A non re-entrant function is a function that could only be executing once at any point in time, regardless of how many times it is being invoked and by how many goroutines.
This post illustrates blocking non re-entrant functions and yielding non re-entrant functions implementations in golang.
A use case
A service is polling for some conditions, monitoring some statuses once per second. We want each status to be checked independently of others without blocking. An implementation might look like:
func main() {
tick := time.Tick(time.Second)
go func() {
for range tick {
go CheckSomeStatus()
go CheckAnotherStatus()
}
}()
}
We choose to run each status check in its own goroutine so that CheckAnotherStatus() doesn’t wait upon CheckSomeStatus() to complete.
Each of these checks typically take a very short amount of time, and much less than a second. What happens, though, if CheckAnotherStatus() itself takes more than one second to run? Perhaps there’s an unexpected network or disk latency affecting the execution time of the check.
Does it make sense for the function to be executed twice at the same time? If not, we want it to be non re-entrant. Continue reading » “Implementing non re-entrant functions in Golang”