在qt中使用asio的io_service
参考：
在Qt程序中使用C++11线程std::thread处理耗时操作
Boost Asio, Multiple threads and multiple io_service
qt的事件循环和io_service的事件循环会冲突。
网上流传有三种做法：
- 弄一个Timer，定时执行io_service的poll或者poll_one。
这个方案我试过，结果是会出现成功发送但是没有成功接收到ACK，导致回调一直不执行。（祭奠我逝去的一下午）
- peper0的方案：https://github.com/peper0/qtasio
我编译没通过，提示很多头文件找不到。可能是因为代码太老了（最后一次commit在2014年）
- 将io_service丢到独立的一个线程跑。
大坑
如果把io_service放到另一个线程跑，在主线程中使用boost::asio::async_read等异步函数后，回调函数会在io_service所在的线程被调用。。。。。。这对qt来说是致命的。
下面的当笑话看就好了
io_service在共享对象时也是线程安全的，所以可以向其他线程提供IO服务。所以可以让io_service在一个独立的线程跑，然后主线程中的socket使用在其他线程跑的io_service即可。
这里使用std::thread
boost::asio::io_service io_service;
//do something with io_service
std::thread run_io_service([&] {
io_service.run();
});
run_io_service.detach();
注意io_service在没有任务要执行时会自动stop，所以要先使用io_service，再run。
其他坑点
- std::cout没输出。可能是被缓冲了。换成std::cerr或者qDebug()就好了。
- 线程创建后要detach，然后main函数返回时会自然销毁。如果没有detach会报错。
代码
#include <QApplication>
#include <QTimer>
#include <QDebug>
#include <iostream>
#include <thread>
#include <boost/asio.hpp>
#include <boost/asio/ssl.hpp>
#include <boost/bind.hpp>
typedef boost::asio::ssl::stream<boost::asio::ip::tcp::socket> ssl_socket;
enum { max_length = 1024 };
class client
{
public:
client(boost::asio::io_service& io_service,
boost::asio::ssl::context& context,
boost::asio::ip::tcp::resolver::iterator endpoint_iterator)
: socket_(io_service, context)
{
socket_.set_verify_mode(boost::asio::ssl::verify_peer);
socket_.set_verify_callback(
boost::bind(&client::verify_certificate, this, _1, _2));
boost::asio::async_connect(socket_.lowest_layer(), endpoint_iterator,
boost::bind(&client::handle_connect, this,
boost::asio::placeholders::error));
}
bool verify_certificate(bool preverified,
boost::asio::ssl::verify_context& ctx)
{
// The verify callback can be used to check whether the certificate that is
// being presented is valid for the peer. For example, RFC 2818 describes
// the steps involved in doing this for HTTPS. Consult the OpenSSL
// documentation for more details. Note that the callback is called once
// for each certificate in the certificate chain, starting from the root
// certificate authority.
// In this example we will simply print the certificate's subject name.
char subject_name[256];
X509* cert = X509_STORE_CTX_get_current_cert(ctx.native_handle());
X509_NAME_oneline(X509_get_subject_name(cert), subject_name, 256);
qDebug() << "Verifying " << subject_name;
return preverified;
}
void handle_connect(const boost::system::error_code& error)
{
if (!error)
{
socket_.async_handshake(boost::asio::ssl::stream_base::client,
boost::bind(&client::handle_handshake, this,
boost::asio::placeholders::error));
}
else
{
std::cout << "Connect failed: " << error.message() << "\n";
}
}
void handle_handshake(const boost::system::error_code& error)
{
if (!error)
{
size_t request_length = 4;
memcpy(request_, "test", request_length);
// std::cout << "Enter message: ";
// std::cin.getline(request_, max_length);
// size_t request_length = strlen(request_);
qDebug() << "Going to send";
boost::asio::async_write(socket_,
boost::asio::buffer(request_, request_length),
boost::bind(&client::handle_write, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
else
{
std::cout << "Handshake failed: " << error.message() << "\n";
}
}
void handle_write(const boost::system::error_code& error,
size_t bytes_transferred)
{
qDebug() << "handle_write";
if (!error)
{
qDebug() << "Going to read";
boost::asio::async_read(socket_,
boost::asio::buffer(reply_, bytes_transferred),
boost::bind(&client::handle_read, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
else
{
std::cout << "Write failed: " << error.message() << "\n";
}
}
void handle_read(const boost::system::error_code& error,
size_t bytes_transferred)
{
if (!error)
{
//std::cout not working
//qDebug() << "Reply: ";
std::cerr << "Reply: ";
reply_[bytes_transferred] = 0;
qDebug() << reply_;
}
else
{
std::cout << "Read failed: " << error.message() << "\n";
}
}
private:
boost::asio::ssl::stream<boost::asio::ip::tcp::socket> socket_;
char request_[max_length];
char reply_[max_length];
};
int main(int argc, char *argv[])
{
//QApplication a(argc, argv);
boost::asio::io_service io_service;
boost::asio::ip::tcp::resolver resolver(io_service);
boost::asio::ip::tcp::resolver::query query("127.0.0.1", "5188");
boost::asio::ip::tcp::resolver::iterator iterator = resolver.resolve(query);
boost::asio::ssl::context ctx(boost::asio::ssl::context::sslv23);
ctx.load_verify_file("ca.pem");
client c(io_service, ctx, iterator);
std::thread run_io_service([&io_service] {
//std::cerr << std::this_thread::get_id() << std::endl;
qDebug() << "io_service going to run";
io_service.run();
qDebug() << "io_service stopped";
});
std::cerr << run_io_service.native_handle() << std::endl;
run_io_service.detach();
//io_service.run();
// QTimer timer;
// QObject::connect(&timer, &QTimer::timeout, [&] {
// qDebug() << "poll";
// io_service.poll_one();
// //io_service.poll();
// });
// timer.start(100);
//return a.exec();
std::this_thread::sleep_for(std::chrono::seconds(2));
qDebug() << "End of main";
}
输出：
Starting /home/searchstar/git/small_projects/qt/learn/build-Learn_qt_and_asio-unknown-Debug/Learn_qt_and_asio...
139752728426240
io_service going to run
Verifying /C=CN/ST=Some-State/O=Internet Widgits Pty Ltd/CN=searchstar/emailAddress=632863986@qq.com
Verifying /C=CN/ST=Some-State/O=Internet Widgits Pty Ltd/CN=searchstar/emailAddress=632863986@qq.com
Going to send
handle_write
Going to read
Reply: test
io_service stopped
End of main
/home/searchstar/git/small_projects/qt/learn/build-Learn_qt_and_asio-unknown-Debug/Learn_qt_and_asio exited with code 0
注意到io_service在主线程退出main函数前就已经stop了，印证了官方文档里说的io_service在没有任务时会自动stop。
让io_service常驻
官方文档提供了让io_service常驻的方法。在
boost::asio::io_service io_service;
后加上
boost::asio::io_service::work work(io_service);
即可。
139633039558400
io_service going to run
Verifying /C=CN/ST=Some-State/O=Internet Widgits Pty Ltd/CN=searchstar/emailAddress=632863986@qq.com
Verifying /C=CN/ST=Some-State/O=Internet Widgits Pty Ltd/CN=searchstar/emailAddress=632863986@qq.com
Going to send
handle_write
Going to read
Reply: test
End of main
注意到没有io_service stopped的提示，说明从main里退出后直接杀死了io_service.run()所在的线程，非常粗暴。
手动让io_service.run()返回
官方文档用的auto_ptr
std::auto_ptr<boost::asio::io_service::work> work(
new boost::asio::io_service::work(io_service));
然后在想让io_service.run()返回时调用
work.reset();
即可。我是在main函数末尾调用的。
输出：
140249420756736
io_service going to run
Verifying /C=CN/ST=Some-State/O=Internet Widgits Pty Ltd/CN=searchstar/emailAddress=632863986@qq.com
Verifying /C=CN/ST=Some-State/O=Internet Widgits Pty Ltd/CN=searchstar/emailAddress=632863986@qq.com
Going to send
handle_write
Going to read
Reply: test
End of main
io_service stopped
如果在main函数末尾不加，按理说auto_ptr析构时也会自动把内部存的指针delete掉，跟手动reset的效果一样，但是实际上这里如果不手动reset，最后没有输出io_service stopped的提示。原因不明。
此外，由于std::auto_ptr已经被弃用了，所以可以用std::unique_ptr，结果是一样的。
