使用 UDP 打破 while() 循环

Question

是否可以在 while() 循环中做一些工作，例如增加计数器，然后用 UDP 消息打破这个 while() 循环？

我有一个 Raspberry Pi 4，它被设置为 UDP 服务器。我使用的编程语言是 C++。 UDP.hpp:

#pragma once

#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <string>
#include <iostream>
#include <cstring>
#include <sys/types.h>
#include <netdb.h>

using namespace std;

/////GLOBAL CONSTANTS/////
const int c_PORT = 8080;

class UDP
{
private:
    int fdSocketUDP_;                  //File descriptor for UDP socket
    int ClientAddressLength_;          //Length of client address
    struct sockaddr_in ServerAddress_; //Struct handling internet address for server
    struct sockaddr_in ClientAddress_; //Struct handling internet address for client

public:
    UDP();                              //Initialize and bind socket
    ~UDP();                             //Close socket
    string readUDP(const int readSize); //Read via UDP protocol (Only for blocking socket)
    void writeUDP(string message);      //Write via UDP protocol (Only for blocking socket)
};

UDP.cpp:

#include "udp.hpp"

UDP::UDP()
{
    if ((fdSocketUDP_ = socket(AF_INET, SOCK_DGRAM, 0)) < 0) //Create UDP socket
    {
        perror("Error - socket creation - udp.cpp");
        exit(EXIT_FAILURE);
    }
    memset(&ServerAddress_, 0, sizeof(ServerAddress_)); //Sets ServerAddress_ to 0
    memset(&ClientAddress_, 0, sizeof(ClientAddress_)); //Sets ClientAddress_ to 0

    ServerAddress_.sin_family = AF_INET;         //Address family, must be AF_INET = IPv4
    ServerAddress_.sin_port = htons(c_PORT);     //PORT number, convert PORT number to network byte order using htons()
    ServerAddress_.sin_addr.s_addr = INADDR_ANY; //IP-Address of host (server IP), INADDR_ANY gets this IP Address

    if (bind(fdSocketUDP_, (const struct sockaddr *)&ServerAddress_, sizeof(ServerAddress_)) < 0) //Bind the socket to ServerAddress_
    {
        perror("Error - socket bind - udp.cpp");
        exit(EXIT_FAILURE);
    }
}

UDP::~UDP()
{
    close(fdSocketUDP_); //Close socket
}                    

string UDP::readUDP(const int readSize)
{
    char readMsg[readSize] = {0}; //Read buffer
    ClientAddressLength_ = sizeof(ClientAddress_);

    if ((recvfrom(fdSocketUDP_, readMsg, readSize, 0, (struct sockaddr *)&ClientAddress_, (socklen_t *)&ClientAddressLength_)) < 0) //Receive data via UDP protocol
    {
        perror("Error - recvfrom - udp.cpp");
        exit(EXIT_FAILURE);
    }

    string str(readMsg);           //Convert char array to string
    str = str.substr(0, readSize); //Make sure the string is the length of readsize
    return str;
}

void UDP::writeUDP(string message)
{
    //Make char array 
    int writeSize = message.size();
    char writeMsg[writeSize + 1] = {'[=11=]'};

    //Convert string message to char array
    for (int i = 0; i < writeSize; i++)
    {
        writeMsg[i] = message[i];
    }

    if ((sendto(fdSocketUDP_, writeMsg, writeSize, 0, (const struct sockaddr *)&ClientAddress_, (socklen_t)ClientAddressLength_)) < 0) //Send data via UDP protocol
    {
        perror("Error - sendto - udp.cpp");
        exit(EXIT_FAILURE);
    }
}

我有一台笔记本电脑，运行一个 Labview 程序。它充当 UDP 客户端。通过从笔记本电脑向 RPi 发送数据，我希望能够通过 UDP 发送特定数据来打破 main() 函数中的 while 循环。

假设我从笔记本电脑向树莓派发送“111”数据。然后 RPi 进入 main() 函数中的 while() 循环，做一些工作。我希望 RPi 保持在这个 while() 循环中，直到我从笔记本电脑发送一些特定数据。假设我要打破这个 while()-loop 的数据是“999”。

这可以使用 UDP 吗？

Answer 1

当然可以。只需将套接字设置为非阻塞，并定期检查套接字上是否收到数据。如果有，请检查它是否是停止命令，如果是，则停止。您可以检查循环的每次迭代，或者，如果循环重复得非常快，则每 10 次或每 100 次迭代检查一次。

Answer 2

感谢@Marquis of Lorne 和@David Schwartz，我已经解决了我的问题。解决方案是使用 fcntl 并将套接字设置为非阻塞。

我已将 UDP.hpp 更新为：

#pragma once

#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <string>
#include <iostream>
#include <cstring>
#include <sys/types.h>
#include <netdb.h>
#include <sys/unistd.h>
#include <sys/fcntl.h>

using namespace std;

/////GLOBAL CONSTANTS/////
const int c_PORT = 8080;

class UDP
{
private:
    int fdSocketUDP_;                  //File descriptor for UDP socket
    int ClientAddressLength_;          //Length of client address
    struct sockaddr_in ServerAddress_; //Struct handling internet address for server
    struct sockaddr_in ClientAddress_; //Struct handling internet address for client

public:
    UDP();                              //Initialize and bind socket
    ~UDP();                             //Close socket
    void initNonBlock();                     //Initialize and bind socket (non blocking)
    void initBlock();                        //Initialize and bind socket (blocking)
    void closeSocket();                            //Close socket
    string readNonBlock(const int readSize);                     //read via UDP protocol with non blocking socket
    string readUDP(const int readSize); //Read via UDP protocol (Only for blocking socket)
    void writeUDP(string message);      //Write via UDP protocol (Only for blocking socket)
};

我已将 UDP.cpp 更新为：

#include "udp.hpp"

UDP::UDP()
{
}

UDP::~UDP()
{
    closeSocket();
}

void UDP::initNonBlock()
{
    if ((fdSocketUDP_ = socket(AF_INET, SOCK_DGRAM, 0)) < 0) //Create UDP socket
    {
        perror("Error - socket creation - udp.cpp");
        exit(EXIT_FAILURE);
    }
    fcntl(fdSocketUDP_, F_SETFL, O_NONBLOCK); //Set to non-blocking mode 

    memset(&ServerAddress_, 0, sizeof(ServerAddress_)); //Sets ServerAddress_ to 0
    memset(&ClientAddress_, 0, sizeof(ClientAddress_)); //Sets ClientAddress_ to 0

    ServerAddress_.sin_family = AF_INET;         //Address family, must be AF_INET = IPv4
    ServerAddress_.sin_port = htons(c_PORT);     //PORT number, convert PORT number to network byte order using htons()
    ServerAddress_.sin_addr.s_addr = INADDR_ANY; //IP-Address of host (server IP), INADDR_ANY gets this IP Address

    if (bind(fdSocketUDP_, (const struct sockaddr *)&ServerAddress_, sizeof(ServerAddress_)) < 0) //Bind the socket to ServerAddress_
    {
        perror("Error - socket bind - udp.cpp");
        exit(EXIT_FAILURE);
    }
}

void UDP::initBlock()
{
    if ((fdSocketUDP_ = socket(AF_INET, SOCK_DGRAM, 0)) < 0) //Create UDP socket
    {
        perror("Error - socket creation - udp.cpp");
        exit(EXIT_FAILURE);
    }

    memset(&ServerAddress_, 0, sizeof(ServerAddress_)); //Sets ServerAddress_ to 0
    memset(&ClientAddress_, 0, sizeof(ClientAddress_)); //Sets ClientAddress_ to 0

    ServerAddress_.sin_family = AF_INET;         //Address family, must be AF_INET = IPv4
    ServerAddress_.sin_port = htons(c_PORT);     //PORT number, convert PORT number to network byte order using htons()
    ServerAddress_.sin_addr.s_addr = INADDR_ANY; //IP-Address of host (server IP), INADDR_ANY gets this IP Address

    if (bind(fdSocketUDP_, (const struct sockaddr *)&ServerAddress_, sizeof(ServerAddress_)) < 0) //Bind the socket to ServerAddress_
    {
        perror("Error - socket bind - udp.cpp");
        exit(EXIT_FAILURE);
    }
}

void UDP::closeSocket()
{
    close(fdSocketUDP_); //Close socket
}

string UDP::readNonBlock(const int readSize)
{
    char readMsg[readSize] = {0}; //Read buffer
    ClientAddressLength_ = sizeof(ClientAddress_);

    recvfrom(fdSocketUDP_, readMsg, readSize, 0, (struct sockaddr *)&ClientAddress_, (socklen_t *)&ClientAddressLength_);

    string str(readMsg);           //Convert char array to string
    str = str.substr(0, readSize); //Make sure the string is the length of readsize
    return str;

}                    

string UDP::readUDP(const int readSize)
{
    char readMsg[readSize] = {0}; //Read buffer
    ClientAddressLength_ = sizeof(ClientAddress_);

    if ((recvfrom(fdSocketUDP_, readMsg, readSize, 0, (struct sockaddr *)&ClientAddress_, (socklen_t *)&ClientAddressLength_)) < 0) //Receive data via UDP protocol
    {
        perror("Error - recvfrom - udp.cpp");
        exit(EXIT_FAILURE);
    }

    string str(readMsg);           //Convert char array to string
    str = str.substr(0, readSize); //Make sure the string is the length of readsize
    return str;
}

void UDP::writeUDP(string message)
{
    //Make char array 
    int writeSize = message.size();
    char writeMsg[writeSize + 1] = {'[=11=]'};

    //Convert string message to char array
    for (int i = 0; i < writeSize; i++)
    {
        writeMsg[i] = message[i];
    }

    if ((sendto(fdSocketUDP_, writeMsg, writeSize, 0, (const struct sockaddr *)&ClientAddress_, (socklen_t)ClientAddressLength_)) < 0) //Send data via UDP protocol
    {
        perror("Error - sendto - udp.cpp");
        exit(EXIT_FAILURE);
    }
}

多亏了这个，我才能够打破 do-while 循环：

udp.closeSocket();
udp.initNonBlock();
do
{
    //Do something 
} while (udp.readNonBlock(3).compare("153") != 0);
udp.closeSocket();
udp.initBlock();

如果从 UDP 客户端发送的消息是“153”，它会打破 do-while 循环。

使用 UDP 打破 while() 循环

Break while()-loop using UDP

c++

udp

do-while