[MNG-7220] Fix threadLocalArtifactsHolder leaking into cloned project

[famod]

Just like #527 but for master.

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[famod]

/cc @michael-o

[rmannibucau]

This broke 3.8.2 so would be great to invest in another working solution IMHO.

[olamy]

why InheritableThreadLocal cannot be a good solution? what are the cons using InheritableThreadLocal?

[rmannibucau]

It mainly leaks and threads it is propagated to are uncontrolled so behavior is.
Guess a reference counting (per module) or alike solution is maybe closer to something portable, and enabling it only in concurrent builds is saner and limit the impacts a lot.

[famod]

My 2 cents:
In mid or long term there should be a better solution for this and the band-aid TL should be dropped.
But so far nobody has come up with a non-api-breaking solution to fix the initial problem. Just reverting the TL re-introduces a nasty concurrency issue, so IMO this is not a good option.
So, since 3.8.2 is out there and introduces some regressions, let's get the two fixes for that merged and release 3.8.3 ASAP.

[rmannibucau]

@famod so minimum is to disable the TL when concurrency = 1 which leads to 0 issues for everyone - even if build is slower. Guess it is acceptable until somebody wants to implement a ref counting or alike solution.

[michael-o]

@famod so minimum is to disable the TL when concurrency = 1 which leads to 0 issues for everyone - even if build is slower. Guess it is acceptable until somebody wants to implement a ref counting or alike solution.

If we can access concurrency information at that point actually...

[michael-o]

Will also test in the next couple of days and merge.

[famod]

@famod so minimum is to disable the TL when concurrency = 1 which leads to 0 issues for everyone - even if build is slower. Guess it is acceptable until somebody wants to implement a ref counting or alike solution.

If we can access concurrency information at that point actually...

I don't see how, unfortunately. (not without adding new public methods to MavenProject that have to be called from...somewhere)

[rmannibucau]

The concurrency is in the session (session.getRequest().getDegreeOfConcurrency(); or something like that) so I guess it is more a matter of wrapper the project injected in mojo instead of changing maven project itself. So maven project would stay untouched and a ConcurrentMavenProject would use a thread local if getDegreeOfConcurrency() > 1.
Had sometihng along those lines in mind but I wouldn't change MavenProject at all.

[michael-o]

The concurrency is in the session (session.getRequest().getDegreeOfConcurrency(); or something like that) so I guess it is more a matter of wrapper the project injected in mojo instead of changing maven project itself. So maven project would stay untouched and a ConcurrentMavenProject would use a thread local if getDegreeOfConcurrency() > 1.
Had sometihng along those lines in mind but I wouldn't change MavenProject at all.

This makes sense and should be evaluated in a separate issue.