/usr/include/asio/handler_invoke_hook.hpp is in libasio-dev 1:1.10.6-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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// handler_invoke_hook.hpp
// ~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2015 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_HANDLER_INVOKE_HOOK_HPP
#define ASIO_HANDLER_INVOKE_HOOK_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/push_options.hpp"
namespace asio {
/** @defgroup asio_handler_invoke asio::asio_handler_invoke
*
* @brief Default invoke function for handlers.
*
* Completion handlers for asynchronous operations are invoked by the
* io_service associated with the corresponding object (e.g. a socket or
* deadline_timer). Certain guarantees are made on when the handler may be
* invoked, in particular that a handler can only be invoked from a thread that
* is currently calling @c run() on the corresponding io_service object.
* Handlers may subsequently be invoked through other objects (such as
* io_service::strand objects) that provide additional guarantees.
*
* When asynchronous operations are composed from other asynchronous
* operations, all intermediate handlers should be invoked using the same
* method as the final handler. This is required to ensure that user-defined
* objects are not accessed in a way that may violate the guarantees. This
* hooking function ensures that the invoked method used for the final handler
* is accessible at each intermediate step.
*
* Implement asio_handler_invoke for your own handlers to specify a custom
* invocation strategy.
*
* This default implementation invokes the function object like so:
* @code function(); @endcode
* If necessary, the default implementation makes a copy of the function object
* so that the non-const operator() can be used.
*
* @par Example
* @code
* class my_handler;
*
* template <typename Function>
* void asio_handler_invoke(Function function, my_handler* context)
* {
* context->strand_.dispatch(function);
* }
* @endcode
*/
/*@{*/
/// Default handler invocation hook used for non-const function objects.
template <typename Function>
inline void asio_handler_invoke(Function& function, ...)
{
function();
}
/// Default handler invocation hook used for const function objects.
template <typename Function>
inline void asio_handler_invoke(const Function& function, ...)
{
Function tmp(function);
tmp();
}
/*@}*/
} // namespace asio
#include "asio/detail/pop_options.hpp"
#endif // ASIO_HANDLER_INVOKE_HOOK_HPP
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