C语言 在DDS中为多个主题创建多个数据编写器

Question

我正在 Linux 32 位中开发 OpenSplice DDS Community Edition。在这里，我可以有多个主题，其中，数据编写者可以写入此主题，发布者将发布这些主题。我尝试修改可用的源代码，我试图在其中获取输出，如下所示：

    Chatter 1: Hi there, I will send you 10 more exxpert messages.
    Chatter 1: Message no. 1
    Chatter 1: Message no. 2
    Chatter 1: Message no. 3
    Chatter 1: Message no. 4
    Chatter 1: Message no. 4
    Chatter 1: Message no. 5
    Chatter 1: Message no. 6
    Chatter 1: Message no. 7
    Chatter 1: Message no. 8
    Chatter 1: Message no. 9
    Chatter 1: Message no. 10

源代码如下图：

/* Initialize the chat messages on Heap. */
msg = Chat_ChatMessage__alloc();
checkHandle(msg, "Chat_ChatMessage__alloc");
msg->userID = ownID;
msg->index = 0;
msg->content = DDS_string_alloc(MAX_MSG_LEN);
checkHandle(msg->content, "DDS_string_alloc");
if (ownID == TERMINATION_MESSAGE) {
    snprintf (msg->content, MAX_MSG_LEN, "Termination message.");
} else {
    snprintf (msg->content, MAX_MSG_LEN, "Hi there, I will send you %d more messages.", NUM_MSG);
}
printf("Writing message: %sn", msg->content);
//Initialize the chat messages on Heap//
/* Register a chat message for this user (pre-allocating resources for it!!) */
userHandle = Chat_ChatMessageDataWriter_register_instance(talker, msg);
/* Write a message using the pre-generated instance handle. */
status = Chat_ChatMessageDataWriter_write(talker, msg, userHandle);
checkStatus(status, "Chat_ChatMessageDataWriter_write");
/* Register a chat message for this user (pre-allocating resources for it!!) */
userHandle = Chat_ChatMessageDataWriter_register_instance(chatterbox, msg);
/* Write a message using the pre-generated instance handle. */
status = Chat_ChatMessageDataWriter_write(chatterbox, msg, userHandle);
checkStatus(status, "Chat_ChatMessageDataWriter_write");
sleep (1); /* do not run so fast! */
/* Write any number of messages, re-using the existing string-buffer: no leak!!. */
for (i = 1; i <= NUM_MSG && ownID != TERMINATION_MESSAGE; i++) {
    msg->index = i;
    snprintf ( msg->content, MAX_MSG_LEN, "Message no. %d", msg->index);
    printf("Writing message: %sn", msg->content);
    status = Chat_ChatMessageDataWriter_write(talker, msg, userHandle);
    checkStatus(status, "Chat_ChatMessageDataWriter_write");
    sleep (1); /* do not run so fast! */
    }
 /* Write any number of messages, re-using the existing string-buffer: no leak!!. */
    for (i = 1; i <= NUM_MSG && ownID != TERMINATION_MESSAGE; i++) {
        msg->index = i;
        snprintf (msg->content, MAX_MSG_LEN, "Hi there, I will send you %d more exxpert_messages.", NUM_MSG);
        snprintf ( msg->content, MAX_MSG_LEN, "Message no. %d", msg->index);
        printf("Writing message: %sn", msg->content);
        status = Chat_ChatMessageDataWriter_write(chatterbox, msg, userHandle);
        checkStatus(status, "Chat_ChatMessageDataWriter_write");
}

但我对上述代码的输出如下：

    Writing message: Hi there, I will send you 10 more messages.
    Writing message: Message no. 1
    Error in Chat_ChatMessageDataWriter_write: DDS_RETCODE_PRECONDITION_NOT_MET

Answer 1

当您向 DataWriter 注册实例时，将返回 InstanceHandle 类型的值，如下面的代码所示：

userHandle = Chat_ChatMessageDataWriter_register_instance(chatterbox, msg);

您只能将该 userHandle 变量用于具有您注册的同一 DataWriter 的后续write()。但是，您尝试执行以下操作：

status = Chat_ChatMessageDataWriter_write(talker, msg, userHandle);

请注意不同的变量 chatterbox 和 talker 。userHandle 变量不属于 talker 数据编写器，因此返回值PRECONDITION_NOT_MET失败。