bpo-39877: Refactor take_gil() function (GH-18885)

* Remove ceval parameter of take_gil(): get it from tstate.
* Move exit_thread_if_finalizing() call inside take_gil(). Replace
  exit_thread_if_finalizing() with tstate_must_exit(): the caller is
  now responsible to call PyThread_exit_thread().
* Move is_tstate_valid() assertion inside take_gil(). Remove
  is_tstate_valid(): inline code into take_gil().
* Move gil_created() assertion inside take_gil().

Python/ceval.c

@@ -198,16 +198,6 @@ ensure_tstate_not_null(const char *func, PyThreadState *tstate)
 }
 
 
-#ifndef NDEBUG
-static int is_tstate_valid(PyThreadState *tstate)
-{
-    assert(!_PyMem_IsPtrFreed(tstate));
-    assert(!_PyMem_IsPtrFreed(tstate->interp));
-    return 1;
-}
-#endif
-
-
 int
 PyEval_ThreadsInitialized(void)
 {
@@ -230,13 +220,15 @@ _PyEval_InitThreads(PyThreadState *tstate)
 
     PyThread_init_thread();
     create_gil(gil);
-    take_gil(ceval, tstate);
+
+    take_gil(tstate);
 
     struct _pending_calls *pending = &ceval->pending;
     pending->lock = PyThread_allocate_lock();
     if (pending->lock == NULL) {
         return _PyStatus_NO_MEMORY();
     }
+
     return _PyStatus_OK();
 }
 
@@ -269,30 +261,6 @@ _PyEval_FiniThreads(struct _ceval_runtime_state *ceval)
     }
 }
 
-/* This function is designed to exit daemon threads immediately rather than
-   taking the GIL if Py_Finalize() has been called.
-
-   The caller must *not* hold the GIL, since this function does not release
-   the GIL before exiting the thread.
-
-   When this function is called by a daemon thread after Py_Finalize() has been
-   called, the GIL does no longer exist.
-
-   tstate must be non-NULL. */
-static inline void
-exit_thread_if_finalizing(PyThreadState *tstate)
-{
-    /* bpo-39877: Access _PyRuntime directly rather than using
-       tstate->interp->runtime to support calls from Python daemon threads.
-       After Py_Finalize() has been called, tstate can be a dangling pointer:
-       point to PyThreadState freed memory. */
-    _PyRuntimeState *runtime = &_PyRuntime;
-    PyThreadState *finalizing = _PyRuntimeState_GetFinalizing(runtime);
-    if (finalizing != NULL && finalizing != tstate) {
-        PyThread_exit_thread();
-    }
-}
-
 void
 _PyEval_Fini(void)
 {
@@ -329,11 +297,7 @@ PyEval_AcquireLock(void)
     PyThreadState *tstate = _PyRuntimeState_GetThreadState(runtime);
     ensure_tstate_not_null(__func__, tstate);
 
-    exit_thread_if_finalizing(tstate);
+    take_gil(tstate);
-    assert(is_tstate_valid(tstate));
-
-    struct _ceval_runtime_state *ceval = &runtime->ceval;
-    take_gil(ceval, tstate);
 }
 
 void
@@ -353,17 +317,10 @@ PyEval_AcquireThread(PyThreadState *tstate)
 {
     ensure_tstate_not_null(__func__, tstate);
 
-    exit_thread_if_finalizing(tstate);
+    take_gil(tstate);
-    assert(is_tstate_valid(tstate));
 
-    _PyRuntimeState *runtime = tstate->interp->runtime;
+    struct _gilstate_runtime_state *gilstate = &tstate->interp->runtime->gilstate;
-    struct _ceval_runtime_state *ceval = &runtime->ceval;
+    if (_PyThreadState_Swap(gilstate, tstate) != NULL) {
-
-    /* Check that _PyEval_InitThreads() was called to create the lock */
-    assert(gil_created(&ceval->gil));
-
-    take_gil(ceval, tstate);
-    if (_PyThreadState_Swap(&runtime->gilstate, tstate) != NULL) {
         Py_FatalError("non-NULL old thread state");
     }
 }
@@ -396,7 +353,8 @@ _PyEval_ReInitThreads(_PyRuntimeState *runtime)
     recreate_gil(&ceval->gil);
     PyThreadState *tstate = _PyRuntimeState_GetThreadState(runtime);
     ensure_tstate_not_null(__func__, tstate);
-    take_gil(ceval, tstate);
+
+    take_gil(tstate);
 
     struct _pending_calls *pending = &ceval->pending;
     pending->lock = PyThread_allocate_lock();
@@ -436,16 +394,10 @@ PyEval_RestoreThread(PyThreadState *tstate)
 {
     ensure_tstate_not_null(__func__, tstate);
 
-    exit_thread_if_finalizing(tstate);
+    take_gil(tstate);
-    assert(is_tstate_valid(tstate));
 
-    _PyRuntimeState *runtime = tstate->interp->runtime;
+    struct _gilstate_runtime_state *gilstate = &tstate->interp->runtime->gilstate;
-    struct _ceval_runtime_state *ceval = &runtime->ceval;
+    _PyThreadState_Swap(gilstate, tstate);
-    assert(gil_created(&ceval->gil));
-
-    take_gil(ceval, tstate);
-
-    _PyThreadState_Swap(&runtime->gilstate, tstate);
 }
 
 
@@ -805,7 +757,6 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)
 
     PyThreadState * const tstate = _PyRuntimeState_GetThreadState(runtime);
     ensure_tstate_not_null(__func__, tstate);
-    assert(is_tstate_valid(tstate));
 
     /* when tracing we set things up so that
 
@@ -1294,10 +1245,7 @@ main_loop:
 
                 /* Other threads may run now */
 
-                /* Check if we should make a quick exit. */
+                take_gil(tstate);
-                exit_thread_if_finalizing(tstate);
-
-                take_gil(ceval, tstate);
 
                 if (_PyThreadState_Swap(&runtime->gilstate, tstate) != NULL) {
                     Py_FatalError("orphan tstate");

Python/ceval_gil.h

@@ -180,17 +180,55 @@ drop_gil(struct _ceval_runtime_state *ceval, PyThreadState *tstate)
 #endif
 }
 
+
+/* Check if a Python thread must exit immediately, rather than taking the GIL
+   if Py_Finalize() has been called.
+
+   When this function is called by a daemon thread after Py_Finalize() has been
+   called, the GIL does no longer exist.
+
+   tstate must be non-NULL. */
+static inline int
+tstate_must_exit(PyThreadState *tstate)
+{
+    /* bpo-39877: Access _PyRuntime directly rather than using
+       tstate->interp->runtime to support calls from Python daemon threads.
+       After Py_Finalize() has been called, tstate can be a dangling pointer:
+       point to PyThreadState freed memory. */
+    _PyRuntimeState *runtime = &_PyRuntime;
+    PyThreadState *finalizing = _PyRuntimeState_GetFinalizing(runtime);
+    return (finalizing != NULL && finalizing != tstate);
+}
+
+
 /* Take the GIL.
 
    The function saves errno at entry and restores its value at exit.
 
    tstate must be non-NULL. */
 static void
-take_gil(struct _ceval_runtime_state *ceval, PyThreadState *tstate)
+take_gil(PyThreadState *tstate)
 {
     int err = errno;
 
+    assert(tstate != NULL);
+
+    /* Check if we should make a quick exit. */
+    if (tstate_must_exit(tstate)) {
+        PyThread_exit_thread();
+    }
+
+    /* Ensure that tstate is valid: sanity check for PyEval_AcquireThread() and
+       PyEval_RestoreThread(). Detect if tstate memory was freed. */
+    assert(!_PyMem_IsPtrFreed(tstate));
+    assert(!_PyMem_IsPtrFreed(tstate->interp));
+
+    struct _ceval_runtime_state *ceval = &tstate->interp->runtime->ceval;
     struct _gil_runtime_state *gil = &ceval->gil;
+
+    /* Check that _PyEval_InitThreads() was called to create the lock */
+    assert(gil_created(gil));
+
     MUTEX_LOCK(gil->mutex);
 
     if (!_Py_atomic_load_relaxed(&gil->locked)) {
@@ -215,6 +253,7 @@ take_gil(struct _ceval_runtime_state *ceval, PyThreadState *tstate)
             SET_GIL_DROP_REQUEST(ceval);
         }
     }
+
 _ready:
 #ifdef FORCE_SWITCHING
     /* This mutex must be taken before modifying gil->last_holder: