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include/asio/detail/win_event.hpp

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+//
+// detail/win_event.hpp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_DETAIL_WIN_EVENT_HPP
+#define ASIO_DETAIL_WIN_EVENT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_WINDOWS)
+
+#include <cstddef>
+#include "asio/detail/assert.hpp"
+#include "asio/detail/noncopyable.hpp"
+#include "asio/detail/socket_types.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+class win_event
+  : private noncopyable
+{
+public:
+  // Constructor.
+  ASIO_DECL win_event();
+
+  // Destructor.
+  ASIO_DECL ~win_event();
+
+  // Signal the event. (Retained for backward compatibility.)
+  template <typename Lock>
+  void signal(Lock& lock)
+  {
+    this->signal_all(lock);
+  }
+
+  // Signal all waiters.
+  template <typename Lock>
+  void signal_all(Lock& lock)
+  {
+    ASIO_ASSERT(lock.locked());
+    (void)lock;
+    state_ |= 1;
+    ::SetEvent(events_[0]);
+  }
+
+  // Unlock the mutex and signal one waiter.
+  template <typename Lock>
+  void unlock_and_signal_one(Lock& lock)
+  {
+    ASIO_ASSERT(lock.locked());
+    state_ |= 1;
+    bool have_waiters = (state_ > 1);
+    lock.unlock();
+    if (have_waiters)
+      ::SetEvent(events_[1]);
+  }
+
+  // Unlock the mutex and signal one waiter who may destroy us.
+  template <typename Lock>
+  void unlock_and_signal_one_for_destruction(Lock& lock)
+  {
+    ASIO_ASSERT(lock.locked());
+    state_ |= 1;
+    bool have_waiters = (state_ > 1);
+    if (have_waiters)
+      ::SetEvent(events_[1]);
+    lock.unlock();
+  }
+
+  // If there's a waiter, unlock the mutex and signal it.
+  template <typename Lock>
+  bool maybe_unlock_and_signal_one(Lock& lock)
+  {
+    ASIO_ASSERT(lock.locked());
+    state_ |= 1;
+    if (state_ > 1)
+    {
+      lock.unlock();
+      ::SetEvent(events_[1]);
+      return true;
+    }
+    return false;
+  }
+
+  // Reset the event.
+  template <typename Lock>
+  void clear(Lock& lock)
+  {
+    ASIO_ASSERT(lock.locked());
+    (void)lock;
+    ::ResetEvent(events_[0]);
+    state_ &= ~std::size_t(1);
+  }
+
+  // Wait for the event to become signalled.
+  template <typename Lock>
+  void wait(Lock& lock)
+  {
+    ASIO_ASSERT(lock.locked());
+    while ((state_ & 1) == 0)
+    {
+      state_ += 2;
+      lock.unlock();
+#if defined(ASIO_WINDOWS_APP)
+      ::WaitForMultipleObjectsEx(2, events_, false, INFINITE, false);
+#else // defined(ASIO_WINDOWS_APP)
+      ::WaitForMultipleObjects(2, events_, false, INFINITE);
+#endif // defined(ASIO_WINDOWS_APP)
+      lock.lock();
+      state_ -= 2;
+    }
+  }
+
+  // Timed wait for the event to become signalled.
+  template <typename Lock>
+  bool wait_for_usec(Lock& lock, long usec)
+  {
+    ASIO_ASSERT(lock.locked());
+    if ((state_ & 1) == 0)
+    {
+      state_ += 2;
+      lock.unlock();
+      DWORD msec = usec > 0 ? (usec < 1000 ? 1 : usec / 1000) : 0;
+#if defined(ASIO_WINDOWS_APP)
+      ::WaitForMultipleObjectsEx(2, events_, false, msec, false);
+#else // defined(ASIO_WINDOWS_APP)
+      ::WaitForMultipleObjects(2, events_, false, msec);
+#endif // defined(ASIO_WINDOWS_APP)
+      lock.lock();
+      state_ -= 2;
+    }
+    return (state_ & 1) != 0;
+  }
+
+private:
+  HANDLE events_[2];
+  std::size_t state_;
+};
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#if defined(ASIO_HEADER_ONLY)
+# include "asio/detail/impl/win_event.ipp"
+#endif // defined(ASIO_HEADER_ONLY)
+
+#endif // defined(ASIO_WINDOWS)
+
+#endif // ASIO_DETAIL_WIN_EVENT_HPP