1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
|
//
// deferred_6.cpp
// ~~~~~~~~~~~~~~
//
// 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)
//
#include <boost/asio.hpp>
#include <iostream>
using boost::asio::append;
using boost::asio::deferred;
template <typename CompletionToken>
auto async_wait_twice(boost::asio::steady_timer& timer, CompletionToken&& token)
{
return deferred.values(&timer)(
deferred(
[](boost::asio::steady_timer* timer)
{
timer->expires_after(std::chrono::seconds(1));
return timer->async_wait(append(deferred, timer));
}
)
)(
deferred(
[](boost::system::error_code ec, boost::asio::steady_timer* timer)
{
std::cout << "first timer wait finished: " << ec.message() << "\n";
timer->expires_after(std::chrono::seconds(1));
return deferred.when(!ec)
.then(timer->async_wait(deferred))
.otherwise(deferred.values(ec));
}
)
)(
deferred(
[](boost::system::error_code ec)
{
std::cout << "second timer wait finished: " << ec.message() << "\n";
return deferred.when(!ec)
.then(deferred.values(42))
.otherwise(deferred.values(0));
}
)
)(
std::forward<CompletionToken>(token)
);
}
int main()
{
boost::asio::io_context ctx;
boost::asio::steady_timer timer(ctx);
timer.expires_after(std::chrono::seconds(1));
async_wait_twice(
timer,
[](int result)
{
std::cout << "result is " << result << "\n";
}
);
// Uncomment the following line to trigger an error in async_wait_twice.
//timer.cancel();
ctx.run();
return 0;
}
|
