Child requests proactively cancel children tasks (#92588)

To make this possible we modify the CancellableTasksTracker to track children tasks by the Request ID as well. That way, we can send an Action to cancel a child based on the parent task and the Request ID.

This is especially useful when parents' children requests timeout on the parents' side.

Fixes #90353
Relates #66992

docs/changelog/92588.yaml

@@ -0,0 +1,6 @@
+pr: 92588
+summary: Failed tasks proactively cancel children tasks
+area: Snapshot/Restore
+type: enhancement
+issues:
+ - 90353

server/src/main/java/org/elasticsearch/action/support/replication/TransportReplicationAction.java

@@ -1335,6 +1335,16 @@ public TaskId getParentTask() {
             return request.getParentTask();
         }
 
+        @Override
+        public void setRequestId(long requestId) {
+            request.setRequestId(requestId);
+        }
+
+        @Override
+        public long getRequestId() {
+            return request.getRequestId();
+        }
+
         @Override
         public Task createTask(long id, String type, String action, TaskId parentTaskId, Map<String, String> headers) {
             return request.createTask(id, type, action, parentTaskId, headers);

server/src/main/java/org/elasticsearch/cluster/service/MasterService.java

@@ -254,6 +254,9 @@ private <T extends ClusterStateTaskListener> void executeAndPublishBatch(
                     @Override
                     public void setParentTask(TaskId taskId) {}
 
+                    @Override
+                    public void setRequestId(long requestId) {}
+
                     @Override
                     public TaskId getParentTask() {
                         return TaskId.EMPTY_TASK_ID;

server/src/main/java/org/elasticsearch/persistent/PersistentTasksNodeService.java

@@ -175,6 +175,11 @@ public void setParentTask(TaskId taskId) {
                 throw new UnsupportedOperationException("parent task if for persistent tasks shouldn't change");
             }
 
+            @Override
+            public void setRequestId(long requestId) {
+                throw new UnsupportedOperationException("does not have a request ID");
+            }
+
             @Override
             public TaskId getParentTask() {
                 return parentTaskId;

server/src/main/java/org/elasticsearch/tasks/CancellableTasksTracker.java

@@ -31,21 +31,45 @@ public CancellableTasksTracker(T[] empty) {
     }
 
     private final Map<Long, T> byTaskId = ConcurrentCollections.newConcurrentMapWithAggressiveConcurrency();
-    private final Map<TaskId, T[]> byParentTaskId = ConcurrentCollections.newConcurrentMapWithAggressiveConcurrency();
+    private final Map<TaskId, Map<Long, T[]>> byParentTaskId = ConcurrentCollections.newConcurrentMapWithAggressiveConcurrency();
+
+    /**
+     * Gets the cancellable children of a parent task.
+     *
+     * Note: children of non-positive request IDs (e.g., -1) may be grouped together.
+     */
+    public Stream<T> getChildrenByRequestId(TaskId parentTaskId, long childRequestId) {
+        Map<Long, T[]> byRequestId = byParentTaskId.get(parentTaskId);
+        if (byRequestId != null) {
+            T[] children = byRequestId.get(childRequestId);
+            if (children != null) {
+                return Arrays.stream(children);
+            }
+        }
+        return Stream.empty();
+    }
 
     /**
      * Add an item for the given task. Should only be called once for each task, and {@code item} must be unique per task too.
      */
-    public void put(Task task, T item) {
+    public void put(Task task, long requestId, T item) {
         final long taskId = task.getId();
         if (task.getParentTaskId().isSet()) {
-            byParentTaskId.compute(task.getParentTaskId(), (ignored, oldValue) -> {
-                if (oldValue == null) {
-                    oldValue = empty;
+            byParentTaskId.compute(task.getParentTaskId(), (taskKey, oldRequestIdMap) -> {
+                if (oldRequestIdMap == null) {
+                    oldRequestIdMap = ConcurrentCollections.newConcurrentMapWithAggressiveConcurrency();
                 }
-                final T[] newValue = Arrays.copyOf(oldValue, oldValue.length + 1);
-                newValue[oldValue.length] = item;
-                return newValue;
+
+                oldRequestIdMap.compute(requestId, (requestIdKey, oldValue) -> {
+                    if (oldValue == null) {
+                        oldValue = empty;
+                    }
+                    final T[] newValue = Arrays.copyOf(oldValue, oldValue.length + 1);
+                    newValue[oldValue.length] = item;
+                    return newValue;
+                });
+
+                return oldRequestIdMap;
             });
         }
         final T oldItem = byTaskId.put(taskId, item);
@@ -60,36 +84,50 @@ public T get(long id) {
     }
 
     /**
-     * Remove (and return) the item that corresponds with the given task. Return {@code null} if not present. Safe to call multiple times
-     * for each task. However, {@link #getByParent} may return this task even after a call to this method completes, if the removal is
-     * actually being completed by a concurrent call that's still ongoing.
+     * Remove (and return) the item that corresponds with the given task and request ID. Return {@code null} if not present. Safe to call
+     * multiple times for each task. However, {@link #getByParent} may return this task even after a call to this method completes, if
+     * the removal is actually being completed by a concurrent call that's still ongoing.
      */
     public T remove(Task task) {
         final long taskId = task.getId();
         final T oldItem = byTaskId.remove(taskId);
         if (oldItem != null && task.getParentTaskId().isSet()) {
-            byParentTaskId.compute(task.getParentTaskId(), (ignored, oldValue) -> {
-                if (oldValue == null) {
+            byParentTaskId.compute(task.getParentTaskId(), (taskKey, oldRequestIdMap) -> {
+                if (oldRequestIdMap == null) {
                     return null;
                 }
-                if (oldValue.length == 1) {
-                    if (oldValue[0] == oldItem) {
-                        return null;
-                    } else {
+
+                for (Long requestId : oldRequestIdMap.keySet()) {
+                    oldRequestIdMap.compute(requestId, (requestIdKey, oldValue) -> {
+                        if (oldValue == null) {
+                            return null;
+                        }
+                        if (oldValue.length == 1) {
+                            if (oldValue[0] == oldItem) {
+                                return null;
+                            } else {
+                                return oldValue;
+                            }
+                        }
+                        if (oldValue[0] == oldItem) {
+                            return Arrays.copyOfRange(oldValue, 1, oldValue.length);
+                        }
+                        for (int i = 1; i < oldValue.length; i++) {
+                            if (oldValue[i] == oldItem) {
+                                final T[] newValue = Arrays.copyOf(oldValue, oldValue.length - 1);
+                                System.arraycopy(oldValue, i + 1, newValue, i, oldValue.length - i - 1);
+                                return newValue;
+                            }
+                        }
                         return oldValue;
-                    }
-                }
-                if (oldValue[0] == oldItem) {
-                    return Arrays.copyOfRange(oldValue, 1, oldValue.length);
+                    });
                 }
-                for (int i = 1; i < oldValue.length; i++) {
-                    if (oldValue[i] == oldItem) {
-                        final T[] newValue = Arrays.copyOf(oldValue, oldValue.length - 1);
-                        System.arraycopy(oldValue, i + 1, newValue, i, oldValue.length - i - 1);
-                        return newValue;
-                    }
+
+                if (oldRequestIdMap.keySet().isEmpty()) {
+                    return null;
                 }
-                return oldValue;
+
+                return oldRequestIdMap;
             });
         }
         return oldItem;
@@ -109,11 +147,11 @@ public Collection<T> values() {
      * started before this method was called have not completed.
      */
     public Stream<T> getByParent(TaskId parentTaskId) {
-        final T[] byParent = byParentTaskId.get(parentTaskId);
+        final Map<Long, T[]> byParent = byParentTaskId.get(parentTaskId);
         if (byParent == null) {
             return Stream.empty();
         }
-        return Arrays.stream(byParent);
+        return byParent.values().stream().flatMap(Stream::of);
     }
 
     // assertion for tests, not an invariant but should eventually be true
@@ -123,12 +161,14 @@ boolean assertConsistent() {
 
         // every by-parent value must be tracked by task too; the converse isn't true since we don't track values without a parent
         final Set<T> byTaskValues = new HashSet<>(byTaskId.values());
-        for (T[] byParent : byParentTaskId.values()) {
-            assert byParent.length > 0;
-            for (T t : byParent) {
-                assert byTaskValues.contains(t);
-            }
-        }
+        byParentTaskId.values().forEach(byParentMap -> {
+            byParentMap.forEach((requestId, byParentArray) -> {
+                assert byParentArray.length > 0;
+                for (T t : byParentArray) {
+                    assert byTaskValues.contains(t);
+                }
+            });
+        });
 
         return true;
     }

server/src/main/java/org/elasticsearch/tasks/TaskAwareRequest.java

@@ -26,6 +26,18 @@ default void setParentTask(String parentTaskNode, long parentTaskId) {
      */
     void setParentTask(TaskId taskId);
 
+    /**
+     * Gets the request ID. Defaults to -1, meaning "no request ID is set".
+     */
+    default long getRequestId() {
+        return -1;
+    }
+
+    /**
+     * Set the request ID related to this task.
+     */
+    void setRequestId(long requestId);
+
     /**
      * Get a reference to the task that created this request. Implementers should default to
      * {@link TaskId#EMPTY_TASK_ID}, meaning "there is no parent".

server/src/main/java/org/elasticsearch/tasks/TaskCancellationService.java

@@ -20,6 +20,7 @@
 import org.elasticsearch.action.support.CountDownActionListener;
 import org.elasticsearch.action.support.GroupedActionListener;
 import org.elasticsearch.action.support.RefCountingRunnable;
+import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.threadpool.ThreadPool;
@@ -44,6 +45,8 @@
 
 public class TaskCancellationService {
     public static final String BAN_PARENT_ACTION_NAME = "internal:admin/tasks/ban";
+    public static final String CANCEL_CHILD_ACTION_NAME = "internal:admin/tasks/cancel_child";
+    public static final TransportVersion VERSION_SUPPORTING_CANCEL_CHILD_ACTION = TransportVersion.V_8_8_0;
     private static final Logger logger = LogManager.getLogger(TaskCancellationService.class);
     private final TransportService transportService;
     private final TaskManager taskManager;
@@ -59,6 +62,12 @@ public TaskCancellationService(TransportService transportService) {
             BanParentTaskRequest::new,
             new BanParentRequestHandler()
         );
+        transportService.registerRequestHandler(
+            CANCEL_CHILD_ACTION_NAME,
+            ThreadPool.Names.SAME,
+            CancelChildRequest::new,
+            new CancelChildRequestHandler()
+        );
     }
 
     private String localNodeId() {
@@ -341,4 +350,69 @@ public void messageReceived(final BanParentTaskRequest request, final TransportC
             }
         }
     }
+
+    private static class CancelChildRequest extends TransportRequest {
+
+        private final TaskId parentTaskId;
+        private final long childRequestId;
+        private final String reason;
+
+        static CancelChildRequest createCancelChildRequest(TaskId parentTaskId, long childRequestId, String reason) {
+            return new CancelChildRequest(parentTaskId, childRequestId, reason);
+        }
+
+        private CancelChildRequest(TaskId parentTaskId, long childRequestId, String reason) {
+            this.parentTaskId = parentTaskId;
+            this.childRequestId = childRequestId;
+            this.reason = reason;
+        }
+
+        private CancelChildRequest(StreamInput in) throws IOException {
+            super(in);
+            parentTaskId = TaskId.readFromStream(in);
+            childRequestId = in.readLong();
+            reason = in.readString();
+        }
+
+        @Override
+        public void writeTo(StreamOutput out) throws IOException {
+            super.writeTo(out);
+            parentTaskId.writeTo(out);
+            out.writeLong(childRequestId);
+            out.writeString(reason);
+        }
+    }
+
+    private class CancelChildRequestHandler implements TransportRequestHandler<CancelChildRequest> {
+        @Override
+        public void messageReceived(final CancelChildRequest request, final TransportChannel channel, Task task) throws Exception {
+            taskManager.cancelChildLocal(request.parentTaskId, request.childRequestId, request.reason);
+            channel.sendResponse(TransportResponse.Empty.INSTANCE);
+        }
+    }
+
+    /**
+     * Sends an action to cancel a child task, associated with the given request ID and parent task.
+     */
+    public void cancelChildRemote(TaskId parentTask, long childRequestId, Transport.Connection childConnection, String reason) {
+        if (childConnection.getTransportVersion().onOrAfter(VERSION_SUPPORTING_CANCEL_CHILD_ACTION)) {
+            DiscoveryNode childNode = childConnection.getNode();
+            logger.debug(
+                "sending cancellation of child of parent task [{}] with request ID [{}] to node [{}] because of [{}]",
+                parentTask,
+                childRequestId,
+                childNode,
+                reason
+            );
+            final CancelChildRequest request = CancelChildRequest.createCancelChildRequest(parentTask, childRequestId, reason);
+            transportService.sendRequest(
+                childNode,
+                CANCEL_CHILD_ACTION_NAME,
+                request,
+                TransportRequestOptions.EMPTY,
+                EmptyTransportResponseHandler.INSTANCE_SAME
+            );
+        }
+    }
+
 }