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Use lock for instance status update. #1566

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Use lock for instance status update. #1566

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29 changes: 21 additions & 8 deletions eureka-client/src/main/java/com/netflix/discovery/DiscoveryClient.java
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Original file line number Diff line number Diff line change
Expand Up @@ -106,6 +106,7 @@
*
* @author Karthik Ranganathan, Greg Kim
* @author Spencer Gibb
* @author Olga Maciaszek-Sharma
*
*/
@Singleton
Expand Down Expand Up @@ -149,6 +150,7 @@ public class DiscoveryClient implements EurekaClient {
private final PreRegistrationHandler preRegistrationHandler;
private final AtomicReference<Applications> localRegionApps = new AtomicReference<>();
private final Lock fetchRegistryUpdateLock = new ReentrantLock();
private final ReentrantLock instanceStatusUpdateLock = new ReentrantLock();
// monotonically increasing generation counter to ensure stale threads do not reset registry to an older version
private final AtomicLong fetchRegistryGeneration;
private final ApplicationInfoManager applicationInfoManager;
Expand Down Expand Up @@ -1381,15 +1383,26 @@ void refreshInstanceInfo() {
applicationInfoManager.refreshLeaseInfoIfRequired();

InstanceStatus status;
try {
status = getHealthCheckHandler().getStatus(instanceInfo.getStatus());
} catch (Exception e) {
logger.warn("Exception from healthcheckHandler.getStatus, setting status to DOWN", e);
status = InstanceStatus.DOWN;
}
if (instanceStatusUpdateLock.tryLock()) {
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I'm not sure if we need the fix here? Since both threads will call healthcheck to find latest status, unless healthcheck itself is flipping, the status would be the same? Maybe there is a race in update sequence, but the value would be consistent?

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@OlgaMaciaszek OlgaMaciaszek Jan 13, 2025 •
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Hi @howardyuan, thanks for the comment. You're right. I've taken another look at it and I now think the approach to take could be to have a compareAndSet logic while changing InstanceInfo.InstanceStatus within DiscoveryClient#refreshInstanceInfo to prevent a situation where the status has been changed by the other thread between getting original status from the field and setting its transformed value there. Could be done by changing that field into an actual AtomicReference or, to remain consistent with the current class implementation and avoid having to change/ add too many methods, keeping it as a volatile field and adding a synchronized method in that class that would first compare the expected field value with the actual one and calling that new method within DiscoveryClient#refreshInstanceInfo. Let me know what you think.

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I think your suggestions of comparing before setting should be safe.

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Will work on it soon.

try {
try {
status = getHealthCheckHandler().getStatus(instanceInfo.getStatus());
}
catch (Exception e) {
logger.warn("Exception from healthcheckHandler.getStatus, setting status to DOWN", e);
status = InstanceStatus.DOWN;
}

if (null != status) {
applicationInfoManager.setInstanceStatus(status);
if (null != status) {
applicationInfoManager.setInstanceStatus(status);
}
}
finally {
instanceStatusUpdateLock.unlock();
}
}
else {
logger.warn("Cannot acquire update lock, aborting instance status refresh");
}
}

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