bpo-25658: Implement PEP 539 for Thread Specific Storage (TSS) API (GH-1362)
See PEP 539 for details.
Highlights of changes:
- Add Thread Specific Storage (TSS) API
- Document the Thread Local Storage (TLS) API as deprecated
- Update code that used TLS API to use TSS API
diff --git a/Doc/whatsnew/3.7.rst b/Doc/whatsnew/3.7.rst
index 3e8617e..ecdd2fe 100644
--- a/Doc/whatsnew/3.7.rst
+++ b/Doc/whatsnew/3.7.rst
@@ -127,6 +127,38 @@
PEP written and implemented by Barry Warsaw
+.. _whatsnew37-pep539:
+
+PEP 539: A New C-API for Thread-Local Storage in CPython
+--------------------------------------------------------
+
+While Python provides a C API for thread-local storage support; the existing
+:ref:`Thread Local Storage (TLS) API <thread-local-storage-api>` has used
+:c:type:`int` to represent TLS keys across all platforms. This has not
+generally been a problem for officially-support platforms, but that is neither
+POSIX-compliant, nor portable in any practical sense.
+
+:pep:`539` changes this by providing a new :ref:`Thread Specific Storage (TSS)
+API <thread-specific-storage-api>` to CPython which supersedes use of the
+existing TLS API within the CPython interpreter, while deprecating the existing
+API. The TSS API uses a new type :c:type:`Py_tss_t` instead of :c:type:`int`
+to represent TSS keys--an opaque type the definition of which may depend on
+the underlying TLS implementation. Therefore, this will allow to build CPython
+on platforms where the native TLS key is defined in a way that cannot be safely
+cast to :c:type:`int`.
+
+Note that on platforms where the native TLS key is defined in a way that cannot
+be safely cast to :c:type:`int`, all functions of the existing TLS API will be
+no-op and immediately return failure. This indicates clearly that the old API
+is not supported on platforms where it cannot be used reliably, and that no
+effort will be made to add such support.
+
+.. seealso::
+
+ :pep:`539` -- A New C-API for Thread-Local Storage in CPython
+ PEP written by Erik M. Bray; implementation by Masayuki Yamamoto.
+
+
Other Language Changes
======================