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Select Default Case
The default case in a select statement executes immediately if no other channel has a value ready. A default case stops the select statement from blocking.
select {
case v := <-ch:
// use v
default:
// receiving from ch would block
// so do something else
}
Ignoring Channels
Sometimes you want to ignore a channel's value. You can do this by not binding it to a variable:
select {
case <-ch:
// event received; value ignored
default:
// so do something else
}
Alternatively, you can use the blank identifier _ to ignore the value:
select {
case _ = <-ch:
// event received; value ignored
default:
// so do something else
}
Tickers
- time.Tick() is a standard library function that returns a channel that sends a value on a given interval.
- time.After() sends a value once after the duration has passed.
- time.Sleep() blocks the current goroutine for the specified duration of time.
The functions take a time.Duration as an argument. For example:
time.Tick(500 * time.Millisecond)
If you don't add time.Millisecond (or another unit), it will default to nanoseconds. That's – taking a wild guess here – probably faster than you want it to be.
Read-Only Channels
A channel can be marked as read-only by casting it from a chan to a <-chan type. For example:
func main() {
ch := make(chan int)
readCh(ch)
}
func readCh(ch <-chan int) {
// ch can only be read from
// in this function
}
Write-Only Channels
The same goes for write-only channels, but the arrow's position moves.
func writeCh(ch chan<- int) {
// ch can only be written to
// in this function
}
Assignment
Like all good back-end engineers, we frequently save backup snapshots of the Textio database.
Complete the saveBackups function.
It should use a loop to read values from the snapshotTicker and saveAfter channels simultaneously and continuously.