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.c

@@ -44,6 +44,11 @@ struct task_spec_impl {
   /** A count of the number of tasks submitted by the parent task before this
    *  one. */
   int64_t parent_counter;
+  /** Actor ID of the task. This is the actor that this task is executed on
+   *  or NIL_ACTOR_ID if the task is just a normal task. */
+  actor_id actor_id;
+  /** Number of tasks that have been submitted to this actor so far. */
+  int64_t actor_counter;
   /** Function ID of the task. */
   function_id function_id;
   /** Total number of arguments. */
@@ -81,6 +86,10 @@ bool task_id_is_nil(task_id id) {
   return task_ids_equal(id, NIL_TASK_ID);
 }
 
+bool actor_ids_equal(actor_id first_id, actor_id second_id) {
+  return UNIQUE_ID_EQ(first_id, second_id);
+}
+
 bool function_ids_equal(function_id first_id, function_id second_id) {
   return UNIQUE_ID_EQ(first_id, second_id);
 }
@@ -147,6 +156,8 @@ object_id task_compute_put_id(task_id task_id, int64_t put_index) {
 task_spec *start_construct_task_spec(unique_id driver_id,
                                      task_id parent_task_id,
                                      int64_t parent_counter,
+                                     actor_id actor_id,
+                                     int64_t actor_counter,
                                      function_id function_id,
                                      int64_t num_args,
                                      int64_t num_returns,
@@ -158,6 +169,8 @@ task_spec *start_construct_task_spec(unique_id driver_id,
   task->task_id = NIL_TASK_ID;
   task->parent_task_id = parent_task_id;
   task->parent_counter = parent_counter;
+  task->actor_id = actor_id;
+  task->actor_counter = actor_counter;
   task->function_id = function_id;
   task->num_args = num_args;
   task->arg_index = 0;
@@ -190,6 +203,18 @@ function_id task_function(task_spec *spec) {
   return spec->function_id;
 }
 
+actor_id task_spec_actor_id(task_spec *spec) {
+  /* Check that the task has been constructed. */
+  DCHECK(!task_ids_equal(spec->task_id, NIL_TASK_ID));
+  return spec->actor_id;
+}
+
+int64_t task_spec_actor_counter(task_spec *spec) {
+  /* Check that the task has been constructed. */
+  DCHECK(!task_ids_equal(spec->task_id, NIL_TASK_ID));
+  return spec->actor_counter;
+}
+
 unique_id task_spec_driver_id(task_spec *spec) {
   /* Check that the task has been constructed. */
   DCHECK(!task_ids_equal(spec->task_id, NIL_TASK_ID));