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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 @@ built-in ``breakpoint()``. 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 ====================== |