gnodet opened a new pull request, #13728:
URL: https://github.com/apache/maven/pull/13728
## Problem
When building with `-b concurrent` and a high thread count (e.g. `--threads
max`), the build fails intermittently with:
```
Failed to execute goal
org.apache.maven.plugins:maven-dependency-plugin:3.11.0:properties
(prepare-for-mockito-agent) on project apache-maven: Cannot invoke
"java.io.File.getAbsolutePath()" because the return value of
"org.apache.maven.artifact.Artifact.getFile()" is null
```
Reproducer (self-build):
```
mvn -b concurrent --threads max install -DskipTests -o
```
## Root cause
In `LifecycleDependencyResolver.resolveProjectDependencies()`, a snapshot of
each reactor project's artifact file was taken up-front into a `Map<Artifact,
File>`:
```java
Map<Artifact, File> reactorProjects = new
HashMap<>(session.getProjects().size());
for (MavenProject reactorProject : session.getProjects()) {
reactorProjects.put(
reactorProject.getArtifact(),
reactorProject.getArtifact().getFile()); // may be null!
}
```
In the concurrent builder, a sibling project may not yet have written its
jar when this snapshot is taken. The map then stores `null` for that artifact's
file. The subsequent guard `if (reactorProjectFile != null)` silently skips the
`setFile()` call, leaving the artifact with a `null` file even after dependency
resolution.
Any plugin that then calls `artifact.getFile().getAbsolutePath()` on a
resolved artifact will NPE. The `maven-dependency-plugin:properties` mojo (used
here to expose the Mockito agent jar path to Surefire) is one such plugin.
This is the same class that MNG-6300 previously fixed for the
`target/classes` case; this is the concurrent-builder variant of the same
problem.
## Fix
Replace `Map<Artifact, File>` with `Map<Artifact, MavenProject>` and defer
`getFile()` to lookup time, so the most up-to-date value is always used:
```java
Map<Artifact, MavenProject> reactorProjects = new
HashMap<>(session.getProjects().size());
for (MavenProject reactorProject : session.getProjects()) {
reactorProjects.put(reactorProject.getArtifact(), reactorProject);
}
// ...
MavenProject reactorProject = reactorProjects.get(artifact);
if (reactorProject != null) {
File reactorProjectFile = reactorProject.getArtifact().getFile();
if (reactorProjectFile != null) {
artifact.setFile(reactorProjectFile);
}
}
```
## Verification
Before fix: `mvn -b concurrent --threads 16 install -DskipTests
-Drat.skip=true -o` fails ~1 in 3 runs.
After fix: 5 consecutive runs all pass (the race is no longer triggerable).
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