c - 如何在 C 中刷新 UDP 套接字的输入缓冲区？

Question

如何在 C 中刷新 UDP 套接字的输入缓冲区(如果存在的话)？

我正在嵌入式 Linux 环境中工作，并使用 C 来创建一些 native 应用程序。在同一个网络上有几台这样的嵌入式机器，当其中一台发生事件时(我们称之为 WHISTLE-BLOWER)，WHISTLE-BLOWER 应该向网络广播地址发送网络消息，以便所有机器上网络(包括 WHISTLE-BLOWER)知道该事件并根据它执行一些操作。 顺便说一下，我正在使用 UDP 套接字......

伪代码如下:

main
{
    startNetworkListenerThread( networkListenerFunction );

    while( not received any SIGTERM or such )
    {
        localEventInfo = checkIfTheLocalEventOccured();
        broadcastOnNetwork( localEventInfo );
    }
}

networkListenerFunction
{
    bindSocket;

    while( not SIGTERM )
    {
// THIS IS WHERE I WANT TO FLUSH THE RECV BUFFER...
        recv_data = recvfrom( socket );
        if( validate recv data )
        {
            startExecuteLocalAction;
            sleep( 5 );
            stopExecuteLocalAction;
        }
    }
}

我期望并希望使用此代码的方式是:

1. LOCAL_EVENT occured
2. Broadcasted LOCAL_EVENT_INFO on network
3. All machines received EVENT_INFO, including the original broadcaster
4. All machines started executing the local action, including the original broadcaster
5. All machines' network listener(thread)s are sleeping
6. Another LOCAL_EVENT2 occured
7. Since all machines' listener are sleeping, LOCAL_EVENT2 is ignored
8. All machines' network listener(thread)s are now active again
9. GO BACK TO 1 / RESTART CYCLE
RESULT = TOTAL 2 EVENTS, 1 IGNORED

它实际工作的方式是:

1. LOCAL_EVENT occured
2. Broadcasted LOCAL_EVENT_INFO on network
3. All machines received EVENT_INFO, including the original broadcaster
4. All machines started executing the local action, including the original broadcaster
5. All machines' network listener(thread)s are sleeping
6. Another LOCAL_EVENT2 occured
7. Eventhough all machines' listener are sleeping; LOCAL_EVENT2 is queued  SOMEHOW
8. All machines' network listener(thread)s are now active again
9. All machines received EVENT_INFO2 and executed local actions again, slept and reactivated
10. GO BACK TO 1 / RESTART CYCLE
RESULT = TOTAL 2 EVENTS, 0 IGNORED

tl,dr:发送到已绑定(bind)套接字的数据包/消息/UDP 广播，其父线程在传递时刻处于休眠状态；以某种方式排队/缓冲并在所述套接字上的下一个“recvfrom”调用中传递。

我希望忽略那些 UDP 广播，所以我考虑刷新接收缓冲区(显然不是我作为 recvfrom 方法参数提供的缓冲区)，如果它在调用 recvfrom 之前存在的话。我怎样才能做到这一点？或者我应该遵循什么路径？

Answer 1

请注意，“刷新”的概念仅适用于输出。刷新清空缓冲区并确保其中的所有内容都被发送到目的地。对于输入缓冲区，数据已经在其目的地。可以读取或清除输入缓冲区，但不能“刷新”。

如果您只是想确保已经读取了输入缓冲区中的所有内容，那么您正在寻找的是非阻塞读取操作。如果您尝试它并且没有输入，它应该返回一个错误。