call_trace(): Add an additional parameter -- pointer to a PyObject*

    that should be used to cache an interned version of the event
    string passed to the profile/trace function.  call_trace() will
    create interned strings and cache them in using the storage
    specified by this additional parameter, avoiding a lot of string
    object creation at runtime when using the profiling or tracing
    functions.

All call sites are modified to pass the additional parameter, and four
static PyObject* variables are allocated to cache the interned string
objects.

This closes SF patch #431257.

Python/ceval.c

@@ -62,7 +62,7 @@ static int prtrace(PyObject *, char *);
 #endif
 static void call_exc_trace(PyObject **, PyObject**, PyFrameObject *);
 static int call_trace(PyObject **, PyObject **,
-		      PyFrameObject *, char *, PyObject *);
+		      PyFrameObject *, char *, PyObject **, PyObject *);
 static PyObject *loop_subscript(PyObject *, PyObject *);
 static PyObject *apply_slice(PyObject *, PyObject *, PyObject *);
 static int assign_slice(PyObject *, PyObject *,
@@ -97,6 +97,15 @@ static long dxp[256];
 #endif
 #endif
 
+/* Cached interned string objects used for calling the profile and
+ * trace functions.
+ */
+static PyObject *str_call = NULL;
+static PyObject *str_exception = NULL;
+static PyObject *str_line = NULL;
+static PyObject *str_return = NULL;
+
+
 #ifdef WITH_THREAD
 
 #ifndef DONT_HAVE_ERRNO_H
@@ -645,7 +654,7 @@ eval_code2(PyCodeObject *co, PyObject *globals, PyObject *locals,
 		   (sys.trace) is also called whenever an exception
 		   is detected. */
 		if (call_trace(&tstate->sys_tracefunc,
-			       &f->f_trace, f, "call",
+			       &f->f_trace, f, "call", &str_call,
 			       Py_None/*XXX how to compute arguments now?*/)) {
 			/* Trace function raised an error */
 			goto fail;
@@ -656,7 +665,7 @@ eval_code2(PyCodeObject *co, PyObject *globals, PyObject *locals,
 		/* Similar for sys_profilefunc, except it needn't return
 		   itself and isn't called for "line" events */
 		if (call_trace(&tstate->sys_profilefunc,
-			       (PyObject**)0, f, "call",
+			       (PyObject**)0, f, "call", &str_call,
 			       Py_None/*XXX*/)) {
 			goto fail;
 		}
@@ -1952,7 +1961,7 @@ eval_code2(PyCodeObject *co, PyObject *globals, PyObject *locals,
 			/* Trace each line of code reached */
 			f->f_lasti = INSTR_OFFSET();
 			err = call_trace(&f->f_trace, &f->f_trace,
-					 f, "line", Py_None);
+					 f, "line", &str_line, Py_None);
 			break;
 
 		case CALL_FUNCTION:
@@ -2297,7 +2306,7 @@ eval_code2(PyCodeObject *co, PyObject *globals, PyObject *locals,
 	if (f->f_trace) {
 		if (why == WHY_RETURN) {
 			if (call_trace(&f->f_trace, &f->f_trace, f,
-				       "return", retval)) {
+				       "return", &str_return, retval)) {
 				Py_XDECREF(retval);
 				retval = NULL;
 				why = WHY_EXCEPTION;
@@ -2307,7 +2316,7 @@ eval_code2(PyCodeObject *co, PyObject *globals, PyObject *locals,
 
 	if (tstate->sys_profilefunc && why == WHY_RETURN) {
 		if (call_trace(&tstate->sys_profilefunc, (PyObject**)0,
-			       f, "return", retval)) {
+			       f, "return", &str_return, retval)) {
 			Py_XDECREF(retval);
 			retval = NULL;
 			why = WHY_EXCEPTION;
@@ -2575,7 +2584,8 @@ call_exc_trace(PyObject **p_trace, PyObject **p_newtrace, PyFrameObject *f)
 		PyErr_Restore(type, value, traceback);
 		return;
 	}
-	err = call_trace(p_trace, p_newtrace, f, "exception", arg);
+	err = call_trace(p_trace, p_newtrace, f,
+			 "exception", &str_exception, arg);
 	Py_DECREF(arg);
 	if (err == 0)
 		PyErr_Restore(type, value, traceback);
@@ -2588,13 +2598,18 @@ call_exc_trace(PyObject **p_trace, PyObject **p_newtrace, PyFrameObject *f)
 
 /* PyObject **p_trace: in/out; may not be NULL;
  				may not point to NULL variable initially
-  PyObject **p_newtrace: in/out; may be NULL;
+   PyObject **p_newtrace: in/out; may be NULL;
   				may point to NULL variable;
- 				may be same variable as p_newtrace */
+ 				may be same variable as p_newtrace
+   PyObject **p_omsg: in/out; may not be NULL;
+				if non-null & *p_omsg == NULL, will be
+				initialized with an interned string
+				corresponding to msg.
+*/
 
 static int
 call_trace(PyObject **p_trace, PyObject **p_newtrace, PyFrameObject *f,
-	   char *msg, PyObject *arg)
+	   char *msg, PyObject **p_omsg, PyObject *arg)
 {
 	PyThreadState *tstate = f->f_tstate;
 	PyObject *args, *what;
@@ -2612,9 +2627,17 @@ call_trace(PyObject **p_trace, PyObject **p_newtrace, PyFrameObject *f,
 	args = PyTuple_New(3);
 	if (args == NULL)
 		goto cleanup;
-	what = PyString_FromString(msg);
-	if (what == NULL)
-		goto cleanup;
+	if (*p_omsg != NULL) {
+		what = *p_omsg;
+		Py_INCREF(what);
+	}
+	else {
+		what = PyString_InternFromString(msg);
+		if (what == NULL)
+			goto cleanup;
+		*p_omsg = what;
+		Py_INCREF(what);
+	}
 	Py_INCREF(f);
 	PyTuple_SET_ITEM(args, 0, (PyObject *)f);
 	PyTuple_SET_ITEM(args, 1, what);