,
velocity-tools been introduced.
In version 1.3, instead of newing the VelocityContext directly,
doxia-site-renderer uses ToolManager.getContext, which delegates to
ToolboxFactory to do some initialization. This initialization logic is
protected with synchronization, which may explain why the bug seems to go away
after the upgrade.
I've included a patch that applies against trunk of the maven-pmd-plugin which
upgrades doxia from version 1.1.3 to 1.3.
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