Is Socket.IO multithread?

I have a socket.io server which listens to sockets:

io.sockets.on('connection', function(socket){
    socket.on('myEvent', function(data){
        socket.emit('eventReceived', { status: 1 });
    });
});

Is this code working in multithread? if two clients will emit the myEvent event, it will work at the same time for both clients? or it will be handled one after the other?

Many thanks!