Repository with a small sample project illustrating a problem with Maven's MojoExecutor when building multi-threaded, reported in MNG-5960
- Apache Maven 3 (tested with 3.3.9 and 3.4.0-SNAPSHOT)
- Java (duh?)
- Clone this repository (
git clone https://github.com/fvanderveen/maven-mojo-jojo.git) - Make sure the clone works single-threaded:
mvn clean package. (This should succeed) - Clean the workspace (
mvn clean) - Attempt multi-threaded compilation with at least 2 threads (
mvn package -T2)
Step 4 will fail (most of the time?) on a race condition, causing it to no longer have junit on the compile classpath for the test-compile execution of the maven-compiler-plugin.
[BuilderThread 3] [INFO] -------------------------------------------------------------
[BuilderThread 3] [ERROR] COMPILATION ERROR :
[BuilderThread 3] [INFO] -------------------------------------------------------------
[BuilderThread 3] [ERROR] /usr/maven-mojo-jojo/sub-parent-a/module-a2/src/test/java/maven/bug/modulea/ModuleA2Test.java:[3,17] package org.junit does not exist
[BuilderThread 3] [ERROR] /usr/maven-mojo-jojo/sub-parent-a/module-a2/src/test/java/maven/bug/modulea/ModuleA2Test.java:[6,10] cannot find symbol
symbol: class Test
location: class maven.bug.modulea.ModuleA2Test
[BuilderThread 3] [INFO] 2 errors
[BuilderThread 3] [INFO] -------------------------------------------------------------
This breaks if, and only if, the following events happen in the following order:
- Mojo configuration for the
maven-compiler-plugin:test-compileinmodule-a2is done. This will configure the resolved artifacts for the project. - Due to the
maven-javadoc-plugininsub-parent-bdefinesaggregator = truegoal andrequiresDependencyResolution = ResolutionScope.COMPILE, theMojoExecutorclass will start resolving dependencies for all projects in the currentMavenSession(sincegetProjects()returns all projects that are included to be built). This will reset the resolved artifacts for the projectmodule-a2to thecompilescope dependencies (and thus missing thetestscoped ones) - The
maven-compiler-pluginstarts, and in its mojo execution queries thegetTestClasspathElementsof themodule-a2project. Since the resolved artifacts have been reset to thecompiledependencies, this will result in a classpath withoutjunit:junit:4.12, causing javac to fail.
Due to this order, the sub-parent sub-parent-b has a maven-javadoc-plugin execution bound to the test-compile phase; increasing the chances of this problem occurring.
If I understand the idea behing MojoExecutor's ensureDependenciesAreResolved method correctly, I'm assuming it should call resolveProjectDependencies only on modules that are housed under the current project. In this sample project, I would expect this method to resolve the dependencies for the modules module-b1 and module-b2, as these are child-modules of sub-parent-b.
Currently, this method calls resolveProjectDependencies for all MavenProject instances returned by MavenSession#getProjects. Given the code; this method seems to return all projects included in the build reactor, which without any --projects argument boils down to all projects housed by the current parent.
I would suggest (recursively) finding projects that are housed under the current project, and only call resolveProjectDependencies for those projects.
A diff for MojoExecutor that seems to result in this behaviour would be:
diff --git a/maven-core/src/main/java/org/apache/maven/lifecycle/internal/MojoExecutor.java b/maven-core/src/main/java/org/apache/maven/life
cycle/internal/MojoExecutor.java
index 8524c5e..9dc3424 100644
--- a/maven-core/src/main/java/org/apache/maven/lifecycle/internal/MojoExecutor.java
+++ b/maven-core/src/main/java/org/apache/maven/lifecycle/internal/MojoExecutor.java
@@ -257,14 +257,11 @@ public void ensureDependenciesAreResolved( MojoDescriptor mojoDescriptor, MavenS
if ( dependencyContext.isResolutionRequiredForAggregatedProjects( scopesToCollect, scopesToResolve ) )
{
- for ( MavenProject aggregatedProject : session.getProjects() )
+ for ( MavenProject aggregatedProject : collectChildModules(project, session.getProjects()) )
{
- if ( aggregatedProject != project )
- {
- lifeCycleDependencyResolver.resolveProjectDependencies( aggregatedProject, scopesToCollect,
- scopesToResolve, session, aggregating,
- Collections.<Artifact>emptySet() );
- }
+ lifeCycleDependencyResolver.resolveProjectDependencies( aggregatedProject, scopesToCollect,
+ scopesToResolve, session, aggregating,
+ Collections.<Artifact>emptySet() );
}
}
}
@@ -279,6 +276,19 @@ public void ensureDependenciesAreResolved( MojoDescriptor mojoDescriptor, MavenS
}
}
+ private List<MavenProject> collectChildModules(MavenProject parent, List<MavenProject> projects) {
+ List<MavenProject> children = new ArrayList<>();
+
+ for (MavenProject project : projects) {
+ if (project.getParent() == parent) {
+ children.add(project);
+ children.addAll(collectChildModules(project, projects));
+ }
+ }
+
+ return children;
+ }
+
private ArtifactFilter getArtifactFilter( MojoDescriptor mojoDescriptor )
{
String scopeToResolve = mojoDescriptor.getDependencyResolutionRequired();