[8.1] Make DiscoveryNodes behave like a collection (elastic#83453)

arteam · arteam · commit 47ecf740c41e · 2022-02-04T17:32:59.000+01:00
Backports elastic#83453 to 8.1 ``` Extend from `AbstractCollection`. Advantages: * Optimized version of `spliterator` based on the size implemented in `AbstractCollection` by default * Exposed `stream` method, so consumers don't need to call `StreamSupport.stream(discoveryNodes.spliterator(), false)` ```
diff --git a/server/src/internalClusterTest/java/org/elasticsearch/action/admin/cluster/node/tasks/CancellableTasksIT.java b/server/src/internalClusterTest/java/org/elasticsearch/action/admin/cluster/node/tasks/CancellableTasksIT.java
@@ -63,7 +63,6 @@
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
-import java.util.stream.StreamSupport;
 
 import static org.hamcrest.Matchers.anyOf;
 import static org.hamcrest.Matchers.empty;
@@ -159,7 +158,7 @@ public void testBanOnlyNodesWithOutstandingDescendantTasks() throws Exception {
         if (randomBoolean()) {
             internalCluster().startNodes(randomIntBetween(1, 3));
         }
-        Set<DiscoveryNode> nodes = StreamSupport.stream(clusterService().state().nodes().spliterator(), false).collect(Collectors.toSet());
+        Set<DiscoveryNode> nodes = clusterService().state().nodes().stream().collect(Collectors.toSet());
         final TestRequest rootRequest = generateTestRequest(nodes, 0, between(1, 4));
         ActionFuture<TestResponse> rootTaskFuture = client().execute(TransportTestAction.ACTION, rootRequest);
         Set<TestRequest> pendingRequests = allowPartialRequest(rootRequest);
@@ -212,7 +211,7 @@ public void testBanOnlyNodesWithOutstandingDescendantTasks() throws Exception {
     }
 
     public void testCancelTaskMultipleTimes() throws Exception {
-        Set<DiscoveryNode> nodes = StreamSupport.stream(clusterService().state().nodes().spliterator(), false).collect(Collectors.toSet());
+        Set<DiscoveryNode> nodes = clusterService().state().nodes().stream().collect(Collectors.toSet());
         TestRequest rootRequest = generateTestRequest(nodes, 0, randomIntBetween(1, 3));
         ActionFuture<TestResponse> mainTaskFuture = client().execute(TransportTestAction.ACTION, rootRequest);
         TaskId taskId = getRootTaskId(rootRequest);
@@ -244,7 +243,7 @@ public void testCancelTaskMultipleTimes() throws Exception {
     }
 
     public void testDoNotWaitForCompletion() throws Exception {
-        Set<DiscoveryNode> nodes = StreamSupport.stream(clusterService().state().nodes().spliterator(), false).collect(Collectors.toSet());
+        Set<DiscoveryNode> nodes = clusterService().state().nodes().stream().collect(Collectors.toSet());
         TestRequest rootRequest = generateTestRequest(nodes, 0, between(1, 3));
         ActionFuture<TestResponse> mainTaskFuture = client().execute(TransportTestAction.ACTION, rootRequest);
         TaskId taskId = getRootTaskId(rootRequest);
@@ -270,7 +269,7 @@ public void testDoNotWaitForCompletion() throws Exception {
     }
 
     public void testFailedToStartChildTaskAfterCancelled() throws Exception {
-        Set<DiscoveryNode> nodes = StreamSupport.stream(clusterService().state().nodes().spliterator(), false).collect(Collectors.toSet());
+        Set<DiscoveryNode> nodes = clusterService().state().nodes().stream().collect(Collectors.toSet());
         TestRequest rootRequest = generateTestRequest(nodes, 0, between(1, 3));
         ActionFuture<TestResponse> rootTaskFuture = client().execute(TransportTestAction.ACTION, rootRequest);
         TaskId taskId = getRootTaskId(rootRequest);
@@ -290,7 +289,7 @@ public void testFailedToStartChildTaskAfterCancelled() throws Exception {
 
     public void testCancelOrphanedTasks() throws Exception {
         final String nodeWithRootTask = internalCluster().startDataOnlyNode();
-        Set<DiscoveryNode> nodes = StreamSupport.stream(clusterService().state().nodes().spliterator(), false).collect(Collectors.toSet());
+        Set<DiscoveryNode> nodes = clusterService().state().nodes().stream().collect(Collectors.toSet());
         TestRequest rootRequest = generateTestRequest(nodes, 0, between(1, 3));
         client(nodeWithRootTask).execute(TransportTestAction.ACTION, rootRequest);
         allowPartialRequest(rootRequest);
@@ -315,7 +314,7 @@ public void testCancelOrphanedTasks() throws Exception {
     }
 
     public void testRemoveBanParentsOnDisconnect() throws Exception {
-        Set<DiscoveryNode> nodes = StreamSupport.stream(clusterService().state().nodes().spliterator(), false).collect(Collectors.toSet());
+        Set<DiscoveryNode> nodes = clusterService().state().nodes().stream().collect(Collectors.toSet());
         final TestRequest rootRequest = generateTestRequest(nodes, 0, between(1, 4));
         client().execute(TransportTestAction.ACTION, rootRequest);
         Set<TestRequest> pendingRequests = allowPartialRequest(rootRequest);
diff --git a/server/src/internalClusterTest/java/org/elasticsearch/search/ccs/CrossClusterSearchIT.java b/server/src/internalClusterTest/java/org/elasticsearch/search/ccs/CrossClusterSearchIT.java
@@ -47,7 +47,6 @@
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
-import java.util.stream.StreamSupport;
 
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertHitCount;
@@ -96,7 +95,10 @@ public void testRemoteClusterClientRole() throws Exception {
         );
 
         final String nodeWithRemoteClusterClientRole = randomFrom(
-            StreamSupport.stream(localCluster.clusterService().state().nodes().spliterator(), false)
+            localCluster.clusterService()
+                .state()
+                .nodes()
+                .stream()
                 .map(DiscoveryNode::getName)
                 .filter(nodeName -> nodeWithoutRemoteClusterClientRole.equals(nodeName) == false)
                 .filter(nodeName -> nodeName.equals(pureDataNode) == false)
@@ -163,7 +165,10 @@ public void testCancel() throws Exception {
         final Settings.Builder allocationFilter = Settings.builder();
         if (randomBoolean()) {
             remoteCluster.ensureAtLeastNumDataNodes(3);
-            List<String> remoteDataNodes = StreamSupport.stream(remoteCluster.clusterService().state().nodes().spliterator(), false)
+            List<String> remoteDataNodes = remoteCluster.clusterService()
+                .state()
+                .nodes()
+                .stream()
                 .filter(DiscoveryNode::canContainData)
                 .map(DiscoveryNode::getName)
                 .collect(Collectors.toList());
diff --git a/server/src/internalClusterTest/java/org/elasticsearch/search/ccs/CrossClusterSearchLeakIT.java b/server/src/internalClusterTest/java/org/elasticsearch/search/ccs/CrossClusterSearchLeakIT.java
@@ -29,7 +29,6 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.stream.Collectors;
-import java.util.stream.StreamSupport;
 
 import static org.elasticsearch.search.aggregations.AggregationBuilders.terms;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
@@ -78,7 +77,10 @@ public void testSearch() throws Exception {
         final InternalTestCluster remoteCluster = cluster("cluster_a");
         int minRemotes = between(2, 5);
         remoteCluster.ensureAtLeastNumDataNodes(minRemotes);
-        List<String> remoteDataNodes = StreamSupport.stream(remoteCluster.clusterService().state().nodes().spliterator(), false)
+        List<String> remoteDataNodes = remoteCluster.clusterService()
+            .state()
+            .nodes()
+            .stream()
             .filter(DiscoveryNode::canContainData)
             .map(DiscoveryNode::getName)
             .collect(Collectors.toList());
diff --git a/server/src/main/java/org/elasticsearch/action/admin/cluster/configuration/AddVotingConfigExclusionsRequest.java b/server/src/main/java/org/elasticsearch/action/admin/cluster/configuration/AddVotingConfigExclusionsRequest.java
@@ -26,7 +26,6 @@
 import java.util.Set;
 import java.util.function.Function;
 import java.util.stream.Collectors;
-import java.util.stream.StreamSupport;
 
 /**
  * A request to add voting config exclusions for certain master-eligible nodes, and wait for these nodes to be removed from the voting
@@ -102,7 +101,7 @@ Set<VotingConfigExclusion> resolveVotingConfigExclusions(ClusterState currentSta
             }
         } else {
             assert nodeNames.length > 0;
-            Map<String, DiscoveryNode> existingNodes = StreamSupport.stream(allNodes.spliterator(), false)
+            Map<String, DiscoveryNode> existingNodes = allNodes.stream()
                 .collect(Collectors.toMap(DiscoveryNode::getName, Function.identity()));
 
             for (String nodeName : nodeNames) {
diff --git a/server/src/main/java/org/elasticsearch/cluster/coordination/Coordinator.java b/server/src/main/java/org/elasticsearch/cluster/coordination/Coordinator.java
@@ -1085,15 +1085,17 @@ ClusterState improveConfiguration(ClusterState clusterState) {
         // ... and also automatically exclude the node IDs of master-ineligible nodes that were previously master-eligible and are still in
         // the voting config. We could exclude all the master-ineligible nodes here, but there could be quite a few of them and that makes
         // the logging much harder to follow.
-        final Stream<String> masterIneligibleNodeIdsInVotingConfig = StreamSupport.stream(clusterState.nodes().spliterator(), false)
+        final Stream<String> masterIneligibleNodeIdsInVotingConfig = clusterState.nodes()
+            .stream()
             .filter(
                 n -> n.isMasterNode() == false
                     && (clusterState.getLastAcceptedConfiguration().getNodeIds().contains(n.getId())
                         || clusterState.getLastCommittedConfiguration().getNodeIds().contains(n.getId()))
             )
             .map(DiscoveryNode::getId);
 
-        final Set<DiscoveryNode> liveNodes = StreamSupport.stream(clusterState.nodes().spliterator(), false)
+        final Set<DiscoveryNode> liveNodes = clusterState.nodes()
+            .stream()
             .filter(DiscoveryNode::isMasterNode)
             .filter(coordinationState.get()::containsJoinVoteFor)
             .collect(Collectors.toSet());
diff --git a/server/src/main/java/org/elasticsearch/cluster/node/DiscoveryNodes.java b/server/src/main/java/org/elasticsearch/cluster/node/DiscoveryNodes.java
@@ -22,6 +22,7 @@
 import org.elasticsearch.core.Nullable;
 
 import java.io.IOException;
+import java.util.AbstractCollection;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -34,15 +35,13 @@
 import java.util.Set;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
-import java.util.stream.StreamSupport;
 
 /**
  * This class holds all {@link DiscoveryNode} in the cluster and provides convenience methods to
  * access, modify merge / diff discovery nodes.
  */
-public class DiscoveryNodes implements SimpleDiffable<DiscoveryNodes>, Iterable<DiscoveryNode> {
+public class DiscoveryNodes extends AbstractCollection<DiscoveryNode> implements SimpleDiffable<DiscoveryNodes> {
 
     public static final DiscoveryNodes EMPTY_NODES = builder().build();
 
@@ -84,6 +83,11 @@ public Iterator<DiscoveryNode> iterator() {
         return nodes.valuesIt();
     }
 
+    @Override
+    public int size() {
+        return nodes.size();
+    }
+
     /**
      * Returns {@code true} if the local node is the elected master node.
      */
@@ -167,17 +171,14 @@ public ImmutableOpenMap<String, DiscoveryNode> getCoordinatingOnlyNodes() {
      * @return
      */
     public Collection<DiscoveryNode> getAllNodes() {
-        return StreamSupport.stream(this.spliterator(), false).collect(Collectors.toUnmodifiableList());
+        return this;
     }
 
     /**
      * Returns a stream of all nodes, with master nodes at the front
      */
     public Stream<DiscoveryNode> mastersFirstStream() {
-        return Stream.concat(
-            masterNodes.stream().map(Map.Entry::getValue),
-            StreamSupport.stream(this.spliterator(), false).filter(n -> n.isMasterNode() == false)
-        );
+        return Stream.concat(masterNodes.stream().map(Map.Entry::getValue), stream().filter(n -> n.isMasterNode() == false));
     }
 
     /**
@@ -339,7 +340,7 @@ public DiscoveryNode resolveNode(String node) {
      */
     public String[] resolveNodes(String... nodes) {
         if (nodes == null || nodes.length == 0) {
-            return StreamSupport.stream(this.spliterator(), false).map(DiscoveryNode::getId).toArray(String[]::new);
+            return stream().map(DiscoveryNode::getId).toArray(String[]::new);
         } else {
             Set<String> resolvedNodesIds = new HashSet<>(nodes.length);
             for (String nodeId : nodes) {
diff --git a/server/src/test/java/org/elasticsearch/cluster/coordination/NodeRemovalClusterStateTaskExecutorTests.java b/server/src/test/java/org/elasticsearch/cluster/coordination/NodeRemovalClusterStateTaskExecutorTests.java
@@ -21,7 +21,6 @@
 import java.util.List;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
-import java.util.stream.StreamSupport;
 
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.mockito.ArgumentMatchers.any;
@@ -45,7 +44,8 @@ public void testRemovingNonExistentNodes() throws Exception {
         for (int i = nodes; i < nodes + randomIntBetween(1, 16); i++) {
             removeBuilder.add(node(i));
         }
-        final List<NodeRemovalClusterStateTaskExecutor.Task> tasks = StreamSupport.stream(removeBuilder.build().spliterator(), false)
+        final List<NodeRemovalClusterStateTaskExecutor.Task> tasks = removeBuilder.build()
+            .stream()
             .map(node -> new NodeRemovalClusterStateTaskExecutor.Task(node, randomBoolean() ? "left" : "failed", () -> {}))
             .collect(Collectors.toList());
 
diff --git a/x-pack/plugin/autoscaling/src/main/java/org/elasticsearch/xpack/autoscaling/capacity/AutoscalingCalculateCapacityService.java b/x-pack/plugin/autoscaling/src/main/java/org/elasticsearch/xpack/autoscaling/capacity/AutoscalingCalculateCapacityService.java
@@ -37,7 +37,6 @@
 import java.util.TreeSet;
 import java.util.function.Function;
 import java.util.stream.Collectors;
-import java.util.stream.StreamSupport;
 
 public class AutoscalingCalculateCapacityService implements PolicyValidator {
     private final Map<String, AutoscalingDeciderService> deciderByName;
@@ -246,7 +245,8 @@ static class DefaultAutoscalingDeciderContext implements AutoscalingDeciderConte
             this.clusterInfo = clusterInfo;
             this.snapshotShardSizeInfo = snapshotShardSizeInfo;
             this.memoryInfo = memoryInfo;
-            this.currentNodes = StreamSupport.stream(state.nodes().spliterator(), false)
+            this.currentNodes = state.nodes()
+                .stream()
                 .filter(this::rolesFilter)
                 .collect(Collectors.toCollection(() -> new TreeSet<>(AutoscalingDeciderResults.DISCOVERY_NODE_COMPARATOR)));
             this.currentCapacity = calculateCurrentCapacity();
diff --git a/x-pack/plugin/autoscaling/src/main/java/org/elasticsearch/xpack/autoscaling/capacity/memory/AutoscalingMemoryInfoService.java b/x-pack/plugin/autoscaling/src/main/java/org/elasticsearch/xpack/autoscaling/capacity/memory/AutoscalingMemoryInfoService.java
@@ -85,9 +85,7 @@ void onClusterChanged(ClusterChangedEvent event) {
 
     Set<DiscoveryNode> relevantNodes(ClusterState state) {
         final Set<Set<DiscoveryNodeRole>> roleSets = calculateAutoscalingRoleSets(state);
-        return StreamSupport.stream(state.nodes().spliterator(), false)
-            .filter(n -> roleSets.contains(n.getRoles()))
-            .collect(Collectors.toSet());
+        return state.nodes().stream().filter(n -> roleSets.contains(n.getRoles())).collect(Collectors.toSet());
     }
 
     private Set<DiscoveryNode> addMissingNodes(Set<DiscoveryNode> nodes) {
diff --git a/x-pack/plugin/autoscaling/src/test/java/org/elasticsearch/xpack/autoscaling/capacity/AutoscalingCalculateCapacityServiceTests.java b/x-pack/plugin/autoscaling/src/test/java/org/elasticsearch/xpack/autoscaling/capacity/AutoscalingCalculateCapacityServiceTests.java
@@ -39,7 +39,6 @@
 import java.util.TreeSet;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
-import java.util.stream.StreamSupport;
 
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
@@ -209,7 +208,7 @@ public void testContext() {
         );
 
         assertThat(context.nodes().size(), equalTo(1));
-        assertThat(context.nodes(), equalTo(StreamSupport.stream(state.nodes().spliterator(), false).collect(Collectors.toSet())));
+        assertThat(context.nodes(), equalTo(state.nodes().stream().collect(Collectors.toSet())));
         if (hasDataRole) {
             assertNull(context.currentCapacity());
         } else {
diff --git a/x-pack/plugin/autoscaling/src/test/java/org/elasticsearch/xpack/autoscaling/storage/ReactiveStorageDeciderDecisionTests.java b/x-pack/plugin/autoscaling/src/test/java/org/elasticsearch/xpack/autoscaling/storage/ReactiveStorageDeciderDecisionTests.java
@@ -521,9 +521,7 @@ private static class TestAutoscalingDeciderContext implements AutoscalingDecider
         private TestAutoscalingDeciderContext(ClusterState state, Set<DiscoveryNodeRole> roles, AutoscalingCapacity currentCapacity) {
             this.state = state;
             this.currentCapacity = currentCapacity;
-            this.nodes = StreamSupport.stream(state.nodes().spliterator(), false)
-                .filter(n -> roles.stream().anyMatch(n.getRoles()::contains))
-                .collect(Collectors.toSet());
+            this.nodes = state.nodes().stream().filter(n -> roles.stream().anyMatch(n.getRoles()::contains)).collect(Collectors.toSet());
             this.roles = roles;
             this.info = createClusterInfo(state);
         }
@@ -567,7 +565,8 @@ public void ensureNotCancelled() {
     private static ClusterInfo createClusterInfo(ClusterState state) {
         // we make a simple setup to detect the right decisions are made. The unmovable calculation is tested in more detail elsewhere.
         // the diskusage is set such that the disk threshold decider never rejects an allocation.
-        Map<String, DiskUsage> diskUsages = StreamSupport.stream(state.nodes().spliterator(), false)
+        Map<String, DiskUsage> diskUsages = state.nodes()
+            .stream()
             .collect(Collectors.toMap(DiscoveryNode::getId, node -> new DiskUsage(node.getId(), null, "the_path", 1000, 1000)));
         ImmutableOpenMap<String, DiskUsage> immutableDiskUsages = ImmutableOpenMap.<String, DiskUsage>builder().putAll(diskUsages).build();
 
diff --git a/x-pack/plugin/autoscaling/src/test/java/org/elasticsearch/xpack/autoscaling/storage/ReactiveStorageDeciderServiceTests.java b/x-pack/plugin/autoscaling/src/test/java/org/elasticsearch/xpack/autoscaling/storage/ReactiveStorageDeciderServiceTests.java
@@ -60,7 +60,6 @@
 import java.util.Set;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
-import java.util.stream.StreamSupport;
 
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.is;
@@ -241,7 +240,7 @@ public void testSizeOf() {
         );
         ShardRouting primaryShard = subjectRoutings.primaryShard();
         ShardRouting replicaShard = subjectRoutings.replicaShards().get(0);
-        DiscoveryNode[] nodes = StreamSupport.stream(initialClusterState.nodes().spliterator(), false).toArray(DiscoveryNode[]::new);
+        DiscoveryNode[] nodes = initialClusterState.nodes().toArray(DiscoveryNode[]::new);
         boolean useReplica = randomBoolean();
         if (useReplica || randomBoolean()) {
             startShard(allocation, primaryShard, nodes[0].getId());
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/XPackPlugin.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/XPackPlugin.java
@@ -105,7 +105,6 @@
 import java.util.function.LongSupplier;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
-import java.util.stream.StreamSupport;
 
 @SuppressWarnings("HiddenField")
 public class XPackPlugin extends XPackClientPlugin
@@ -262,7 +261,7 @@ public static boolean isReadyForXPackCustomMetadata(ClusterState clusterState) {
      */
     public static List<DiscoveryNode> nodesNotReadyForXPackCustomMetadata(ClusterState clusterState) {
         // check that all nodes would be capable of deserializing newly added x-pack metadata
-        final List<DiscoveryNode> notReadyNodes = StreamSupport.stream(clusterState.nodes().spliterator(), false).filter(node -> {
+        final List<DiscoveryNode> notReadyNodes = clusterState.nodes().stream().filter(node -> {
             final String xpackInstalledAttr = node.getAttributes().getOrDefault(XPACK_INSTALLED_NODE_ATTR, "false");
             return Booleans.parseBoolean(xpackInstalledAttr) == false;
         }).collect(Collectors.toList());
diff --git a/x-pack/plugin/core/src/test/java/org/elasticsearch/license/AbstractLicenseServiceTestCase.java b/x-pack/plugin/core/src/test/java/org/elasticsearch/license/AbstractLicenseServiceTestCase.java
@@ -27,7 +27,7 @@
 import org.junit.Before;
 
 import java.nio.file.Path;
-import java.util.Arrays;
+import java.util.stream.Stream;
 
 import static java.util.Collections.emptySet;
 import static java.util.Collections.singletonMap;
@@ -78,7 +78,7 @@ protected void setInitialState(License license, XPackLicenseState licenseState,
         when(state.metadata()).thenReturn(metadata);
         final DiscoveryNode mockNode = getLocalNode();
         when(discoveryNodes.getMasterNode()).thenReturn(mockNode);
-        when(discoveryNodes.spliterator()).thenReturn(Arrays.asList(mockNode).spliterator());
+        when(discoveryNodes.stream()).thenAnswer(invocation -> Stream.of(mockNode));
         when(discoveryNodes.isLocalNodeElectedMaster()).thenReturn(false);
         when(discoveryNodes.getMinNodeVersion()).thenReturn(mockNode.getVersion());
         when(state.nodes()).thenReturn(discoveryNodes);
diff --git a/x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/TransformNodes.java b/x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/TransformNodes.java

Original file line number	Diff line number	Diff line change
`@@ -85,9 +85,7 @@ void onClusterChanged(ClusterChangedEvent event) {`
`85`	`85`
`86`	`86`	`Set<DiscoveryNode> relevantNodes(ClusterState state) {`
`87`	`87`	`final Set<Set<DiscoveryNodeRole>> roleSets = calculateAutoscalingRoleSets(state);`
`88`		`- return StreamSupport.stream(state.nodes().spliterator(), false)`
`89`		`- .filter(n -> roleSets.contains(n.getRoles()))`
`90`		`- .collect(Collectors.toSet());`
	`88`	`+ return state.nodes().stream().filter(n -> roleSets.contains(n.getRoles())).collect(Collectors.toSet());`
`91`	`89`	`}`
`92`	`90`
`93`	`91`	`private Set<DiscoveryNode> addMissingNodes(Set<DiscoveryNode> nodes) {`