From 77461e0f0bec9b8f5992c6f9c48387ece960eddb 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 123d3a77172..bbe36bdd744 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 @@ private boolean retainCluster(String cluster) {
 
     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());
             }
           }
         });