src/bindings/python/bt2/bt2/object.py

   1 # SPDX-License-Identifier: MIT
   2 #
   3 # Copyright (c) 2017 Philippe Proulx <pproulx@efficios.com>
   4
   5
   6 import abc
   7
   8
   9 class _BaseObject:
  10     # Ensure that the object always has _ptr set, even if it throws during
  11     # construction.
  12
  13     def __new__(cls, *args, **kwargs):
  14         obj = super().__new__(cls)
  15         obj._ptr = None
  16         return obj
  17
  18     def __init__(self, ptr):
  19         self._ptr = ptr
  20
  21     @property
  22     def addr(self):
  23         return int(self._ptr)
  24
  25     def __repr__(self):
  26         return "<{}.{} object @ {}>".format(
  27             self.__class__.__module__, self.__class__.__name__, hex(self.addr)
  28         )
  29
  30     def __copy__(self):
  31         raise NotImplementedError
  32
  33     def __deepcopy__(self, memo):
  34         raise NotImplementedError
  35
  36
  37 # A Python object that is itself not refcounted, but is wholly owned by an
  38 # object that is itself refcounted (a _SharedObject).  A Babeltrace unique
  39 # object gets destroyed once its owner gets destroyed (its refcount drops to
  40 # 0).
  41 #
  42 # In the Python bindings, to avoid having to deal with issues with the lifetime
  43 # of unique objects, we make it so acquiring a reference on a unique object
  44 # acquires a reference on its owner.
  45
  46
  47 class _UniqueObject(_BaseObject):
  48
  49     # Create a _UniqueObject.
  50     #
  51     #   - ptr: SWIG Object, pointer to the unique object.
  52     #   - owner_ptr: SWIG Object, pointer to the owner of the unique
  53     #     object.  A new reference is acquired.
  54     #   - owner_get_ref: Callback to get a reference on the owner
  55     #   - owner_put_ref: Callback to put a reference on the owner.
  56
  57     @classmethod
  58     def _create_from_ptr_and_get_ref(cls, ptr, owner_ptr, owner_get_ref, owner_put_ref):
  59         obj = cls.__new__(cls)
  60
  61         obj._ptr = ptr
  62         obj._owner_ptr = owner_ptr
  63         obj._owner_get_ref = owner_get_ref
  64         obj._owner_put_ref = owner_put_ref
  65
  66         obj._owner_get_ref(obj._owner_ptr)
  67
  68         return obj
  69
  70     def __del__(self):
  71         self._owner_put_ref(self._owner_ptr)
  72
  73
  74 # Python object that owns a reference to a Babeltrace object.
  75 class _SharedObject(_BaseObject, abc.ABC):
  76     # Get a new reference on ptr.
  77     #
  78     # This must be implemented by subclasses to work correctly with a pointer
  79     # of the native type they wrap.
  80
  81     @staticmethod
  82     @abc.abstractmethod
  83     def _get_ref(ptr):
  84         raise NotImplementedError
  85
  86     # Put a reference on ptr.
  87     #
  88     # This must be implemented by subclasses to work correctly with a pointer
  89     # of the native type they wrap.
  90
  91     @staticmethod
  92     @abc.abstractmethod
  93     def _put_ref(ptr):
  94         raise NotImplementedError
  95
  96     # Create a _SharedObject from an existing reference.
  97     #
  98     # This assumes that the caller owns a reference to the Babeltrace object
  99     # and transfers this ownership to the newly created Python object.
 100
 101     @classmethod
 102     def _create_from_ptr(cls, ptr_owned):
 103         obj = cls.__new__(cls)
 104         obj._ptr = ptr_owned
 105         return obj
 106
 107     # Like _create_from_ptr, but acquire a new reference rather than
 108     # stealing the caller's reference.
 109
 110     @classmethod
 111     def _create_from_ptr_and_get_ref(cls, ptr):
 112         obj = cls._create_from_ptr(ptr)
 113         cls._get_ref(obj._ptr)
 114         return obj
 115
 116     def __del__(self):
 117         self._put_ref(self._ptr)