Allow subinterpreters to handle signals.

Author: ZeroIntensity

Include/cpython/pylifecycle.h

@@ -47,6 +47,7 @@ typedef struct {
     int allow_daemon_threads;
     int check_multi_interp_extensions;
     int gil;
+    int can_handle_signals;
 } PyInterpreterConfig;
 
 #define _PyInterpreterConfig_INIT \
@@ -58,6 +59,7 @@ typedef struct {
         .allow_daemon_threads = 0, \
         .check_multi_interp_extensions = 1, \
         .gil = PyInterpreterConfig_OWN_GIL, \
+        .can_handle_signals = 1, \
     }
 
 // gh-117649: The free-threaded build does not currently support single-phase
@@ -78,6 +80,7 @@ typedef struct {
         .allow_daemon_threads = 1, \
         .check_multi_interp_extensions = _PyInterpreterConfig_LEGACY_CHECK_MULTI_INTERP_EXTENSIONS, \
         .gil = PyInterpreterConfig_SHARED_GIL, \
+        .can_handle_signals = 0, \
     }
 
 PyAPI_FUNC(PyStatus) Py_NewInterpreterFromConfig(

Include/internal/pycore_interp.h

@@ -93,6 +93,9 @@ might not be allowed in the current interpreter (i.e. os.fork() would fail).
 /* Set if os.exec*() is allowed. */
 #define Py_RTFLAGS_EXEC (1UL << 16)
 
+/* Set if signal handling is allowed. */
+#define Py_RTFLAGS_CAN_HANDLE_SIGNALS (1UL << 17)
+
 extern int _PyInterpreterState_HasFeature(PyInterpreterState *interp,
                                           unsigned long feature);
 

Include/internal/pycore_pystate.h

@@ -11,7 +11,7 @@ extern "C" {
 #include "pycore_pythonrun.h"     // _PyOS_STACK_MARGIN_SHIFT
 #include "pycore_typedefs.h"      // _PyRuntimeState
 #include "pycore_tstate.h"
-
+#include "pycore_interp.h"        // _PyInterpreterState_HasFeature
 
 // Values for PyThreadState.state. A thread must be in the "attached" state
 // before calling most Python APIs. If the GIL is enabled, then "attached"
@@ -78,11 +78,12 @@ extern void _PyInterpreterState_ReinitRunningMain(PyThreadState *);
 extern const PyConfig* _Py_GetMainConfig(void);
 
 
-/* Only handle signals on the main thread of the main interpreter. */
+/* Only handle signals on the main thread of an interpreter that supports it. */
 static inline int
 _Py_ThreadCanHandleSignals(PyInterpreterState *interp)
 {
-    return (_Py_IsMainThread() && _Py_IsMainInterpreter(interp));
+    return (_Py_IsMainThread()
+            && _PyInterpreterState_HasFeature(interp, Py_RTFLAGS_CAN_HANDLE_SIGNALS));
 }
 
 

Python/interpconfig.c

@@ -87,6 +87,7 @@ _PyInterpreterConfig_AsDict(PyInterpreterConfig *config)
     ADD_BOOL(allow_threads);
     ADD_BOOL(allow_daemon_threads);
     ADD_BOOL(check_multi_interp_extensions);
+    ADD_BOOL(can_handle_signals);
 
     ADD_STR(gil, gil_flag_to_str(config->gil));
 
@@ -182,6 +183,7 @@ interp_config_from_dict(PyObject *origdict, PyInterpreterConfig *config,
     COPY_BOOL(allow_threads);
     COPY_BOOL(allow_daemon_threads);
     COPY_BOOL(check_multi_interp_extensions);
+    COPY_BOOL(can_handle_signals);
 
     // PyInterpreterConfig.gil
     char buf[20];

Python/pylifecycle.c

@@ -566,6 +566,10 @@ init_interp_settings(PyInterpreterState *interp,
         interp->feature_flags |= Py_RTFLAGS_MULTI_INTERP_EXTENSIONS;
     }
 
+    if (config->can_handle_signals) {
+        interp->feature_flags |= Py_RTFLAGS_CAN_HANDLE_SIGNALS;
+    }
+
     switch (config->gil) {
     case PyInterpreterConfig_DEFAULT_GIL: break;
     case PyInterpreterConfig_SHARED_GIL: break;
@@ -636,10 +640,11 @@ pycore_create_interpreter(_PyRuntimeState *runtime,
     }
 
     PyInterpreterConfig config = _PyInterpreterConfig_LEGACY_INIT;
-    // The main interpreter always has its own GIL and supports single-phase
-    // init extensions.
+    // The main interpreter always has its own GIL, supports single-phase
+    // init extensions, and can handle signals.
     config.gil = PyInterpreterConfig_OWN_GIL;
     config.check_multi_interp_extensions = 0;
+    config.can_handle_signals = 1;
     status = init_interp_settings(interp, &config);
     if (_PyStatus_EXCEPTION(status)) {
         return status;