Expose whether a task is cancellable in the _tasks list API

Closes #17369

core/src/main/java/org/elasticsearch/action/admin/cluster/node/tasks/list/TaskInfo.java

@@ -57,10 +57,12 @@ public class TaskInfo implements Writeable<TaskInfo>, ToXContent {
 
     private final Task.Status status;
 
+    private final boolean cancellable;
+
     private final TaskId parentTaskId;
 
     public TaskInfo(DiscoveryNode node, long id, String type, String action, String description, Task.Status status, long startTime,
-                    long runningTimeNanos, TaskId parentTaskId) {
+                    long runningTimeNanos, boolean cancellable, TaskId parentTaskId) {
         this.node = node;
         this.taskId = new TaskId(node.getId(), id);
         this.type = type;
@@ -69,6 +71,7 @@ public class TaskInfo implements Writeable<TaskInfo>, ToXContent {
         this.status = status;
         this.startTime = startTime;
         this.runningTimeNanos = runningTimeNanos;
+        this.cancellable = cancellable;
         this.parentTaskId = parentTaskId;
     }
 
@@ -85,6 +88,7 @@ public class TaskInfo implements Writeable<TaskInfo>, ToXContent {
         }
         startTime = in.readLong();
         runningTimeNanos = in.readLong();
+        cancellable = in.readBoolean();
         parentTaskId = new TaskId(in);
     }
 
@@ -134,6 +138,13 @@ public class TaskInfo implements Writeable<TaskInfo>, ToXContent {
         return runningTimeNanos;
     }
 
+    /**
+     * Returns true if the task supports cancellation
+     */
+    public boolean isCancellable() {
+        return cancellable;
+    }
+
     /**
      * Returns the parent task id
      */
@@ -161,6 +172,7 @@ public class TaskInfo implements Writeable<TaskInfo>, ToXContent {
         }
         out.writeLong(startTime);
         out.writeLong(runningTimeNanos);
+        out.writeBoolean(cancellable);
         parentTaskId.writeTo(out);
     }
 
@@ -178,6 +190,7 @@ public class TaskInfo implements Writeable<TaskInfo>, ToXContent {
         }
         builder.dateValueField("start_time_in_millis", "start_time", startTime);
         builder.timeValueField("running_time_in_nanos", "running_time", runningTimeNanos, TimeUnit.NANOSECONDS);
+        builder.field("cancellable", cancellable);
         if (parentTaskId.isSet()) {
             builder.field("parent_task_id", parentTaskId.toString());
         }

core/src/main/java/org/elasticsearch/tasks/Task.java

@@ -80,7 +80,7 @@ public class Task {
             status = getStatus();
         }
         return new TaskInfo(node, getId(), getType(), getAction(), description, status, startTime, System.nanoTime() - startTimeNanos,
-            parentTask);
+            this instanceof CancellableTask, parentTask);
     }
 
     /**

core/src/test/java/org/elasticsearch/action/admin/cluster/node/tasks/CancellableTasksTests.java

@@ -25,6 +25,7 @@ import org.elasticsearch.action.admin.cluster.node.tasks.cancel.CancelTasksReque
 import org.elasticsearch.action.admin.cluster.node.tasks.cancel.CancelTasksResponse;
 import org.elasticsearch.action.admin.cluster.node.tasks.list.ListTasksRequest;
 import org.elasticsearch.action.admin.cluster.node.tasks.list.ListTasksResponse;
+import org.elasticsearch.action.admin.cluster.node.tasks.list.TaskInfo;
 import org.elasticsearch.action.support.nodes.BaseNodeRequest;
 import org.elasticsearch.action.support.nodes.BaseNodesRequest;
 import org.elasticsearch.action.support.replication.ClusterStateCreationUtils;
@@ -267,6 +268,10 @@ public class CancellableTasksTests extends TaskManagerTestCase {
             // We should have the information about the cancelled task in the cancel operation response
             assertEquals(1, response.getTasks().size());
             assertEquals(mainTask.getId(), response.getTasks().get(0).getId());
+            // Verify that all cancelled tasks reported that they support cancellation
+            for(TaskInfo taskInfo : response.getTasks()) {
+                assertTrue(taskInfo.isCancellable());
+            }
         }
 
         // Make sure that tasks are no longer running

core/src/test/java/org/elasticsearch/action/admin/cluster/node/tasks/TransportTasksActionTests.java

@@ -565,6 +565,10 @@ public class TransportTasksActionTests extends TaskManagerTestCase {
         ListTasksResponse listResponse = testNodes[randomIntBetween(0, testNodes.length - 1)].transportListTasksAction.execute
             (listTasksRequest).get();
         assertEquals(1, listResponse.getPerNodeTasks().size());
+        // Verify that tasks are marked as non-cancellable
+        for (TaskInfo taskInfo : listResponse.getTasks()) {
+            assertFalse(taskInfo.isCancellable());
+        }
 
         // Release all tasks and wait for response
         checkLatch.countDown();

docs/reference/cluster/tasks.asciidoc

@@ -40,6 +40,7 @@ The result will look similar to the following:
           "action" : "cluster:monitor/tasks/lists[n]",
           "start_time_in_millis" : 1458585884904,
           "running_time_in_nanos" : 47402,
+          "cancellable" : false,
           "parent_task_id" : "oTUltX4IQMOUUVeiohTt8A:123"
         },
         "oTUltX4IQMOUUVeiohTt8A:123" : {
@@ -48,7 +49,8 @@ The result will look similar to the following:
           "type" : "transport",
           "action" : "cluster:monitor/tasks/lists",
           "start_time_in_millis" : 1458585884904,
-          "running_time_in_nanos" : 236042
+          "running_time_in_nanos" : 236042,
+          "cancellable" : false
         }
       }
     }