gh-124622: Add PyGILState_EnsureOrFail() function

Add new "OrFail" functions:

* _PyEval_AcquireLockOrFail()
* _PyEval_RestoreThreadOrFail()
* _PyThreadState_AttachOrFail()
* take_gil_or_fail()

Author: vstinner

Doc/c-api/init.rst

@@ -1279,6 +1279,15 @@ with sub-interpreters:
       Hangs the current thread, rather than terminating it, if called while the
       interpreter is finalizing.
 
+
+.. c:function:: int PyGILState_EnsureOrFail(PyGILState_STATE *state)
+
+   Similar to :c:func:`PyGILState_Ensure`, but *state* is an argument
+   and return ``-1`` if the thread must exit. Return ``0`` on success.
+
+   .. versionadded:: next
+
+
 .. c:function:: void PyGILState_Release(PyGILState_STATE)
 
    Release any resources previously acquired.  After this call, Python's state will

Doc/whatsnew/3.14.rst

@@ -1334,6 +1334,9 @@ New features
   and get an attribute of the module.
   (Contributed by Victor Stinner in :gh:`128911`.)
 
+* Add :c:func:`PyGILState_EnsureOrFail` function: similar to
+  :c:func:`PyGILState_Ensure`, but return ``-1`` if the thread must exit.
+  (Contributed by Victor Stinner in :gh:`124622`.)
 
 Limited C API changes
 ---------------------

Include/internal/pycore_ceval.h

@@ -327,6 +327,8 @@ void _Py_unset_eval_breaker_bit_all(PyInterpreterState *interp, uintptr_t bit);
 
 PyAPI_FUNC(PyObject *) _PyFloat_FromDouble_ConsumeInputs(_PyStackRef left, _PyStackRef right, double value);
 
+extern int _PyEval_AcquireLockOrFail(PyThreadState *tstate);
+extern int _PyEval_RestoreThreadOrFail(PyThreadState *tstate);
 
 #ifdef __cplusplus
 }

Include/internal/pycore_pystate.h

@@ -313,6 +313,8 @@ _Py_AssertHoldsTstateFunc(const char *func)
 #define _Py_AssertHoldsTstate()
 #endif
 
+extern int _PyThreadState_AttachOrFail(PyThreadState *tstate);
+
 #ifdef __cplusplus
 }
 #endif

Misc/NEWS.d/next/C_API/2025-02-05-15-01-23.gh-issue-124622.jnROuN.rst

@@ -0,0 +1,3 @@
+Add :c:func:`PyGILState_EnsureOrFail` function: similar to
+:c:func:`PyGILState_Ensure`, but return ``-1`` if the thread must exit.
+Patch by Victor Stinner.

Python/ceval_gil.c

@@ -277,12 +277,15 @@ drop_gil(PyInterpreterState *interp, PyThreadState *tstate, int final_release)
 
 /* Take the GIL.
 
+   Return 0 on success.
+   Return -1 if the thread must exit.
+
    The function saves errno at entry and restores its value at exit.
    It may hang rather than return if the interpreter has been finalized.
 
    tstate must be non-NULL. */
-static void
-take_gil(PyThreadState *tstate)
+static int
+take_gil_or_fail(PyThreadState *tstate)
 {
     int err = errno;
 
@@ -304,15 +307,15 @@ take_gil(PyThreadState *tstate)
            C++. gh-87135: The best that can be done is to hang the thread as
            the public APIs calling this have no error reporting mechanism (!).
          */
-        PyThread_hang_thread();
+        goto tstate_must_exit;
     }
 
     assert(_PyThreadState_CheckConsistency(tstate));
     PyInterpreterState *interp = tstate->interp;
     struct _gil_runtime_state *gil = interp->ceval.gil;
 #ifdef Py_GIL_DISABLED
     if (!_Py_atomic_load_int_relaxed(&gil->enabled)) {
-        return;
+        goto done;
     }
 #endif
 
@@ -348,9 +351,7 @@ take_gil(PyThreadState *tstate)
                 if (drop_requested) {
                     _Py_unset_eval_breaker_bit(holder_tstate, _PY_GIL_DROP_REQUEST_BIT);
                 }
-                // gh-87135: hang the thread as *thread_exit() is not a safe
-                // API. It lacks stack unwind and local variable destruction.
-                PyThread_hang_thread();
+                goto tstate_must_exit;
             }
             assert(_PyThreadState_CheckConsistency(tstate));
 
@@ -366,7 +367,7 @@ take_gil(PyThreadState *tstate)
         // return.
         COND_SIGNAL(gil->cond);
         MUTEX_UNLOCK(gil->mutex);
-        return;
+        goto done;
     }
 #endif
 
@@ -401,7 +402,7 @@ take_gil(PyThreadState *tstate)
         /* tstate could be a dangling pointer, so don't pass it to
            drop_gil(). */
         drop_gil(interp, NULL, 1);
-        PyThread_hang_thread();
+        goto tstate_must_exit;
     }
     assert(_PyThreadState_CheckConsistency(tstate));
 
@@ -411,8 +412,25 @@ take_gil(PyThreadState *tstate)
 
     MUTEX_UNLOCK(gil->mutex);
 
+#ifdef Py_GIL_DISABLED
+done:
+#endif
     errno = err;
-    return;
+    return 0;
+
+tstate_must_exit:
+    errno = err;
+    return -1;
+}
+
+static void
+take_gil(PyThreadState *tstate)
+{
+    if (take_gil_or_fail(tstate) < 0) {
+        // gh-87135: hang the thread as *thread_exit() is not a safe
+        // API. It lacks stack unwind and local variable destruction.
+        PyThread_hang_thread();
+    }
 }
 
 void _PyEval_SetSwitchInterval(unsigned long microseconds)
@@ -586,6 +604,13 @@ _PyEval_AcquireLock(PyThreadState *tstate)
     take_gil(tstate);
 }
 
+int
+_PyEval_AcquireLockOrFail(PyThreadState *tstate)
+{
+    _Py_EnsureTstateNotNULL(tstate);
+    return take_gil_or_fail(tstate);
+}
+
 void
 _PyEval_ReleaseLock(PyInterpreterState *interp,
                     PyThreadState *tstate,
@@ -641,19 +666,32 @@ PyEval_SaveThread(void)
     return tstate;
 }
 
-void
-PyEval_RestoreThread(PyThreadState *tstate)
+
+int
+_PyEval_RestoreThreadOrFail(PyThreadState *tstate)
 {
 #ifdef MS_WINDOWS
     int err = GetLastError();
 #endif
 
     _Py_EnsureTstateNotNULL(tstate);
-    _PyThreadState_Attach(tstate);
+    if (_PyThreadState_AttachOrFail(tstate) < 0) {
+        return -1;
+    }
 
 #ifdef MS_WINDOWS
     SetLastError(err);
 #endif
+    return 0;
+}
+
+
+void
+PyEval_RestoreThread(PyThreadState *tstate)
+{
+    if (_PyEval_RestoreThreadOrFail(tstate) < 0) {
+        PyThread_hang_thread();
+    }
 }
 
 

Python/pystate.c

@@ -2060,8 +2060,8 @@ tstate_wait_attach(PyThreadState *tstate)
     } while (!tstate_try_attach(tstate));
 }
 
-void
-_PyThreadState_Attach(PyThreadState *tstate)
+int
+_PyThreadState_AttachOrFail(PyThreadState *tstate)
 {
 #if defined(Py_DEBUG)
     // This is called from PyEval_RestoreThread(). Similar
@@ -2076,7 +2076,9 @@ _PyThreadState_Attach(PyThreadState *tstate)
 
 
     while (1) {
-        _PyEval_AcquireLock(tstate);
+        if (_PyEval_AcquireLockOrFail(tstate) < 0) {
+            return -1;
+        }
 
         // XXX assert(tstate_is_alive(tstate));
         current_fast_set(&_PyRuntime, tstate);
@@ -2111,6 +2113,15 @@ _PyThreadState_Attach(PyThreadState *tstate)
 #if defined(Py_DEBUG)
     errno = err;
 #endif
+    return 0;
+}
+
+void
+_PyThreadState_Attach(PyThreadState *tstate)
+{
+    if (_PyThreadState_AttachOrFail(tstate) < 0) {
+        PyThread_hang_thread();
+    }
 }
 
 static void
@@ -2730,8 +2741,9 @@ PyGILState_Check(void)
     return (tstate == tcur);
 }
 
-PyGILState_STATE
-PyGILState_Ensure(void)
+
+int
+PyGILState_EnsureOrFail(PyGILState_STATE *state)
 {
     _PyRuntimeState *runtime = &_PyRuntime;
 
@@ -2770,7 +2782,10 @@ PyGILState_Ensure(void)
     }
 
     if (!has_gil) {
-        PyEval_RestoreThread(tcur);
+        if (_PyEval_RestoreThreadOrFail(tcur) < 0) {
+            *state = PyGILState_UNLOCKED;
+            return -1;
+        }
     }
 
     /* Update our counter in the thread-state - no need for locks:
@@ -2780,9 +2795,22 @@ PyGILState_Ensure(void)
     */
     ++tcur->gilstate_counter;
 
-    return has_gil ? PyGILState_LOCKED : PyGILState_UNLOCKED;
+    *state = has_gil ? PyGILState_LOCKED : PyGILState_UNLOCKED;
+    return 0;
+}
+
+
+PyGILState_STATE
+PyGILState_Ensure(void)
+{
+    PyGILState_STATE state;
+    if (PyGILState_EnsureOrFail(&state) < 0) {
+        PyThread_hang_thread();
+    }
+    return state;
 }
 
+
 void
 PyGILState_Release(PyGILState_STATE oldstate)
 {