From bb120a8cbb9de63d1514ac8c6a52568d946a60a7 Mon Sep 17 00:00:00 2001
From: Eric Anderson <ejona@google.com>
Date: Wed, 5 Mar 2025 13:29:55 -0800
Subject: [PATCH] xds: Assert XdsNR's cluster ref counting is consistent

It is much harder to debug refcounting problems when we ignore
impossible situations. So make such impossible cases complain loudly so
the bug is obvious.
---
 .../main/java/io/grpc/xds/XdsNameResolver.java | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/xds/src/main/java/io/grpc/xds/XdsNameResolver.java b/xds/src/main/java/io/grpc/xds/XdsNameResolver.java
index 123d3a7717..bbe36bdd74 100644
--- a/xds/src/main/java/io/grpc/xds/XdsNameResolver.java
+++ b/xds/src/main/java/io/grpc/xds/XdsNameResolver.java
@@ -537,17 +537,21 @@ final class XdsNameResolver extends NameResolver {
 
     private void releaseCluster(final String cluster) {
       int count = clusterRefs.get(cluster).refCount.decrementAndGet();
+      if (count < 0) {
+        throw new AssertionError();
+      }
       if (count == 0) {
         syncContext.execute(new Runnable() {
           @Override
           public void run() {
-            if (clusterRefs.get(cluster).refCount.get() == 0) {
-              clusterRefs.remove(cluster);
-              if (resolveState.lastConfigOrStatus.hasValue()) {
-                updateResolutionResult(resolveState.lastConfigOrStatus.getValue());
-              } else {
-                resolveState.cleanUpRoutes(resolveState.lastConfigOrStatus.getStatus());
-              }
+            if (clusterRefs.get(cluster).refCount.get() != 0) {
+              throw new AssertionError();
+            }
+            clusterRefs.remove(cluster);
+            if (resolveState.lastConfigOrStatus.hasValue()) {
+              updateResolutionResult(resolveState.lastConfigOrStatus.getValue());
+            } else {
+              resolveState.cleanUpRoutes(resolveState.lastConfigOrStatus.getStatus());
             }
           }
         });