Maybe "resume" should be removed? Incremental builds, and build cache make up for loss of efficiency.
It doesn't really have a place nowadays. The IDE and CI don't use it, and devs often just push "up + enter" rather than extra typing. Removing it results in atomic builds and guarantees the resulting artifacts aren't dirty. That's an improvement. Honestly I'd just remove it. Delany On Tue, 4 Aug 2026, 14:08 Tamás Cservenák, <[email protected]> wrote: > Howdy, > > I would just reflect on a funny fact (for me at least): > > This whole problem (being solved on this thread), stems from one > single thing: the unsolicited install that Maven 4 does (cf this to > user invoking `mvn install` explicitly). > > Moreover, this unsolicited install happens, for one thing, to make the > resume `-r` feature work. > > And the true irony is, that this resume feature is backed and > advertised by folks, whose mantra is "do not `mvn install` but `mvn > verify`" (as install "pollutes' your local repository", whatever that > means). > > That mantra can be now extended with "... as Maven 4 will install it, > even if you did not ask for it" :) > > The more I think about it, the more I find this funny. > > Thanks > T > > On Tue, 4 Aug 2026 at 14:56, Guillaume Nodet <[email protected]> wrote: > > > > I like the .mvn/target/project-local-repo which solves the problem, > > and also provides a good location where plugins could move some > > temporary data files without being disturbed by the clean plugin. I'm > > thinking about the flatten plugin, the release plugin, and probably > > more. > > > > Le lun. 3 août 2026 à 16:47, Slawomir Jaranowski > > <[email protected]> a écrit : > > > > > > Hi, > > > > > > On Mon, 3 Aug 2026 at 14:09, Guillaume Nodet <[email protected]> > 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? > > > > > > maybe .mvn/target/project-local-repo > > > it should be ignored by git > > > > > > > - 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 > > > > > > > > > > > > -- > > > Sławomir Jaranowski > > > > > > --------------------------------------------------------------------- > > > To unsubscribe, e-mail: [email protected] > > > For additional commands, e-mail: [email protected] > > > > > > > > > -- > > ------------------------ > > Guillaume Nodet > > > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: [email protected] > > For additional commands, e-mail: [email protected] > > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [email protected] > For additional commands, e-mail: [email protected] > >
