UDP是IPC的可靠协议吗? [英] Is UDP a reliable protocol for IPC?

问题描述

如果我仅将UDP用于进程间通信(即在1个系统中，不涉及网络)，我是否认为它是可靠的?还是我仍然需要担心数据包丢失等?

If I use UDP purely for inter-process communication (i.e., in 1 system, with no network involved), can I consider it to be reliable? Or do I still need to worry about packets getting dropped, etc.?

注意，这是一个实用问题，而不是理论上的问题.如果不同操作系统的答案不同，请说明具体操作方法，尤其是Windows，Linux和Mac.

Note that this is a practical question, not a theoretical one. If the answer differs across OSes, please explain how, in particular including Windows, Linux, and Mac.

感谢当前的回答，指出了正确的方向.
这段代码在Windows 8.1上丢弃了一个数据包(我得到了Received: 18432 (DROPPED PACKET)).
(我不确定为什么它不能在Linux上运行，但是应该可以正常工作了.)

Thanks to the current answer for pointing me in the right direction.
This code drops a packet on Windows 8.1 (I get Received: 18432 (DROPPED PACKET)).
(I'm not sure why it doesn't run on Linux, but it should be close to working.)

#include <stdio.h>
#ifdef _WIN32
#include <ws2tcpip.h>
#else
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#endif

int main()
{
#ifdef _WIN32
    typedef int socklen_t;
#else
    typedef int SOCKET;
#endif
    SOCKET r = socket(AF_INET, SOCK_DGRAM, 0);
    struct sockaddr_in addr = { AF_INET };
    addr.sin_addr.s_addr = htonl(0x7F000001);
    {
        socklen_t addrlen = sizeof(addr);
        if (bind(r, (struct sockaddr *)(&addr), addrlen) == -1 ||
            getsockname(r, (struct sockaddr *)(&addr), &addrlen) == -1)
        {
            return 1;
        }
    }
    SOCKET s = socket(AF_INET, SOCK_DGRAM, 0);
    int tids = 0;
    for (long c = 0, i = 0, j = 0; c < 1000000; ++c)
    {
        if ((c + 1) % 10)
        {
            int n = sendto(s, (char const *)(&i), sizeof(i), 0, (struct sockaddr const *)(&addr), sizeof(addr));
            if (n != sizeof(i)) { return 1; }
            // else { fprintf(stderr, "Sent:     %lu\n", i); }
            ++i;
        }
        else
        {
            struct sockaddr temp;
            socklen_t templen = sizeof(temp);
            long v;
            int n = recvfrom(r, (char *)(&v), sizeof(v), 0, (struct sockaddr *)(&temp), &templen);
            if (n != sizeof(v)) { return 2; }
            else if (v != j) { fprintf(stderr, "Received: %lu (DROPPED PACKET)\n", v); return 3; }
            // else { fprintf(stderr, "Received: %lu\n", v); }
            ++j;
        }
    }
}

推荐答案

如果我仅将UDP用于进程间通信(即1 系统，不涉及网络)，我可以认为它是可靠的吗?

If I use UDP purely for inter-process communication (i.e., in 1 system, with no network involved), can I consider it to be reliable?

不.即使所有通信都是在同一主机上进行的，UDP数据包仍可以(有时仍会被丢弃).

No. UDP packets can (and sometimes will) still be dropped even when all communication is being done over the same host.

如果需要，您可以亲自演示一下；在同一主机上设置两个使用UDP套接字的程序，程序A向程序B发送UDP数据包，然后接收并记录它们. (在UDP数据包中包含序列号，以便程序B可以很容易地分辨出何时未收到数据包).

You can demonstrate this for yourself, if you want; set up two UDP-socket-using programs on the same host, with program A sending UDP packets to program B that receives them and records them. (Include sequence numbers in the UDP packets so that program B can easily tell when a packet was not received).

一旦正常工作并且数据包以适当的速率传输，请将一些代码放入程序B中，以便它经常调用sleep(5)(或类似的程序，因此程序B无法在其B上调用recv()) UDP套接字的时间很长).您可能会看到在sleep()调用返回之后，程序B报告跳过了某些数据包-因为当B处于睡眠状态时，其UDP套接字的传入数据包缓冲区已满，然后一些数据包被网络丢弃堆栈，因为没有放置它们的地方.

Once that is working and packets are being transmitted at a decent rate, put some code into program B so that every so often it calls sleep(5) (or similar, so that program B fails to call recv() on its UDP socket for a significant amount of time). You'll likely see that after the sleep() call returns, program B reports that some packets were skipped -- because while B was asleep, the incoming-packets buffer for its UDP socket became full and then some packets were dropped by the networking stack because there was no place to put them.

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