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xds: xdsClient caches transient error for new watchers #12262

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xds: xdsClient caches transient error for new watchers #12262

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xds: xdsClient caches transient error for new watchers
shivaspeaks Aug 7, 2025
033a4b1
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shivaspeaks Aug 8, 2025
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12 changes: 12 additions & 0 deletions xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java
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Original file line number Diff line number Diff line change
Expand Up @@ -676,6 +676,8 @@ private final class ResourceSubscriber<T extends ResourceUpdate> {
private ResourceMetadata metadata;
@Nullable
private String errorDescription;
@Nullable
private Status lastError;
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FYI: Change data to StatusOr<T> data would have kept this a bit more clear. You still have data vs absent, but at least you don't have yet another thing to deal with.

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I'm concerned that it's a more invasive refactoring change since it would require touching every method that uses the data field. I can try to do it in a follow up PR and keep this PR's scope limited to bug fix?

I'll agree that we are moving to more usage of StatusOr<T> in our codebase everywhere. We should consider here as well for consistency.

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There's only a few other places that access data. It does look like it'd make all of them more complicated. Most are of the form data != null, and would likely need to become data != null && data.hasValue().


ResourceSubscriber(XdsResourceType<T> type, String resource) {
syncContext.throwIfNotInThisSynchronizationContext();
Expand Down Expand Up @@ -712,11 +714,16 @@ void addWatcher(ResourceWatcher<T> watcher, Executor watcherExecutor) {
watchers.put(watcher, watcherExecutor);
T savedData = data;
boolean savedAbsent = absent;
Status savedError = lastError;
watcherExecutor.execute(() -> {
if (errorDescription != null) {
watcher.onError(Status.INVALID_ARGUMENT.withDescription(errorDescription));
return;
}
if (savedError != null) {
watcher.onError(savedError);
return;
}
if (savedData != null) {
notifyWatcher(watcher, savedData);
} else if (savedAbsent) {
Expand Down Expand Up @@ -808,6 +815,7 @@ void onData(ParsedResource<T> parsedResource, String version, long updateTime,
this.metadata = ResourceMetadata
.newResourceMetadataAcked(parsedResource.getRawResource(), version, updateTime);
absent = false;
lastError = null;
if (resourceDeletionIgnored) {
logger.log(XdsLogLevel.FORCE_INFO, "xds server {0}: server returned new version "
+ "of resource for which we previously ignored a deletion: type {1} name {2}",
Expand Down Expand Up @@ -857,6 +865,7 @@ void onAbsent(@Nullable ProcessingTracker processingTracker, ServerInfo serverIn
if (!absent) {
data = null;
absent = true;
lastError = null;
metadata = serverInfo.resourceTimerIsTransientError()
? ResourceMetadata.newResourceMetadataTimeout()
: ResourceMetadata.newResourceMetadataDoesNotExist();
Expand Down Expand Up @@ -894,6 +903,9 @@ void onError(Status error, @Nullable ProcessingTracker tracker) {
Status errorAugmented = Status.fromCode(error.getCode())
.withDescription(description + "nodeID: " + bootstrapInfo.node().getId())
.withCause(error.getCause());
this.lastError = errorAugmented;
this.data = null;
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Cached data should continue to get used when available, until we implement A88 onResourceChanged

this.absent = false;
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We should not change this, only a onData arrival should reset this to false as there is reading logic using this value on onAbsent.


for (ResourceWatcher<T> watcher : watchers.keySet()) {
if (tracker != null) {
Expand Down