bpo-40268: Rename _PyInterpreterState_GET_UNSAFE() (GH-19509)

Rename _PyInterpreterState_GET_UNSAFE() to _PyInterpreterState_GET()
for consistency with _PyThreadState_GET() and to have a shorter name
(help to fit into 80 columns).

Add also "assert(tstate != NULL);" to the function.
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index 492988e..95b023d 100644
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -994,7 +994,7 @@
 {
     assert(errors != NULL && errors != Py_None);
 
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
 #ifndef Py_DEBUG
     /* In release mode, only check in development mode (-X dev) */
     if (!_PyInterpreterState_GetConfig(interp)->dev_mode) {
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index 9853699..5636140 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -1091,7 +1091,7 @@
     boot = PyMem_NEW(struct bootstate, 1);
     if (boot == NULL)
         return PyErr_NoMemory();
-    boot->interp = _PyInterpreterState_GET_UNSAFE();
+    boot->interp = _PyInterpreterState_GET();
     boot->func = func;
     boot->args = args;
     boot->keyw = keyw;
@@ -1213,7 +1213,7 @@
 static PyObject *
 thread__count(PyObject *self, PyObject *Py_UNUSED(ignored))
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
     return PyLong_FromLong(interp->num_threads);
 }
 
@@ -1556,7 +1556,7 @@
     PyObject *m, *d, *v;
     double time_max;
     double timeout_max;
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
 
     /* Initialize types: */
     if (PyType_Ready(&localdummytype) < 0)
diff --git a/Modules/main.c b/Modules/main.c
index a9de70b..fb24c6c 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -498,7 +498,7 @@
 static void
 pymain_run_python(int *exitcode)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
     /* pymain_run_stdin() modify the config */
     PyConfig *config = (PyConfig*)_PyInterpreterState_GetConfig(interp);
 
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 57f1487..2d603d1 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -451,7 +451,7 @@
 void
 PyOS_BeforeFork(void)
 {
-    run_at_forkers(_PyInterpreterState_GET_UNSAFE()->before_forkers, 1);
+    run_at_forkers(_PyInterpreterState_GET()->before_forkers, 1);
 
     _PyImport_AcquireLock();
 }
@@ -462,7 +462,7 @@
     if (_PyImport_ReleaseLock() <= 0)
         Py_FatalError("failed releasing import lock after fork");
 
-    run_at_forkers(_PyInterpreterState_GET_UNSAFE()->after_forkers_parent, 0);
+    run_at_forkers(_PyInterpreterState_GET()->after_forkers_parent, 0);
 }
 
 void
@@ -476,7 +476,7 @@
     _PyRuntimeState_ReInitThreads(runtime);
     _PyInterpreterState_DeleteExceptMain(runtime);
 
-    run_at_forkers(_PyInterpreterState_GET_UNSAFE()->after_forkers_child, 0);
+    run_at_forkers(_PyInterpreterState_GET()->after_forkers_child, 0);
 }
 
 static int
@@ -6185,7 +6185,7 @@
         check_null_or_callable(after_in_parent, "after_in_parent")) {
         return NULL;
     }
-    interp = _PyInterpreterState_GET_UNSAFE();
+    interp = _PyInterpreterState_GET();
 
     if (register_at_forker(&interp->before_forkers, before)) {
         return NULL;
@@ -6216,7 +6216,7 @@
 {
     pid_t pid;
 
-    if (_PyInterpreterState_GET_UNSAFE() != PyInterpreterState_Main()) {
+    if (_PyInterpreterState_GET() != PyInterpreterState_Main()) {
         PyErr_SetString(PyExc_RuntimeError, "fork not supported for subinterpreters");
         return NULL;
     }
@@ -6251,7 +6251,7 @@
 {
     pid_t pid;
 
-    if (_PyInterpreterState_GET_UNSAFE() != PyInterpreterState_Main()) {
+    if (_PyInterpreterState_GET() != PyInterpreterState_Main()) {
         PyErr_SetString(PyExc_RuntimeError, "fork not supported for subinterpreters");
         return NULL;
     }
@@ -6859,7 +6859,7 @@
     int master_fd = -1;
     pid_t pid;
 
-    if (_PyInterpreterState_GET_UNSAFE() != PyInterpreterState_Main()) {
+    if (_PyInterpreterState_GET() != PyInterpreterState_Main()) {
         PyErr_SetString(PyExc_RuntimeError, "fork not supported for subinterpreters");
         return NULL;
     }
diff --git a/Modules/signalmodule.c b/Modules/signalmodule.c
index b089a80..ceb986b 100644
--- a/Modules/signalmodule.c
+++ b/Modules/signalmodule.c
@@ -1784,7 +1784,7 @@
 int
 PyOS_InterruptOccurred(void)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
     if (!_Py_ThreadCanHandleSignals(interp)) {
         return 0;
     }
@@ -1821,7 +1821,7 @@
 int
 _PyOS_IsMainThread(void)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
     return _Py_ThreadCanHandleSignals(interp);
 }