TaskCancellation (#7669)

* Smol comment

* WIP, not passing ray.init

* Fixed small problem

* wip

* Pseudo interrupt things

* Basic prototype operational

* correct proc title

* Mostly done

* Cleanup

* cleaner raylet error

* Cleaning up a few loose ends

* Fixing Race Conds

* Prelim testing

* Fixing comments and adding second_check for kill

* Working_new_impl

* demo_ready

* Fixing my english

* Fixing a few problems

* Small problems

* Cleaning up

* Response to changes

* Fixing error passing

* Merged to master

* fixing lock

* Cleaning up print statements

* Format

* Fixing Unit test build failure

* mock_worker fix

* java_fix

* Canel

* Switching to Cancel

* Responding to Review

* FixFormatting

* Lease cancellation

* FInal comments?

* Moving exist check to CoreWorker

* Fix Actor Transport Test

* Fixing task manager test

* chaning clock repr

* Fix build

* fix white space

* lint fix

* Updating to medium size

* Fixing Java test compilation issue

* lengthen bad timeouts

src/ray/common/ray_config_def.h

@@ -278,6 +278,9 @@ RAY_CONFIG(uint32_t, object_store_full_initial_delay_ms, 1000)
 /// Duration to wait between retries for failed tasks.
 RAY_CONFIG(uint32_t, task_retry_delay_ms, 5000)
 
+/// Duration to wait between retrying to kill a task.
+RAY_CONFIG(uint32_t, cancellation_retry_ms, 2000)
+
 /// Whether to enable gcs service.
 /// RAY_GCS_SERVICE_ENABLED is an env variable which only set in ci job.
 /// If the value of RAY_GCS_SERVICE_ENABLED is false, we will disable gcs service,

src/ray/core_worker/core_worker.cc

@@ -429,7 +429,7 @@ CoreWorker::CoreWorker(const CoreWorkerOptions &options, const WorkerID &worker_
           rpc_address_, local_raylet_client_, client_factory, raylet_client_factory,
           memory_store_, task_manager_, local_raylet_id,
           RayConfig::instance().worker_lease_timeout_milliseconds(),
-          std::move(actor_create_callback)));
+          std::move(actor_create_callback), boost::asio::steady_timer(io_service_)));
   future_resolver_.reset(new FutureResolver(memory_store_, client_factory));
   // Unfortunately the raylet client has to be constructed after the receivers.
   if (direct_task_receiver_ != nullptr) {
@@ -590,10 +590,10 @@ const WorkerID &CoreWorker::GetWorkerID() const { return worker_context_.GetWork
 
 void CoreWorker::SetCurrentTaskId(const TaskID &task_id) {
   worker_context_.SetCurrentTaskId(task_id);
-  main_thread_task_id_ = task_id;
   bool not_actor_task = false;
   {
     absl::MutexLock lock(&mutex_);
+    main_thread_task_id_ = task_id;
     not_actor_task = actor_id_.IsNil();
   }
   if (not_actor_task && task_id.IsNil()) {
@@ -1056,6 +1056,7 @@ TaskID CoreWorker::GetCallerId() const {
   if (!actor_id.IsNil()) {
     caller_id = TaskID::ForActorCreationTask(actor_id);
   } else {
+    absl::MutexLock lock(&mutex_);
     caller_id = main_thread_task_id_;
   }
   return caller_id;
@@ -1203,6 +1204,25 @@ Status CoreWorker::SubmitActorTask(const ActorID &actor_id, const RayFunction &f
   return status;
 }
 
+Status CoreWorker::CancelTask(const ObjectID &object_id, bool force_kill) {
+  ActorHandle *h = nullptr;
+  if (!object_id.CreatedByTask() ||
+      GetActorHandle(object_id.TaskId().ActorId(), &h).ok()) {
+    return Status::Invalid("Actor task cancellation is not supported.");
+  }
+  rpc::Address obj_addr;
+  if (!reference_counter_->GetOwner(object_id, nullptr, &obj_addr) ||
+      obj_addr.SerializeAsString() != rpc_address_.SerializeAsString()) {
+    return Status::Invalid("Task is not locally submitted.");
+  }
+
+  auto task_spec = task_manager_->GetTaskSpec(object_id.TaskId());
+  if (task_spec.has_value() && !task_spec.value().IsActorCreationTask()) {
+    return direct_task_submitter_->CancelTask(task_spec.value(), force_kill);
+  }
+  return Status::OK();
+}
+
 Status CoreWorker::KillActor(const ActorID &actor_id, bool force_kill,
                              bool no_reconstruction) {
   ActorHandle *actor_handle = nullptr;
@@ -1735,6 +1755,33 @@ void CoreWorker::HandleWaitForRefRemoved(const rpc::WaitForRefRemovedRequest &re
                                             owner_address, ref_removed_callback);
 }
 
+void CoreWorker::HandleCancelTask(const rpc::CancelTaskRequest &request,
+                                  rpc::CancelTaskReply *reply,
+                                  rpc::SendReplyCallback send_reply_callback) {
+  absl::MutexLock lock(&mutex_);
+  TaskID task_id = TaskID::FromBinary(request.intended_task_id());
+  bool success = main_thread_task_id_ == task_id;
+
+  // Try non-force kill
+  if (success && !request.force_kill()) {
+    RAY_LOG(INFO) << "Interrupting a running task " << main_thread_task_id_;
+    success = options_.kill_main();
+  }
+
+  reply->set_attempt_succeeded(success);
+  send_reply_callback(Status::OK(), nullptr, nullptr);
+
+  // Do force kill after reply callback sent
+  if (success && request.force_kill()) {
+    RAY_LOG(INFO) << "Force killing a worker running " << main_thread_task_id_;
+    RAY_IGNORE_EXPR(local_raylet_client_->Disconnect());
+    if (options_.log_dir != "") {
+      RayLog::ShutDownRayLog();
+    }
+    exit(1);
+  }
+}
+
 void CoreWorker::HandleKillActor(const rpc::KillActorRequest &request,
                                  rpc::KillActorReply *reply,
                                  rpc::SendReplyCallback send_reply_callback) {

src/ray/core_worker/core_worker.h

@@ -106,6 +106,8 @@ struct CoreWorkerOptions {
   std::function<void()> gc_collect;
   /// Language worker callback to get the current call stack.
   std::function<void(std::string *)> get_lang_stack;
+  // Function that tries to interrupt the currently running Python thread.
+  std::function<bool()> kill_main;
   /// Whether to enable object ref counting.
   bool ref_counting_enabled;
   /// Is local mode being used.
@@ -501,7 +503,7 @@ class CoreWorker : public rpc::CoreWorkerServiceHandler {
   /// For actors, this is the current actor ID. To make sure that all caller
   /// IDs have the same type, we embed the actor ID in a TaskID with the rest
   /// of the bytes zeroed out.
-  TaskID GetCallerId() const;
+  TaskID GetCallerId() const LOCKS_EXCLUDED(mutex_);
 
   /// Push an error to the relevant driver.
   ///
@@ -586,6 +588,12 @@ class CoreWorker : public rpc::CoreWorkerServiceHandler {
   /// \param[out] Status
   Status KillActor(const ActorID &actor_id, bool force_kill, bool no_reconstruction);
 
+  /// Stops the task associated with the given Object ID.
+  ///
+  /// \param[in] object_id of the task to kill (must be a Non-Actor task)
+  /// \param[in] force_kill Whether to force kill a task by killing the worker.
+  /// \param[out] Status
+  Status CancelTask(const ObjectID &object_id, bool force_kill);
   /// Decrease the reference count for this actor. Should be called by the
   /// language frontend when a reference to the ActorHandle destroyed.
   ///
@@ -694,6 +702,11 @@ class CoreWorker : public rpc::CoreWorkerServiceHandler {
   void HandleKillActor(const rpc::KillActorRequest &request, rpc::KillActorReply *reply,
                        rpc::SendReplyCallback send_reply_callback) override;
 
+  /// Implements gRPC server handler.
+  void HandleCancelTask(const rpc::CancelTaskRequest &request,
+                        rpc::CancelTaskReply *reply,
+                        rpc::SendReplyCallback send_reply_callback);
+
   /// Implements gRPC server handler.
   void HandlePlasmaObjectReady(const rpc::PlasmaObjectReadyRequest &request,
                                rpc::PlasmaObjectReadyReply *reply,
@@ -893,7 +906,7 @@ class CoreWorker : public rpc::CoreWorkerServiceHandler {
   /// The ID of the current task being executed by the main thread. If there
   /// are multiple threads, they will have a thread-local task ID stored in the
   /// worker context.
-  TaskID main_thread_task_id_;
+  TaskID main_thread_task_id_ GUARDED_BY(mutex_);
 
   // Flag indicating whether this worker has been shut down.
   bool shutdown_ = false;

src/ray/core_worker/lib/java/io_ray_runtime_RayNativeRuntime.cc

@@ -122,6 +122,7 @@ JNIEXPORT void JNICALL Java_io_ray_runtime_RayNativeRuntime_nativeInitialize(
       nullptr,                                       // check_signals
       nullptr,                                       // gc_collect
       nullptr,                                       // get_lang_stack
+      nullptr,                                       // kill_main
       false,                                         // ref_counting_enabled
       false,                                         // is_local_mode
       static_cast<int>(numWorkersPerProcess),        // num_workers

src/ray/core_worker/task_manager.cc

@@ -412,6 +412,15 @@ void TaskManager::RemoveLineageReference(const ObjectID &object_id,
   }
 }
 
+bool TaskManager::MarkTaskCanceled(const TaskID &task_id) {
+  absl::MutexLock lock(&mu_);
+  auto it = submissible_tasks_.find(task_id);
+  if (it != submissible_tasks_.end()) {
+    it->second.num_retries_left = 0;
+  }
+  return it != submissible_tasks_.end();
+}
+
 void TaskManager::MarkPendingTaskFailed(const TaskID &task_id,
                                         const TaskSpecification &spec,
                                         rpc::ErrorType error_type) {
@@ -432,4 +441,13 @@ void TaskManager::MarkPendingTaskFailed(const TaskID &task_id,
   }
 }
 
+absl::optional<TaskSpecification> TaskManager::GetTaskSpec(const TaskID &task_id) const {
+  absl::MutexLock lock(&mu_);
+  auto it = submissible_tasks_.find(task_id);
+  if (it == submissible_tasks_.end()) {
+    return absl::optional<TaskSpecification>();
+  }
+  return it->second.spec;
+}
+
 }  // namespace ray

src/ray/core_worker/task_manager.h

@@ -39,6 +39,8 @@ class TaskFinisherInterface {
       const std::vector<ObjectID> &inlined_dependency_ids,
       const std::vector<ObjectID> &contained_ids) = 0;
 
+  virtual bool MarkTaskCanceled(const TaskID &task_id) = 0;
+
   virtual ~TaskFinisherInterface() {}
 };
 
@@ -129,6 +131,15 @@ class TaskManager : public TaskFinisherInterface, public TaskResubmissionInterfa
   void OnTaskDependenciesInlined(const std::vector<ObjectID> &inlined_dependency_ids,
                                  const std::vector<ObjectID> &contained_ids) override;
 
+  /// Set number of retries to zero for a task that is being canceled.
+  ///
+  /// \param[in] task_id to cancel.
+  /// \return Whether the task was pending and was marked for cancellation.
+  bool MarkTaskCanceled(const TaskID &task_id);
+
+  /// Return the spec for a pending task.
+  absl::optional<TaskSpecification> GetTaskSpec(const TaskID &task_id) const;
+
   /// Return whether this task can be submitted for execution.
   ///
   /// \param[in] task_id ID of the task to query.

src/ray/core_worker/test/core_worker_test.cc

@@ -271,6 +271,7 @@ class CoreWorkerTest : public ::testing::Test {
           nullptr,                        // check_signals
           nullptr,                        // gc_collect
           nullptr,                        // get_lang_stack
+          nullptr,                        // kill_main
           true,                           // ref_counting_enabled
           false,                          // is_local_mode
           1,                              // num_workers

src/ray/core_worker/test/direct_actor_transport_test.cc

@@ -64,6 +64,8 @@ class MockTaskFinisher : public TaskFinisherInterface {
 
   MOCK_METHOD2(OnTaskDependenciesInlined,
                void(const std::vector<ObjectID> &, const std::vector<ObjectID> &));
+
+  MOCK_METHOD1(MarkTaskCanceled, bool(const TaskID &task_id));
 };
 
 TaskSpecification CreateActorTaskHelper(ActorID actor_id, int64_t counter) {

src/ray/core_worker/test/direct_task_transport_test.cc

@@ -52,7 +52,15 @@ class MockWorkerClient : public rpc::CoreWorkerClientInterface {
     return true;
   }
 
+  ray::Status CancelTask(
+      const rpc::CancelTaskRequest &request,
+      const rpc::ClientCallback<rpc::CancelTaskReply> &callback) override {
+    kill_requests.push_front(request);
+    return Status::OK();
+  }
+
   std::list<rpc::ClientCallback<rpc::PushTaskReply>> callbacks;
+  std::list<rpc::CancelTaskRequest> kill_requests;
 };
 
 class MockTaskFinisher : public TaskFinisherInterface {
@@ -75,6 +83,8 @@ class MockTaskFinisher : public TaskFinisherInterface {
     num_contained_ids += contained_ids.size();
   }
 
+  bool MarkTaskCanceled(const TaskID &task_id) override { return true; }
+
   int num_tasks_complete = 0;
   int num_tasks_failed = 0;
   int num_inlined_dependencies = 0;
@@ -935,6 +945,105 @@ TEST(DirectTaskTransportTest, TestWorkerLeaseTimeout) {
   ASSERT_FALSE(raylet_client->ReplyCancelWorkerLease());
 }
 
+TEST(DirectTaskTransportTest, TestKillExecutingTask) {
+  rpc::Address address;
+  auto raylet_client = std::make_shared<MockRayletClient>();
+  auto worker_client = std::make_shared<MockWorkerClient>();
+  auto store = std::make_shared<CoreWorkerMemoryStore>();
+  auto factory = [&](const rpc::Address &addr) { return worker_client; };
+  auto task_finisher = std::make_shared<MockTaskFinisher>();
+  CoreWorkerDirectTaskSubmitter submitter(address, raylet_client, factory, nullptr, store,
+                                          task_finisher, ClientID::Nil(), kLongTimeout);
+  std::unordered_map<std::string, double> empty_resources;
+  ray::FunctionDescriptor empty_descriptor =
+      ray::FunctionDescriptorBuilder::BuildPython("", "", "", "");
+  TaskSpecification task = BuildTaskSpec(empty_resources, empty_descriptor);
+
+  ASSERT_TRUE(submitter.SubmitTask(task).ok());
+  ASSERT_TRUE(raylet_client->GrantWorkerLease("localhost", 1234, ClientID::Nil()));
+
+  // Try force kill, exiting the worker
+  ASSERT_TRUE(submitter.CancelTask(task, true).ok());
+  ASSERT_EQ(worker_client->kill_requests.front().intended_task_id(),
+            task.TaskId().Binary());
+  ASSERT_TRUE(worker_client->ReplyPushTask(Status::IOError("workerdying"), true));
+  ASSERT_EQ(worker_client->callbacks.size(), 0);
+  ASSERT_EQ(raylet_client->num_workers_returned, 0);
+  ASSERT_EQ(raylet_client->num_workers_disconnected, 0);
+  ASSERT_EQ(task_finisher->num_tasks_complete, 0);
+  ASSERT_EQ(task_finisher->num_tasks_failed, 1);
+
+  task.GetMutableMessage().set_task_id(
+      TaskID::ForNormalTask(JobID::Nil(), TaskID::Nil(), 1).Binary());
+  ASSERT_TRUE(submitter.SubmitTask(task).ok());
+  ASSERT_TRUE(raylet_client->GrantWorkerLease("localhost", 1234, ClientID::Nil()));
+
+  // Try non-force kill, worker returns normally
+  ASSERT_TRUE(submitter.CancelTask(task, false).ok());
+  ASSERT_TRUE(worker_client->ReplyPushTask());
+  ASSERT_EQ(worker_client->kill_requests.front().intended_task_id(),
+            task.TaskId().Binary());
+  ASSERT_EQ(worker_client->callbacks.size(), 0);
+  ASSERT_EQ(raylet_client->num_workers_returned, 1);
+  ASSERT_EQ(raylet_client->num_workers_disconnected, 0);
+  ASSERT_EQ(task_finisher->num_tasks_complete, 1);
+  ASSERT_EQ(task_finisher->num_tasks_failed, 1);
+}
+
+TEST(DirectTaskTransportTest, TestKillPendingTask) {
+  rpc::Address address;
+  auto raylet_client = std::make_shared<MockRayletClient>();
+  auto worker_client = std::make_shared<MockWorkerClient>();
+  auto store = std::make_shared<CoreWorkerMemoryStore>();
+  auto factory = [&](const rpc::Address &addr) { return worker_client; };
+  auto task_finisher = std::make_shared<MockTaskFinisher>();
+  CoreWorkerDirectTaskSubmitter submitter(address, raylet_client, factory, nullptr, store,
+                                          task_finisher, ClientID::Nil(), kLongTimeout);
+  std::unordered_map<std::string, double> empty_resources;
+  ray::FunctionDescriptor empty_descriptor =
+      ray::FunctionDescriptorBuilder::BuildPython("", "", "", "");
+  TaskSpecification task = BuildTaskSpec(empty_resources, empty_descriptor);
+
+  ASSERT_TRUE(submitter.SubmitTask(task).ok());
+  ASSERT_TRUE(submitter.CancelTask(task, true).ok());
+  ASSERT_EQ(worker_client->kill_requests.size(), 0);
+  ASSERT_EQ(worker_client->callbacks.size(), 0);
+  ASSERT_EQ(raylet_client->num_workers_returned, 0);
+  ASSERT_EQ(raylet_client->num_workers_disconnected, 0);
+  ASSERT_EQ(task_finisher->num_tasks_complete, 0);
+  ASSERT_EQ(task_finisher->num_tasks_failed, 1);
+  ASSERT_EQ(raylet_client->num_leases_canceled, 1);
+  ASSERT_TRUE(raylet_client->ReplyCancelWorkerLease());
+}
+
+TEST(DirectTaskTransportTest, TestKillResolvingTask) {
+  rpc::Address address;
+  auto raylet_client = std::make_shared<MockRayletClient>();
+  auto worker_client = std::make_shared<MockWorkerClient>();
+  auto store = std::make_shared<CoreWorkerMemoryStore>();
+  auto factory = [&](const rpc::Address &addr) { return worker_client; };
+  auto task_finisher = std::make_shared<MockTaskFinisher>();
+  CoreWorkerDirectTaskSubmitter submitter(address, raylet_client, factory, nullptr, store,
+                                          task_finisher, ClientID::Nil(), kLongTimeout);
+  std::unordered_map<std::string, double> empty_resources;
+  ray::FunctionDescriptor empty_descriptor =
+      ray::FunctionDescriptorBuilder::BuildPython("", "", "", "");
+  TaskSpecification task = BuildTaskSpec(empty_resources, empty_descriptor);
+  ObjectID obj1 = ObjectID::FromRandom().WithTransportType(TaskTransportType::DIRECT);
+  task.GetMutableMessage().add_args()->add_object_ids(obj1.Binary());
+  ASSERT_TRUE(submitter.SubmitTask(task).ok());
+  ASSERT_EQ(task_finisher->num_inlined_dependencies, 0);
+  ASSERT_TRUE(submitter.CancelTask(task, true).ok());
+  auto data = GenerateRandomObject();
+  ASSERT_TRUE(store->Put(*data, obj1));
+  ASSERT_EQ(worker_client->kill_requests.size(), 0);
+  ASSERT_EQ(worker_client->callbacks.size(), 0);
+  ASSERT_EQ(raylet_client->num_workers_returned, 0);
+  ASSERT_EQ(raylet_client->num_workers_disconnected, 0);
+  ASSERT_EQ(task_finisher->num_tasks_complete, 0);
+  ASSERT_EQ(task_finisher->num_tasks_failed, 1);
+}
+
 }  // namespace ray
 
 int main(int argc, char **argv) {

src/ray/core_worker/test/mock_worker.cc

@@ -54,6 +54,7 @@ class MockWorker {
         nullptr,        // check_signals
         nullptr,        // gc_collect
         nullptr,        // get_lang_stack
+        nullptr,        // kill_main
         true,           // ref_counting_enabled
         false,          // is_local_mode
         1,              // num_workers

src/ray/core_worker/test/task_manager_test.cc

@@ -187,6 +187,31 @@ TEST_F(TaskManagerTest, TestTaskRetry) {
   ASSERT_EQ(reference_counter_->NumObjectIDsInScope(), 0);
 }
 
+TEST_F(TaskManagerTest, TestTaskKill) {
+  TaskID caller_id = TaskID::Nil();
+  rpc::Address caller_address;
+  ASSERT_EQ(reference_counter_->NumObjectIDsInScope(), 0);
+  auto spec = CreateTaskHelper(1, {});
+  ASSERT_FALSE(manager_.IsTaskPending(spec.TaskId()));
+  int num_retries = 3;
+  manager_.AddPendingTask(caller_id, caller_address, spec, "", num_retries);
+  ASSERT_TRUE(manager_.IsTaskPending(spec.TaskId()));
+  ASSERT_EQ(reference_counter_->NumObjectIDsInScope(), 1);
+  auto return_id = spec.ReturnId(0, TaskTransportType::DIRECT);
+  WorkerContext ctx(WorkerType::WORKER, WorkerID::FromRandom(), JobID::FromInt(0));
+
+  manager_.MarkTaskCanceled(spec.TaskId());
+  auto error = rpc::ErrorType::TASK_CANCELLED;
+  manager_.PendingTaskFailed(spec.TaskId(), error);
+  ASSERT_FALSE(manager_.IsTaskPending(spec.TaskId()));
+  std::vector<std::shared_ptr<RayObject>> results;
+  RAY_CHECK_OK(store_->Get({return_id}, 1, 0, ctx, false, &results));
+  ASSERT_EQ(results.size(), 1);
+  rpc::ErrorType stored_error;
+  ASSERT_TRUE(results[0]->IsException(&stored_error));
+  ASSERT_EQ(stored_error, error);
+}
+
 // Test to make sure that the task spec and dependencies for an object are
 // evicted when lineage pinning is disabled in the ReferenceCounter.
 TEST_F(TaskManagerTest, TestLineageEvicted) {

src/ray/core_worker/transport/direct_task_transport.cc

@@ -23,17 +23,17 @@ Status CoreWorkerDirectTaskSubmitter::SubmitTask(TaskSpecification task_spec) {
   resolver_.ResolveDependencies(task_spec, [this, task_spec]() {
     RAY_LOG(DEBUG) << "Task dependencies resolved " << task_spec.TaskId();
     if (actor_create_callback_ && task_spec.IsActorCreationTask()) {
-      // If gcs actor management is enabled, the actor creation task will be sent to gcs
-      // server directly after the in-memory dependent objects are resolved.
-      // For more details please see the protocol of actor management based on gcs.
+      // If gcs actor management is enabled, the actor creation task will be sent to
+      // gcs server directly after the in-memory dependent objects are resolved. For
+      // more details please see the protocol of actor management based on gcs.
       // https://docs.google.com/document/d/1EAWide-jy05akJp6OMtDn58XOK7bUyruWMia4E-fV28/edit?usp=sharing
       auto actor_id = task_spec.ActorCreationId();
       auto task_id = task_spec.TaskId();
       RAY_LOG(INFO) << "Submitting actor creation task to GCS: " << actor_id;
       auto status =
           actor_create_callback_(task_spec, [this, actor_id, task_id](Status status) {
-            // If GCS is failed, GcsRpcClient may receive IOError status but it will not
-            // trigger this callback, because GcsRpcClient has retry logic at the
+            // If GCS is failed, GcsRpcClient may receive IOError status but it will
+            // not trigger this callback, because GcsRpcClient has retry logic at the
             // bottom. So if this callback is invoked with an error there must be
             // something wrong with the protocol of gcs-based actor management.
             // So just check `status.ok()` here.
@@ -46,18 +46,33 @@ Status CoreWorkerDirectTaskSubmitter::SubmitTask(TaskSpecification task_spec) {
       return;
     }
 
-    absl::MutexLock lock(&mu_);
-    // Note that the dependencies in the task spec are mutated to only contain
-    // plasma dependencies after ResolveDependencies finishes.
-    const SchedulingKey scheduling_key(
-        task_spec.GetSchedulingClass(), task_spec.GetDependencies(),
-        task_spec.IsActorCreationTask() ? task_spec.ActorCreationId() : ActorID::Nil());
-    auto it = task_queues_.find(scheduling_key);
-    if (it == task_queues_.end()) {
-      it = task_queues_.emplace(scheduling_key, std::deque<TaskSpecification>()).first;
+    bool keep_executing = true;
+    {
+      absl::MutexLock lock(&mu_);
+      if (cancelled_tasks_.find(task_spec.TaskId()) != cancelled_tasks_.end()) {
+        cancelled_tasks_.erase(task_spec.TaskId());
+        keep_executing = false;
+      }
+      if (keep_executing) {
+        // Note that the dependencies in the task spec are mutated to only contain
+        // plasma dependencies after ResolveDependencies finishes.
+        const SchedulingKey scheduling_key(
+            task_spec.GetSchedulingClass(), task_spec.GetDependencies(),
+            task_spec.IsActorCreationTask() ? task_spec.ActorCreationId()
+                                            : ActorID::Nil());
+        auto it = task_queues_.find(scheduling_key);
+        if (it == task_queues_.end()) {
+          it =
+              task_queues_.emplace(scheduling_key, std::deque<TaskSpecification>()).first;
+        }
+        it->second.push_back(task_spec);
+        RequestNewWorkerIfNeeded(scheduling_key);
+      }
+    }
+    if (!keep_executing) {
+      task_finisher_->PendingTaskFailed(task_spec.TaskId(),
+                                        rpc::ErrorType::TASK_CANCELLED, nullptr);
     }
-    it->second.push_back(task_spec);
-    RequestNewWorkerIfNeeded(scheduling_key);
   });
   return Status::OK();
 }
@@ -93,8 +108,9 @@ void CoreWorkerDirectTaskSubmitter::OnWorkerIdle(
     worker_to_lease_client_.erase(addr);
   } else {
     auto &client = *client_cache_[addr];
-    PushNormalTask(addr, client, scheduling_key, queue_entry->second.front(),
-                   assigned_resources);
+    auto task_spec = queue_entry->second.front();
+    PushNormalTask(addr, client, scheduling_key, task_spec, assigned_resources);
+    executing_tasks_.emplace(task_spec.TaskId(), addr);
     queue_entry->second.pop_front();
     // Delete the queue if it's now empty. Note that the queue cannot already be empty
     // because this is the only place tasks are removed from it.
@@ -248,6 +264,10 @@ void CoreWorkerDirectTaskSubmitter::PushNormalTask(
       std::move(request),
       [this, task_id, is_actor, is_actor_creation, scheduling_key, addr,
        assigned_resources](Status status, const rpc::PushTaskReply &reply) {
+        {
+          absl::MutexLock lock(&mu_);
+          executing_tasks_.erase(task_id);
+        }
         if (reply.worker_exiting()) {
           // The worker is draining and will shutdown after it is done. Don't return
           // it to the Raylet since that will kill it early.
@@ -273,4 +293,78 @@ void CoreWorkerDirectTaskSubmitter::PushNormalTask(
         }
       }));
 }
+
+Status CoreWorkerDirectTaskSubmitter::CancelTask(TaskSpecification task_spec,
+                                                 bool force_kill) {
+  RAY_LOG(INFO) << "Killing task: " << task_spec.TaskId();
+  const SchedulingKey scheduling_key(
+      task_spec.GetSchedulingClass(), task_spec.GetDependencies(),
+      task_spec.IsActorCreationTask() ? task_spec.ActorCreationId() : ActorID::Nil());
+  std::shared_ptr<rpc::CoreWorkerClientInterface> client = nullptr;
+  {
+    absl::MutexLock lock(&mu_);
+    if (cancelled_tasks_.find(task_spec.TaskId()) != cancelled_tasks_.end() ||
+        !task_finisher_->MarkTaskCanceled(task_spec.TaskId())) {
+      return Status::OK();
+    }
+
+    auto scheduled_tasks = task_queues_.find(scheduling_key);
+    // This cancels tasks that have completed dependencies and are awaiting
+    // a worker lease.
+    if (scheduled_tasks != task_queues_.end()) {
+      for (auto spec = scheduled_tasks->second.begin();
+           spec != scheduled_tasks->second.end(); spec++) {
+        if (spec->TaskId() == task_spec.TaskId()) {
+          scheduled_tasks->second.erase(spec);
+
+          if (scheduled_tasks->second.empty()) {
+            task_queues_.erase(scheduling_key);
+            CancelWorkerLeaseIfNeeded(scheduling_key);
+          }
+          task_finisher_->PendingTaskFailed(task_spec.TaskId(),
+                                            rpc::ErrorType::TASK_CANCELLED);
+          return Status::OK();
+        }
+      }
+    }
+    // This will get removed either when the RPC call to cancel is returned
+    // or when all dependencies are resolved.
+    RAY_CHECK(cancelled_tasks_.emplace(task_spec.TaskId()).second);
+    auto rpc_client = executing_tasks_.find(task_spec.TaskId());
+    // Looks for an RPC handle for the worker executing the task.
+    if (rpc_client != executing_tasks_.end() &&
+        client_cache_.find(rpc_client->second) != client_cache_.end()) {
+      client = client_cache_.find(rpc_client->second)->second;
+    }
+  }
+
+  // This case is reached for tasks that have unresolved dependencies.
+  if (client == nullptr) {
+    return Status::OK();
+  }
+
+  auto request = rpc::CancelTaskRequest();
+  request.set_intended_task_id(task_spec.TaskId().Binary());
+  request.set_force_kill(force_kill);
+  RAY_UNUSED(client->CancelTask(
+      request, [this, task_spec, force_kill](const Status &status,
+                                             const rpc::CancelTaskReply &reply) {
+        absl::MutexLock lock(&mu_);
+        cancelled_tasks_.erase(task_spec.TaskId());
+        if (status.ok() && !reply.attempt_succeeded()) {
+          if (cancel_retry_timer_.has_value()) {
+            if (cancel_retry_timer_->expiry().time_since_epoch() <=
+                std::chrono::high_resolution_clock::now().time_since_epoch()) {
+              cancel_retry_timer_->expires_after(boost::asio::chrono::milliseconds(
+                  RayConfig::instance().cancellation_retry_ms()));
+            }
+            cancel_retry_timer_->async_wait(boost::bind(
+                &CoreWorkerDirectTaskSubmitter::CancelTask, this, task_spec, force_kill));
+          }
+        }
+        // Retry is not attempted if !status.ok() because force-kill may kill the worker
+        // before the reply is sent.
+      }));
+  return Status::OK();
+}
 };  // namespace ray

src/ray/core_worker/transport/direct_task_transport.h

@@ -56,7 +56,8 @@ class CoreWorkerDirectTaskSubmitter {
       std::shared_ptr<TaskFinisherInterface> task_finisher, ClientID local_raylet_id,
       int64_t lease_timeout_ms,
       std::function<Status(const TaskSpecification &, const gcs::StatusCallback &)>
-          actor_create_callback = nullptr)
+          actor_create_callback = nullptr,
+      absl::optional<boost::asio::steady_timer> cancel_timer = absl::nullopt)
       : rpc_address_(rpc_address),
         local_lease_client_(lease_client),
         client_factory_(client_factory),
@@ -65,13 +66,20 @@ class CoreWorkerDirectTaskSubmitter {
         task_finisher_(task_finisher),
         lease_timeout_ms_(lease_timeout_ms),
         local_raylet_id_(local_raylet_id),
-        actor_create_callback_(std::move(actor_create_callback)) {}
+        actor_create_callback_(std::move(actor_create_callback)),
+        cancel_retry_timer_(std::move(cancel_timer)) {}
 
   /// Schedule a task for direct submission to a worker.
   ///
   /// \param[in] task_spec The task to schedule.
   Status SubmitTask(TaskSpecification task_spec);
 
+  /// Either remove a pending task or send an RPC to kill a running task
+  ///
+  /// \param[in] task_spec The task to kill.
+  /// \param[in] force_kill Whether to kill the worker executing the task.
+  Status CancelTask(TaskSpecification task_spec, bool force_kill);
+
  private:
   /// Schedule more work onto an idle worker or return it back to the raylet if
   /// no more tasks are queued for submission. If an error was encountered
@@ -180,6 +188,15 @@ class CoreWorkerDirectTaskSubmitter {
   // Invariant: if a queue is in this map, it has at least one task.
   absl::flat_hash_map<SchedulingKey, std::deque<TaskSpecification>> task_queues_
       GUARDED_BY(mu_);
+
+  // Tasks that were cancelled while being resolved.
+  absl::flat_hash_set<TaskID> cancelled_tasks_ GUARDED_BY(mu_);
+
+  // Keeps track of where currently executing tasks are being run.
+  absl::flat_hash_map<TaskID, rpc::WorkerAddress> executing_tasks_ GUARDED_BY(mu_);
+
+  // Retries cancelation requests if they were not successful.
+  absl::optional<boost::asio::steady_timer> cancel_retry_timer_;
 };
 
 };  // namespace ray

src/ray/protobuf/core_worker.proto

@@ -111,7 +111,8 @@ message PushTaskRequest {
   // caller, which might happen theoretically when network has issues.
   // - For an actor, this is set to the timestamp when the actor is created,
   //   so it can be used to differentiate which is the new reconstructed actor.
-  // - For a non-actor task, it's set to the timestamp the task starts execution.
+  // - For a non-actor task, it's set to the timestamp the task starts
+  // execution.
   int64 caller_version = 7;
 }
 
@@ -121,9 +122,11 @@ message PushTaskReply {
   // Set to true if the worker will be exiting.
   bool worker_exiting = 2;
   // The references that the worker borrowed during the task execution. A
-  // borrower is a process that is currently using the object ID, in one of 3 ways:
+  // borrower is a process that is currently using the object ID, in one of 3
+  // ways:
   // 1. Has an ObjectID copy in Python.
-  // 2. Has submitted a task that depends on the object and that is still pending.
+  // 2. Has submitted a task that depends on the object and that is still
+  // pending.
   // 3. Owns another object that is in scope and whose value contains the
   // ObjectID.
   // This list includes the reference counts for any IDs that were passed to
@@ -156,9 +159,7 @@ message GetObjectStatusRequest {
 }
 
 message GetObjectStatusReply {
-  enum ObjectStatus {
-    CREATED = 0;
-  }
+  enum ObjectStatus { CREATED = 0; }
   ObjectStatus status = 1;
 }
 
@@ -184,6 +185,18 @@ message KillActorRequest {
 message KillActorReply {
 }
 
+message CancelTaskRequest {
+  // ID of task that should be killed.
+  bytes intended_task_id = 1;
+  // Whether to kill the worker.
+  bool force_kill = 2;
+}
+
+message CancelTaskReply {
+  // Whether the requested task is the currently running task.
+  bool attempt_succeeded = 1;
+}
+
 message GetCoreWorkerStatsRequest {
   // The ID of the worker this message is intended for.
   bytes intended_worker_id = 1;
@@ -281,6 +294,8 @@ service CoreWorkerService {
       returns (WaitForObjectEvictionReply);
   // Request that the worker shut down without completing outstanding work.
   rpc KillActor(KillActorRequest) returns (KillActorReply);
+  // Request that a worker cancels a task.
+  rpc CancelTask(CancelTaskRequest) returns (CancelTaskReply);
   // Get metrics from core workers.
   rpc GetCoreWorkerStats(GetCoreWorkerStatsRequest) returns (GetCoreWorkerStatsReply);
   // Wait for a borrower to finish using an object. Sent by the object's owner.

src/ray/protobuf/gcs.proto

@@ -340,4 +340,7 @@ enum ErrorType {
   // exposed to user code; it is only used internally to indicate the result of a direct
   // call has been placed in plasma.
   OBJECT_IN_PLASMA = 4;
+
+  // Indicates that an object has been cancelled.
+  TASK_CANCELLED = 5;
 }

src/ray/rpc/worker/core_worker_client.h

@@ -157,6 +157,11 @@ class CoreWorkerClientInterface {
     return Status::NotImplemented("");
   }
 
+  virtual ray::Status CancelTask(const CancelTaskRequest &request,
+                                 const ClientCallback<CancelTaskReply> &callback) {
+    return Status::NotImplemented("");
+  }
+
   virtual ray::Status GetCoreWorkerStats(
       const GetCoreWorkerStatsRequest &request,
       const ClientCallback<GetCoreWorkerStatsReply> &callback) {
@@ -210,6 +215,8 @@ class CoreWorkerClient : public std::enable_shared_from_this<CoreWorkerClient>,
 
   RPC_CLIENT_METHOD(CoreWorkerService, KillActor, grpc_client_, override)
 
+  RPC_CLIENT_METHOD(CoreWorkerService, CancelTask, grpc_client_, override)
+
   RPC_CLIENT_METHOD(CoreWorkerService, WaitForObjectEviction, grpc_client_, override)
 
   RPC_CLIENT_METHOD(CoreWorkerService, GetCoreWorkerStats, grpc_client_, override)

src/ray/rpc/worker/core_worker_server.h

@@ -17,7 +17,6 @@
 
 #include "ray/rpc/grpc_server.h"
 #include "ray/rpc/server_call.h"
-
 #include "src/ray/protobuf/core_worker.grpc.pb.h"
 #include "src/ray/protobuf/core_worker.pb.h"
 
@@ -36,6 +35,7 @@ namespace rpc {
   RPC_SERVICE_HANDLER(CoreWorkerService, WaitForObjectEviction)          \
   RPC_SERVICE_HANDLER(CoreWorkerService, WaitForRefRemoved)              \
   RPC_SERVICE_HANDLER(CoreWorkerService, KillActor)                      \
+  RPC_SERVICE_HANDLER(CoreWorkerService, CancelTask)                     \
   RPC_SERVICE_HANDLER(CoreWorkerService, GetCoreWorkerStats)             \
   RPC_SERVICE_HANDLER(CoreWorkerService, LocalGC)                        \
   RPC_SERVICE_HANDLER(CoreWorkerService, PlasmaObjectReady)
@@ -48,6 +48,7 @@ namespace rpc {
   DECLARE_VOID_RPC_SERVICE_HANDLER_METHOD(WaitForObjectEviction)          \
   DECLARE_VOID_RPC_SERVICE_HANDLER_METHOD(WaitForRefRemoved)              \
   DECLARE_VOID_RPC_SERVICE_HANDLER_METHOD(KillActor)                      \
+  DECLARE_VOID_RPC_SERVICE_HANDLER_METHOD(CancelTask)                     \
   DECLARE_VOID_RPC_SERVICE_HANDLER_METHOD(GetCoreWorkerStats)             \
   DECLARE_VOID_RPC_SERVICE_HANDLER_METHOD(LocalGC)                        \
   DECLARE_VOID_RPC_SERVICE_HANDLER_METHOD(PlasmaObjectReady)