With forks (*nix), when you have multiple processes all waiting to accept on a shared socket, when a client connects, *every* listening process receives the connect.

That would be horrible, but fortunately it's not true. If multiple processes waiting for a connection on the same socket, when client connects, *only one* listening process accepts connection. Here's a simple example that demonstrates it:

use 5.010;
use strict;
use warnings;

use IO::Socket::INET;

my $sock = IO::Socket::INET->new(LocalPort => 7777, Listen => 10);

for (1..3) {
    my $pid = fork;
    unless($pid) {
        my $cli = $sock->accept;
        say "Process $$ accepted connection from " . $cli->peerport;
        print while <$cli>;
        exit 0;
    }
}
[download]

Try to connect to 7777 and you will see that only one process will accept connection. Hence there's no need to have any global mutexes.

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