[Bug] Thread leak in NacosRegistry.scheduleServiceNamesLookup due to race condition

[QiuYucheng2003]

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Apache Dubbo Component

Java SDK (apache/dubbo)

Dubbo Version

Dubbo 3.3.x (Confirmed in latest master branch) & Dubbo 2.7.x.
JDK 1.8+, All Operating Systems.

Steps to reproduce this issue

1. This issue is identified via static code analysis (concurrency safety check).
2. It is located in org.apache.dubbo.registry.nacos.NacosRegistry method scheduleServiceNamesLookup.
3. The method uses a "Check-Then-Act" pattern to lazily initialize the scheduledExecutorService.
4. Although the field is volatile, the initialization block is NOT synchronized.

Code Analysis:
When scheduleServiceNamesLookup is called concurrently (e.g. via admin protocol), a race condition occurs:
if (scheduledExecutorService == null) { // Thread A and B can pass here simultaneously
scheduledExecutorService = Executors.newSingleThreadScheduledExecutor(); // Executed twice
// ...
}

What you expected to happen

The scheduledExecutorService should be initialized as a Singleton in a thread-safe manner (e.g., using Double-Checked Locking). Only one thread pool should be created to avoid thread leaks.

Anything else

Proposed Solution (Double-Checked Locking)

I suggest modifying the code to use synchronized DCL:

private void scheduleServiceNamesLookup(final URL url, final NacosAggregateListener listener) {
if (scheduledExecutorService == null) {
synchronized (this) {
if (scheduledExecutorService == null) {
// Recommend naming the thread for better debuggability
scheduledExecutorService = Executors.newSingleThreadScheduledExecutor(
new NamedThreadFactory("Dubbo-Nacos-Registry-Scheduler", true)
);
scheduledExecutorService.scheduleAtFixedRate(
() -> {
// ... existing logic ...
},
LOOKUP_INTERVAL,
LOOKUP_INTERVAL,
TimeUnit.SECONDS);
}
}
}
}

Are you willing to submit a pull request to fix on your own?

• Yes I am willing to submit a pull request on my own!

Code of Conduct

• I agree to follow this project's Code of Conduct

[EarthChen]

Would you be willing to submit a PR to fix this?

[QiuYucheng2003]

I'd like to fix this