commit af2d2a8b6f0b97a53a897a9848fa19c41f2b422d
author Louis Dionne <ldionne.2@gmail.com> Wed Nov 17 10:59:31 2021 -0500
committer Copybara-Service <copybara-worker@google.com> Wed Nov 17 20:06:56 2021 -0800
tree 91db782cf133d6b4dc63576a75b9e16bf97a3a18
parent de6134228d55db998689e0b3717dd3f3a4a54f87

[libc++] Enable <atomic> when threads are disabled

std::atomic is, for the most part, just a thin veneer on top of compiler
builtins. Hence, it should be available even when threads are not available
on the system, and in fact there has been requests for such support.

This patch:
- Moves __libcpp_thread_poll_with_backoff to its own header so it can
  be used in <atomic> when threads are disabled.
- Adds a dummy backoff policy for atomic polling that doesn't know about
  threads.
- Adjusts the <atomic> feature-test macros so they are provided even when
  threads are disabled.
- Runs the <atomic> tests when threads are disabled.

rdar://77873569

Differential Revision: https://reviews.llvm.org/D114109

NOKEYCHECK=True
GitOrigin-RevId: 92832e4889ae6038cc8b3e6e449af2a9b9374ab4

include/version

diff --git a/include/version b/include/version
index a4809eb..d2286f5 100644
--- a/include/version
+++ b/include/version
@@ -205,9 +205,7 @@
 # define __cpp_lib_apply                                201603L
 # define __cpp_lib_array_constexpr                      201603L
 # define __cpp_lib_as_const                             201510L
-# if !defined(_LIBCPP_HAS_NO_THREADS)
-#   define __cpp_lib_atomic_is_always_lock_free         201603L
-# endif
+# define __cpp_lib_atomic_is_always_lock_free           201603L
 # define __cpp_lib_bool_constant                        201505L
 // # define __cpp_lib_boyer_moore_searcher                 201603L
 # define __cpp_lib_byte                                 201603L
@@ -261,25 +259,13 @@
 # undef  __cpp_lib_array_constexpr
 # define __cpp_lib_array_constexpr                      201811L
 // # define __cpp_lib_assume_aligned                       201811L
-# if !defined(_LIBCPP_HAS_NO_THREADS)
-#   define __cpp_lib_atomic_flag_test                   201907L
-# endif
-# if !defined(_LIBCPP_HAS_NO_THREADS)
-// #   define __cpp_lib_atomic_float                       201711L
-# endif
-# if !defined(_LIBCPP_HAS_NO_THREADS)
-#   define __cpp_lib_atomic_lock_free_type_aliases      201907L
-# endif
-# if !defined(_LIBCPP_HAS_NO_THREADS)
-// #   define __cpp_lib_atomic_ref                         201806L
-# endif
-# if !defined(_LIBCPP_HAS_NO_THREADS)
-// #   define __cpp_lib_atomic_shared_ptr                  201711L
-# endif
-# if !defined(_LIBCPP_HAS_NO_THREADS)
-#   define __cpp_lib_atomic_value_initialization        201911L
-# endif
-# if !defined(_LIBCPP_HAS_NO_THREADS) && !defined(_LIBCPP_AVAILABILITY_DISABLE_FTM___cpp_lib_atomic_wait)
+# define __cpp_lib_atomic_flag_test                     201907L
+// # define __cpp_lib_atomic_float                         201711L
+# define __cpp_lib_atomic_lock_free_type_aliases        201907L
+// # define __cpp_lib_atomic_ref                           201806L
+// # define __cpp_lib_atomic_shared_ptr                    201711L
+# define __cpp_lib_atomic_value_initialization          201911L
+# if !defined(_LIBCPP_AVAILABILITY_DISABLE_FTM___cpp_lib_atomic_wait)
 #   define __cpp_lib_atomic_wait                        201907L
 # endif
 # if !defined(_LIBCPP_HAS_NO_THREADS) && !defined(_LIBCPP_AVAILABILITY_DISABLE_FTM___cpp_lib_barrier)