将select()用于非阻塞套接字

Question

我正在尝试使用select函数在服务器和1个客户端(不再)之间进行非阻塞i/o,其中通信流畅(可以随时发送而另一个将在不等待发送的情况下接收).我找到了一些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;
}

客户端(基本上只是减去接受电话) -

#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,没有任何反应.我可以输入一个并按Enter键,而其他屏幕上则不会显示任何内容(反之亦然).这不是我调试的全部信息,这是我第一次使用select的真正尝试,所以我想也许我只是没有意识到一些简单的事情.如果发现任何错误或奇怪的东西请指出,任何帮助表示赞赏.

Answer 1

问题是,当我运行它们时,没有任何反应.

真正的问题是人们多年来一直粘贴Beej的东西而不理解它.这就是为什么我不喜欢那个指南; 它提供了大量代码而没有真正详细解释它们.

你没有读任何东西,也没有发送任何东西; 没有fgets,scanf,cin等.这就是我要做的:

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

/* .. snip .. */

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

stdin当输入可用时,它将监视并读取它; 然后,当socket si writeable(FD_ISSET(sock, &write_flags))时它将发送缓冲区.

Answer 2

我的程序现在可以正常工作了。

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;
}

客户基本上是一样的......唯一的区别是缺乏倾听和接受。