Use Mutex#synchronize to solve JRuby mutex not locked error

[p-datadog]

What does this PR do?
Uses Mutex#synchronize instead of manual lock & unlock calls to (hopefully) properly unlock the mutex in remote config worker.

Motivation:
Flaky tests on JRuby: https://github.com/DataDog/ruby-guild/issues/256, https://datadoghq.atlassian.net/browse/LANGPLAT-871

The issue is that sometimes mutex is attempted to be unlocked when it is not locked.

Change log entry
Yes: core/fix: improve locking code for remote configuration worker

Additional Notes:

I also attempted this alternate diff which also fixed the issue:

diff --git a/lib/datadog/core/remote/component.rb b/lib/datadog/core/remote/component.rb
index 18e33bea25..f73d9742b6 100644
--- a/lib/datadog/core/remote/component.rb
+++ b/lib/datadog/core/remote/component.rb
@@ -137,11 +137,13 @@ module Datadog
           def lift
             @mutex.lock
 
-            @once ||= true
+            begin
+              @once ||= true
 
-            @condition.broadcast
-          ensure
-            @mutex.unlock
+              @condition.broadcast
+            ensure
+              @mutex.unlock
+            end
           end
         end
 

How to test the change?

Following @Strech 's investigation in https://datadoghq.atlassian.net/browse/LANGPLAT-871, I reproduced the failure locally (both in and not in docker) using the following:

export BUNDLE_GEMFILE=gemfiles/ruby_3.4_mongo_min.gemfile

while true; do if ! TEST_DATADOG_INTEGRATION=1 BUNDLE_GEMFILE=./gemfiles/jruby_9.4_contrib.gemfile bundle exec rspec --pattern spec/datadog/tracing/contrib/suite/\*\*/\*_spec.rb --format=doc; then break; fi; done

After a couple of iterations, this would fail with the above error. The seeds specified in the ticket did not reproduce the failure for me - running the tests without explicitly specifying the seeds was needed.

With the change in this PR, I ran the above command for ~5 minutes without errors.

I have not further investigated the interaction between remote config worker and test polling intervals.

[datadog-official]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 100.00%
• Total Coverage: 101.94% (-0.03%)

View detailed report

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🔗 Commit SHA: ee83db1 | Docs | Was this helpful? Give us feedback!}

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-10-07 19:22:39

Comparing candidate commit ee83db1 in PR branch jruby-deadlock with baseline commit d865382 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 44 metrics, 2 unstable metrics.

[Strech]

👏🏼

[ivoanjo]

👍 I believe this is the best + correct solution