使用use_future的多播Boost Asio async_recieve_与async_send_to不能同时工作 [英] Boost Asio async_recieve_from multicast with use_future does not work simultaneously with async_send_to
问题描述
ITNOA
我想编写如下所示的可以同时发送和接收多播的程序
I want to write program that send and receive multicast simultaneously like below
int main()
{
const string group_address = "235.127.1.1";
constexpr uint16_t PORT_NUMBER = 8765;
boost::asio::io_context io_context;
auto work_guard = boost::asio::make_work_guard(io_context);
BoostMessageSender message_sender(group_address, "eth1", PORT_NUMBER, io_context);
BoostMessageReceiver message_receiver(group_address, "eth1", PORT_NUMBER, io_context);
std::thread t1([&io_context]()
{
cout << __LINE__ << endl;
io_context.run();
});
this_thread::sleep_for(1s);
std::array<char, 20> data = {};
auto result = std::async(std::launch::async, [&message_receiver, &data]()
{
message_receiver.receive(gw::buffer(data));
cout << " receive finished" << endl; // does not reach this line :(((
});
this_thread::sleep_for(1s);
message_sender.send("Any body there!");
result.wait(); // Raise exception what(): std::future_error: No associated state
cout << "receive message: ";
std::copy(std::begin(data),
std::end(data),
std::ostream_iterator<char>(std::cout, ""));
io_context.stop();
t1.join();
return 0;
}
我的问题是为什么result.wait()引发异常?
My problem is why result.wait() cause to raise exception?
可能重要的一点是,当我删除 message_sender.send
行时,该程序不会引发任何异常,并且 result.wait()
块行直到结束.但是当添加 message_sender.send
行时,此程序引发异常并且无法正常工作.
the maybe important note that is when I remove message_sender.send
line, this program does not raise any exception and line of result.wait()
block until end. but when line of message_sender.send
added, this program raise exception and does not work properly.
我的message_sender等于此代码.
My message_sender is equal to this code.
我的message_receiver如下所示
And my message_receiver is like below
BoostMessageReceiver::BoostMessageReceiver(const std::string& group_address, const std::string& interface_name, uint16_t port_number, ba::io_context& io_context)
: AbstractMessageReceiver(group_address, interface_name, port_number)
, io_context(io_context)
, listen_endpoint(ba::ip::address_v4::any(), port_number)
, socket(io_context)
{
socket.open(listen_endpoint.protocol());
socket.set_option(ba::ip::udp::socket::reuse_address(true));
socket.bind(listen_endpoint);
// Join to multicast group
socket.set_option(ba::ip::multicast::enable_loopback(true));
socket.set_option(ba::ip::multicast::join_group(ba::ip::address::from_string(group_address)));
}
std::pair<bool, std::size_t> BoostMessageReceiver::receive(const AbstractMessageReceiver::MutableBuffer& buffer) noexcept
{
ba::ip::udp::endpoint sender_endpoint;
std::future<std::size_t> result = socket.async_receive_from(ba::buffer(buffer.data(), buffer.size()), sender_endpoint, ba::use_future);
return std::make_pair(result.get() != 0, result.get());
}
我哪里错了?
我在以下平台上测试了这些代码
I test these code on below platforms
Visual Studio 2019 16.7.4
Windows 10 1909 latest update
Boost 1.73.0
Ubuntu 20.04.1 LTS
GCC 9.3.0
Boost 1.71.0
推荐答案
您将获得 no_state
,因为只能调用 future
上的 get
一次.
You are getting no_state
because get
on future
can be called only once.
下面
std::make_pair(result.get() != 0, result.get());
get
被调用两次.
请参见参考:
注意事项鼓励实现在以下情况下检测情况:调用前有效()为false并抛出一个std :: future_error并带有std :: future_errc :: no_state的错误状态.
Notes The implementations are encouraged to detect the case when valid() is false before the call and throw a std::future_error with an error condition of std::future_errc::no_state.
在第一次调用 get
后, valid
返回 false
.
After first call of get
, valid
returns false
.
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