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https://issues.apache.org/jira/browse/MSHADE-329?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17265656#comment-17265656
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Bruno Medeiros commented on MSHADE-329:
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> There is no problem running {{mvn}} in single-thread mode.
I can confirm this bug, same thing happening here if `-T4C` is added to the
build.
I'm attaching a thread dump taken while maven build was stuck, we can seem some
builder threads in `RUNNABLE` state, but writing to files like crazy.
As disabling parallel build seems a very harsh workaround, we are doing this
here:
{code:java}
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>3.2.4</version>
<configuration>
<!-- disabling reduced pom generation due to
https://issues.apache.org/jira/browse/MSHADE-329 -->
<createDependencyReducedPom>false</createDependencyReducedPom>
</configuration>
</plugin>
{code}
I even dare to suggest we disable reduced pom generation by default as most
people using it are just generating a uber jar and don't need a pom for that
(personal opinion).
> Concurrent writes of dependency-reduced-pom.xml adds same exclusion ad
> infinitum
> --------------------------------------------------------------------------------
>
> Key: MSHADE-329
> URL: https://issues.apache.org/jira/browse/MSHADE-329
> Project: Maven Shade Plugin
> Issue Type: Bug
> Affects Versions: 3.2.1
> Reporter: Håkon Hallingstad
> Priority: Major
> Attachments: mshade-329-thread-dump.txt
>
>
> I have a multi-threaded {{mvn install}} that seems to halt but ends up using
> 200% CPU, in about 50% of the invocations. The {{mvn}} command used is:
> {panel}
> mvn -T1C -nsu -Dmaven.source.skip -Dmaven.javadoc.skip -Dmaven.test.skip
> install -rf :MODULE
> {panel}
> Using {{mvnDebug}} I have found out that there are 2 running Java threads,
> each writing {{dependency-reduced-pom.xml}} in two different modules {{A}}
> and {{B}}, respectively. These files seems to become several MB large, before
> they're deleted and then written again, and so forth.
> I have looked into one of the threads, and there is a
> {{rewriteDependencyReducedPomIfWeHaveReduction}} in ShadeMojo with a
> {{loopCounter}} with value 2735, that just keeps increasing. Presumably there
> is something like one dependency-reduced-pom.xml written per iteration.
> From the source code it seems this can only happen if
> https://github.com/apache/maven-shade-plugin/blob/master/src/main/java/org/apache/maven/plugins/shade/mojo/ShadeMojo.java#L1172
> is hit at least that number of times, meaning the ShadeMojo adds that many
> exclusions, which seems to correspond to hamcrest-core:
> {noformat}
> <dependencies>
> <dependency>
> <groupId>junit</groupId>
> <artifactId>junit</artifactId>
> <version>4.12</version>
> <scope>test</scope>
> <exclusions>
> <exclusion>
> <artifactId>hamcrest-core</artifactId>
> <groupId>org.hamcrest</groupId>
> </exclusion>
> <exclusion>
> <artifactId>hamcrest-core</artifactId>
> <groupId>org.hamcrest</groupId>
> </exclusion>
> ...
> {noformat}
> {panel}
> grep hamcrest-core dependency-reduced-pom.xml | wc -l
> 2735
> {panel}
>
> The same exclusion is added {{loopCounter}} times in {{updateExcludesInDeps}}.
> There is no problem running {{mvn}} in single-thread mode.
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