[libc++] Deprecate the C++20 synchronization library before C++20

libcxx/.clang-format

@@ -24,6 +24,7 @@ AttributeMacros: [
                   '_LIBCPP_CONSTEXPR_SINCE_CXX23',
                   '_LIBCPP_CONSTEXPR',
                   '_LIBCPP_CONSTINIT',
+                  '_LIBCPP_DEPRECATED_ATOMIC_SYNC',
                   '_LIBCPP_DEPRECATED_IN_CXX11',
                   '_LIBCPP_DEPRECATED_IN_CXX14',
                   '_LIBCPP_DEPRECATED_IN_CXX17',

libcxx/docs/ReleaseNotes/19.rst

@@ -55,6 +55,10 @@ Improvements and New Features
 Deprecations and Removals
 -------------------------
 
+- The C++20 synchronization library (``<barrier>``, ``<latch>``, ``atomic::wait``, etc.) has been deprecated
+  in language modes prior to C++20. If you are using these features prior to C++20, please update to ``-std=c++20``.
+  In LLVM 20, the C++20 synchronization library will be removed entirely in language modes prior to C++20.
+
 - TODO: The ``LIBCXX_ENABLE_ASSERTIONS`` CMake variable that was used to enable the safe mode has been deprecated and setting
   it triggers an error; use the ``LIBCXX_HARDENING_MODE`` CMake variable with the value ``extensive`` instead. Similarly,
   the ``_LIBCPP_ENABLE_ASSERTIONS`` macro has been deprecated (setting it to ``1`` still enables the extensive mode in

libcxx/include/__atomic/atomic.h

@@ -462,22 +462,26 @@ atomic_wait_explicit(const atomic<_Tp>* __o, typename atomic<_Tp>::value_type __
 // atomic_notify_one
 
 template <class _Tp>
-_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void atomic_notify_one(volatile atomic<_Tp>* __o) _NOEXCEPT {
+_LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
+atomic_notify_one(volatile atomic<_Tp>* __o) _NOEXCEPT {
   __o->notify_one();
 }
 template <class _Tp>
-_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void atomic_notify_one(atomic<_Tp>* __o) _NOEXCEPT {
+_LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
+atomic_notify_one(atomic<_Tp>* __o) _NOEXCEPT {
   __o->notify_one();
 }
 
 // atomic_notify_all
 
 template <class _Tp>
-_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void atomic_notify_all(volatile atomic<_Tp>* __o) _NOEXCEPT {
+_LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
+atomic_notify_all(volatile atomic<_Tp>* __o) _NOEXCEPT {
   __o->notify_all();
 }
 template <class _Tp>
-_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void atomic_notify_all(atomic<_Tp>* __o) _NOEXCEPT {
+_LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
+atomic_notify_all(atomic<_Tp>* __o) _NOEXCEPT {
   __o->notify_all();
 }
 

libcxx/include/__atomic/atomic_flag.h

@@ -49,22 +49,26 @@ struct atomic_flag {
     __cxx_atomic_store(&__a_, _LIBCPP_ATOMIC_FLAG_TYPE(false), __m);
   }
 
-  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait(bool __v, memory_order __m = memory_order_seq_cst) const
-      volatile _NOEXCEPT {
+  _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
+  wait(bool __v, memory_order __m = memory_order_seq_cst) const volatile _NOEXCEPT {
     std::__atomic_wait(*this, _LIBCPP_ATOMIC_FLAG_TYPE(__v), __m);
   }
-  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
+  _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
   wait(bool __v, memory_order __m = memory_order_seq_cst) const _NOEXCEPT {
     std::__atomic_wait(*this, _LIBCPP_ATOMIC_FLAG_TYPE(__v), __m);
   }
-  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() volatile _NOEXCEPT {
+  _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() volatile _NOEXCEPT {
+    std::__atomic_notify_one(*this);
+  }
+  _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() _NOEXCEPT {
     std::__atomic_notify_one(*this);
   }
-  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_one() _NOEXCEPT { std::__atomic_notify_one(*this); }
   _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() volatile _NOEXCEPT {
     std::__atomic_notify_all(*this);
   }
-  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() _NOEXCEPT { std::__atomic_notify_all(*this); }
+  _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void notify_all() _NOEXCEPT {
+    std::__atomic_notify_all(*this);
+  }
 
 #if _LIBCPP_STD_VER >= 20
   _LIBCPP_HIDE_FROM_ABI constexpr atomic_flag() _NOEXCEPT : __a_(false) {}
@@ -141,41 +145,43 @@ inline _LIBCPP_HIDE_FROM_ABI void atomic_flag_clear_explicit(atomic_flag* __o, m
   __o->clear(__m);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
+inline _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
 atomic_flag_wait(const volatile atomic_flag* __o, bool __v) _NOEXCEPT {
   __o->wait(__v);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
+inline _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
 atomic_flag_wait(const atomic_flag* __o, bool __v) _NOEXCEPT {
   __o->wait(__v);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
+inline _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
 atomic_flag_wait_explicit(const volatile atomic_flag* __o, bool __v, memory_order __m) _NOEXCEPT {
   __o->wait(__v, __m);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
+inline _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
 atomic_flag_wait_explicit(const atomic_flag* __o, bool __v, memory_order __m) _NOEXCEPT {
   __o->wait(__v, __m);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
+inline _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
 atomic_flag_notify_one(volatile atomic_flag* __o) _NOEXCEPT {
   __o->notify_one();
 }
 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void atomic_flag_notify_one(atomic_flag* __o) _NOEXCEPT {
+inline _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
+atomic_flag_notify_one(atomic_flag* __o) _NOEXCEPT {
   __o->notify_one();
 }
 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
+inline _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
 atomic_flag_notify_all(volatile atomic_flag* __o) _NOEXCEPT {
   __o->notify_all();
 }
 
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void atomic_flag_notify_all(atomic_flag* __o) _NOEXCEPT {
+inline _LIBCPP_DEPRECATED_ATOMIC_SYNC _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_SYNC void
+atomic_flag_notify_all(atomic_flag* __o) _NOEXCEPT {
   __o->notify_all();
 }
 

libcxx/include/__config

@@ -954,6 +954,14 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_DEPRECATED_(m)
 #  endif
 
+#  if _LIBCPP_STD_VER < 20
+#    define _LIBCPP_DEPRECATED_ATOMIC_SYNC                                                                             \
+      _LIBCPP_DEPRECATED_("The C++20 synchronization library has been deprecated prior to C++20. Please update to "    \
+                          "using -std=c++20 if you need to use these facilities.")
+#  else
+#    define _LIBCPP_DEPRECATED_ATOMIC_SYNC /* nothing */
+#  endif
+
 #  if !defined(_LIBCPP_CXX03_LANG)
 #    define _LIBCPP_DEPRECATED_IN_CXX11 _LIBCPP_DEPRECATED
 #  else

libcxx/include/barrier

@@ -257,7 +257,7 @@ public:
 #  endif // !_LIBCPP_HAS_NO_TREE_BARRIER
 
 template <class _CompletionF = __empty_completion>
-class barrier {
+class _LIBCPP_DEPRECATED_ATOMIC_SYNC barrier {
   __barrier_base<_CompletionF> __b_;
 
 public:

libcxx/include/latch

@@ -66,7 +66,7 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-class latch {
+class _LIBCPP_DEPRECATED_ATOMIC_SYNC latch {
   __atomic_base<ptrdiff_t> __a_;
 
 public:

libcxx/include/semaphore

@@ -127,7 +127,7 @@ private:
 };
 
 template <ptrdiff_t __least_max_value = _LIBCPP_SEMAPHORE_MAX>
-class counting_semaphore {
+class _LIBCPP_DEPRECATED_ATOMIC_SYNC counting_semaphore {
   __atomic_semaphore_base __semaphore_;
 
 public:
@@ -172,7 +172,9 @@ public:
   }
 };
 
-using binary_semaphore = counting_semaphore<1>;
+_LIBCPP_SUPPRESS_DEPRECATED_PUSH
+using binary_semaphore _LIBCPP_DEPRECATED_ATOMIC_SYNC = counting_semaphore<1>;
+_LIBCPP_SUPPRESS_DEPRECATED_POP
 
 _LIBCPP_END_NAMESPACE_STD
 

libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_all.pass.cpp

@@ -7,9 +7,12 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: no-threads
-// XFAIL: c++03
+// UNSUPPORTED: c++03
 // XFAIL: !has-1024-bit-atomics
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <atomic>

libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_one.pass.cpp

@@ -7,9 +7,12 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: no-threads
-// XFAIL: c++03
+// UNSUPPORTED: c++03
 // XFAIL: !has-1024-bit-atomics
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <atomic>

libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_wait.pass.cpp

@@ -7,9 +7,12 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: no-threads
-// XFAIL: c++03
+// UNSUPPORTED: c++03
 // XFAIL: !has-1024-bit-atomics
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <atomic>

libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_wait_explicit.pass.cpp

@@ -7,9 +7,12 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: no-threads
-// XFAIL: c++03
+// UNSUPPORTED: c++03
 // XFAIL: !has-1024-bit-atomics
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <atomic>

libcxx/test/std/thread/thread.barrier/arrive.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <barrier>

libcxx/test/std/thread/thread.barrier/arrive_and_drop.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <barrier>

libcxx/test/std/thread/thread.barrier/arrive_and_wait.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <barrier>

libcxx/test/std/thread/thread.barrier/completion.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <barrier>

libcxx/test/std/thread/thread.barrier/ctor.compile.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // <barrier>
 
 // explicit barrier(ptrdiff_t __count, _CompletionF __completion = _CompletionF());

libcxx/test/std/thread/thread.barrier/max.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // <barrier>
 
 #include <barrier>

libcxx/test/std/thread/thread.latch/arrive_and_wait.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <latch>

libcxx/test/std/thread/thread.latch/count_down.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <latch>

libcxx/test/std/thread/thread.latch/ctor.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // <latch>
 
 // inline constexpr explicit latch(ptrdiff_t __expected);

libcxx/test/std/thread/thread.latch/max.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // <latch>
 
 #include <latch>

libcxx/test/std/thread/thread.latch/try_wait.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <latch>

libcxx/test/std/thread/thread.semaphore/acquire.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <semaphore>

libcxx/test/std/thread/thread.semaphore/binary.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // XFAIL: availability-synchronization_library-missing
 
 // <semaphore>

libcxx/test/std/thread/thread.semaphore/ctor.compile.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // <semaphore>
 
 // constexpr explicit counting_semaphore(ptrdiff_t desired);

libcxx/test/std/thread/thread.semaphore/max.pass.cpp

@@ -9,6 +9,9 @@
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11
 
+// Until we drop support for the synchronization library in C++11/14/17
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // <semaphore>
 
 #include <semaphore>