gh-157746: Make PyErr_CheckSignals() cheap when no signal is pending (#157748)

Author: eendebakpt

Misc/NEWS.d/next/Core_and_Builtins/2026-09-25-11-05-00.gh-issue-157746.q7Lk3d.rst

@@ -0,0 +1,3 @@
+Reduce the overhead of :c:func:`PyErr_CheckSignals` when no signal is
+pending: the cheap flag checks are now done before the main-thread check and
+the remote debugger configuration lookup.

Modules/signalmodule.c

@@ -1796,25 +1796,18 @@ PyErr_CheckSignals(void)
     _PyRunRemoteDebugger(tstate);
 #endif
 
-    if (_Py_ThreadCanHandleSignals(tstate->interp)) {
-        if (_PyErr_CheckSignalsTstate(tstate) < 0) {
-            return -1;
-        }
+    if (_PyErr_CheckSignalsTstate(tstate) < 0) {
+        return -1;
     }
 
     return 0;
 }
 
 
-/* Declared in cpython/pyerrors.h */
-int
-_PyErr_CheckSignalsTstate(PyThreadState *tstate)
+// Out of line, to keep the common case of _PyErr_CheckSignalsTstate() cheap.
+Py_NO_INLINE static int
+run_tripped_handlers(PyThreadState *tstate)
 {
-    _Py_CHECK_EMSCRIPTEN_SIGNALS();
-    if (!_Py_atomic_load_int(&is_tripped)) {
-        return 0;
-    }
-
     /*
      * The is_tripped variable is meant to speed up the calls to
      * PyErr_CheckSignals (both directly or via pending calls) when no
@@ -1895,6 +1888,20 @@ _PyErr_CheckSignalsTstate(PyThreadState *tstate)
 }
 
 
+/* Declared in pycore_pyerrors.h */
+int
+_PyErr_CheckSignalsTstate(PyThreadState *tstate)
+{
+    _Py_CHECK_EMSCRIPTEN_SIGNALS();
+    if (!_Py_atomic_load_int(&is_tripped)) {
+        return 0;
+    }
+    if (!_Py_ThreadCanHandleSignals(tstate->interp)) {
+        return 0;
+    }
+    return run_tripped_handlers(tstate);
+}
+
 
 int
 _PyErr_CheckSignals(void)

Python/ceval_gil.c

@@ -830,9 +830,6 @@ handle_signals(PyThreadState *tstate)
 {
     assert(_PyThreadState_CheckConsistency(tstate));
     _Py_unset_eval_breaker_bit(tstate, _PY_SIGNALS_PENDING_BIT);
-    if (!_Py_ThreadCanHandleSignals(tstate->interp)) {
-        return 0;
-    }
     if (_PyErr_CheckSignalsTstate(tstate) < 0) {
         /* On failure, re-schedule a call to handle_signals(). */
         _Py_set_eval_breaker_bit(tstate, _PY_SIGNALS_PENDING_BIT);
@@ -1258,10 +1255,11 @@ static inline void run_remote_debugger_script(PyObject *path)
 
 int _PyRunRemoteDebugger(PyThreadState *tstate)
 {
+    if (tstate->remote_debugger_support.debugger_pending_call != 1) {
+        return 0;
+    }
     const PyConfig *config = _PyInterpreterState_GetConfig(tstate->interp);
-    if (config->remote_debug == 1
-         && tstate->remote_debugger_support.debugger_pending_call == 1)
-    {
+    if (config->remote_debug == 1) {
         tstate->remote_debugger_support.debugger_pending_call = 0;
 
         // Immediately make a copy in case of a race with another debugger