Fix a bug in dangling reference/pointer detection. Thanks to Daniel

dabrahams · dabrahams · commit 9675e4233b65 · 2003-05-22T15:13:22.000Z
Paull &lt;dlp-at-fractaltechnologies.com&gt; for reporting it.


[SVN r18498]
diff --git a/include/boost/python/call.hpp b/include/boost/python/call.hpp
@@ -52,13 +52,22 @@ call(PyObject* callable
     , boost::type<R>* = 0
     )
 {
-    converter::return_from_python<R> converter;
-    return converter(
+    PyObject* const result = 
         PyEval_CallFunction(
             callable
             , const_cast<char*>("(" BOOST_PP_REPEAT_1ST(N, BOOST_PYTHON_FIXED, "O") ")")
             BOOST_PP_REPEAT_1ST(N, BOOST_PYTHON_FAST_ARG_TO_PYTHON_GET, nil)
-            ));
+            );
+    
+    // This conversion *must not* be done in the same expression as
+    // the call, because, in the special case where the result is a
+    // reference a Python object which was created by converting a C++
+    // argument for passing to PyEval_CallFunction, its reference
+    // count will be 2 until the end of the full expression containing
+    // the conversion, and that interferes with dangling
+    // pointer/reference detection.
+    converter::return_from_python<R> converter;
+    return converter(result);
 }
 
 # undef N
diff --git a/include/boost/python/call_method.hpp b/include/boost/python/call_method.hpp
@@ -51,14 +51,23 @@ call_method(PyObject* self, char const* name
     , boost::type<R>* = 0
     )
 {
-    converter::return_from_python<R> converter;
-    return converter(
+    PyObject* const result = 
         PyEval_CallMethod(
             self
             , const_cast<char*>(name)
             , const_cast<char*>("(" BOOST_PP_REPEAT_1ST(N, BOOST_PYTHON_FIXED, "O") ")")
             BOOST_PP_REPEAT_1ST(N, BOOST_PYTHON_FAST_ARG_TO_PYTHON_GET, nil)
-            ));
+            );
+    
+    // This conversion *must not* be done in the same expression as
+    // the call, because, in the special case where the result is a
+    // reference a Python object which was created by converting a C++
+    // argument for passing to PyEval_CallFunction, its reference
+    // count will be 2 until the end of the full expression containing
+    // the conversion, and that interferes with dangling
+    // pointer/reference detection.
+    converter::return_from_python<R> converter;
+    return converter(result);
 }
 
 # undef N
diff --git a/src/converter/from_python.cpp b/src/converter/from_python.cpp
@@ -218,7 +218,7 @@ namespace
       , char const* ref_type)
   {
       handle<> holder(source);
-      if (source->ob_refcnt <= 2)
+      if (source->ob_refcnt <= 1)
       {
           handle<> msg(
               ::PyString_FromFormat(
diff --git a/test/callbacks.py b/test/callbacks.py
@@ -15,9 +15,18 @@
 succeed<wink>:
 
 >>> try: apply_to_string_literal(identity)
-... except: pass # expected
+... except ReferenceError: pass # expected
 ... else: print 'expected an exception!'
 
+>>> try: apply_X_ref_handle(lambda ignored:X(42), None)
+... except ReferenceError: pass # expected
+... else: print 'expected an exception!'
+
+>>> x = X(42)
+>>> x.y = X(7)
+>>> apply_X_ref_handle(lambda z:z.y, x).value()
+7
+
 >>> x = apply_X_X(identity, X(42))
 >>> x.value()
 42

Original file line number	Diff line number	Diff line change
`@@ -218,7 +218,7 @@ namespace`
`218`	`218`	`, char const* ref_type)`
`219`	`219`	`{`
`220`	`220`	`handle<> holder(source);`
`221`		`- if (source->ob_refcnt <= 2)`
	`221`	`+ if (source->ob_refcnt <= 1)`
`222`	`222`	`{`
`223`	`223`	`handle<> msg(`
`224`	`224`	`::PyString_FromFormat(`