Timeout for WaitGroup.Wait()

Question

What is an idiomatic way to assign a timeout to WaitGroup.Wait() ?

The reason I want to do this, is to safeguard my \'scheduler\' from potentially awaiting an errant \'w

Answer 1

Mostly your solution you posted below is as good as it can get. Couple of tips to improve it:

• Alternatively you may close the channel to signal completion instead of sending a value on it, a receive operation on a closed channel can always proceed immediately.
• And it's better to use defer statement to signal completion, it is executed even if a function terminates abruptly.
• Also if there is only one "job" to wait for, you can completely omit the WaitGroup and just send a value or close the channel when job is complete (the same channel you use in your select statement).
• Specifying 1 second duration is as simple as: timeout := time.Second. Specifying 2 seconds for example is: timeout := 2 * time.Second. You don't need the conversion, time.Second is already of type time.Duration, multiplying it with an untyped constant like 2 will also yield a value of type time.Duration.

I would also create a helper / utility function wrapping this functionality. Note that WaitGroup must be passed as a pointer else the copy will not get "notified" of the WaitGroup.Done() calls. Something like:

// waitTimeout waits for the waitgroup for the specified max timeout.
// Returns true if waiting timed out.
func waitTimeout(wg *sync.WaitGroup, timeout time.Duration) bool {
    c := make(chan struct{})
    go func() {
        defer close(c)
        wg.Wait()
    }()
    select {
    case <-c:
        return false // completed normally
    case <-time.After(timeout):
        return true // timed out
    }
}

Using it:

if waitTimeout(&wg, time.Second) {
    fmt.Println("Timed out waiting for wait group")
} else {
    fmt.Println("Wait group finished")
}

Try it on the Go Playground.