[multi-language part 1] add a 'language' field to task specification (#2639)

src/common/format/common.fbs

@@ -20,6 +20,14 @@ table ResourcePair {
   value: double;
 }
 
+// NOTE: This enum is duplicate with the `Language` enum in `gcs.fbs`,
+// because we cannot include this file in `gcs.fbs` due to cyclic dependency.
+// TODO(raulchen): remove it once we get rid of legacy ray.
+enum TaskLanguage:int {
+  PYTHON = 0,
+  JAVA = 1
+}
+
 table TaskInfo {
   // ID of the driver that created this task.
   driver_id: string;
@@ -52,6 +60,8 @@ table TaskInfo {
   // The required_resources vector indicates the quantities of the different
   // resources required by this task.
   required_resources: [ResourcePair];
+  // The language that this task belongs to
+  language: TaskLanguage;
 }
 
 // Object information data structure.

src/common/lib/python/common_extension.cc

@@ -462,7 +462,8 @@ static int PyTask_init(PyTask *self, PyObject *args, PyObject *kwds) {
     self->task_spec = new ray::raylet::TaskSpecification(
         driver_id, parent_task_id, parent_counter, actor_creation_id,
         actor_creation_dummy_object_id, actor_id, actor_handle_id,
-        actor_counter, function_id, args, num_returns, required_resources);
+        actor_counter, function_id, args, num_returns, required_resources,
+        Language::PYTHON);
   }
 
   /* Set the task's execution dependencies. */