Lock based on a flag

I want to lock few lines of code based on a flag from App config. So based on that flag I run the application asynchronously or not. So i need to lock execution of few lines of code by checking the flag. So i need to write code repetitive. Below is the sample

if (flag) {
    lock(dataLock){
        //few lines of code
    }
} else {
    //repeat the above code gain here (few lines of code)
}

Is there any alternative way where I can save my repeated codes.