Fix completely broken lock during setuping local repo on Linux

[unlsycn]

After recently bumping Scala-CLI, I noticed that the race condition in the local repository setup still persists even after merging #3693. I then identified a critical issue: the withLock mechanism does not work at all on Linux.

According to https://bugs.openjdk.org/browse/JDK-7095452, the root cause is that a .lock file cannot be observed by other processes:

On Solaris/Linux if DELETE_ON_CLOSE is specified, the appropriate file is unlinked from the directory when opened and therefore appears inaccessible via path.

In this case, each Scala-CLI process considers itself holding the lock, leading to a race condition.

This issue is difficult to fully capture with a single test due to its concurrent nature, but adding a Thread.sleep before extractZip and run multiple Scala-CLI instances in parallel can reproduce the issue reliably nearly 100% of the time.

[Gedochao]

This issue is difficult to fully capture with a single test due to its concurrent nature, but adding a Thread.sleep before extractZip and run multiple Scala-CLI instances in parallel can reproduce the issue reliably nearly 100% of the time.

We have tests for running multiple Scala CLI instances in parallel right here:
https://github.com/VirtusLab/scala-cli/blob/main/modules/integration/src/test/scala/scala/cli/integration/RunTestDefinitions.scala#L2320-L2361

Can you try adding a similar test for your case? Optimally, I'd like to be able to track if this works correctly on all platforms.

[unlsycn]

This issue is difficult to fully capture with a single test due to its concurrent nature, but adding a Thread.sleep before extractZip and run multiple Scala-CLI instances in parallel can reproduce the issue reliably nearly 100% of the time.

We have tests for running multiple Scala CLI instances in parallel right here: https://github.com/VirtusLab/scala-cli/blob/main/modules/integration/src/test/scala/scala/cli/integration/RunTestDefinitions.scala#L2320-L2361

Can you try adding a similar test for your case? Optimally, I'd like to be able to track if this works correctly on all platforms.

Sure. Could you provide some guidance on accessing localRepoDir in integration tests? Since the setup only occurs in environments without cached local repo, I need to remove the local repo for this test. Alternatively, is there a way to run this test in a sandboxed environment to ensure the setup process executes?

[Gedochao]

You can print all relevant locations (including the local repository) with the following command:

scala-cli directories --power

Where the output should look like (example for a Mac):

Local repository: ~/Library/Caches/ScalaCli/local-repo
Completions: ~/Library/Application Support/ScalaCli/completions
Virtual projects: ~/Library/Caches/ScalaCli/virtual-projects
BSP sockets: ~/Library/Caches/ScalaCli/bsp-sockets
Bloop daemon directory: ~/Library/Caches/ScalaCli/bloop/daemon
Secrets directory: ~/Library/Application Support/ScalaCli/secret

The definition in-code can be found here:

scala-cli/modules/build/src/main/scala/scala/build/Directories.scala

Lines 40 to 41 in 32b11d9

	lazy val localRepoDir: os.Path =
	os.Path(projDirs.cacheDir, Os.pwd) / "local-repo"

[unlsycn]

You can print all relevant locations (including the local repository) with the following command:

scala-cli directories --power

Where the output should look like (example for a Mac):

Local repository: ~/Library/Caches/ScalaCli/local-repo
Completions: ~/Library/Application Support/ScalaCli/completions
Virtual projects: ~/Library/Caches/ScalaCli/virtual-projects
BSP sockets: ~/Library/Caches/ScalaCli/bsp-sockets
Bloop daemon directory: ~/Library/Caches/ScalaCli/bloop/daemon
Secrets directory: ~/Library/Application Support/ScalaCli/secret

The definition in-code can be found here:

scala-cli/modules/build/src/main/scala/scala/build/Directories.scala

Lines 40 to 41 in 32b11d9

	lazy val localRepoDir: os.Path =
	os.Path(projDirs.cacheDir, Os.pwd) / "local-repo"

Thanks for your help! I've added a test that fails before this patch and passes after it.

[Gedochao]

LGTM, thanks for the contribution!