bpo-43760: Add PyThreadState_EnterTracing() (GH-28542)

Add PyThreadState_EnterTracing() and PyThreadState_LeaveTracing()
functions to the limited C API to suspend and resume tracing and
profiling.

Add an unit test on the PyThreadState C API to _testcapi.

Add also internal _PyThreadState_DisableTracing() and
_PyThreadState_ResetTracing().

3 files changed, 27 insertions, 18 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index de71ae5..8986872 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -6187,7 +6187,7 @@ call_trace(Py_tracefunc func, PyObject *obj,
     if (tstate->tracing)
         return 0;
     tstate->tracing++;
-    tstate->cframe->use_tracing = 0;
+    _PyThreadState_DisableTracing(tstate);
     PyFrameObject *f = _PyFrame_GetFrameObject(frame);
     if (f == NULL) {
         return -1;
@@ -6201,8 +6201,7 @@ call_trace(Py_tracefunc func, PyObject *obj,
     }
     result = func(obj, f, what, arg);
     f->f_lineno = 0;
-    tstate->cframe->use_tracing = ((tstate->c_tracefunc != NULL)
-                           || (tstate->c_profilefunc != NULL)) ? 255 : 0;
+    _PyThreadState_ResetTracing(tstate);
     tstate->tracing--;
     return result;
 }
@@ -6216,8 +6215,7 @@ _PyEval_CallTracing(PyObject *func, PyObject *args)
     PyObject *result;
 
     tstate->tracing = 0;
-    tstate->cframe->use_tracing = ((tstate->c_tracefunc != NULL)
-                           || (tstate->c_profilefunc != NULL)) ? 255 : 0;
+    _PyThreadState_ResetTracing(tstate);
     result = PyObject_Call(func, args, NULL);
     tstate->tracing = save_tracing;
     tstate->cframe->use_tracing = save_use_tracing;
@@ -6274,7 +6272,7 @@ _PyEval_SetProfile(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
     tstate->c_profilefunc = NULL;
     tstate->c_profileobj = NULL;
     /* Must make sure that tracing is not ignored if 'profileobj' is freed */
-    tstate->cframe->use_tracing = tstate->c_tracefunc != NULL;
+    _PyThreadState_ResetTracing(tstate);
     Py_XDECREF(profileobj);
 
     Py_XINCREF(arg);
@@ -6282,7 +6280,7 @@ _PyEval_SetProfile(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
     tstate->c_profilefunc = func;
 
     /* Flag that tracing or profiling is turned on */
-    tstate->cframe->use_tracing = (func != NULL) || (tstate->c_tracefunc != NULL) ? 255 : 0;
+    _PyThreadState_ResetTracing(tstate);
     return 0;
 }
 
@@ -6315,7 +6313,7 @@ _PyEval_SetTrace(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
     tstate->c_tracefunc = NULL;
     tstate->c_traceobj = NULL;
     /* Must make sure that profiling is not ignored if 'traceobj' is freed */
-    tstate->cframe->use_tracing = (tstate->c_profilefunc != NULL) ? 255 : 0;
+    _PyThreadState_ResetTracing(tstate);
     Py_XDECREF(traceobj);
 
     Py_XINCREF(arg);
@@ -6323,8 +6321,7 @@ _PyEval_SetTrace(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
     tstate->c_tracefunc = func;
 
     /* Flag that tracing or profiling is turned on */
-    tstate->cframe->use_tracing = ((func != NULL)
-                           || (tstate->c_profilefunc != NULL)) ? 255 : 0;
+    _PyThreadState_ResetTracing(tstate);
 
     return 0;
 }
diff --git a/Python/pystate.c b/Python/pystate.c
index ee9507c..abd711e 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -1201,6 +1201,22 @@ PyThreadState_SetAsyncExc(unsigned long id, PyObject *exc)
 }
 
 
+void
+PyThreadState_EnterTracing(PyThreadState *tstate)
+{
+    tstate->tracing++;
+    _PyThreadState_DisableTracing(tstate);
+}
+
+void
+PyThreadState_LeaveTracing(PyThreadState *tstate)
+{
+    tstate->tracing--;
+    _PyThreadState_ResetTracing(tstate);
+}
+
+
+
 /* Routines for advanced debuggers, requested by David Beazley.
    Don't use unless you know what you are doing! */
 
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index ad9be71..5e663c1 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -256,8 +256,7 @@ sys_audit_tstate(PyThreadState *ts, const char *event,
         }
 
         /* Disallow tracing in hooks unless explicitly enabled */
-        ts->tracing++;
-        ts->cframe->use_tracing = 0;
+        PyThreadState_EnterTracing(ts);
         while ((hook = PyIter_Next(hooks)) != NULL) {
             _Py_IDENTIFIER(__cantrace__);
             PyObject *o;
@@ -270,14 +269,12 @@ sys_audit_tstate(PyThreadState *ts, const char *event,
                 break;
             }
             if (canTrace) {
-                ts->cframe->use_tracing = (ts->c_tracefunc || ts->c_profilefunc) ? 255 : 0;
-                ts->tracing--;
+                PyThreadState_LeaveTracing(ts);
             }
             PyObject* args[2] = {eventName, eventArgs};
             o = _PyObject_FastCallTstate(ts, hook, args, 2);
             if (canTrace) {
-                ts->tracing++;
-                ts->cframe->use_tracing = 0;
+                PyThreadState_EnterTracing(ts);
             }
             if (!o) {
                 break;
@@ -285,8 +282,7 @@ sys_audit_tstate(PyThreadState *ts, const char *event,
             Py_DECREF(o);
             Py_CLEAR(hook);
         }
-        ts->cframe->use_tracing = (ts->c_tracefunc || ts->c_profilefunc) ? 255 : 0;
-        ts->tracing--;
+        PyThreadState_LeaveTracing(ts);
         if (_PyErr_Occurred(ts)) {
             goto exit;
         }