https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116843
Bug ID: 116843
Summary: Native platform wait on Windows
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
Target: *-w64-mingw32
Copied from Bug 107886 comment 15 and Bug 107886 comment 16:
we might be able to support some subset of C++20 concurrency primitives for the
Win32 model. As https://github.com/luncliff/latch/blob/master/latch_windows.cpp
shows all that's needed are atomic decrements and
WaitOnAddress/WakeByAddressAll.
If our std::__atomic_wait_address and __atomic_impl::notify_all used those, we
could provide std::latch, and maybe others.
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 = int;
inline constexpr size_t __platform_wait_alignment = 4;
+#elif _WIN32
+ using __platform_wait_t = __UINTPTR_TYPE__;
+ inline constexpr size_t __platform_wait_alignment
+ = 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 = 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
