[PY][FFI] runtime.String to subclass str

To make runtime.String to work as naturally as possible in the python side,
we make it sub-class the python's str object. Note that however, we cannot
sub-class Object at the same time due to python's type layout constraint(
cannot subclass from multiple classes with slots).

We introduce a PyNativeObject class to handle this kind of object sub-classing.

CMakeLists.txt

@@ -108,7 +108,7 @@ if(MSVC)
   endif()
 else(MSVC)
   if ("${CMAKE_BUILD_TYPE}" STREQUAL "Debug")
-    message("Build in Debug mode")
+    message(STATUS "Build in Debug mode")
     set(CMAKE_C_FLAGS "-O0 -g -Wall -fPIC ${CMAKE_C_FLAGS}")
     set(CMAKE_CXX_FLAGS "-O0 -g -Wall -fPIC ${CMAKE_CXX_FLAGS}")
     set(CMAKE_CUDA_FLAGS "-O0 -g -Xcompiler=-Wall -Xcompiler=-fPIC ${CMAKE_CUDA_FLAGS}")

python/tvm/_ffi/_ctypes/object.py

@@ -50,6 +50,10 @@ def _return_object(x):
     tindex = ctypes.c_uint()
     check_call(_LIB.TVMObjectGetTypeIndex(handle, ctypes.byref(tindex)))
     cls = OBJECT_TYPE.get(tindex.value, _CLASS_OBJECT)
+    if issubclass(cls, PyNativeObject):
+        obj = _CLASS_OBJECT.__new__(_CLASS_OBJECT)
+        obj.handle = handle
+        return cls.__from_tvm_object__(cls, obj)
     # Avoid calling __init__ of cls, instead directly call __new__
     # This allows child class to implement their own __init__
     obj = cls.__new__(cls)
@@ -64,6 +68,33 @@ def _return_object(x):
     _return_object, TypeCode.OBJECT_RVALUE_REF_ARG)
 
 
+class PyNativeObject:
+    """Base class of all TVM objects that also subclass python's builtin types."""
+    __slots__ = []
+
+    def __init_tvm_object_by_constructor__(self, fconstructor, *args):
+        """Initialize the internal tvm_object by calling constructor function.
+
+        Parameters
+        ----------
+        fconstructor : Function
+            Constructor function.
+
+        args: list of objects
+            The arguments to the constructor
+
+        Note
+        ----
+        We have a special calling convention to call constructor functions.
+        So the return object is directly set into the object
+        """
+        # pylint: disable=assigning-non-slot
+        obj = _CLASS_OBJECT.__new__(_CLASS_OBJECT)
+        obj.__init_handle_by_constructor__(fconstructor, *args)
+        self.__tvm_object__ = obj
+
+
+
 class ObjectBase(object):
     """Base object for all object types"""
     __slots__ = ["handle"]

python/tvm/_ffi/_ctypes/packed_func.py

@@ -29,7 +29,7 @@
 from .types import TVMValue, TypeCode
 from .types import TVMPackedCFunc, TVMCFuncFinalizer
 from .types import RETURN_SWITCH, C_TO_PY_ARG_SWITCH, _wrap_arg_func, _ctx_to_int64
-from .object import ObjectBase, _set_class_object
+from .object import ObjectBase, PyNativeObject, _set_class_object
 from . import object as _object
 
 PackedFuncHandle = ctypes.c_void_p
@@ -123,6 +123,9 @@ def _make_tvm_args(args, temp_args):
             values[i].v_handle = ctypes.cast(arg.handle, ctypes.c_void_p)
             type_codes[i] = (TypeCode.NDARRAY_HANDLE
                              if not arg.is_view else TypeCode.DLTENSOR_HANDLE)
+        elif isinstance(arg, PyNativeObject):
+            values[i].v_handle = arg.__tvm_object__.handle
+            type_codes[i] = TypeCode.OBJECT_HANDLE
         elif isinstance(arg, _nd._TVM_COMPATS):
             values[i].v_handle = ctypes.c_void_p(arg._tvm_handle)
             type_codes[i] = arg.__class__._tvm_tcode

python/tvm/_ffi/_cython/object.pxi

@@ -39,18 +39,49 @@ cdef inline object make_ret_object(void* chandle):
     object_type = OBJECT_TYPE
     handle = ctypes_handle(chandle)
     CALL(TVMObjectGetTypeIndex(chandle, &tindex))
+
     if tindex < len(OBJECT_TYPE):
         cls = OBJECT_TYPE[tindex]
         if cls is not None:
+            if issubclass(cls, PyNativeObject):
+                obj = _CLASS_OBJECT.__new__(_CLASS_OBJECT)
+                (<ObjectBase>obj).chandle = chandle
+                return cls.__from_tvm_object__(cls, obj)
             obj = cls.__new__(cls)
         else:
             obj = _CLASS_OBJECT.__new__(_CLASS_OBJECT)
     else:
         obj = _CLASS_OBJECT.__new__(_CLASS_OBJECT)
+
     (<ObjectBase>obj).chandle = chandle
     return obj
 
 
+class PyNativeObject:
+    """Base class of all TVM objects that also subclass python's builtin types."""
+    __slots__ = []
+
+    def __init_tvm_object_by_constructor__(self, fconstructor, *args):
+        """Initialize the internal tvm_object by calling constructor function.
+
+        Parameters
+        ----------
+        fconstructor : Function
+            Constructor function.
+
+        args: list of objects
+            The arguments to the constructor
+
+        Note
+        ----
+        We have a special calling convention to call constructor functions.
+        So the return object is directly set into the object
+        """
+        obj = _CLASS_OBJECT.__new__(_CLASS_OBJECT)
+        obj.__init_handle_by_constructor__(fconstructor, *args)
+        self.__tvm_object__ = obj
+
+
 cdef class ObjectBase:
     cdef void* chandle
 

python/tvm/_ffi/_cython/packed_func.pxi

@@ -109,6 +109,9 @@ cdef inline int make_arg(object arg,
         value[0].v_handle = (<NDArrayBase>arg).chandle
         tcode[0] = (kTVMNDArrayHandle if
                     not (<NDArrayBase>arg).c_is_view else kTVMDLTensorHandle)
+    elif isinstance(arg, PyNativeObject):
+        value[0].v_handle = (<ObjectBase>(arg.__tvm_object__)).chandle
+        tcode[0] = kTVMObjectHandle
     elif isinstance(arg, _TVM_COMPATS):
         ptr = arg._tvm_handle
         value[0].v_handle = (<void*>ptr)

python/tvm/runtime/container.py

@@ -16,9 +16,10 @@
 # under the License.
 """Runtime container structures."""
 import tvm._ffi
-from tvm._ffi.base import string_types
-from tvm.runtime import Object, ObjectTypes
-from tvm.runtime import _ffi_api
+from .object import Object, PyNativeObject
+from .object_generic import ObjectTypes
+from . import _ffi_api
+
 
 def getitem_helper(obj, elem_getter, length, idx):
     """Helper function to implement a pythonic getitem function.
@@ -112,64 +113,26 @@ def tuple_object(fields=None):
 
 
 @tvm._ffi.register_object("runtime.String")
-class String(Object):
-    """The string object.
+class String(str, PyNativeObject):
+    """TVM runtime.String object, represented as a python str.
 
     Parameters
     ----------
-    string : str
-        The string used to construct a runtime String object
-
-    Returns
-    -------
-    ret : String
-        The created object.
+    content : str
+        The content string used to construct the object.
     """
-    def __init__(self, string):
-        self.__init_handle_by_constructor__(_ffi_api.String, string)
-
-    def __str__(self):
-        return _ffi_api.GetStdString(self)
-
-    def __len__(self):
-        return _ffi_api.GetStringSize(self)
-
-    def __hash__(self):
-        return _ffi_api.StringHash(self)
-
-    def __eq__(self, other):
-        if isinstance(other, string_types):
-            return self.__str__() == other
-
-        if not isinstance(other, String):
-            return False
-
-        return _ffi_api.CompareString(self, other) == 0
-
-    def __ne__(self, other):
-        return not self.__eq__(other)
-
-    def __gt__(self, other):
-        return _ffi_api.CompareString(self, other) > 0
-
-    def __lt__(self, other):
-        return _ffi_api.CompareString(self, other) < 0
-
-    def __getitem__(self, key):
-        return self.__str__()[key]
-
-    def startswith(self, string):
-        """Check if the runtime string starts with a given string
-
-        Parameters
-        ----------
-        string : str
-            The provided string
-
-        Returns
-        -------
-        ret : boolean
-            Return true if the runtime string starts with the given string,
-        otherwise, false.
-        """
-        return self.__str__().startswith(string)
+    __slots__ = ["__tvm_object__"]
+
+    def __new__(cls, content):
+        """Construct from string content."""
+        val = str.__new__(cls, content)
+        val.__init_tvm_object_by_constructor__(_ffi_api.String, content)
+        return val
+
+    @staticmethod
+    def __from_tvm_object__(cls, obj):
+        """Construct from a given tvm object."""
+        content = _ffi_api.GetFFIString(obj)
+        val = str.__new__(cls, content)
+        val.__tvm_object__ = obj
+        return val

python/tvm/runtime/object.py

@@ -27,11 +27,11 @@
     if _FFI_MODE == "ctypes":
         raise ImportError()
     from tvm._ffi._cy3.core import _set_class_object, _set_class_object_generic
-    from tvm._ffi._cy3.core import ObjectBase
+    from tvm._ffi._cy3.core import ObjectBase, PyNativeObject
 except (RuntimeError, ImportError):
     # pylint: disable=wrong-import-position,unused-import
     from tvm._ffi._ctypes.packed_func import _set_class_object, _set_class_object_generic
-    from tvm._ffi._ctypes.object import ObjectBase
+    from tvm._ffi._ctypes.object import ObjectBase, PyNativeObject
 
 
 def _new_object(cls):
@@ -41,6 +41,7 @@ def _new_object(cls):
 
 class Object(ObjectBase):
     """Base class for all tvm's runtime objects."""
+    __slots__ = []
     def __repr__(self):
         return _ffi_node_api.AsRepr(self)
 
@@ -78,13 +79,10 @@ def __getstate__(self):
     def __setstate__(self, state):
         # pylint: disable=assigning-non-slot, assignment-from-no-return
         handle = state['handle']
+        self.handle = None
         if handle is not None:
-            json_str = handle
-            other = _ffi_node_api.LoadJSON(json_str)
-            self.handle = other.handle
-            other.handle = None
-        else:
-            self.handle = None
+            self.__init_handle_by_constructor__(
+                _ffi_node_api.LoadJSON, handle)
 
     def _move(self):
         """Create an RValue reference to the object and mark the object as moved.

python/tvm/runtime/object_generic.py

@@ -21,7 +21,7 @@
 from tvm._ffi.runtime_ctypes import ObjectRValueRef
 
 from . import _ffi_node_api, _ffi_api
-from .object import ObjectBase, _set_class_object_generic
+from .object import ObjectBase, PyNativeObject, _set_class_object_generic
 from .ndarray import NDArrayBase
 from .packed_func import PackedFuncBase, convert_to_tvm_func
 from .module import Module
@@ -34,7 +34,7 @@ def asobject(self):
         raise NotImplementedError()
 
 
-ObjectTypes = (ObjectBase, NDArrayBase, Module, ObjectRValueRef)
+ObjectTypes = (ObjectBase, NDArrayBase, Module, ObjectRValueRef, PyNativeObject)
 
 
 def convert_to_object(value):

src/runtime/container.cc

@@ -19,7 +19,7 @@
 
 /*!
  * \file src/runtime/container.cc
- * \brief Implementations of common plain old data (POD) containers.
+ * \brief Implementations of common containers.
  */
 #include <tvm/runtime/container.h>
 #include <tvm/runtime/memory.h>
@@ -81,26 +81,11 @@ TVM_REGISTER_GLOBAL("runtime.String")
   return String(std::move(str));
 });
 
-TVM_REGISTER_GLOBAL("runtime.GetStringSize")
-.set_body_typed([](String str) {
-  return static_cast<int64_t>(str.size());
-});
-
-TVM_REGISTER_GLOBAL("runtime.GetStdString")
+TVM_REGISTER_GLOBAL("runtime.GetFFIString")
 .set_body_typed([](String str) {
   return std::string(str);
 });
 
-TVM_REGISTER_GLOBAL("runtime.CompareString")
-.set_body_typed([](String lhs, String rhs) {
-  return lhs.compare(rhs);
-});
-
-TVM_REGISTER_GLOBAL("runtime.StringHash")
-.set_body_typed([](String str) {
-  return static_cast<int64_t>(std::hash<String>()(str));
-});
-
 TVM_REGISTER_OBJECT_TYPE(ADTObj);
 TVM_REGISTER_OBJECT_TYPE(StringObj);
 TVM_REGISTER_OBJECT_TYPE(ClosureObj);

src/support/ffi_testing.cc

@@ -58,6 +58,11 @@ TVM_REGISTER_GLOBAL("testing.nop")
 .set_body([](TVMArgs args,  TVMRetValue *ret) {
   });
 
+TVM_REGISTER_GLOBAL("testing.echo")
+.set_body([](TVMArgs args,  TVMRetValue *ret) {
+  *ret = args[0];
+  });
+
 TVM_REGISTER_GLOBAL("testing.test_wrap_callback")
 .set_body([](TVMArgs args,  TVMRetValue *ret) {
     PackedFunc pf = args[0];

tests/python/unittest/test_runtime_container.py

@@ -17,6 +17,7 @@
 
 import numpy as np
 import tvm
+import pickle
 from tvm import te
 from tvm import nd, relay
 from tvm.runtime import container as _container
@@ -56,6 +57,30 @@ def test_tuple_object():
     tvm.testing.assert_allclose(out.asnumpy(), np.array(11))
 
 
+def test_string():
+    s = tvm.runtime.String("xyz")
+
+    assert isinstance(s, tvm.runtime.String)
+    assert isinstance(s, str)
+    assert s.startswith("xy")
+    assert s + "1" == "xyz1"
+    y = tvm.testing.echo(s)
+    assert isinstance(y, tvm.runtime.String)
+    assert s.__tvm_object__.same_as(y.__tvm_object__)
+    assert s == y
+
+    x = tvm.ir.load_json(tvm.ir.save_json(y))
+    assert isinstance(x, tvm.runtime.String)
+    assert x == y
+
+    # test pickle
+    z = pickle.loads(pickle.dumps(s))
+    assert isinstance(z, tvm.runtime.String)
+    assert s == z
+
+
 if __name__ == "__main__":
+    test_string()
+
     test_adt_constructor()
     test_tuple_object()