bt2: update bindings to make test_component_class pass

[babeltrace.git] / bindings / python / bt2 / bt2 / object.py

# The MIT License (MIT)
#
# Copyright (c) 2017 Philippe Proulx <pproulx@efficios.com>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.


class _BaseObject:
    # Ensure that the object always has _ptr set, even if it throws during
    # construction.

    def __new__(cls, *args, **kwargs):
        obj = super().__new__(cls)
        obj._ptr = None
        return obj

    def __init__(self, ptr):
        self._ptr = ptr

    @property
    def addr(self):
        return int(self._ptr)

    def __repr__(self):
        return '<{}.{} object @ {}>'.format(self.__class__.__module__,
                                            self.__class__.__name__,
                                            hex(self.addr))

    def __copy__(self):
        raise NotImplementedError

    def __deepcopy__(self, memo):
        raise NotImplementedError


# A Python object that is itself not refcounted, but is wholly owned by an
# object that is itself refcounted (a _SharedObject).  A Babeltrace unique
# object gets destroyed once its owner gets destroyed (its refcount drops to
# 0).
#
# In the Python bindings, to avoid having to deal with issues with the lifetime
# of unique objects, we make it so acquiring a reference on a unique object
# acquires a reference on its owner.

class _UniqueObject(_BaseObject):

    # Create a _UniqueObject.
    #
    #   - ptr: SWIG Object, pointer to the unique object.
    #   - owner_ptr: SWIG Object, pointer to the owner of the unique
    #     object.  A new reference is acquired.
    #   - owner_get_ref: Callback to get a reference on the owner
    #   - owner_put_ref: Callback to put a reference on the owner.

    @classmethod
    def _create_from_ptr_and_get_ref(cls, ptr, owner_ptr,
                                     owner_get_ref, owner_put_ref):
        obj = cls.__new__(cls)
        obj._ptr = ptr
        obj._owner_ptr = owner_ptr
        obj._owner_put_ref = owner_put_ref
        owner_get_ref(obj._owner_ptr)
        return obj

    def __del__(self):
        self._owner_put_ref(self._owner_ptr)


# Python object that owns a reference to a Babeltrace object.
class _SharedObject(_BaseObject):

    # Get a new reference on ptr.
    #
    # This must be implemented by subclasses to work correctly with a pointer
    # of the native type they wrap.

    @staticmethod
    def _get_ref(ptr):
        raise NotImplementedError

    # Put a reference on ptr.
    #
    # This must be implemented by subclasses to work correctly with a pointer
    # of the native type they wrap.

    @staticmethod
    def _put_ref(ptr):
        raise NotImplementedError

    # Create a _SharedObject from an existing reference.
    #
    # This assumes that the caller owns a reference to the Babeltrace object
    # and transfers this ownership to the newly created Python object.

    @classmethod
    def _create_from_ptr(cls, ptr_owned):
        obj = cls.__new__(cls)
        obj._ptr = ptr_owned
        return obj

    # Like _create_from_ptr, but acquire a new reference rather than
    # stealing the caller's reference.

    @classmethod
    def _create_from_ptr_and_get_ref(cls, ptr):
        obj = cls._create_from_ptr(ptr)
        cls._get_ref(obj._ptr)
        return obj

    def _release(self):
        """Return the wrapped pointer, transfer its ownership to the
        caller."""
        ptr = self._ptr
        self._ptr = None
        return ptr

    def __del__(self):
        self._put_ref(self._ptr)