[RHDM-2028] Deadlock between KieRepositoryImpl.kieModuleRepo and KieScannerHolder.kieScanner

[tkobayas]

Ports
This is PR for 7.x
Potentially we may port it to 7.67.x

JIRA:

• https://issues.redhat.com/browse/RHDM-2028

How to replicate CI configuration locally?

Build Chain tool does "simple" maven build(s), the builds are just Maven commands, but because the repositories relates and depends on each other and any change in API or class method could affect several of those repositories there is a need to use build-chain tool to handle cross repository builds and be sure that we always use latest version of the code for each repository.

build-chain tool is a build tool which can be used on command line locally or in Github Actions workflow(s), in case you need to change multiple repositories and send multiple dependent pull requests related with a change you can easily reproduce the same build by executing it on Github hosted environment or locally in your development environment. See local execution details to get more information about it.

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How to backport a pull request to a different branch?

In order to automatically create a backporting pull request please add one or more labels having the following format backport-<branch-name>, where <branch-name> is the name of the branch where the pull request must be backported to (e.g., backport-7.67.x to backport the original PR to the 7.67.x branch).

NOTE: backporting is an action aiming to move a change (usually a commit) from a branch (usually the main one) to another one, which is generally referring to a still maintained release branch. Keeping it simple: it is about to move a specific change or a set of them from one branch to another.

Once the original pull request is successfully merged, the automated action will create one backporting pull request per each label (with the previous format) that has been added.

If something goes wrong, the author will be notified and at this point a manual backporting is needed.

NOTE: this automated backporting is triggered whenever a pull request on main branch is labeled or closed, but both conditions must be satisfied to get the new PR created.

[tkobayas]

Ensuring the lock order (kieModuleRepo -> kieScanner) is the basic solution for a deadlock. As I see, problematic scenario is only this place, so I solved with this small fix.

An alternative approach would be to create a ReentrantLock and lock it for both kieModuleRepo and KieScannerHolder.kieScanner all usage. But it would require more code changes. Which do you prefer? > @mariofusco

[mariofusco]

We should replace all these synchronized block with ReentrantLocks, but this change can be done only on the main branch and it is not urgent however.

[tkobayas]

Thanks, I'll do that for the main branch.

[tkobayas]

I simulate the reported scenario and reproduce the deadlock with this test. However, this doesn't reproduce the deadlock in Drools 8 (upstream main), because ReleaseIdImpl usage is refactored and we no longer use ReleaseIdImpl.setSnapshotVersion, so the scenario is not reproducible. It's a good thing, but I will likely forward-port the same fix without this unit test. I will still likely forward-port the same unit test to ensure that a deadlock doesn't happen with concurrent builds.