SO_REUSEADDR and SO_REUSEPORT behavior changed?

Question

On older versions of Mac OS X, wildcard binding works as described here:

Socket parameters SO_REUSEADDR and SO_REUSEPORT, how do they differ? Do they mean the same thing on all major operating systems?

Multicast addresses

The SO_REUSEADDR value is changed for multicast addresses, as it allows multiple sockets to bind to the exact same combination of source multicast address and port. In other words, for multicast addresses, SO_REUSEADDR behaves exactly like SO_REUSEPORT for unicast addresses. Actually, the code handles SO_REUSEADDR and SO_REUSEPORT the same for multicast addresses, which means you can say that SO_REUSEADDR means SO_REUSEPORT for all multicast addresses and vice versa.

and

MacOS x

At its core, MacOS X is simply BSD-style UNIX, based on a rather late version of BSD code that was even synced with FreeBSD 5 for Mac OS 10.3. This is why MacOS X offers the same options as BSD, and they also behave the same as in BSD.

10.10.5 , .

() UDP (errno = EADDRINUSE), SO_REUSEADDR. SO_REUSEPORT , .

:

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

int main() {
    for(int p = 0; p < 4; ++p) {
        printf("Flags set: ");
        if(p&1) printf("SO_REUSEADDR ");
        if(p&2) printf("SO_REUSEPORT");
        printf("\n");

        int handles[2];
        bool success = true;
        for(int i = 0; i < sizeof(handles)/sizeof(int); ++i) {
            handles[i] = socket(AF_INET, SOCK_DGRAM, 0);

            int flag = 1;
            if((p&1) && setsockopt(handles[i], SOL_SOCKET, SO_REUSEADDR, &flag, sizeof(flag)) == -1) {
                printf("Setsockopt %d, SO_REUSEADDR failed with errno\n", i, errno);
                success = false;
                break;
            }
            if((p&2) && setsockopt(handles[i], SOL_SOCKET, SO_REUSEPORT, &flag, sizeof(flag)) == -1) {
                printf("Setsockopt %d, SO_REUSEPORT failed with errno\n", i, errno);
                success = false;
                break;
            }

            struct sockaddr_in addr;
            memset(&addr, 0, sizeof(addr));
            addr.sin_family = AF_INET;
            addr.sin_port = 2000; // does not matter as long as it is currently free
            addr.sin_addr.s_addr = 0; // wildcard address

            if(bind(handles[i], (struct sockaddr*)&addr, sizeof(addr)) == -1) {
                printf("Bind %d failed with errno %d\n", i, errno);
                success = false;
                break;
            }
        }
        if(success)
            printf("Alright\n");

        for(int i = 0; i < sizeof(handles)/sizeof(int); ++i)
            close(handles[i]);
        printf("\n");
    }

    return 0;
}

:

Flags set: 
Bind 1 failed with errno 48

Flags set: SO_REUSEADDR 
Bind 1 failed with errno 48

Flags set: SO_REUSEPORT
Alright

Flags set: SO_REUSEADDR SO_REUSEPORT
Alright

Answer 1

Mac OS X , :

Socket SO_REUSEADDR SO_REUSEPORT, ? ?

  ...

, . . , ( ):

SO_REUSEPORT

SO_REUSEPORT - , SO_REUSEADDR. , SO_REUSEPORT , SO_REUSEPORT ....

.

Answer 2

! . SO_REUSEADDR SO_REUSEPORT. , * nix-. , , , Mac OS.

, . , .

lsof -i:<Port used by you>

, PID. -9, SO_REUSEPORT. !