c - 处理多个客户端时，pthread_join 无法 fork TCP 服务器

Question

我必须创建一个多线程 TCP/IP 服务器，其中包含一个变量来计算连接的客户端数量(以及断开连接的客户端数量)，并在客户端连接到服务器时打印连接的客户端数量。

这是我的client.c文件:

#define PORT 4444

int main ()
{
    int clientSocket;
    struct sockaddr_in serverAddress;
    char buffer[1024];
    ssize_t nread;

    clientSocket = socket(AF_INET, SOCK_STREAM, 0);
    if (clientSocket == -1) {
        perror("[-]Errore durante la creazione della socket\n");
        exit(-1);
    }
    printf("[+]Client socket has been created\n");


    memset(&serverAddress, '\0', sizeof(serverAddress));

    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port = htons(PORT);
    serverAddress.sin_addr.s_addr = INADDR_ANY;

    if (connect(clientSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress)) == -1) {
        perror("Errore con la connessione\n");
        exit(-1);
    }

    while (1) {

        printf("> ");
        fflush(stdin);
        scanf("%s", buffer);

        if (nread != -1)
            buffer[nread] = '\0';*/

        if (send(clientSocket, buffer, strlen(buffer), 0) == -1) {
            perror("Errore con l'invio");
            exit(1);
        }

        if(strcmp(buffer, ":exit") == 0) {
            close(clientSocket);
            printf("[-]Disconnected from Server\n");
            exit(0);
        }

        if ( (nread=recv(clientSocket, buffer, sizeof buffer - 1, 0)) <= 0) {
            perror("[-]Error in receiving data from server\n");
        }
        else {
            buffer[nread] = '\0';
            printf("Server received: %s\n", buffer);
        }

    }

    close(clientSocket);

    return 0;
}

这是我的server.c文件:

#define PORT 4444
#define MAX_CONNESSIONI 100

typedef struct myStruct {
    int clientCollegati;
    int clientCheSiSonoScollegati;
    pthread_mutex_t mutex; // Creazione del mutex per sincronizzare la struttura
} myStruct;

myStruct *test; 

myStruct *initStruct();
void *incrementa(void*);

int main ()
{
    int serverSocket, bindStatus;
    struct sockaddr_in serverAddress;
    int clientSocket;
    struct sockaddr_in newAddress;
    char buffer[1024];
    pid_t child;
    socklen_t addrSize;
    ssize_t nread;
    pthread_t tid;

    test = initStruct(); 

    if (pthread_create(&tid, NULL, incrementa, NULL) != 0) {
        perror("Errore nella creazione del thread t1\n");
        exit(1);
    }
    serverSocket = socket(AF_INET, SOCK_STREAM, 0);
    if (serverSocket == -1) {
        perror("[-]Errore durante la creazione della socket\n");
        exit(-1);
    }


    memset(&serverAddress, '\0', sizeof(serverAddress));

    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port = htons(PORT);
    serverAddress.sin_addr.s_addr = INADDR_ANY;
    bindStatus = bind(serverSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress));
    if (bindStatus == -1) {
        perror("[-]Errore durante il binding\n");
        exit(1);
    }
    printf("[+]Bind to port %d\n", PORT);


    if (listen(serverSocket, MAX_CONNESSIONI) != -1) {
        printf("Listening . . .\n\n");
    }
    else {
        perror("[-]Error during listening\n");
        exit(1);
    }


    while (1) {

        clientSocket = accept(serverSocket, (struct sockaddr*)&newAddress, &addrSize);
        if (clientSocket == -1) {
            exit(-1);
        }
        printf("%s:%d joined\n", inet_ntoa(newAddress.sin_addr), ntohs(newAddress.sin_port));

        if (pthread_join(tid, NULL)) { // returns 3
            perror("pthread_join error\n");
            exit(1);
        }

        printf("There is/are %d client(s) connected\n", test->clientCollegati);

        child = fork();
        if (child == 0) {

            close(serverSocket);

            while (1) {

                if ( (nread=recv(clientSocket, buffer, sizeof buffer - 1, 0)) <= 0) {
                    perror("[-]Error in receiving data from server\n");
                }
                else {
                    buffer[nread] = '\0';
                }


                if (strcmp(buffer, ":exit") == 0) {
                    printf("%s:%d left\n", inet_ntoa(newAddress.sin_addr), ntohs(newAddress.sin_port));
                    break;
                }
                else {
                    printf("%s:%d wrote: %s\n", inet_ntoa(newAddress.sin_addr), ntohs(newAddress.sin_port), buffer);
                    send(clientSocket, buffer, strlen(buffer), 0);
                    bzero(buffer, sizeof(buffer));
                }

            }

        }

    }

    close(clientSocket);

    return 0;
}

myStruct *initStruct()
{
    struct myStruct *ptr = malloc(sizeof(myStruct));

    ptr->clientCollegati = 0;
    ptr->clientCheSiSonoScollegati = 0;

    pthread_mutex_init(&ptr->mutex, NULL); // inizializzazione dinamica del mutex

    return ptr;

}

void *incrementa(void *ptr)
{

    pthread_mutex_lock(&test->mutex); 


    test->clientCollegati++;


    pthread_mutex_unlock(&test->mutex);

    pthread_exit(0);

}

不幸的是，这似乎无法正常工作，您可以看到 server output在这里client1在这里client2 output

• 哪里错了？我认为问题是当 tid 完成并且对 pthread_join 的第二次调用被调用到一个不存在的线程时(因为有一个线程)

Answer 1

你的代码逻辑有问题。您正在执行一个 pthread_create()，然后执行多个 pthread_join()。如果您想增加每个已连接客户端的值，则必须在每次成功的 accept() 后执行一次 pthread_create()，然后执行一次 pthread_join() 。注意:所有这些都必须在调用 fork() 之前发生。

Where's the mistake? I suppose that the problem is when tid finish and a second call to that pthread_join is invoked to a non-existent thread (because there is a single thread)

这正是发生的事情。在当前程序中，第一个 pthread_join() 成功，任何后续调用都会失败并显示 errno 3(没有这样的进程)，因为线程不再存在。所以你已经明白了这一点。如果您知道这是错误的，为什么还要创建一个线程却多次加入它？

你的程序的编写方式(增量后 fork )也意味着根本没有理由使用线程来进行增量，你甚至不需要互斥体，因为只有一个线程会访问任何给定时间的值。换句话说，您的服务器根本不是多线程的。如果您只想将其作为一个实验，那也可以，但是没有多大意义。

您可能想要做的(拥有多线程服务器)是每个客户端一个线程，而不是每次都 fork ，并将客户端代码放在线程函数中(在这种情况下有一个互斥体是有道理的)。但请注意，这对于大量客户端来说不能很好地扩展(一般来说，经典的 fork() 方法更好，在这种情况下您实际上不需要任何线程)。