Add _PyThreadState_UncheckedGet()

Issue #26154: Add a new private _PyThreadState_UncheckedGet() function which
gets the current thread state, but don't call Py_FatalError() if it is NULL.

Python 3.5.1 removed the _PyThreadState_Current symbol from the Python C API to
no more expose complex and private atomic types. Atomic types depends on the
compiler or can even depend on compiler options. The new function
_PyThreadState_UncheckedGet() allows to get the variable value without having
to care of the exact implementation of atomic types.

Changes:

* Replace direct usage of the _PyThreadState_Current variable with a call to
  _PyThreadState_UncheckedGet().
* In pystate.c, replace direct usage of the _PyThreadState_Current variable
  with the PyThreadState_GET() macro for readability.
* Document also PyThreadState_Get() in pystate.h

1 files changed, 7 insertions, 0 deletions

diff --git a/Misc/NEWS b/Misc/NEWS
index 3fe9bd0..4baf757 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,13 @@ Release date: tba
 Core and Builtins
 -----------------
 
+- Issue #26154: Add a new private _PyThreadState_UncheckedGet() function to get
+  the current Python thread state, but don't issue a fatal error if it is NULL.
+  This new function must be used instead of accessing directly the
+  _PyThreadState_Current variable.  The variable is no more exposed since
+  Python 3.5.1 to hide the exact implementation of atomic C types, to avoid
+  compiler issues.
+
 - Issue #25731: Fix set and deleting __new__ on a class.
 
 - Issue #22995: [UPDATE] Comment out the one of the pickleability tests in