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include/asio/detail/completion_handler.hpp

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+//
+// detail/completion_handler.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_COMPLETION_HANDLER_HPP
+#define ASIO_DETAIL_COMPLETION_HANDLER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/fenced_block.hpp"
+#include "asio/detail/handler_alloc_helpers.hpp"
+#include "asio/detail/handler_work.hpp"
+#include "asio/detail/memory.hpp"
+#include "asio/detail/operation.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename Handler, typename IoExecutor>
+class completion_handler : public operation
+{
+public:
+  ASIO_DEFINE_HANDLER_PTR(completion_handler);
+
+  completion_handler(Handler& h, const IoExecutor& io_ex)
+    : operation(&completion_handler::do_complete),
+      handler_(static_cast<Handler&&>(h)),
+      work_(handler_, io_ex)
+  {
+  }
+
+  static void do_complete(void* owner, operation* base,
+      const asio::error_code& /*ec*/,
+      std::size_t /*bytes_transferred*/)
+  {
+    // Take ownership of the handler object.
+    completion_handler* h(static_cast<completion_handler*>(base));
+    ptr p = { asio::detail::addressof(h->handler_), h, h };
+
+    ASIO_HANDLER_COMPLETION((*h));
+
+    // Take ownership of the operation's outstanding work.
+    handler_work<Handler, IoExecutor> w(
+        static_cast<handler_work<Handler, IoExecutor>&&>(
+          h->work_));
+
+    // Make a copy of the handler so that the memory can be deallocated before
+    // the upcall is made. Even if we're not about to make an upcall, a
+    // sub-object of the handler may be the true owner of the memory associated
+    // with the handler. Consequently, a local copy of the handler is required
+    // to ensure that any owning sub-object remains valid until after we have
+    // deallocated the memory here.
+    Handler handler(static_cast<Handler&&>(h->handler_));
+    p.h = asio::detail::addressof(handler);
+    p.reset();
+
+    // Make the upcall if required.
+    if (owner)
+    {
+      fenced_block b(fenced_block::half);
+      ASIO_HANDLER_INVOCATION_BEGIN(());
+      w.complete(handler, handler);
+      ASIO_HANDLER_INVOCATION_END;
+    }
+  }
+
+private:
+  Handler handler_;
+  handler_work<Handler, IoExecutor> work_;
+};
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_DETAIL_COMPLETION_HANDLER_HPP