CsdsService not properly synchronized with XdsClient

[ejona86]

Consider this code from CsdsService:

grpc-java/xds/src/main/java/io/grpc/xds/CsdsService.java

Lines 152 to 155 in a46560e

	static ClientConfig getClientConfigForXdsClient(XdsClient xdsClient) {
	ListenersConfigDump ldsConfig = dumpLdsConfig(
	xdsClient.getSubscribedResourcesMetadata(ResourceType.LDS),
	xdsClient.getCurrentVersion(ResourceType.LDS));

The initial issue is that getSubscribedResourcesMetadata() and getCurrentVersion() have no synchronization:

grpc-java/xds/src/main/java/io/grpc/xds/ClientXdsClient.java

Lines 1842 to 1848 in 14eb3b2

	Map<String, ResourceMetadata> getSubscribedResourcesMetadata(ResourceType type) {
	Map<String, ResourceMetadata> metadataMap = new HashMap<>();
	for (Map.Entry<String, ResourceSubscriber> entry : getSubscribedResourcesMap(type).entrySet()) {
	metadataMap.put(entry.getKey(), entry.getValue().metadata);
	}
	return metadataMap;
	}

grpc-java/xds/src/main/java/io/grpc/xds/AbstractXdsClient.java

Lines 257 to 258 in a46560e

	// Must be synchronized.
	String getCurrentVersion(ResourceType type) {

That is bad. However, the xdsClient API itself is insufficient for CSDS because those two method calls need to be atomic; even if each of those methods were thread-safe the version needs to match the resources returned.

[sergiitk]

Good catch. Thank you.

[dapengzhang0]

#8675 removed getCurrentVersion(), but getSubscribedResourcesMetadata() is still unsynchronized.

[ejona86]

@sergiitk, was this resolved?

[sergiitk]

Yes, this is resolved. Apparently Fixes notation didn't work in a comment: #8795 (comment).