对非阻塞套接字使用select（）

我正在尝试使用select函数在服务器和1个客户端之间实现无阻塞I/o，这样通信流就可以随时发送，而另一个客户端则可以在不等待发送的情况下接收。我找到了一个包含一些代码的教程，并尝试将其改编为我的。这就是我所拥有的-

服务器

#define PORT "4950"
#define STDIN 0

struct sockaddr name;

void set_nonblock(int socket) {
    int flags;
    flags = fcntl(socket,F_GETFL,0);
    assert(flags != -1);
    fcntl(socket, F_SETFL, flags | O_NONBLOCK);
}


// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa) {
    if (sa->sa_family == AF_INET)
        return &(((struct sockaddr_in*)sa)->sin_addr);

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(int agrc, char** argv) {
    int status, sock, adrlen, new_sd;

    struct addrinfo hints;
    struct addrinfo *servinfo;  //will point to the results

    //store the connecting address and size
    struct sockaddr_storage their_addr;
    socklen_t their_addr_size;

    fd_set read_flags,write_flags; // the flag sets to be used
    struct timeval waitd;          // the max wait time for an event
    int sel;                      // holds return value for select();

    //socket infoS
    memset(&hints, 0, sizeof hints); //make sure the struct is empty
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM; //tcp
    hints.ai_flags = AI_PASSIVE;     //use local-host address

    //get server info, put into servinfo
    if ((status = getaddrinfo("127.0.0.1", PORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
        exit(1);
    }

    //make socket
    sock = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
    if (sock < 0) {
        printf("\nserver socket failure %m", errno);
        exit(1);
    }

    //allow reuse of port
    int yes=1;
    if (setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {
        perror("setsockopt");
        exit(1);
    }

    //unlink and bind
    unlink("127.0.0.1");
    if(bind (sock, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
        printf("\nBind error %m", errno);
        exit(1);
    }

    freeaddrinfo(servinfo);

    //listen
    if(listen(sock, 5) < 0) {
        printf("\nListen error %m", errno);
        exit(1);
    }
    their_addr_size = sizeof(their_addr);

    //accept
    new_sd = accept(sock, (struct sockaddr*)&their_addr, &their_addr_size);
    if( new_sd < 0) {
        printf("\nAccept error %m", errno);
        exit(1);
    }

    set_nonblock(new_sd);
    cout<<"\nSuccessful Connection!";

    char* in = new char[255];
    char* out = new char[255];
    int numSent;
    int numRead;


    while(1) {

        waitd.tv_sec = 10;
        FD_ZERO(&read_flags);
        FD_ZERO(&write_flags);
        FD_SET(new_sd, &read_flags);

        if(strlen(out) != 0)
            FD_SET(new_sd, &write_flags);

        sel = select(new_sd+1, &read_flags, &write_flags, (fd_set*)0, &waitd);
        if(sel < 0)
            continue;

        //socket ready for reading
        if(FD_ISSET(new_sd, &read_flags)) {
            FD_CLR(new_sd, &read_flags);

            memset(&in, 0, sizeof(in));

            if(recv(new_sd, in, sizeof(in), 0) <= 0) {
                close(new_sd);
                break;
            }
            else
                cout<<"\n"<<in;
        }   //end if ready for read

        //socket ready for writing
        if(FD_ISSET(new_sd, &write_flags)) {

            FD_CLR(new_sd, &write_flags);
            send(new_sd, out, strlen(out), 0);
            memset(&out, 0, sizeof(out));
        }
    }   //end while

    cout<<"\n\nExiting normally\n";
    return 0;
}

客户机基本相同，只是减去一个接受呼叫-

#define PORT "4950"

struct sockaddr name;

void set_nonblock(int socket) {
    int flags;
    flags = fcntl(socket,F_GETFL,0);
    assert(flags != -1);
    fcntl(socket, F_SETFL, flags | O_NONBLOCK);
}

// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa) {
    if (sa->sa_family == AF_INET)
        return &(((struct sockaddr_in*)sa)->sin_addr);

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(int agrc, char** argv) {
    int status, sock, adrlen;

    struct addrinfo hints;
    struct addrinfo *servinfo;  //will point to the results

    fd_set read_flags,write_flags; // the flag sets to be used
    struct timeval waitd;          // the max wait time for an event
    int sel;                      // holds return value for select();

    memset(&hints, 0, sizeof hints); //make sure the struct is empty
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM; //tcp
    hints.ai_flags = AI_PASSIVE;     //use local-host address

    //get server info, put into servinfo
    if ((status = getaddrinfo("127.0.0.1", PORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
        exit(1);
    }

    //make socket
    sock = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
    if (sock < 0) {
        printf("\nserver socket failure %m", errno);
        exit(1);
    }

    if(connect(sock, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
        printf("\nclient connection failure %m", errno);
        exit(1);
    }

    cout<<"\nSuccessful connection!";

    set_nonblock(sock);

    char* out = new char[255];
    char* in = new char[255];
    int numRead;
    int numSent;

    while(1) {

        waitd.tv_sec = 10;
        FD_ZERO(&read_flags);
        FD_ZERO(&write_flags);
        FD_SET(sock, &read_flags);

        if(strlen(out) != 0)
            FD_SET(sock, &write_flags);


        sel = select(sock+1, &read_flags, &write_flags, (fd_set*)0, &waitd);
        if(sel < 0)
            continue;

        //socket ready for reading
        if(FD_ISSET(sock, &read_flags)) {
            FD_CLR(sock, &read_flags);

            memset(&in, 0, sizeof(in));

            if(recv(sock, in, sizeof(in), 0) <= 0) {
                close(sock);
                break;
            }
            else
                cout<<"\n"<<in;
        }   //end if ready for read

        //socket ready for writing
        if(FD_ISSET(sock, &write_flags)) {
            FD_CLR(sock, &write_flags);
            send(sock, out, strlen(out), 0);
            memset(&out, 0, sizeof(out));
        }
    }   //end while

    cout<<"\n\nExiting normally\n";
    return 0;
}

问题是当我运行它们时，什么都没有发生。我可以输入一个，然后按回车键，在另一个屏幕上什么也不显示，反之亦然。这不是我要调试的全部信息，这是我第一次真正尝试使用select，所以我想也许我只是不知道一些简单的事情。如果发现任何错误或怪异之处，请指出，感谢您的帮助

问题是当我运行它们时，什么都没有发生

真正的问题是，人们多年来一直在粘贴来自Beej的东西，却不了解它。这就是为什么我真的不喜欢那个指南；它给出了大量的代码块，但没有真正详细地解释它们

你没有阅读任何东西，也没有发送任何东西；没有FGET、scanf、cin等。以下是我要做的：

FD_SET(sock, &read_flags);
FD_SET(STDIN_FILENO, &read_flags);

/* .. snip .. */

if(FD_ISSET(STDIN_FILENO, &read_flags)) {
    fgets(out, len, stdin);
}

---

这将监控标准输入，并在输入可用时读取标准输入；然后，当套接字是可写的FD_ISSETsock，&write_标志时，它将发送缓冲区。

我现在让程序正常工作

服务器-

#define PORT "4950"
#define STDIN 0

struct sockaddr name;

void set_nonblock(int socket) {
    int flags;
    flags = fcntl(socket,F_GETFL,0);
    assert(flags != -1);
    fcntl(socket, F_SETFL, flags | O_NONBLOCK);
}


// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa) {
    if (sa->sa_family == AF_INET)
        return &(((struct sockaddr_in*)sa)->sin_addr);

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}


int main(int agrc, char** argv) {
    int status, sock, adrlen, new_sd;

    struct addrinfo hints;
    struct addrinfo *servinfo;  //will point to the results

    //store the connecting address and size
    struct sockaddr_storage their_addr;
    socklen_t their_addr_size;

    fd_set read_flags,write_flags; // the flag sets to be used
    struct timeval waitd = {10, 0};          // the max wait time for an event
    int sel;                      // holds return value for select();


    //socket infoS
    memset(&hints, 0, sizeof hints); //make sure the struct is empty
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM; //tcp
    hints.ai_flags = AI_PASSIVE;     //use local-host address

    //get server info, put into servinfo
    if ((status = getaddrinfo("127.0.0.1", PORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
        exit(1);
    }

    //make socket
    sock = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
    if (sock < 0) {
        printf("\nserver socket failure %m", errno);
        exit(1);
    }

    //allow reuse of port
    int yes=1;
    if (setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {
        perror("setsockopt");
        exit(1);
    }

    //unlink and bind
    unlink("127.0.0.1");
    if(bind (sock, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
        printf("\nBind error %m", errno);
        exit(1);
    }

    freeaddrinfo(servinfo);

    //listen
    if(listen(sock, 5) < 0) {
        printf("\nListen error %m", errno);
        exit(1);
    }
    their_addr_size = sizeof(their_addr);

    //accept
    new_sd = accept(sock, (struct sockaddr*)&their_addr, &their_addr_size);
    if( new_sd < 0) {
        printf("\nAccept error %m", errno);
        exit(1);
    }

    //set non blocking
    set_nonblock(new_sd);
    cout<<"\nSuccessful Connection!\n";

    char in[255];
    char out[255];
    memset(&in, 0, 255);
    memset(&out, 0, 255);
    int numSent;
    int numRead;

    while(1) {

        FD_ZERO(&read_flags);
        FD_ZERO(&write_flags);
        FD_SET(new_sd, &read_flags);
        FD_SET(new_sd, &write_flags);
        FD_SET(STDIN_FILENO, &read_flags);
        FD_SET(STDIN_FILENO, &write_flags);

        sel = select(new_sd+1, &read_flags, &write_flags, (fd_set*)0, &waitd);

        //if an error with select
        if(sel < 0)
            continue;

        //socket ready for reading
        if(FD_ISSET(new_sd, &read_flags)) {

            //clear set
            FD_CLR(new_sd, &read_flags);

            memset(&in, 0, 255);

            numRead = recv(new_sd, in, 255, 0);
            if(numRead <= 0) {
                printf("\nClosing socket");
                close(new_sd);
                break;
            }
            else if(in[0] != '\0')
                cout<<"\nClient: "<<in;

        }   //end if ready for read

        //if stdin is ready to be read
        if(FD_ISSET(STDIN_FILENO, &read_flags))
            fgets(out, 255, stdin);


        //socket ready for writing
        if(FD_ISSET(new_sd, &write_flags)) {
            //printf("\nSocket ready for write");
            FD_CLR(new_sd, &write_flags);
            send(new_sd, out, 255, 0);
            memset(&out, 0, 255);
        }   //end if
    }   //end while

   cout<<"\n\nExiting normally\n";
    return 0;
}

---

客户机基本上是一样的……唯一的区别是缺少侦听和接受功能。

我只想补充一点，上面的示例可能无法在Linux上正常工作。在Linux上，可通过选择修改waitd。所以对于Linux，在选择之前应该重写waitd

---

有关选择，请参阅手册页中的超时部分。

谢谢您的回复。是的，过去几天我一直在读比杰的教程，几乎过不去。我尝试将其添加到我的代码中，但现在每当我在终端上的任意一个终端中键入内容时，就会出现分段错误，该终端类型为“hi”进入服务器，服务器分段错误，客户端关闭正常，反之亦然。我试着用getline来确定这不仅仅是FGET。GDB没有真正的帮助-告诉我回溯在main中仅为0 0x08048c93。很抱歉，在这一点上，我有点不顾一切，但你知道这可能是什么原因吗？@Sterling使用-g编译。此外，对于初学者来说，声明out和in也是如此：char out[255]；。奇怪…当我只是更改这些声明时，程序不会seg fault，但它会直接通过while循环并退出。@Sterling尝试调试它。如果需要，请添加printf行。在select printfSelect激发后添加一行printf\n；等等就行了。另一件奇怪的事情可能值得注意……select为这两个程序触发了不同的次数，每次我运行它的次数也不同。有时10，有时20，有时5，然后关闭插座。不知何故，recv调用是因为我太累了，无法解释它，因此如果将来有人需要该信息，我将发布代码与上述代码进行比较，这不是编写有用答案的方式-1在本节中：FD_SETnew_sd，&read_flags；FD_SETnew_sd和write_标志；FD_设置文件编号和读取标志；FD_设置din_文件编号和写入_标志；前两个FD_集被后两个FD_集覆盖。为什么要麻烦？@EngledLoops我不同意-这四行将向集合read_标志和write_标志添加新的_sd和STDIN_文件号。From:FD_SET和FD_CLR分别从集合中添加和删除给定的文件描述符。@pepan我现在看到的显然是正确的；不记得我在十月份读的时候是怎么想的+一个健全的例子