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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/107886] Problem witch std::latch,
 std::binary_semaphores in C++20
Date: Mon, 28 Nov 2022 16:29:57 +0000
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X-Bugzilla-Component: libstdc++
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X-Bugzilla-Who: redi at gcc dot gnu.org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107886

--- Comment #16 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Something like ...

--- include/bits/atomic_wait.h  2022-11-07 15:38:32.551751184 +0000
+++ /tmp/inc/bits/atomic_wait.h 2022-11-28 16:27:51.352489618 +0000
@@ -33,7 +33,7 @@
 #pragma GCC system_header

 #include <bits/c++config.h>
-#if defined _GLIBCXX_HAS_GTHREADS || defined _GLIBCXX_HAVE_LINUX_FUTEX
+#if defined _GLIBCXX_HAS_GTHREADS || defined _GLIBCXX_HAVE_LINUX_FUTEX ||
_WIN32
 #include <bits/functional_hash.h>
 #include <bits/gthr.h>
 #include <ext/numeric_traits.h>
@@ -59,6 +59,10 @@
 #define _GLIBCXX_HAVE_PLATFORM_WAIT 1
     using __platform_wait_t =3D int;
     inline constexpr size_t __platform_wait_alignment =3D 4;
+#elif _WIN32
+    using __platform_wait_t =3D __UINTPTR_TYPE__;
+    inline constexpr size_t __platform_wait_alignment
+      =3D alignof(__platform_wait_t);
 #else
 // define _GLIBCX_HAVE_PLATFORM_WAIT and implement __platform_wait()
 // and __platform_notify() if there is a more efficient primitive supported
@@ -122,6 +126,30 @@
                 static_cast<int>(__futex_wait_flags::__wake_private),
                 __all ? INT_MAX : 1);
       }
+#elif _WIN32
+    extern "C" int __glibcxx_get_last_error() __asm("GetLastError");
+
+    template<typename _Tp>
+      void
+      __platform_wait(const _Tp* __addr, __platform_wait_t __val) noexcept
+      {
+        const long __timeout =3D 0xffffffff;
+       if (WaitOnAddress(__addr, &__val, sizeof(__platform_wait_t),
__timeout))
+         return;
+        _GLIBCXX_THROW_OR_ABORT(std::system_error(__glibcxx_get_last_error=
(),
+                                                 std::system_category(),
+                                                 "WaitOnAddress"));
+      }
+
+    template<typename _Tp>
+      void
+      __platform_notify(const _Tp* __addr, bool __all) noexcept
+      {
+       if (__all)
+         WakeByAddressAll(__addr);
+       else
+         WakeByAddressOne(__addr);
+      }
 #endif

     inline void=