> The key detail is that classified/attached artifacts (sources.jar, test-jar, javadoc.jar, consumer POMs) are only resolvable from project-local-repo during resume. The target/classes fallback in ReactorReader only handles plain jars without classifiers. <
Ok, is it an option to create module/target/local-repo-classifier.xml with the index of exposed artifacts, create only on successful build, so module of the reactor (which is even skipped in "-pl" option) is aware of which artifacts it can take from the module target directory. In this case we do not need a special rootDir/target/project-local-repo On Wed, Aug 5, 2026 at 5:07 PM Sergey Chernov <[email protected]> wrote: > >I am by no means familiar with this part of Maven, but would it be an > option to place "clean" and "install" in separate TaskSegments to avoid > the race condition completely? > > Yes, I was talking about the same. There was a comment regarding it that > "compile 4.x+ plugin will compile the code of all modules", but I have very > strong concerns it's how actually the thing work. > > "mvn clean install -T4" now executes all phases of clean lifecycle + > all phases of install lifecycle (subset of "default" lifecycle) in a list > of mojos, in a single foreach loop. > Instead, it should run clean lifecycle for all modules, and only then run > install lifecycle for all modules. > > For example, Gradle does it this way and I find this more correct. > > > On Wed, Aug 5, 2026 at 10:49 AM Maarten Mulders <[email protected]> > wrote: > >> Hi Guillaume, >> >> Your problem statement seems clear to me, but from the three approaches, >> it seems to me all three target a consequence of the root cause. >> > Since clean and install are placed into the same TaskSegment [...] >> >> I am by no means familiar with this part of Maven, but would it be an >> option to place "clean" and "install" in separate TaskSegments to avoid >> the race condition completely? If I understand correctly, it would also >> make it practically impossible to "clean" something that was "install"ed >> just (the ordering problem when using a lock-based approach). >> >> Apart from that, I would not be a big fan of a solution that moves the >> project-local-repo *outside* the project directory (approach 2). >> >> Thanks, >> >> Maarten >> >> On 03/08/2026 14:09, Guillaume Nodet wrote: >> > Hi all, >> > >> > I'd like to get your input on the fix for GH-12646 — a race condition >> with >> > project-local-repo during parallel clean install builds. >> > >> > The problem >> > >> > When the root pom.xml has a parent that is also part of the reactor >> (e.g. a >> > super-pom), MultiThreadedBuilder schedules the parent first, then runs >> the >> > root project and child modules concurrently. Since clean and install are >> > placed into the same TaskSegment, there is no barrier between them — the >> > root project's maven-clean-plugin can delete target/ while sibling >> modules >> > are concurrently writing artifacts into target/project-local-repo, >> causing >> > the build to fail. >> > >> > Approaches considered >> > >> > 1. Lock-based synchronization (ReentrantReadWriteLock in ReactorReader) >> > >> > Acquire a write lock when the project owning target/ enters its clean >> > phase, and a read lock when installing artifacts. This prevents the >> crash >> > (concurrent access) but does not guarantee ordering — a module could >> > install artifacts before the root's clean starts, only to have them >> wiped. >> > It also adds complexity to ReactorReader for what is fundamentally an >> > architectural problem. >> > >> > 2. Move project-local-repo to ~/.m2/ (user home) >> > >> > E.g. ~/.m2/local-repository/${projectName}_${hash}, similar to how >> IntelliJ >> > stores project caches. This avoids both the race and the git concern, >> but: >> > - Hard links (already used by ReactorReader) cannot cross filesystem >> > boundaries — if ~/.m2/ is on a different volume, every artifact becomes >> a >> > full copy >> > - Stale directories accumulate when projects are deleted/moved, with no >> > cleanup mechanism >> > - CI containers often share ~/.m2/ across builds, causing unwanted >> > accumulation >> > - Loses project locality (harder to inspect/debug) >> > >> > 3. Move project-local-repo to .mvn/project-local-repo (chosen) >> > >> > Move the directory from target/project-local-repo to >> > .mvn/project-local-repo. Since maven-clean-plugin only deletes target/, >> the >> > race becomes structurally impossible. ReactorReader fully owns the >> > lifecycle — per-GAV cleanup when a project enters its clean phase, >> install >> > on project success. The existing hard-link optimization continues to >> work >> > since both directories are on the same filesystem. >> > >> > The trade-off is that .mvn/project-local-repo needs to be gitignored. >> This >> > follows the Gradle convention where .gradle/ at the project root is >> > universally in .gitignore templates. Maven could also document this >> > convention or consider auto-appending the entry. >> > >> > The fix itself is minimal — the core change is a single line in >> > getProjectLocalRepo(), and the rest is removing the lock infrastructure >> > (net -40 lines). >> > >> > 4. Keep in target/ but use maven-clean-plugin fast mode >> > >> > The fast clean option (maven.clean.fast=true, since plugin 3.2) >> atomically >> > renames target/ instead of recursively deleting it. This would likely >> avoid >> > the race, but it's opt-in and not the default — users hitting the bug >> would >> > need to know about it. >> > >> > FWIW, a PR has been raised on m-clean-p master branch (4.x) to refactor >> the >> > fast cleaner (fixing problems) and make it the default. >> > >> > Open questions >> > >> > - Is .mvn/ the right location, or should we consider a different >> > project-root directory? >> > - Should Maven auto-add .mvn/project-local-repo to .gitignore, or >> document >> > it as a convention? >> > - Are there other considerations I'm missing? >> > >> > PR: https://github.com/apache/maven/pull/12650 >> > Issue: https://github.com/apache/maven/issues/12646 >> > >> > Looking forward to your thoughts. >> > >> > Cheers >> > Guillaume Nodet >> > >> >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: [email protected] >> For additional commands, e-mail: [email protected] >> >>
