FIX-#26: Reduce memory consumption in Python backend

docs/developer/architecture.rst

@@ -80,8 +80,7 @@ details just pick module you are interested in.
            │   │   └─── :doc:`remote_function </flow/unidist/core/backends/multiprocessing/remote_function>`
            │   ├───python
            │   |   ├───core
-           │   │   │    ├─── :doc:`api </flow/unidist/core/backends/python/core/api>`
-           │   │   │    └─── :doc:`object_store </flow/unidist/core/backends/python/core/object_store>`
+           │   │   │    └─── :doc:`api </flow/unidist/core/backends/python/core/api>` 
            │   │   ├─── :doc:`actor </flow/unidist/core/backends/python/actor>`
            │   │   ├─── :doc:`backend </flow/unidist/core/backends/python/backend>`
            │   │   └─── :doc:`remote_function </flow/unidist/core/backends/python/remote_function>`

docs/flow/unidist/core/backends/python/core/api.rst

@@ -8,25 +8,23 @@
 Python High-level API
 """""""""""""""""""""
 
-Python API module provides high-level functions for initialization of the backend,
-for working with object storage and submitting tasks.
+Python API module provides high-level functions for wrapping/unwrapping objects and
+submitting tasks.
 
 API
 ===
 
-Function :py:func:`~unidist.core.backends.python.core.api.init` creates an instance of singleton
+Functions :py:func:`~unidist.core.backends.python.core.api.init` creates an instance of singleton
 class :py:class:`~unidist.core.backends.python.core.object_store.ObjectStore`.
 
-.. autofunction:: unidist.core.backends.python.core.api.init
+Functions :py:func:`~unidist.core.backends.python.core.api.unwrap` and
+:`~unidist.core.backends.python.core.api.wrap` are responsible for
+unwrap/wrap, respectively, objects from/in :py:class:`~unidist.backends.common.data_id.DataID`.
 
-Functions :py:func:`~unidist.core.backends.python.core.api.get` and
-:py:func:`~unidist.core.backends.python.core.api.put` are responsible for
-read/write, respectively, objects from/to :py:class:`~unidist.core.backends.python.core.object_store.ObjectStore`.
+.. autofunction:: unidist.core.backends.python.core.api.unwrap
+.. autofunction:: unidist.core.backends.python.core.api.wrap
 
-.. autofunction:: unidist.core.backends.python.core.api.get
-.. autofunction:: unidist.core.backends.python.core.api.put
-
-:py:func:`~unidist.core.backends.python.core.api.submit` executes a task, which result will be put into
-:py:class:`~unidist.core.backends.python.core.object_store.ObjectStore`.
+:py:func:`~unidist.core.backends.python.core.api.submit` executes a task, which result will be wrapped
+in :py:class:`~unidist.backends.common.data_id.DataID`-(s).
 
 .. autofunction:: unidist.core.backends.python.core.api.submit

unidist/core/backends/common/data_id.py

@@ -8,7 +8,10 @@
 
 
 class DataID:
-    """Class that holds unique identifier.
+    """
+    Class that holds unique identifier.
+
+    In the case of Python backend this class holds an original object.
 
     Parameters
     ----------

unidist/core/backends/python/backend.py

@@ -61,7 +61,7 @@ def make_actor(cls, num_cpus, resources):
     @staticmethod
     def get(data_ids):
         """
-        Get an object or a list of objects from object store.
+        Get an object or a list of objects from ``DataID``-(s).
 
         Parameters
         ----------
@@ -73,12 +73,12 @@ def get(data_ids):
         object
             A Python object or a list of Python objects.
         """
-        return py.get(data_ids)
+        return py.unwrap(data_ids)
 
     @staticmethod
     def put(data):
         """
-        Put `data` into object store.
+        Put `data` into ``DataID``.
 
         Parameters
         ----------
@@ -90,7 +90,7 @@ def put(data):
         unidist.core.backends.common.data_id.DataID
             ``DataID`` matching to data.
         """
-        return py.put(data)
+        return py.wrap(data)
 
     @staticmethod
     def wait(data_ids, num_returns=1):

unidist/core/backends/python/core/__init__.py

@@ -4,6 +4,6 @@
 
 """Python backend core functionality."""
 
-from .api import put, get, submit, init
+from .api import wrap, unwrap, submit
 
-__all__ = ["put", "get", "submit", "init"]
+__all__ = ["wrap", "unwrap", "submit"]

unidist/core/backends/python/core/api.py

@@ -6,52 +6,52 @@
 
 
 from unidist.core.backends.common.data_id import DataID
-from unidist.core.backends.python.core.object_store import ObjectStore
 
 
-def init():
+def wrap(data):
     """
-    Initialize an object storage.
-
-    Notes
-    -----
-    Run initialization of singleton object ``unidist.core.backends.python.core.object_store.ObjectStore``.
-    """
-    ObjectStore.get_instance()
-
-
-def put(data):
-    """
-    Put data into object storage.
+    Wrap data in ``DataID``.
 
     Parameters
     ----------
     data : object
-        Data to be put.
+        Data to be wrapped.
 
     Returns
     -------
     unidist.core.backends.common.data_id.DataID
-        An ID of object in object storage.
     """
-    return ObjectStore.get_instance().put(data)
+    return DataID(data)
 
 
-def get(data_ids):
+def unwrap(data_ids):
     """
-    Get object(s) associated with `data_ids` from the object storage.
+    Unwrap object(s) from `data_ids`.
 
     Parameters
     ----------
     data_ids : unidist.core.backends.common.data_id.DataID or list
-        ID(s) to object(s) to get data from.
+        ID(s) of object(s) to be unwrapped.
 
     Returns
     -------
     object
         A Python object.
     """
-    return ObjectStore.get_instance().get(data_ids)
+    is_list = isinstance(data_ids, list)
+    if not is_list:
+        data_ids = [data_ids]
+    if not all(isinstance(data_id, DataID) for data_id in data_ids):
+        raise ValueError("`data_ids` must either be a data ID or a list of data IDs.")
+
+    def check_exception(value):
+        if isinstance(value, Exception):
+            raise value
+        return value
+
+    values = [check_exception(data_id._id) for data_id in data_ids]
+
+    return values if is_list else values[0]
 
 
 def submit(func, *args, num_returns=1, **kwargs):
@@ -78,13 +78,11 @@ def submit(func, *args, num_returns=1, **kwargs):
         * if `num_returns > 1`, list of ``DataID``-s will be returned.
         * if `num_returns == 0`, ``None`` will be returned.
     """
-    obj_store = ObjectStore.get_instance()
-
     materialized_args = [
-        obj_store.get(arg) if isinstance(arg, DataID) else arg for arg in args
+        unwrap(arg) if isinstance(arg, DataID) else arg for arg in args
     ]
     materialized_kwargs = {
-        key: obj_store.get(value) if isinstance(value, DataID) else value
+        key: unwrap(value) if isinstance(value, DataID) else value
         for key, value in kwargs.items()
     }
 
@@ -96,8 +94,8 @@ def submit(func, *args, num_returns=1, **kwargs):
     if num_returns == 0:
         data_ids = None
     elif num_returns > 1:
-        data_ids = [obj_store.put(result[idx]) for idx in range(num_returns)]
+        data_ids = [DataID(result[idx]) for idx in range(num_returns)]
     else:
-        data_ids = obj_store.put(result)
+        data_ids = DataID(result)
 
     return data_ids

unidist/core/base/utils.py

@@ -45,9 +45,7 @@ def init_backend():
         backend_cls = MultiProcessingBackend()
     elif backend_name == "Python":
         from unidist.core.backends.python.backend import PythonBackend
-        from unidist.core.backends.python.utils import initialize_python
 
-        initialize_python()
         backend_cls = PythonBackend()
     elif backend_name == "MPI":
         from unidist.core.backends.mpi.backend import MPIBackend