gh-76785: Minor Cleanup of Exception-related Cross-interpreter State (gh-126602)

This change makes it easier to backport the _interpreters, _interpqueues, and _interpchannels modules to Python 3.12.

Include/internal/pycore_crossinterp.h

@@ -11,6 +11,7 @@ extern "C" {
 #include "pycore_lock.h"            // PyMutex
 #include "pycore_pyerrors.h"
 
+
 /**************/
 /* exceptions */
 /**************/
@@ -163,8 +164,13 @@ struct _xi_state {
     // heap types
     _PyXIData_lookup_t data_lookup;
 
-    // heap types
+    struct xi_exceptions {
-    PyObject *PyExc_NotShareableError;
+        // static types
+        PyObject *PyExc_InterpreterError;
+        PyObject *PyExc_InterpreterNotFoundError;
+        // heap types
+        PyObject *PyExc_NotShareableError;
+    } exceptions;
 };
 
 extern PyStatus _PyXI_Init(PyInterpreterState *interp);

Modules/_interpretersmodule.c

@@ -1507,7 +1507,7 @@ module_exec(PyObject *mod)
         goto error;
     }
     PyObject *PyExc_NotShareableError = \
-                _PyInterpreterState_GetXIState(interp)->PyExc_NotShareableError;
+                _PyInterpreterState_GetXIState(interp)->exceptions.PyExc_NotShareableError;
     if (PyModule_AddType(mod, (PyTypeObject *)PyExc_NotShareableError) < 0) {
         goto error;
     }

Python/crossinterp.c

@@ -17,11 +17,11 @@
 /* exceptions */
 /**************/
 
-static int init_exceptions(PyInterpreterState *);
+typedef struct xi_exceptions exceptions_t;
-static void fini_exceptions(PyInterpreterState *);
+static int init_static_exctypes(exceptions_t *, PyInterpreterState *);
-static int _init_not_shareable_error_type(PyInterpreterState *);
+static void fini_static_exctypes(exceptions_t *, PyInterpreterState *);
-static void _fini_not_shareable_error_type(PyInterpreterState *);
+static int init_heap_exctypes(exceptions_t *);
-static PyObject * _get_not_shareable_error_type(PyInterpreterState *);
+static void fini_heap_exctypes(exceptions_t *);
 #include "crossinterp_exceptions.h"
 
 
@@ -205,7 +205,8 @@ static inline void
 _set_xid_lookup_failure(PyInterpreterState *interp,
                         PyObject *obj, const char *msg)
 {
-    PyObject *exctype = _get_not_shareable_error_type(interp);
+    exceptions_t *state = &_PyInterpreterState_GetXIState(interp)->exceptions;
+    PyObject *exctype = state->PyExc_NotShareableError;
     assert(exctype != NULL);
     if (msg != NULL) {
         assert(obj == NULL);
@@ -1605,7 +1606,9 @@ _propagate_not_shareable_error(_PyXI_session *session)
         return;
     }
     PyInterpreterState *interp = PyInterpreterState_Get();
-    if (PyErr_ExceptionMatches(_get_not_shareable_error_type(interp))) {
+    exceptions_t *state = &_PyInterpreterState_GetXIState(interp)->exceptions;
+    assert(state->PyExc_NotShareableError != NULL);
+    if (PyErr_ExceptionMatches(state->PyExc_NotShareableError)) {
         // We want to propagate the exception directly.
         session->_error_override = _PyXI_ERR_NOT_SHAREABLE;
         session->error_override = &session->_error_override;
@@ -1782,9 +1785,11 @@ _PyXI_Init(PyInterpreterState *interp)
     }
     xid_lookup_init(&_PyXI_GET_STATE(interp)->data_lookup);
 
-    // Initialize exceptions (heap types).
+    // Initialize exceptions.(heap types).
-    if (_init_not_shareable_error_type(interp) < 0) {
+    // See _PyXI_InitTypes() for the static types.
-        return _PyStatus_ERR("failed to initialize NotShareableError");
+    if (init_heap_exctypes(&_PyXI_GET_STATE(interp)->exceptions) < 0) {
+        PyErr_PrintEx(0);
+        return _PyStatus_ERR("failed to initialize exceptions");
     }
 
     return _PyStatus_OK();
@@ -1797,7 +1802,8 @@ void
 _PyXI_Fini(PyInterpreterState *interp)
 {
     // Finalize exceptions (heap types).
-    _fini_not_shareable_error_type(interp);
+    // See _PyXI_FiniTypes() for the static types.
+    fini_heap_exctypes(&_PyXI_GET_STATE(interp)->exceptions);
 
     // Finalize the XID lookup state (e.g. registry).
     xid_lookup_fini(&_PyXI_GET_STATE(interp)->data_lookup);
@@ -1809,17 +1815,21 @@ _PyXI_Fini(PyInterpreterState *interp)
 PyStatus
 _PyXI_InitTypes(PyInterpreterState *interp)
 {
-    if (init_exceptions(interp) < 0) {
+    if (init_static_exctypes(&_PyXI_GET_STATE(interp)->exceptions, interp) < 0) {
         PyErr_PrintEx(0);
         return _PyStatus_ERR("failed to initialize an exception type");
     }
+    // We would initialize heap types here too but that leads to ref leaks.
+    // Instead, we intialize them in _PyXI_Init().
     return _PyStatus_OK();
 }
 
 void
 _PyXI_FiniTypes(PyInterpreterState *interp)
 {
-    fini_exceptions(interp);
+    // We would finalize heap types here too but that leads to ref leaks.
+    // Instead, we finalize them in _PyXI_Fini().
+    fini_static_exctypes(&_PyXI_GET_STATE(interp)->exceptions, interp);
 }
 
 

Python/crossinterp_exceptions.h

@@ -25,71 +25,78 @@ static PyTypeObject _PyExc_InterpreterNotFoundError = {
 };
 PyObject *PyExc_InterpreterNotFoundError = (PyObject *)&_PyExc_InterpreterNotFoundError;
 
-/* NotShareableError extends ValueError */
-
-static int
-_init_not_shareable_error_type(PyInterpreterState *interp)
-{
-    const char *name = "interpreters.NotShareableError";
-    PyObject *base = PyExc_ValueError;
-    PyObject *ns = NULL;
-    PyObject *exctype = PyErr_NewException(name, base, ns);
-    if (exctype == NULL) {
-        return -1;
-    }
-
-    _PyInterpreterState_GetXIState(interp)->PyExc_NotShareableError = exctype;
-    return 0;
-}
-
-static void
-_fini_not_shareable_error_type(PyInterpreterState *interp)
-{
-    Py_CLEAR(_PyInterpreterState_GetXIState(interp)->PyExc_NotShareableError);
-}
-
-static PyObject *
-_get_not_shareable_error_type(PyInterpreterState *interp)
-{
-    assert(_PyInterpreterState_GetXIState(interp)->PyExc_NotShareableError != NULL);
-    return _PyInterpreterState_GetXIState(interp)->PyExc_NotShareableError;
-}
-
 
 /* lifecycle */
 
 static int
-init_exceptions(PyInterpreterState *interp)
+init_static_exctypes(exceptions_t *state, PyInterpreterState *interp)
 {
+    assert(state == &_PyXI_GET_STATE(interp)->exceptions);
     PyTypeObject *base = (PyTypeObject *)PyExc_Exception;
 
-    // builtin static types
+    // PyExc_InterpreterError
-
     _PyExc_InterpreterError.tp_base = base;
     _PyExc_InterpreterError.tp_traverse = base->tp_traverse;
     _PyExc_InterpreterError.tp_clear = base->tp_clear;
     if (_PyStaticType_InitBuiltin(interp, &_PyExc_InterpreterError) < 0) {
-        return -1;
+        goto error;
     }
+    state->PyExc_InterpreterError = (PyObject *)&_PyExc_InterpreterError;
 
+    // PyExc_InterpreterNotFoundError
     _PyExc_InterpreterNotFoundError.tp_traverse = base->tp_traverse;
     _PyExc_InterpreterNotFoundError.tp_clear = base->tp_clear;
     if (_PyStaticType_InitBuiltin(interp, &_PyExc_InterpreterNotFoundError) < 0) {
-        return -1;
+        goto error;
     }
-
+    state->PyExc_InterpreterNotFoundError =
-    // heap types
+            (PyObject *)&_PyExc_InterpreterNotFoundError;
-
-    // We would  call _init_not_shareable_error_type() here too,
-    // but that leads to ref leaks
 
     return 0;
+
+error:
+    fini_static_exctypes(state, interp);
+    return -1;
 }
 
 static void
-fini_exceptions(PyInterpreterState *interp)
+fini_static_exctypes(exceptions_t *state, PyInterpreterState *interp)
 {
-    // Likewise with _fini_not_shareable_error_type().
+    assert(state == &_PyXI_GET_STATE(interp)->exceptions);
-    _PyStaticType_FiniBuiltin(interp, &_PyExc_InterpreterNotFoundError);
+    if (state->PyExc_InterpreterNotFoundError != NULL) {
-    _PyStaticType_FiniBuiltin(interp, &_PyExc_InterpreterError);
+        state->PyExc_InterpreterNotFoundError = NULL;
+        _PyStaticType_FiniBuiltin(interp, &_PyExc_InterpreterNotFoundError);
+    }
+    if (state->PyExc_InterpreterError != NULL) {
+        state->PyExc_InterpreterError = NULL;
+        _PyStaticType_FiniBuiltin(interp, &_PyExc_InterpreterError);
+    }
+}
+
+static int
+init_heap_exctypes(exceptions_t *state)
+{
+    PyObject *exctype;
+
+    /* NotShareableError extends ValueError */
+    const char *name = "interpreters.NotShareableError";
+    PyObject *base = PyExc_ValueError;
+    PyObject *ns = NULL;
+    exctype = PyErr_NewException(name, base, ns);
+    if (exctype == NULL) {
+        goto error;
+    }
+    state->PyExc_NotShareableError = exctype;
+
+    return 0;
+
+error:
+    fini_heap_exctypes(state);
+    return -1;
+}
+
+static void
+fini_heap_exctypes(exceptions_t *state)
+{
+    Py_CLEAR(state->PyExc_NotShareableError);
 }