What will happen if codes inside a NodeMCU timer execute over the timer interval I set?

With NodeMCU, we can easily create timer function in esp8266 chip. However, I wonder what will happen if codes inside a timer execute over the timer interval I set?

Please see the code below. If I set a timer with 2 seconds interval, and "Something to do" inside this timer executes over 2 seconds, then what will happen?

tmr.alarm(0, 2000, 1, function ()
    --Something to do
end)

a) Will "Something to do" be terminated once the interval reaches 2 seconds?

b) Or "Something to do" will continue execute until finish, and the next "Something to do" will be delayed?

c) Or the each round of this timer will wait for "Something to do" to finish regardless of the 2-seconds-interval? (the interval is automatically expanded)

d) or else?