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//
// prioritised_handlers.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2019 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 <iostream>
#include <memory>
#include <queue>
using boost::asio::ip::tcp;
class handler_priority_queue : public boost::asio::execution_context
{
public:
template <typename Function>
void add(int priority, Function function)
{
std::unique_ptr<queued_handler_base> handler(
new queued_handler<Function>(
priority, std::move(function)));
handlers_.push(std::move(handler));
}
void execute_all()
{
while (!handlers_.empty())
{
handlers_.top()->execute();
handlers_.pop();
}
}
class executor
{
public:
executor(handler_priority_queue& q, int p)
: context_(q), priority_(p)
{
}
handler_priority_queue& context() const noexcept
{
return context_;
}
template <typename Function, typename Allocator>
void dispatch(Function f, const Allocator&) const
{
context_.add(priority_, std::move(f));
}
template <typename Function, typename Allocator>
void post(Function f, const Allocator&) const
{
context_.add(priority_, std::move(f));
}
template <typename Function, typename Allocator>
void defer(Function f, const Allocator&) const
{
context_.add(priority_, std::move(f));
}
void on_work_started() const noexcept {}
void on_work_finished() const noexcept {}
bool operator==(const executor& other) const noexcept
{
return &context_ == &other.context_ && priority_ == other.priority_;
}
bool operator!=(const executor& other) const noexcept
{
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), std::move(handler));
}
private:
class queued_handler_base
{
public:
queued_handler_base(int p)
: priority_(p)
{
}
virtual ~queued_handler_base()
{
}
virtual void execute() = 0;
friend bool operator<(const std::unique_ptr<queued_handler_base>& a,
const std::unique_ptr<queued_handler_base>& b) noexcept
{
return a->priority_ < b->priority_;
}
private:
int priority_;
};
template <typename Function>
class queued_handler : public queued_handler_base
{
public:
queued_handler(int p, Function f)
: queued_handler_base(p), function_(std::move(f))
{
}
void execute() override
{
function_();
}
private:
Function function_;
};
std::priority_queue<std::unique_ptr<queued_handler_base>> handlers_;
};
//----------------------------------------------------------------------
void high_priority_handler(const boost::system::error_code& /*ec*/,
tcp::socket /*socket*/)
{
std::cout << "High priority handler\n";
}
void middle_priority_handler(const boost::system::error_code& /*ec*/)
{
std::cout << "Middle priority handler\n";
}
struct low_priority_handler
{
// Make the handler a move-only type.
low_priority_handler() = default;
low_priority_handler(const low_priority_handler&) = delete;
low_priority_handler(low_priority_handler&&) = default;
void operator()()
{
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(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::clock_type::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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