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[英]Boost ASIO UDP client async_receive_from calls handler even when there are no incoming messages
[英]boost asio udp socket async_receive_from does not call the handler
我想創建一個自治線程,專門用於使用boost庫(asio)從UDP套接字接收數據。 該線程應該是由UDP套接字接收的一些數據觸發的無限循環。 在我的應用程序中,我需要使用異步接收操作。
如果我使用同步函數receive_from,一切都按預期工作。
但是,如果我使用async_receive_from,則永遠不會調用處理程序。 由於我使用信號量來檢測是否已收到某些數據,因此程序會鎖定並且永遠不會觸發循環。
我已經驗證(使用網絡分析器)發送方設備正確地在UDP套接字上發送數據。
我已在以下代碼中隔離了該問題。
#include <boost\array.hpp>
#include <boost\asio.hpp>
#include <boost\thread.hpp>
#include <boost\interprocess\sync\interprocess_semaphore.hpp>
#include <iostream>
typedef boost::interprocess::interprocess_semaphore Semaphore;
using namespace boost::asio::ip;
class ReceiveUDP
{
public:
boost::thread* m_pThread;
boost::asio::io_service m_io_service;
udp::endpoint m_local_endpoint;
udp::endpoint m_sender_endpoint;
udp::socket m_socket;
size_t m_read_bytes;
Semaphore m_receive_semaphore;
ReceiveUDP() :
m_socket(m_io_service),
m_local_endpoint(boost::asio::ip::address::from_string("192.168.0.254"), 11),
m_sender_endpoint(boost::asio::ip::address::from_string("192.168.0.11"), 5550),
m_receive_semaphore(0)
{
Start();
}
void Start()
{
m_pThread = new boost::thread(&ReceiveUDP::_ThreadFunction, this);
}
void _HandleReceiveFrom(
const boost::system::error_code& error,
size_t received_bytes)
{
m_receive_semaphore.post();
m_read_bytes = received_bytes;
}
void _ThreadFunction()
{
try
{
boost::array<char, 100> recv_buf;
m_socket.open(udp::v4());
m_socket.bind(m_local_endpoint);
m_io_service.run();
while (1)
{
#if 1 // THIS WORKS
m_read_bytes = m_socket.receive_from(
boost::asio::buffer(recv_buf), m_sender_endpoint);
#else // THIS DOESN'T WORK
m_socket.async_receive_from(
boost::asio::buffer(recv_buf),
m_sender_endpoint,
boost::bind(&ReceiveUDP::_HandleReceiveFrom, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
/* The program locks on this wait since _HandleReceiveFrom
is never called. */
m_receive_semaphore.wait();
#endif
std::cout.write(recv_buf.data(), m_read_bytes);
}
m_socket.close();
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
}
};
void main()
{
ReceiveUDP receive_thread;
receive_thread.m_pThread->join();
}
信號量上的timed_wait是首選,但是出於調試目的,我使用了阻塞等待,如上面的代碼所示。
我錯過了什么? 我的錯誤在哪里?
您對io_service.run()
調用正在退出,因為io_service
沒有工作要做。 然后代碼進入while
循環並調用m_socket.async_receive_from
。 此時io_service
沒有運行,它從不讀取數據並調用您的處理程序。
你需要在調用io_service run之前安排工作:
即:
// Configure io service
ReceiveUDP receiver;
m_socket.open(udp::v4());
m_socket.bind(m_local_endpoint);
m_socket.async_receive_from(
boost::asio::buffer(recv_buf),
m_sender_endpoint,
boost::bind(&ReceiveUDP::_HandleReceiveFrom, receiver,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
處理函數將執行以下操作:
// start the io service
void HandleReceiveFrom(
const boost::system::error_code& error,
size_t received_bytes)
{
m_receive_semaphore.post();
// schedule the next asynchronous read
m_socket.async_receive_from(
boost::asio::buffer(recv_buf),
m_sender_endpoint,
boost::bind(&ReceiveUDP::_HandleReceiveFrom, receiver,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
m_read_bytes = received_bytes;
}
然后你的線程只是等待信號量:
while (1)
{
m_receive_semaphore.wait();
std::cout.write(recv_buf.data(), m_read_bytes);
}
筆記:
m_io_service.run()
立即返回,因此沒有人調度完成處理程序。 請注意, io_service::run
是基於asio的應用程序的一種“消息循環”,只要您希望asio功能可用,它就應該運行(這是一個簡單的描述,但它對您的情況來說已經足夠了) 。
此外,您不應該在循環中調用async.operation。 相反,在前一個完成處理程序中發出后續的async.operation - 以確保2個async.reads不會同時運行。
請參閱asio示例以查看典型的asio應用程序設計。
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