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//
// prioritised_handlers.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2023 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)
//
#include <boost/asio.hpp>
#include <boost/function.hpp>
#include <iostream>
#include <queue>
using boost::asio::ip::tcp;
class handler_priority_queue : public boost::asio::execution_context
{
public:
void add(int priority, boost::function<void()> function)
{
handlers_.push(queued_handler(priority, function));
}
void execute_all()
{
while (!handlers_.empty())
{
queued_handler handler = handlers_.top();
handler.execute();
handlers_.pop();
}
}
class executor
{
public:
executor(handler_priority_queue& q, int p)
: context_(q), priority_(p)
{
}
handler_priority_queue& context() const
{
return context_;
}
template <typename Function, typename Allocator>
void dispatch(const Function& f, const Allocator&) const
{
context_.add(priority_, f);
}
template <typename Function, typename Allocator>
void post(const Function& f, const Allocator&) const
{
context_.add(priority_, f);
}
template <typename Function, typename Allocator>
void defer(const Function& f, const Allocator&) const
{
context_.add(priority_, f);
}
void on_work_started() const {}
void on_work_finished() const {}
bool operator==(const executor& other) const
{
return &context_ == &other.context_ && priority_ == other.priority_;
}
bool operator!=(const executor& other) const
{
return !operator==(other);
}
private:
handler_priority_queue& context_;
int priority_;
};
template <typename Handler>
boost::asio::executor_binder<Handler, executor>
wrap(int priority, Handler handler)
{
return boost::asio::bind_executor(executor(*this, priority), handler);
}
private:
class queued_handler
{
public:
queued_handler(int p, boost::function<void()> f)
: priority_(p), function_(f)
{
}
void execute()
{
function_();
}
friend bool operator<(const queued_handler& a,
const queued_handler& b)
{
return a.priority_ < b.priority_;
}
private:
int priority_;
boost::function<void()> function_;
};
std::priority_queue<queued_handler> handlers_;
};
//----------------------------------------------------------------------
void high_priority_handler(const boost::system::error_code& /*ec*/)
{
std::cout << "High priority handler\n";
}
void middle_priority_handler(const boost::system::error_code& /*ec*/)
{
std::cout << "Middle priority handler\n";
}
void low_priority_handler()
{
std::cout << "Low priority handler\n";
}
int main()
{
boost::asio::io_context io_context;
handler_priority_queue pri_queue;
// Post a completion handler to be run immediately.
boost::asio::post(io_context, pri_queue.wrap(0, low_priority_handler));
// Start an asynchronous accept that will complete immediately.
tcp::endpoint endpoint(boost::asio::ip::address_v4::loopback(), 0);
tcp::acceptor acceptor(io_context, endpoint);
tcp::socket server_socket(io_context);
acceptor.async_accept(server_socket,
pri_queue.wrap(100, high_priority_handler));
tcp::socket client_socket(io_context);
client_socket.connect(acceptor.local_endpoint());
// Set a deadline timer to expire immediately.
boost::asio::steady_timer timer(io_context);
timer.expires_at(boost::asio::steady_timer::time_point::min());
timer.async_wait(pri_queue.wrap(42, middle_priority_handler));
while (io_context.run_one())
{
// The custom invocation hook adds the handlers to the priority queue
// rather than executing them from within the poll_one() call.
while (io_context.poll_one())
;
pri_queue.execute_all();
}
return 0;
}
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