SF patch 576101, by Oren Tirosh: alternative implementation of
interning. I modified Oren's patch significantly, but the basic idea
and most of the implementation is unchanged. Interned strings created
with PyString_InternInPlace() are now mortal, and you must keep a
reference to the resulting string around; use the new function
PyString_InternImmortal() to create immortal interned strings.
diff --git a/Include/stringobject.h b/Include/stringobject.h
index fd0f49a..ff30704 100644
--- a/Include/stringobject.h
+++ b/Include/stringobject.h
@@ -25,7 +25,7 @@
*/
/* Caching the hash (ob_shash) saves recalculation of a string's hash value.
- Interning strings (ob_sinterned) tries to ensure that only one string
+ Interning strings (ob_sstate) tries to ensure that only one string
object with a given value exists, so equality tests can be one pointer
comparison. This is generally restricted to strings that "look like"
Python identifiers, although the intern() builtin can be used to force
@@ -35,10 +35,14 @@
typedef struct {
PyObject_VAR_HEAD
long ob_shash;
- PyObject *ob_sinterned;
+ int ob_sstate;
char ob_sval[1];
} PyStringObject;
+#define SSTATE_NOT_INTERNED 0
+#define SSTATE_INTERNED_MORTAL 1
+#define SSTATE_INTERNED_IMMORTAL 2
+
PyAPI_DATA(PyTypeObject) PyBaseString_Type;
PyAPI_DATA(PyTypeObject) PyString_Type;
@@ -66,9 +70,13 @@
const char *);
PyAPI_FUNC(void) PyString_InternInPlace(PyObject **);
+PyAPI_FUNC(void) PyString_InternImmortal(PyObject **);
PyAPI_FUNC(PyObject *) PyString_InternFromString(const char *);
PyAPI_FUNC(void) _Py_ReleaseInternedStrings(void);
+/* Use only if you know it's a string */
+#define PyString_CHECK_INTERNED(op) (((PyStringObject *)(op))->ob_sstate)
+
/* Macro, trading safety for speed */
#define PyString_AS_STRING(op) (((PyStringObject *)(op))->ob_sval)
#define PyString_GET_SIZE(op) (((PyStringObject *)(op))->ob_size)