Resolve race when staging multiple classic templates at the same time

[Abacn]

context: #3833 (comment)

There is a racing condition when multiple classic templates get staged, jars are overwrittened by each other. gcsio correctly handles this race, but unfortunately, it's printing an log triggering a JDK bug.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a race condition occurring when multiple classic templates are staged simultaneously, which previously led to file corruption. By implementing conditional synchronization specifically for classic templates, the change ensures thread safety during the staging process while avoiding unnecessary performance impacts on flex templates.

Highlights

• Race Condition Resolution: Introduced a synchronized block for classic templates to prevent file overwriting during the staging process.
• Code Refactoring: Extracted the staging logic into a Callable to allow for conditional synchronization based on the template type.

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.21%. Comparing base (74e5f1f) to head (48faf51).
⚠️ Report is 60 commits behind head on main.

Files with missing lines	Patch %	Lines
.../java/org/apache/beam/it/gcp/TemplateTestBase.java	0.00%	6 Missing ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3839      +/-   ##
============================================
+ Coverage     53.06%   54.21%   +1.15%     
- Complexity     6018     6895     +877     
============================================
  Files          1070     1096      +26     
  Lines         64941    67358    +2417     
  Branches       7193     7559     +366     
============================================
+ Hits          34463    36521    +2058     
- Misses        28166    28373     +207     
- Partials       2312     2464     +152     

Components	Coverage Δ
spanner-templates	73.35% <ø> (+0.48%)	⬆️
spanner-import-export	68.65% <ø> (ø)
spanner-live-forward-migration	83.02% <ø> (+2.02%)	⬆️
spanner-live-reverse-replication	77.09% <ø> (-0.12%)	⬇️
spanner-bulk-migration	90.97% <ø> (-0.18%)	⬇️
gcs-spanner-dv	85.75% <ø> (-0.08%)	⬇️

Files with missing lines	Coverage Δ
.../java/org/apache/beam/it/gcp/TemplateTestBase.java	0.00% <0.00%> (ø)

... and 79 files with indirect coverage changes

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[gemini-code-assist]

Code Review

This pull request modifies TemplateTestBase.java to refactor the template staging process. It extracts the staging logic into a Callable and introduces conditional synchronization on the stagedTemplates object when processing non-flex templates, likely to ensure thread safety during the staging operation. There were no review comments provided for this pull request, so I have no feedback to provide.

[Abacn]

Still stuck on https://github.com/GoogleCloudPlatform/DataflowTemplates/actions/runs/26197041852