Use flatbuffers for some messages from Redis. (#341)

* Compile the Ray redis module with C++.

* Redo parsing of object table notifications with flatbuffers.

* Update redis module python tests.

* Redo parsing of task table notifications with flatbuffers.

* Fix linting.

* Redo parsing of db client notifications with flatbuffers.

* Redo publishing of local scheduler heartbeats with flatbuffers.

* Fix linting.

* Remove usage of fixed-width formatting of scheduling state in channel name.

* Reply with flatbuffer object to task table queries, also simplify redis string to flatbuffer string conversion.

* Fix linting and tests.

* fix

* cleanup

* simplify logic in ReplyWithTask

src/common/format/common.fbs

@@ -50,3 +50,62 @@ table TaskInfo {
 }
 
 root_type TaskInfo;
+
+table SubscribeToNotificationsReply {
+  // The object ID of the object that the notification is about.
+  object_id: string;
+  // The size of the object.
+  object_size: long;
+  // The IDs of the managers that contain this object.
+  manager_ids: [string];
+}
+
+root_type SubscribeToNotificationsReply;
+
+table TaskReply {
+  // The task ID of the task that the message is about.
+  task_id: string;
+  // The state of the task. This is encoded as a bit mask of scheduling_state
+  // enum values in task.h.
+  state: long;
+  // A local scheduler ID.
+  local_scheduler_id: string;
+  // A string of bytes representing the task specification.
+  task_spec: string;
+}
+
+root_type TaskReply;
+
+table SubscribeToDBClientTableReply {
+  // The db client ID of the client that the message is about.
+  db_client_id: string;
+  // The type of the client.
+  client_type: string;
+  // If the client is a local scheduler, this is the address of the plasma
+  // manager that the local scheduler is connected to. Otherwise, it is empty.
+  aux_address: string;
+  // True if the message is about the addition of a client and false if it is
+  // about the deletion of a client.
+  is_insertion: bool;
+}
+
+root_type SubscribeToDBClientTableReply;
+
+table LocalSchedulerInfoMessage {
+  // The db client ID of the client that the message is about.
+  db_client_id: string;
+  // The total number of workers that are connected to this local scheduler.
+  total_num_workers: long;
+  // The number of tasks queued in this local scheduler.
+  task_queue_length: long;
+  // The number of workers that are available and waiting for tasks.
+  available_workers: long;
+  // The resource vector of resources generally available to this local
+  // scheduler.
+  static_resources: [double];
+  // The resource vector of resources currently available to this local
+  // scheduler.
+  dynamic_resources: [double];
+}
+
+root_type LocalSchedulerInfoMessage;