Avoid object aliasing (with Seth Warn)

git-svn-id: http://llvm-py.googlecode.com/svn/trunk@65 8d1e9007-1d4e-0410-b67e-1979fd6579aa

llvm/_util.py

@@ -33,6 +33,8 @@
 Used only in other modules, not for public use."""
 
 import llvm
+import llvm._core as _core  # for PyCObjectVoidPtrToPyLong
+from weakref import WeakValueDictionary
 
 
 #===----------------------------------------------------------------------===
@@ -90,3 +92,39 @@ class dummy_owner(object):
     def __init__(self, ownee):
         ownee._own(self)
 
+
+#===----------------------------------------------------------------------===
+# A metaclass to prevent aliasing.  It stores a (weak) reference to objects
+# constructed based on a PyCObject.  If an object is constructed based on a
+# PyCObject with the same underlying pointer as a previous object, a reference
+# to the previous object is returned rather than a new one.
+#===----------------------------------------------------------------------===
+
+class ObjectCache(type):
+    """A metaclass to prevent aliasing.
+
+    Classes using 'ObjectCache' as a metaclass must have constructors
+    that take a PyCObject as their first argument.  When the class is
+    called (to create a new instance of the class), the value of the
+    pointer wrapped by the PyCObj is checked:
+
+        If no previous object has been created based on the same
+        underlying pointer (note that different PyCObject objects can
+        wrap the same pointer), the object will be initialized as
+        usual and returned.
+
+        If a previous has been created based on the same pointer,
+        then a reference to that object will be returned, and no
+        object initialization is performed.
+    """
+
+    __instances = WeakValueDictionary()
+
+    def __call__(cls, ptr, *args, **kwargs):
+        id = _core.PyCObjectVoidPtrToPyLong(ptr)
+        obj = ObjectCache.__instances.get(id)
+        if obj is None:
+            obj = super(ObjectCache, cls).__call__(ptr, *args, **kwargs)
+            ObjectCache.__instances[id] = obj
+        return obj
+

llvm/core.py

@@ -878,17 +878,6 @@ def _to_int(v):
     else:
         return 0
 
-__all_modules = weakref.WeakValueDictionary()
-
-def _report_new_module(ptr, obj):
-    __all_modules[_core.PyCObjectVoidPtrToPyLong(ptr)] = obj
-
-def _module_from_ptr(ptr):
-    i = _core.PyCObjectVoidPtrToPyLong(ptr)
-    if i not in __all_modules:
-        raise llvm.LLVMException, "module not found in internal list"
-    return __all_modules[i]
-
 
 #===----------------------------------------------------------------------===
 # Module
@@ -909,6 +898,8 @@ class Module(llvm.Ownable):
     module_obj = Module.new('my_module')
     """
 
+    __metaclass__ = ObjectCache
+
     @staticmethod
     def new(id):
         """Create a new Module instance.
@@ -952,7 +943,6 @@ class Module(llvm.Ownable):
         Use the static method `Module.new' instead.
         """
         llvm.Ownable.__init__(self, ptr, _core.LLVMDisposeModule)
-        _report_new_module(ptr, self)
 
     def __str__(self):
         """Text representation of a module.
@@ -1468,6 +1458,8 @@ class TypeHandle(object):
 
 class Value(object):
 
+    __metaclass__ = ObjectCache
+
     def __init__(self, ptr):
         self.ptr = ptr
 
@@ -1803,8 +1795,7 @@ class GlobalValue(Constant):
 
     @property
     def module(self):
-        module_ptr = _core.LLVMGetGlobalParent(self.ptr)
-        return _module_from_ptr(module_ptr)
+        return Module(_core.LLVMGetGlobalParent(self.ptr))
 
 
 class GlobalVariable(GlobalValue):
@@ -2174,6 +2165,12 @@ class Builder(object):
 
     @property
     def block(self):
+        """Deprecated, use basic_block property instead."""
+        return _make_value(_core.LLVMGetInsertBlock(self.ptr))
+
+    @property
+    def basic_block(self):
+        """The basic block where the builder is positioned."""
         return _make_value(_core.LLVMGetInsertBlock(self.ptr))
 
     # terminator instructions