Assert no thread context pollution in InternalClusterInfoService

Author: DaveCTurner

server/src/main/java/org/elasticsearch/cluster/InternalClusterInfoService.java

@@ -181,15 +181,29 @@ void execute() {
             logger.trace("starting async refresh");
 
             try (var ignoredRefs = fetchRefs) {
+
+                assert assertEmptySystemContext();
                 try (var ignored = threadPool.getThreadContext().clearTraceContext()) {
                     fetchNodeStats();
+                    assert assertEmptySystemContext();
                 }
                 try (var ignored = threadPool.getThreadContext().clearTraceContext()) {
                     fetchIndicesStats();
+                    assert assertEmptySystemContext();
                 }
             }
         }
 
+        private boolean assertEmptySystemContext() {
+            final var threadContext = threadPool.getThreadContext();
+            final var headers = threadContext.getHeaders();
+            assert headers.isEmpty() : headers;
+            final var transientHeaders = threadContext.getTransientHeaders();
+            assert transientHeaders.isEmpty() : transientHeaders;
+            assert threadContext.isSystemContext();
+            return true;
+        }
+
         private void fetchIndicesStats() {
             final IndicesStatsRequest indicesStatsRequest = new IndicesStatsRequest();
             indicesStatsRequest.clear();
@@ -205,6 +219,7 @@ private void fetchIndicesStats() {
                         ActionListener.releaseAfter(new ActionListener<>() {
                             @Override
                             public void onResponse(IndicesStatsResponse indicesStatsResponse) {
+                                assert assertEmptySystemContext();
                                 logger.trace("received indices stats response");
 
                                 if (indicesStatsResponse.getShardFailures().length > 0) {
@@ -289,6 +304,7 @@ private void fetchNodeStats() {
             client.admin().cluster().nodesStats(nodesStatsRequest, ActionListener.releaseAfter(new ActionListener<>() {
                 @Override
                 public void onResponse(NodesStatsResponse nodesStatsResponse) {
+                    assert assertEmptySystemContext();
                     logger.trace("received node stats response");
 
                     for (final FailedNodeException failure : nodesStatsResponse.failures()) {
@@ -321,6 +337,7 @@ public void onFailure(Exception e) {
 
         private void callListeners() {
             try {
+                assert assertEmptySystemContext();
                 logger.trace("stats all received, computing cluster info and notifying listeners");
                 final ClusterInfo clusterInfo = getClusterInfo();
                 boolean anyListeners = false;
@@ -339,6 +356,7 @@ private void callListeners() {
                     listener.onResponse(clusterInfo);
                 }
             } finally {
+                assert assertEmptySystemContext();
                 onRefreshComplete(this);
             }
         }