Question

目标： N个节点（在不同的机器上运行）应该通过建立彼此的TCP连接来相互通信。发送和接收消息由进程创建的2个线程完成。最初，主进程将所有节点相互连接，创建2个线程并为其提供文件描述符列表，线程可以使用这些文件描述符来发送和接收数据。下面的结构由主进程填充并传递给线程。

typedef struct
{
    char hostName[MAXIMUM_CHARACTERS_IN_HOSTNAME];  /* Host name of the node */
    char portNumber[MAXIMUM_PORT_LENGTH];           /* Port number of the node */
    char nodeId[MAXIMUM_NODE_ID_LENGTH];            /* Node ID of the node */
    int socketFd;                                   /* Socket file descriptor */
    int socketReady;        /* Flag to indicate if socket information is filled */
}SNodeInformation;

PS：socketFd是accept（）或socket（）接收的套接字描述符，具体取决于连接的建立方式（从节点侦听连接或连接到节点）。

使用大小为MAX_NUM_OF_NODES的SNodeInformation数组。

发送线程通过nodeInformation并向所有节点发送消息“Hello”，如下所示。

void *sendMessageThread(void *pNodeInformation) {

    int i;
    int ownNodeId;
    int bytesSent = 0;
    char ownHostName[MAXIMUM_CHARACTERS_IN_HOSTNAME];

    SNodeInformation *nodeInformation = (SNodeInformation *) pNodeInformation;
    SNodeInformation *iterNodeInformation;

    printf("SendMessageThread: Send thread created\n");

    if(gethostname(ownHostName, MAXIMUM_CHARACTERS_IN_HOSTNAME) != 0) {
        perror("Error: sendMessageThread, gethostname failed\n");
        exit(1);
    }

    for(i=0, iterNodeInformation=nodeInformation ; i<MAXIMUM_NUMBER_OF_NODES ; i++, iterNodeInformation++) {
        if(strcmp((const char*) iterNodeInformation->hostName, (const char*) ownHostName) != 0)  {
            /* Send message to all nodes except yourself */
            bytesSent = send(iterNodeInformation->socketFd, "Hello", 6, 0);

            if(bytesSent == -1) {
                printf("Error: sendMessageThread, sending failed, code: %s FD %d\n",     strerror(errno), iterNodeInformation->socketFd);
            }
        }
    }

    pthread_exit(NULL);
}

接收线程通过nodeInformation，设置文件描述符集并使用select等待传入数据，如下所示。

void *receiveMessageThread(void *pNodeInformation)
{
    int i;
    int fileDescriptorMax = -1;
    int doneReceiving = 0;
    int numberOfBytesReceived = 0;
    int receiveCount = 0;
    fd_set readFileDescriptorList;
    char inMessage[6];

    SNodeInformation *nodeInformation = (SNodeInformation *) pNodeInformation;
    SNodeInformation *iterNodeInformation;

    printf("ReceiveMessageThread: Receive thread created\n");

    /* Initialize the read file descriptor */
    FD_ZERO(&readFileDescriptorList);

    for(i=0, iterNodeInformation=nodeInformation ; i<MAXIMUM_NUMBER_OF_NODES ; i++, iterNodeInformation++) {
        FD_SET(iterNodeInformation->socketFd, &readFileDescriptorList);

        if(iterNodeInformation->socketFd > fileDescriptorMax) {
            fileDescriptorMax = iterNodeInformation->socketFd;
        }
    }

    printf("ReceiveMessageThread: fileDescriptorMax:%d\n", fileDescriptorMax);

    while(!doneReceiving) {
        if (select(fileDescriptorMax+1, &readFileDescriptorList, NULL, NULL, NULL) == -1) {
            perror("Error receiveMessageThread, select failed \n");
            return -1;
        }

        for(i=0 ; i<fileDescriptorMax ; i++) {
            if (FD_ISSET(i, &readFileDescriptorList)) {
                /* Check if any FD was set */
                printf("ReceiveThread: FD set %d\n", i);

                /* Receive data from one of the nodes */
                if ((numberOfBytesReceived = recv(i, &inMessage, 6, 0)) <= 0) {
                    /* Got error or connection closed by client */
                    if (numberOfBytesReceived == 0) {
                        /* Connection closed */
                        printf("Info: receiveMessageThread, node %d hung up\n", i);
                    }
                    else {
                        perror("Error: receiveMessageThread, recv FAILED\n");
                    }

                    close(i);

                    /* Remove from Master file descriptor set */
                    FD_CLR(i, &readFileDescriptorList); 
                    doneReceiving = 1;
                }
                else {
                    /* Valid data from a node */
                    inMessage[6] = '\0';

                    if(++receiveCount == MAXIMUM_NUMBER_OF_NODES-1) {
                        doneReceiving = 1;
                    }

                    printf("ReceiveThread: %s received, count: %d\n", inMessage, rece    iveCount);
                }
            }
        }
    }
    pthread_exit(NULL);
}

预期输出：我尝试了只有2个进程，P1（先启动）和P2在machine1上运行，另一个在machine2上运行。机器中的两个进程应首先连接，然后线程应发送和接收消息“Hello”并退出。

观察到的输出：P1能够发送消息，P2（接收者线程）能够接收消息“Hello”。但P1（接收方线程）无法从P2（发送线程）获取消息。两台机器中的应用程序代码相同，但每次启动的进程都不会从其他进程获取消息。我添加了一个打印，只是检查是否设置了一些文件描述符，但我没有看到它用于P1但仅用于P2。接收过程中的发送没有失败，它返回6.我检查了文件描述符的最大值，它是正确的。

如果我首先启动P2然后启动P1，那么我可以看到P1从P2接收消息并且在P2等待来自P1的消息时无处不在。

我不确定问题是因为套接字描述符的使用不正确还是因为线程？

Answer 1

两个问题：

1正在设置的文件描述符的循环测试不包括放入集合中的所有文件描述符。（预计此编程错误是OP中描述的故障的原因。）

2传递给select()的文件描述符集由select()修改，因此需要在select()之前重新初始化该集合。（只有在收到多个套接字数据时才会出现编程错误。）

请参阅OP代码的以下mod / s：

void *receiveMessageThread(void *pNodeInformation)
{
    ...

    printf("ReceiveMessageThread: Receive thread created\n");

    while(!doneReceiving) {
        /* Initialize the read-set of file descriptors */

        /* Issue 2 fixed from here ... */
        FD_ZERO(&readFileDescriptorList);

        for(i=0, iterNodeInformation=nodeInformation ; i<MAXIMUM_NUMBER_OF_NODES ; i++, iterNodeInformation++) {
            FD_SET(iterNodeInformation->socketFd, &readFileDescriptorList);

            if (iterNodeInformation->socketFd > fileDescriptorMax) {
                fileDescriptorMax = iterNodeInformation->socketFd;
            }
        }
        /* ... up to here. */

        printf("ReceiveMessageThread: fileDescriptorMax:%d\n", fileDescriptorMax);

        if (select(fileDescriptorMax+1, &readFileDescriptorList, NULL, NULL, NULL) == -1) {
            perror("Error receiveMessageThread, select failed \n");
            return -1;
        }

        for(i=0 ; i <= fileDescriptorMax ; i++) { /* Issue 1 fixed here. */
            ...

select（）不检测传入数据

1 个答案: