1 files changed, 112 insertions, 0 deletions
diff --git a/contrib/llvm-project/libcxx/include/latch b/contrib/llvm-project/libcxx/include/latch
new file mode 100644
index 000000000000..10ae5721fbec
--- /dev/null
+++ b/contrib/llvm-project/libcxx/include/latch
@@ -0,0 +1,112 @@
+// -*- C++ -*-
+//===--------------------------- latch -----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_LATCH
+#define _LIBCPP_LATCH
+
+/*
+    latch synopsis
+
+namespace std
+{
+
+  class latch
+  {
+  public:
+    static constexpr ptrdiff_t max() noexcept;
+
+    constexpr explicit latch(ptrdiff_t __expected);
+    ~latch();
+
+    latch(const latch&) = delete;
+    latch& operator=(const latch&) = delete;
+
+    void count_down(ptrdiff_t __update = 1);
+    bool try_wait() const noexcept;
+    void wait() const;
+    void arrive_and_wait(ptrdiff_t __update = 1);
+
+  private:
+    ptrdiff_t __counter; // exposition only
+  };
+
+}
+
+*/
+
+#include <__availability>
+#include <__config>
+#include <atomic>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+#ifdef _LIBCPP_HAS_NO_THREADS
+# error <latch> is not supported on this single threaded system
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+#if _LIBCPP_STD_VER >= 14
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+class latch
+{
+    __atomic_base<ptrdiff_t> __a;
+
+public:
+    static constexpr ptrdiff_t max() noexcept {
+        return numeric_limits<ptrdiff_t>::max();
+    }
+
+    inline _LIBCPP_INLINE_VISIBILITY
+    constexpr explicit latch(ptrdiff_t __expected) : __a(__expected) { }
+
+    ~latch() = default;
+    latch(const latch&) = delete;
+    latch& operator=(const latch&) = delete;
+
+    inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    void count_down(ptrdiff_t __update = 1)
+    {
+        auto const __old = __a.fetch_sub(__update, memory_order_release);
+        if(__old == __update)
+            __a.notify_all();
+    }
+    inline _LIBCPP_INLINE_VISIBILITY
+    bool try_wait() const noexcept
+    {
+        return 0 == __a.load(memory_order_acquire);
+    }
+    inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    void wait() const
+    {
+        auto const __test_fn = [=]() -> bool {
+            return try_wait();
+        };
+        __cxx_atomic_wait(&__a.__a_, __test_fn);
+    }
+    inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
+    void arrive_and_wait(ptrdiff_t __update = 1)
+    {
+        count_down(__update);
+        wait();
+    }
+};
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER >= 14
+
+_LIBCPP_POP_MACROS
+
+#endif //_LIBCPP_LATCH