Read from one channel and write to another within one select-case

Question

Consider this Go code which shall call worker.DoWork() immediately and then once every minute:

triggerChan := make(chan time.Time, 1)
triggerChan <- time.Now() // We don't want to wait a minute for the first call of worker.DoWork() to happen.
ticker := time.NewTicker(time.Minute)
defer ticker.Stop()
for {
    select {
    case triggerChan <- <-ticker.C:
    case <-triggerChan:
        worker.DoWork()
    }
}

A value is written to triggerChan before the first select to direct it into case <-triggerChan to have worker.DoWork() called immediately. However, in the case that ticker.C already had a value available (not all that unlikely if we used something like time.Microsecond instead of time.Minute ), what would happen? Would the runtime see that triggerChan <- <-ticker.C would block, or would it happily soft-lock unaware of what is trying to be done with the result of <-ticker.C ? Is it aware of this "from channel into channel"-situation?

Answer 1

The select decides based on the state of triggerChan , however it first evaluates the right hand side expressions for send operations. So on entry, it will wait until <-ticker.C returns. Then it will read the first value from the channel, and then write to it...