bpo-40010: COMPUTE_EVAL_BREAKER() checks for subinterpreter (GH-19087)

COMPUTE_EVAL_BREAKER() now also checks if the Python thread state
belongs to the main interpreter. Don't break the evaluation loop if
there are pending signals but the Python thread state it belongs to a
subinterpeter.

* Add _Py_IsMainThread() function.
* Add _Py_ThreadCanHandleSignals() function.

1 files changed, 27 insertions, 1 deletions

diff --git a/Include/internal/pycore_pystate.h b/Include/internal/pycore_pystate.h
index 92eeac762f..da034e185a 100644
--- a/Include/internal/pycore_pystate.h
+++ b/Include/internal/pycore_pystate.h
@@ -294,7 +294,33 @@ _PyRuntimeState_SetFinalizing(_PyRuntimeState *runtime, PyThreadState *tstate) {
     _Py_atomic_store_relaxed(&runtime->_finalizing, (uintptr_t)tstate);
 }
 
-PyAPI_FUNC(int) _Py_IsMainInterpreter(PyThreadState* tstate);
+/* Check if the current thread is the main thread.
+   Use _Py_IsMainInterpreter() to check if it's the main interpreter. */
+static inline int
+_Py_IsMainThread(void)
+{
+    unsigned long thread = PyThread_get_thread_ident();
+    return (thread == _PyRuntime.main_thread);
+}
+
+
+static inline int
+_Py_IsMainInterpreter(PyThreadState* tstate)
+{
+    /* Use directly _PyRuntime rather than tstate->interp->runtime, since
+       this function is used in performance critical code path (ceval) */
+    return (tstate->interp == _PyRuntime.interpreters.main);
+}
+
+
+/* Only handle signals on the main thread of the main interpreter. */
+static inline int
+_Py_ThreadCanHandleSignals(PyThreadState *tstate)
+{
+    /* Use directly _PyRuntime rather than tstate->interp->runtime, since
+       this function is used in performance critical code path (ceval) */
+    return (_Py_IsMainThread() && _Py_IsMainInterpreter(tstate));
+}
 
 
 /* Variable and macro for in-line access to current thread