考虑以下代码：

#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>

#define SERVADDR "::1"
#define PORT 12345

int main() {
    int sd = -1;

    if ((sd = socket(AF_INET6, SOCK_STREAM, 0)) < 0) {
        fprintf(stderr, "socket() failed: %d", errno);
        exit(1);
    }

    int flag = 1;
    if(setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, &flag, sizeof(flag)) == -1) {
        fprintf(stderr, "Setsockopt %d, SO_REUSEADDR failed with errno %d\n", sd, errno);
        exit(2);
    }
    if(setsockopt(sd, SOL_SOCKET, SO_REUSEPORT, &flag, sizeof(flag)) == -1) {
        fprintf(stderr, "Setsockopt %d, SO_REUSEPORT failed with errno %d\n", sd, errno);
        exit(3);
    }

    struct sockaddr_in6 addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin6_family = AF_INET6;
    addr.sin6_port = htons(23456);

    if(bind(sd, (struct sockaddr*)&addr, sizeof(addr)) == -1) {
        fprintf(stderr, "Bind %d failed with errno %d: %s\n", sd, errno, strerror(errno));
        exit(4);
    }

    struct sockaddr_in6 server_addr;
    memset(&server_addr, 0, sizeof(server_addr));

    server_addr.sin6_family = AF_INET6;
    inet_pton(AF_INET6, SERVADDR, &server_addr.sin6_addr);
    server_addr.sin6_port = htons(PORT);

    if (connect(sd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
        fprintf(stderr, "Connect %d failed with errno %d: %s\n", sd, errno, strerror(errno));
        exit(5);
    }

    printf("Seems like it worked this time!\n");
    close(sd);
}

很简单：

• 创建套接字
• 设置SO_REUSEADDR
• 设置SO_REUSEPORT
• 绑定到本地端口23456
• 连接到端口12345上的::1

奇怪的是，在MacOS上连续运行这个会导致这样的结果：

$ for i in {1..5}; do ./ipv6; done
Seems like it worked this time!
Connect 3 failed with errno 48: Address already in use
Connect 3 failed with errno 48: Address already in use
Connect 3 failed with errno 48: Address already in use
Connect 3 failed with errno 48: Address already in use
$

虽然在Linux上运行它似乎工作得很好：

$ for i in {1..5}; do ./ipv6; done
Seems like it worked this time!
Seems like it worked this time!
Seems like it worked this time!
Seems like it worked this time!
Seems like it worked this time!
$

我在端口12345上有一个侦听器：

$ nc -6 -l -v -p12345 -k

这并不局限于IPv6，尝试了与IPv4相同的事情-相同的行为。
有人能解释一下吗？
我以前以为它在bind()中失败，但它在connect()中。

编辑#1

根据How do SO_REUSEADDR and SO_REUSEPORT differ?，这适用于BSD：
因此，如果您将相同协议的两个套接字绑定到相同的源地址和端口，并尝试将它们连接到相同的目的地址和端口，则connect()实际上会失败，并对您尝试连接的第二个套接字显示错误EADDRINUSE，这意味着具有相同五值元组的套接字已经连接。
这就解释了为什么它不起作用。如果这在Linux上实际上是可行的，那么什么是没有意义的呢？
我当然希望在MacOS上完成这项工作，但我目前觉得这可能是不可能的--然而，我仍然想了解Linux是如何做到这一点的。