In the following snippet for having a function representing work send a
heartbeat to any listeners.
Why is a select statement used in `sendPulse` instead of just executing
`heartbeat <- struct{}{}`?
And why provide an empty default case?
doWork := func(
done <-chan interface{},
pulseInterval time.Duration,
) (<-chan interface{}, <-chan time.Time) {
heartbeat := make(chan interface{})
results := make(chan time.Time)
go func() {
defer close(heartbeat)
defer close(results)
pulse := time.Tick(pulseInterval)
workGen := time.Tick(2 * pulseInterval)
sendPulse := func() {
select { // why have a select statement?
case heartbeat <- struct{}{}:
default: // why have the default case?
}
}
sendResult := func(r time.Time) {
for {
select {
case <-done:
return
case <-pulse:
sendPulse()
case results <- r:
return
}
}
}
for {
select {
case <-done:
return
case <-pulse:
sendPulse()
case r := <-workGen:
sendResult(r)
}
}
}()
return heartbeat, results
}
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