solo.go

package command

import (
	"fmt"
	"net"
	"os"
)

const (
	message = "This process is already running in SOLO mode."
)

// Solo is used to ensure only 1 instance of the current command runs at the same time.
// This can be used to ensure long cron processes don't start the same application before
// the previous one completes. Make sure to invoke Solo with "go", as it does not
// return.  Invoke it like so: "go command.Solo(12345)".
//
// Inspired by : http://timkay.com/solo/solo
func Solo(port int) {

	service := fmt.Sprintf(":%d", port)

	tcpAddr, err := net.ResolveTCPAddr("tcp4", service)
	checkError(err)

	// checkError is triggered when second process tries to open this port
	listener, err := net.ListenTCP("tcp", tcpAddr)
	checkError(err)

	for {
		conn, err := listener.Accept()
		if err != nil {
			continue
		}

		conn.Close()
	}
}

func checkError(err error) {
	if err != nil {
		fmt.Fprintf(os.Stderr, message)
		os.Exit(1)
	}
}