Implement actor checkpointing (#3839)

* Implement Actor checkpointing

* docs

* fix

* fix

* fix

* move restore-from-checkpoint to HandleActorStateTransition

* Revert "move restore-from-checkpoint to HandleActorStateTransition"

This reverts commit 9aa4447c1e3e321f42a1d895d72f17098b72de12.

* resubmit waiting tasks when actor frontier restored

* add doc about num_actor_checkpoints_to_keep=1

* add num_actor_checkpoints_to_keep to Cython

* add checkpoint_expired api

* check if actor class is abstract

* change checkpoint_ids to long string

* implement java

* Refactor to delay actor creation publish until checkpoint is resumed

* debug, lint

* Erase from checkpoints to restore if task fails

* fix lint

* update comments

* avoid duplicated actor notification log

* fix unintended change

* add actor_id to checkpoint_expired

* small java updates

* make checkpoint info per actor

* lint

* Remove logging

* Remove old actor checkpointing Python code, move new checkpointing code to FunctionActionManager

* Replace old actor checkpointing tests

* Fix test and lint

* address comments

* consolidate kill_actor

* Remove __ray_checkpoint__

* fix non-ascii char

* Loosen test checks

* fix java

* fix sphinx-build

python/ray/__init__.py

@@ -49,9 +49,20 @@ except ImportError as e:
 modin_path = os.path.join(os.path.abspath(os.path.dirname(__file__)), "modin")
 sys.path.append(modin_path)
 
-from ray._raylet import (UniqueID, ObjectID, DriverID, ClientID, ActorID,
-                         ActorHandleID, FunctionID, ActorClassID, TaskID,
-                         _ID_TYPES, Config as _Config)  # noqa: E402
+from ray._raylet import (
+    ActorCheckpointID,
+    ActorClassID,
+    ActorHandleID,
+    ActorID,
+    ClientID,
+    Config as _Config,
+    DriverID,
+    FunctionID,
+    ObjectID,
+    TaskID,
+    UniqueID,
+    _ID_TYPES,
+)  # noqa: E402
 
 _config = _Config()
 
@@ -82,8 +93,16 @@ __all__ = [
 ]
 
 __all__ += [
-    "UniqueID", "ObjectID", "DriverID", "ClientID", "ActorID", "ActorHandleID",
-    "FunctionID", "ActorClassID", "TaskID"
+    "ActorCheckpointID",
+    "ActorClassID",
+    "ActorHandleID",
+    "ActorID",
+    "ClientID",
+    "DriverID",
+    "FunctionID",
+    "ObjectID",
+    "TaskID",
+    "UniqueID",
 ]
 
 import ctypes  # noqa: E402