Broadcast cancellation to only nodes have outstanding child tasks

client/rest-high-level/src/main/java/org/elasticsearch/client/TasksRequestConverters.java

@@ -39,6 +39,9 @@ static Request cancelTasks(CancelTasksRequest req) {
         params
             .withNodes(req.getNodes())
             .withActions(req.getActions());
+        if (req.getWaitForCompletion() != null) {
+            params.withWaitForCompletion(req.getWaitForCompletion());
+        }
         request.addParameters(params.asMap());
         return request;
     }

client/rest-high-level/src/main/java/org/elasticsearch/client/tasks/CancelTasksRequest.java

@@ -33,6 +33,7 @@ public class CancelTasksRequest implements Validatable {
     private Optional<TimeValue> timeout = Optional.empty();
     private Optional<TaskId> parentTaskId = Optional.empty();
     private Optional<TaskId> taskId = Optional.empty();
+    private Boolean waitForCompletion;
 
     CancelTasksRequest(){}
 
@@ -76,6 +77,14 @@ public Optional<TaskId> getTaskId() {
         return taskId;
     }
 
+    public Boolean getWaitForCompletion() {
+        return waitForCompletion;
+    }
+
+    public void setWaitForCompletion(boolean waitForCompletion) {
+        this.waitForCompletion = waitForCompletion;
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;
@@ -85,12 +94,13 @@ public boolean equals(Object o) {
             Objects.equals(getActions(), that.getActions()) &&
             Objects.equals(getTimeout(), that.getTimeout()) &&
             Objects.equals(getParentTaskId(), that.getParentTaskId()) &&
-            Objects.equals(getTaskId(), that.getTaskId()) ;
+            Objects.equals(getTaskId(), that.getTaskId()) &&
+            Objects.equals(waitForCompletion, that.waitForCompletion);
     }
 
     @Override
     public int hashCode() {
-        return Objects.hash(getNodes(), getActions(), getTimeout(), getParentTaskId(), getTaskId());
+        return Objects.hash(getNodes(), getActions(), getTimeout(), getParentTaskId(), getTaskId(), waitForCompletion);
     }
 
     @Override
@@ -101,6 +111,7 @@ public String toString() {
             ", timeout=" + timeout +
             ", parentTaskId=" + parentTaskId +
             ", taskId=" + taskId +
+            ", waitForCompletion=" + waitForCompletion +
             '}';
     }
 
@@ -110,6 +121,7 @@ public static class Builder {
         private Optional<TaskId> parentTaskId = Optional.empty();
         private List<String> actionsFilter = new ArrayList<>();
         private List<String> nodesFilter = new ArrayList<>();
+        private Boolean waitForCompletion;
 
         public Builder withTimeout(TimeValue timeout){
             this.timeout = Optional.of(timeout);
@@ -138,13 +150,21 @@ public Builder withNodesFiltered(List<String> nodes){
             return this;
         }
 
+        public Builder withWaitForCompletion(boolean waitForCompletion) {
+            this.waitForCompletion = waitForCompletion;
+            return this;
+        }
+
         public CancelTasksRequest build() {
             CancelTasksRequest request = new CancelTasksRequest();
             timeout.ifPresent(request::setTimeout);
             taskId.ifPresent(request::setTaskId);
             parentTaskId.ifPresent(request::setParentTaskId);
             request.setNodes(nodesFilter);
             request.setActions(actionsFilter);
+            if (waitForCompletion != null) {
+                request.setWaitForCompletion(waitForCompletion);
+            }
             return request;
         }
     }

client/rest-high-level/src/test/java/org/elasticsearch/client/TasksRequestConvertersTests.java

@@ -22,6 +22,7 @@
 import org.apache.http.client.methods.HttpGet;
 import org.apache.http.client.methods.HttpPost;
 import org.elasticsearch.action.admin.cluster.node.tasks.list.ListTasksRequest;
+import org.elasticsearch.client.tasks.CancelTasksRequest;
 import org.elasticsearch.tasks.TaskId;
 import org.elasticsearch.test.ESTestCase;
 
@@ -40,14 +41,15 @@ public void testCancelTasks() {
             new org.elasticsearch.client.tasks.TaskId(randomAlphaOfLength(5), randomNonNegativeLong());
         org.elasticsearch.client.tasks.TaskId parentTaskId =
             new org.elasticsearch.client.tasks.TaskId(randomAlphaOfLength(5), randomNonNegativeLong());
-        org.elasticsearch.client.tasks.CancelTasksRequest request =
-            new org.elasticsearch.client.tasks.CancelTasksRequest.Builder()
-                .withTaskId(taskId)
-                .withParentTaskId(parentTaskId)
-                .build();
+        CancelTasksRequest.Builder builder = new CancelTasksRequest.Builder().withTaskId(taskId).withParentTaskId(parentTaskId);
         expectedParams.put("task_id", taskId.toString());
         expectedParams.put("parent_task_id", parentTaskId.toString());
-        Request httpRequest = TasksRequestConverters.cancelTasks(request);
+        if (randomBoolean()) {
+            boolean waitForCompletion = randomBoolean();
+            builder.withWaitForCompletion(waitForCompletion);
+            expectedParams.put("wait_for_completion", Boolean.toString(waitForCompletion));
+        }
+        Request httpRequest = TasksRequestConverters.cancelTasks(builder.build());
         assertThat(httpRequest, notNullValue());
         assertThat(httpRequest.getMethod(), equalTo(HttpPost.METHOD_NAME));
         assertThat(httpRequest.getEntity(), nullValue());

client/rest-high-level/src/test/java/org/elasticsearch/client/documentation/TasksClientDocumentationIT.java

@@ -164,7 +164,8 @@ public void testCancelTasks() throws IOException {
             // tag::cancel-tasks-request-filter
             CancelTasksRequest byTaskIdRequest = new org.elasticsearch.client.tasks.CancelTasksRequest.Builder() // <1>
                 .withTaskId(new org.elasticsearch.client.tasks.TaskId("myNode",44L)) // <2>
-                .build(); // <3>
+                .withWaitForCompletion(true) // <3>
+                .build(); // <4>
             // end::cancel-tasks-request-filter
 
         }

docs/java-rest/high-level/tasks/cancel_tasks.asciidoc

@@ -22,7 +22,9 @@ include-tagged::{doc-tests}/TasksClientDocumentationIT.java[cancel-tasks-request
 --------------------------------------------------
 <1> Cancel a task
 <2> Cancel only cluster-related tasks
-<3> Cancel all tasks running on nodes nodeId1 and nodeId2
+<3> Should the request block until the cancellation of the task and its child tasks is completed.
+Otherwise, the request can return soon after the cancellation is started. Defaults to `false`.
+<4> Cancel all tasks running on nodes nodeId1 and nodeId2
 
 ==== Synchronous Execution
 

docs/reference/cluster/tasks.asciidoc

@@ -232,6 +232,11 @@ list tasks command, so multiple tasks can be cancelled at the same time. For
 example, the following command will cancel all reindex tasks running on the 
 nodes `nodeId1` and `nodeId2`.
 
+`wait_for_completion`::
+(Optional, boolean) If `true`, the request blocks until the cancellation of the
+task and its child tasks is completed. Otherwise, the request can return soon
+after the cancellation is started. Defaults to `false`.
+
 [source,console]
 --------------------------------------------------
 POST _tasks/_cancel?nodes=nodeId1,nodeId2&actions=*reindex

rest-api-spec/src/main/resources/rest-api-spec/api/tasks.cancel.json

@@ -39,6 +39,10 @@
       "parent_task_id":{
         "type":"string",
         "description":"Cancel tasks with specified parent task id (node_id:task_number). Set to -1 to cancel all."
+      },
+      "wait_for_completion": {
+        "type":"boolean",
+        "description":"Should the request block until the cancellation of the task and its child tasks is completed. Defaults to false"
       }
     }
   }

server/src/main/java/org/elasticsearch/action/admin/cluster/node/tasks/cancel/CancelTasksRequest.java

@@ -19,6 +19,7 @@
 
 package org.elasticsearch.action.admin.cluster.node.tasks.cancel;
 
+import org.elasticsearch.Version;
 import org.elasticsearch.action.support.tasks.BaseTasksRequest;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -33,20 +34,28 @@
 public class CancelTasksRequest extends BaseTasksRequest<CancelTasksRequest> {
 
     public static final String DEFAULT_REASON = "by user request";
+    public static final boolean DEFAULT_WAIT_FOR_COMPLETION = false;
 
     private String reason = DEFAULT_REASON;
+    private boolean waitForCompletion = DEFAULT_WAIT_FOR_COMPLETION;
 
     public CancelTasksRequest() {}
 
     public CancelTasksRequest(StreamInput in) throws IOException {
         super(in);
         this.reason = in.readString();
+        if (in.getVersion().onOrAfter(Version.V_8_0_0)) {
+            waitForCompletion = in.readBoolean();
+        }
     }
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         out.writeString(reason);
+        if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
+            out.writeBoolean(waitForCompletion);
+        }
     }
 
     @Override
@@ -68,4 +77,16 @@ public CancelTasksRequest setReason(String reason) {
     public String getReason() {
         return reason;
     }
+
+    /**
+     * If {@code true}, the request blocks until the cancellation of the task and its child tasks is completed.
+     * Otherwise, the request can return soon after the cancellation is started. Defaults to {@code false}.
+     */
+    public void setWaitForCompletion(boolean waitForCompletion) {
+        this.waitForCompletion = waitForCompletion;
+    }
+
+    public boolean waitForCompletion() {
+        return waitForCompletion;
+    }
 }

server/src/main/java/org/elasticsearch/action/admin/cluster/node/tasks/cancel/CancelTasksRequestBuilder.java

@@ -31,4 +31,8 @@ public CancelTasksRequestBuilder(ElasticsearchClient client, CancelTasksAction a
         super(client, action, new CancelTasksRequest());
     }
 
+    public CancelTasksRequestBuilder waitForCompletion(boolean waitForCompletion) {
+        request.setWaitForCompletion(waitForCompletion);
+        return this;
+    }
 }