Compute task IDs and object IDs deterministically. (#31)

* Put infrastructure in place to compute task IDs and object IDs.

* Fix version number for common library.

* Compute task IDs and object IDs deterministically.

* Address Stephanie's comments.

* Update task documentation.

* Fix formatting.

* Add more tests and checks.

* Fix formatting.

* Enable DCHECKs and change CHECKs to DCHECKs.

src/common/lib/python/common_extension.c

@@ -120,8 +120,13 @@ static int PyTask_init(PyTask *self, PyObject *args, PyObject *kwds) {
   UT_array *val_repr_ptrs;
   utarray_new(val_repr_ptrs, &ut_ptr_icd);
   int num_returns;
-  if (!PyArg_ParseTuple(args, "O&Oi", &PyObjectToUniqueID, &function_id,
-                        &arguments, &num_returns)) {
+  /* The ID of the task that called this task. */
+  task_id parent_task_id;
+  /* The number of tasks that the parent task has called prior to this one. */
+  int parent_counter;
+  if (!PyArg_ParseTuple(args, "O&OiO&i", &PyObjectToUniqueID, &function_id,
+                        &arguments, &num_returns, &PyObjectToUniqueID,
+                        &parent_task_id, &parent_counter)) {
     return -1;
   }
   size_t size = PyList_Size(arguments);
@@ -138,7 +143,8 @@ static int PyTask_init(PyTask *self, PyObject *args, PyObject *kwds) {
   /* Construct the task specification. */
   int val_repr_index = 0;
   self->spec =
-      alloc_task_spec(function_id, size, num_returns, value_data_bytes);
+      start_construct_task_spec(parent_task_id, parent_counter, function_id,
+                                size, num_returns, value_data_bytes);
   /* Add the task arguments. */
   for (size_t i = 0; i < size; ++i) {
     PyObject *arg = PyList_GetItem(arguments, i);
@@ -154,14 +160,8 @@ static int PyTask_init(PyTask *self, PyObject *args, PyObject *kwds) {
     }
   }
   utarray_free(val_repr_ptrs);
-  /* Generate and add the object IDs for the return values. */
-  for (size_t i = 0; i < num_returns; ++i) {
-    /* TODO(rkn): Later, this should be computed as a deterministic hash of (1)
-     * the contents of the task, (2) the index i, and (3) a counter of the
-     * number of tasks launched so far by the parent task. For now, we generate
-     * it randomly. */
-    *task_return(self->spec, i) = globally_unique_id();
-  }
+  /* Compute the task ID and the return object IDs. */
+  finish_construct_task_spec(self->spec);
   return 0;
 }
 
@@ -171,17 +171,22 @@ static void PyTask_dealloc(PyTask *self) {
 }
 
 static PyObject *PyTask_function_id(PyObject *self) {
-  function_id function_id = *task_function(((PyTask *) self)->spec);
+  function_id function_id = task_function(((PyTask *) self)->spec);
   return PyObjectID_make(function_id);
 }
 
+static PyObject *PyTask_task_id(PyObject *self) {
+  task_id task_id = task_task_id(((PyTask *) self)->spec);
+  return PyObjectID_make(task_id);
+}
+
 static PyObject *PyTask_arguments(PyObject *self) {
   int64_t num_args = task_num_args(((PyTask *) self)->spec);
   PyObject *arg_list = PyList_New((Py_ssize_t) num_args);
   task_spec *task = ((PyTask *) self)->spec;
   for (int i = 0; i < num_args; ++i) {
     if (task_arg_type(task, i) == ARG_BY_REF) {
-      object_id object_id = *task_arg_id(task, i);
+      object_id object_id = task_arg_id(task, i);
       PyList_SetItem(arg_list, i, PyObjectID_make(object_id));
     } else {
       PyObject *s =
@@ -198,7 +203,7 @@ static PyObject *PyTask_returns(PyObject *self) {
   PyObject *return_id_list = PyList_New((Py_ssize_t) num_returns);
   task_spec *task = ((PyTask *) self)->spec;
   for (int i = 0; i < num_returns; ++i) {
-    object_id object_id = *task_return(task, i);
+    object_id object_id = task_return(task, i);
     PyList_SetItem(return_id_list, i, PyObjectID_make(object_id));
   }
   return return_id_list;
@@ -207,6 +212,8 @@ static PyObject *PyTask_returns(PyObject *self) {
 static PyMethodDef PyTask_methods[] = {
     {"function_id", (PyCFunction) PyTask_function_id, METH_NOARGS,
      "Return the function ID for this task."},
+    {"task_id", (PyCFunction) PyTask_task_id, METH_NOARGS,
+     "Return the task ID for this task."},
     {"arguments", (PyCFunction) PyTask_arguments, METH_NOARGS,
      "Return the arguments for the task."},
     {"returns", (PyCFunction) PyTask_returns, METH_NOARGS,

src/common/lib/python/setup.py

@@ -7,6 +7,6 @@ common_module = Extension("common",
                           extra_compile_args=["--std=c99", "-Werror"])
 
 setup(name="Common",
-      version="0.1",
+      version="0.01",
       description="Common library for Ray",
       ext_modules=[common_module])