added new server with epoll(4).

echo-epoll.pl

@@ -0,0 +1,64 @@
+use strict;
+use warnings;
+use Getopt::Long;
+use IO::Socket::INET;
+use IO::Epoll;
+use Fcntl;
+
+my $concurrent = 10; # max event
+my $port = 9010;
+GetOptions(
+    'concurrent=s' => \$concurrent,
+    'port=i'       => \$port,
+);
+
+print "$0: http://localhost:$port/\n";
+print "concurrency: $concurrent\n";
+
+#my $EPOLLONESHOT = (1 << 30);
+my $epfd = epoll_create($concurrent);
+
+my $listener = IO::Socket::INET->new(
+    LocalHost => '0.0.0.0',
+    LocalPort => $port,
+    Listen    => 10,
+    ReuseAddr => 1
+) or die $!;
+
+my @Sock_Holder;
+my $listener_fd = fileno $listener;
+
+epoll_ctl($epfd, EPOLL_CTL_ADD, $listener_fd, EPOLLIN) >= 0
+    || die "epoll_ctl: $!\n";
+
+while (1) {
+    my $events = epoll_wait($epfd, $concurrent, -1); # Max 10 events returned, 1s timeout
+
+    ### $events
+    for my $ev (@$events) {
+        ### ev: $ev;
+        if ($ev->[0] == $listener_fd) {
+            ### >listenr: $$
+            my $sock = $listener->accept;
+            my $sock_fd = fileno $sock;
+            $Sock_Holder[$sock_fd] = $sock;
+            my $flags = fcntl($sock, F_GETFL, 0) or die "fcntl  GET_FL: $!";
+            fcntl($sock, F_SETFL, $flags|O_NONBLOCK) or die "fcntl  SET_FL: $!";
+            epoll_ctl($epfd, EPOLL_CTL_ADD, $sock_fd, EPOLLIN) >= 0
+                || die "epoll_ctl: $!\n";
+        } else {
+            ### >client: $ev->[0], $$
+            open my $sock, "+<&=".$ev->[0] or die "fdopen: $!";
+            my $line = <$sock>;
+            if ($line) {
+                print $sock $line;
+            } else {
+                ### no data: $ev->[0], $$
+                epoll_ctl($epfd, EPOLL_CTL_DEL, $ev->[0], 0) >= 0
+                    || die "epoll_ctl: $!\n";
+                $Sock_Holder[$ev->[0]] = undef;
+                close $sock;
+            }
+        }
+    }
+}