Implement a first pass at actors in the API. (#242)

* Implement actor field for tasks

* Implement actor management in local scheduler.

* initial python frontend for actors

* import actors on worker

* IPython code completion and tests

* prepare creating actors through local schedulers

* add actor id to PyTask

* submit actor calls to local scheduler

* starting to integrate

* simple fix

* Fixes from rebasing.

* more work on python actors

* Improve local scheduler actor handlers.

* Pass actor ID to local scheduler when connecting a client.

* first working version of actors

* fixing actors

* fix creating two copies of the same actor

* fix actors

* remove sleep

* get rid of export synchronization

* update

* insert actor methods into the queue in the right order

* remove print statements

* make it compile again after rebase

* Minor updates.

* fix python actor ids

* Pass actor_id to start_worker.

* add test

* Minor changes.

* Update actor tests.

* Temporary plan for import counter.

* Temporarily fix import counters.

* Fix some tests.

* Fixes.

* Make actor creation non-blocking.

* Fix test?

* Fix actors on Python 2.

* fix rare case.

* Fix python 2 test.

* More tests.

* Small fixes.

* Linting.

* Revert tensorflow version to 0.12.0 temporarily.

* Small fix.

* Enhance inheritance test.

src/common/task.h

@@ -15,6 +15,7 @@
 #include "utstring.h"
 
 #define NIL_TASK_ID NIL_ID
+#define NIL_ACTOR_ID NIL_ID
 #define NIL_FUNCTION_ID NIL_ID
 
 typedef unique_id function_id;
@@ -23,6 +24,10 @@ typedef unique_id function_id;
  *  executes and the argument IDs or argument values. */
 typedef unique_id task_id;
 
+/** The actor ID is the ID of the actor that a task must run on. If the task is
+ *  not run on an actor, then NIL_ACTOR_ID should be used. */
+typedef unique_id actor_id;
+
 /** The task instance ID is a globally unique ID generated which identifies this
  *  particular execution of the task. */
 typedef unique_id task_iid;
@@ -55,6 +60,15 @@ bool task_ids_equal(task_id first_id, task_id second_id);
  */
 bool task_id_is_nil(task_id id);
 
+/**
+ * Compare two actor IDs.
+ *
+ * @param first_id The first actor ID to compare.
+ * @param second_id The first actor ID to compare.
+ * @return True if the actor IDs are the same and false otherwise.
+ */
+bool actor_ids_equal(actor_id first_id, actor_id second_id);
+
 /**
  * Compare two function IDs.
  *
@@ -83,6 +97,8 @@ bool function_id_is_nil(function_id id);
  * @param parent_task_id The task ID of the task that submitted this task.
  * @param parent_counter A counter indicating how many tasks were submitted by
  *        the parent task prior to this one.
+ * @param actor_id The ID of the actor this task belongs to.
+ * @param actor_counter Number of tasks that have been executed on this actor.
  * @param function_id The function ID of the function to execute in this task.
  * @param num_args The number of arguments that this task has.
  * @param num_returns The number of return values that this task has.
@@ -93,6 +109,8 @@ bool function_id_is_nil(function_id id);
 task_spec *start_construct_task_spec(unique_id driver_id,
                                      task_id parent_task_id,
                                      int64_t parent_counter,
+                                     unique_id actor_id,
+                                     int64_t actor_counter,
                                      function_id function_id,
                                      int64_t num_args,
                                      int64_t num_returns,
@@ -124,6 +142,23 @@ int64_t task_spec_size(task_spec *spec);
  */
 function_id task_function(task_spec *spec);
 
+/**
+ * Return the actor ID of the task.
+ *
+ * @param spec The task_spec in question.
+ * @return The actor ID of the actor the task is part of.
+ */
+unique_id task_spec_actor_id(task_spec *spec);
+
+/**
+ * Return the actor counter of the task. This starts at 0 and increments by 1
+ * every time a new task is submitted to run on the actor.
+ *
+ * @param spec The task_spec in question.
+ * @return The actor counter of the task.
+ */
+int64_t task_spec_actor_counter(task_spec *spec);
+
 /**
  * Return the driver ID of the task.
  *