1 #include <boost/asio/associated_executor.hpp>
2 #include <boost/asio/bind_executor.hpp>
3 #include <boost/asio/execution.hpp>
4 #include <boost/asio/static_thread_pool.hpp>
5 #include <iostream>
6 #include <string>
7
8 using boost::asio::bind_executor;
9 using boost::asio::get_associated_executor;
10 using boost::asio::static_thread_pool;
11 namespace execution = boost::asio::execution;
12
13 // A function to asynchronously read a single line from an input stream.
14 template <class IoExecutor, class Handler>
async_getline(IoExecutor io_ex,std::istream & is,Handler handler)15 void async_getline(IoExecutor io_ex, std::istream& is, Handler handler)
16 {
17 // Track work for the handler's associated executor.
18 auto work_ex = boost::asio::prefer(
19 get_associated_executor(handler, io_ex),
20 execution::outstanding_work.tracked);
21
22 // Post a function object to do the work asynchronously.
23 execution::execute(
24 boost::asio::require(io_ex, execution::blocking.never),
25 [&is, work_ex, handler=std::move(handler)]() mutable
26 {
27 std::string line;
28 std::getline(is, line);
29
30 // Pass the result to the handler, via the associated executor.
31 execution::execute(
32 boost::asio::prefer(work_ex, execution::blocking.possibly),
33 [line=std::move(line), handler=std::move(handler)]() mutable
34 {
35 handler(std::move(line));
36 });
37 });
38 }
39
40 // A function to asynchronously read multiple lines from an input stream.
41 template <class IoExecutor, class Handler>
async_getlines(IoExecutor io_ex,std::istream & is,std::string init,Handler handler)42 void async_getlines(IoExecutor io_ex, std::istream& is, std::string init, Handler handler)
43 {
44 // Track work for the I/O executor.
45 auto io_work_ex = boost::asio::prefer(io_ex,
46 execution::outstanding_work.tracked);
47
48 // Track work for the handler's associated executor.
49 auto handler_work_ex = boost::asio::prefer(
50 get_associated_executor(handler, io_ex),
51 execution::outstanding_work.tracked);
52
53 // Use the associated executor for each operation in the composition.
54 async_getline(io_work_ex, is,
55 bind_executor(handler_work_ex,
56 [io_work_ex, &is, lines=std::move(init), handler=std::move(handler)]
57 (std::string line) mutable
58 {
59 if (line.empty())
60 handler(lines);
61 else
62 async_getlines(io_work_ex, is, lines + line + "\n", std::move(handler));
63 }));
64 }
65
main()66 int main()
67 {
68 static_thread_pool io_pool(1);
69 static_thread_pool completion_pool(1);
70
71 std::cout << "Enter text, terminating with a blank line:\n";
72
73 async_getlines(io_pool.executor(), std::cin, "",
74 bind_executor(completion_pool.executor(), [](std::string lines)
75 {
76 std::cout << "Lines:\n" << lines << "\n";
77 }));
78
79 io_pool.wait();
80 completion_pool.wait();
81 }
82