从 pthread C 调用时 read() 不起作用

Question

我目前正在编写一个 C 服务器，其目标是使用 pthreads 来处理客户端连接，在我引入 pthreads 之前，一切都可以正常工作。我在 pthread 上启动了一个客户端，它被创建并运行良好；但是，它将不再从客户端的文件描述符中“读取（）”。

我已经尝试解决这个问题大约 2 周了。我已经包含了服务器代码（包括和不包括 pthread）和客户端处理程序代码的代码 sn-ps。

这是我的主服务器循环（pthread）：

/*Sets up and runs the server. (MAX 10 CLIENTS)*/
void publicServer(void)
{
    //Server locals
    int serverSocket_fd;
    int clientSocket_fd;
    socklen_t serverLength;
    socklen_t clientLength;
    struct sockaddr_in serverAddress;
    struct sockaddr_in clientAddress;

    //Threading locals
    pthread_t threadPool[20];   //Pool of threads, used in a FIFO fashion.
    int threadPointer = 0;      //Points to the location of the next available thread.

    //Clear old sockets
    puts("Unlinking server socket");
    unlink("server_socket");

    //Setup server socket
    printf("Setting server socket properties..\n");
    serverSocket_fd                 = socket(AF_INET, SOCK_STREAM, 0);
    serverAddress.sin_family        = AF_INET;
    serverAddress.sin_addr.s_addr   = htonl(INADDR_ANY);
    serverAddress.sin_port          = htons(5000);
    serverLength = sizeof(serverAddress);

    //Bind the socket
    printf("Binding socket\n");
    bind(serverSocket_fd, (struct sockaddr*)&serverAddress, serverLength);

    //Create listener
    listen(serverSocket_fd, 20);

    //Main server loop
    printf("Entering main loop\n");
    while (1)
    {
        clientLength = sizeof(clientAddress);

        //Accept connection
        printf("Blocking for connection\n");
        clientSocket_fd = accept(serverSocket_fd, (struct sockaddr*)&clientAddress, &clientLength);

        //Handle Client
        pthread_create(&threadPool[0], NULL, clientHandler, clientSocket_fd);

        //Increment thread pointer
        threadPointer++;
        if (threadPointer == 20)
        {
            threadPointer = 0;
        }

        //End client
        close(clientSocket_fd);
    }
}

这是没有 pthreads 的服务器代码（工作正常。）：

/*Sets up and runs the server. (MAX 10 CLIENTS)*/
void publicServer(void)
{
    //Server locals
    int serverSocket_fd;
    int clientSocket_fd;
    socklen_t serverLength;
    socklen_t clientLength;
    struct sockaddr_in serverAddress;
    struct sockaddr_in clientAddress;

    //Clear old sockets
    puts("Unlinking server socket");
    unlink("server_socket");

    //Setup server socket
    printf("Setting server socket properties..\n");
    serverSocket_fd                 = socket(AF_INET, SOCK_STREAM, 0);
    serverAddress.sin_family        = AF_INET;
    serverAddress.sin_addr.s_addr   = htonl(INADDR_ANY);
    serverAddress.sin_port          = htons(5000);
    serverLength = sizeof(serverAddress);

    //Bind the socket
    printf("Binding socket\n");
    bind(serverSocket_fd, (struct sockaddr*)&serverAddress, serverLength);

    //Create listener
    listen(serverSocket_fd, 20);

    //Main server loop
    printf("Entering main loop\n");
    while (1)
    {
        clientLength = sizeof(clientAddress);

        //Accept connection
        printf("Blocking for connection\n");
        clientSocket_fd = accept(serverSocket_fd, (struct sockaddr*)&clientAddress, &clientLength);

        //Handle Client
        clientHandler(clientSocket_fd);

        //End client
        close(clientSocket_fd);
    }
}

这是客户端处理程序代码：

/*
 * Handles the client's request.
 * <int : client_fd> Client's file descriptor.
 */
void *clientHandler(int client_fd)
{
    char request = ' ';

    puts("Waiting for request");
    read(client_fd, &request, 1);

    //Determine what to do for user
    if (request == '1')                 //Output current temp and pressure
    {
        outputCurrentTemperaturePressure(client_fd);
    }
    else if (request == '2')            //Begin regular sampling of temp and pressure
    {
        startSampling();
    }
    else if (request == '3')            //Stop regular sampling of temp and pressure
    {
        stopSampling();
    }
    else if (request == '4')            //Clear the EEPROM
    {
        eraseEEPROM();
    }
    else if (request == '5')            //Retrieve all stored temperature and pressure values
    {
        outputSavedTempPressValues(client_fd);
    }
    else if (request == '6')            //Retrieve a certain number of temperature and pressure values
    {
        outputLastNTempPressValues(client_fd);
    }
    else if (request == '7')            //Output current noise level
    {
        outputCurrentNoiseLevel(client_fd);
    }

    close(client_fd);
    pthread_exit(1);
}

当我尝试从客户端读取数据时，问题出在 clientHandler 方法中的第 6 行。当在 pthread 上运行时，它一直读取 0。但是，当没有 pthreads 运行时，它会读取正确的值。我希望有人能帮忙解决这个问题，因为这真的让我很困惑。

提前致谢， 安迪

Answer 1

据我所知，pthread 入口点必须有一个 void * 参数。您定义 clientHandler 的方式似乎是错误的。读这个： http://timmurphy.org/2010/05/04/pthreads-in-c-a-minimal-working-example/ .

Answer 2

int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
                      void *(*start_routine) (void *), void *arg);


pthread_create(&threadPool[0], NULL, clientHandler, (void*)&clientSocket_fd);

void *clientHandler(void *args) {
int client_fd = *((int*) args);

Answer 3

只关闭线程中的客户端socket_fd，而不是主函数

while (1)
{
    clientLength = sizeof(clientAddress);

    //Accept connection
    printf("Blocking for connection\n");
    clientSocket_fd = accept(serverSocket_fd, (struct sockaddr*)&clientAddress, &clientLength);

    //Handle Client
    pthread_create(&threadPool[0], NULL, clientHandler, clientSocket_fd);

    //Increment thread pointer
    threadPointer++;
    if (threadPointer == 20)
    {
        threadPointer = 0;
    }

    //End client
    /* remove close(clientSocket_fd) from here */
}

当你在 while 中运行新线程时，循环仍然关闭客户端文件描述符，这就是 read() 不起作用的原因