当关闭缓冲通道时，是否应该排空缓冲通道

Question

Given a (partially) filled buffered channel in Go

ch := make(chan *MassiveStruct, n)
for i := 0; i < n; i++ {
    ch <- NewMassiveStruct()
}

is it advisable to also drain the channel when closing it (by the writer) in case it is unknown when readers are going read from it (e.g. there is a limited number of those and they are currently busy)? That is

close(ch)
for range ch {}

Is such a loop guaranteed to end if there are other concurrent readers on the channel?

Context: a queue service with a fixed number of workers, which should drop processing anything queued when the service is going down (but not necessarily being GCed right after). So I am closing to indicate to the workers that the service is being terminated. I could drain the remaining "queue" immediately letting the GC free the resources allocated, I could read and ignore the values in the workers and I could leave the channel as is running down the readers and setting the channel to nil in the writer so that the GC cleans up everything. I am not sure which is the cleanest way.

Answer 1

There are better ways to achieve what you're trying to achieve. Your current approach can just lead to throwing away some records, and processing other records randomly (since the draining loop is racing all the consumers). That doesn't really address the goal.

What you want is cancellation. Here's an example from Go Concurrency Patterns: Pipelines and cancellation

func sq(done <-chan struct{}, in <-chan int) <-chan int {
    out := make(chan int)
    go func() {
        defer close(out)
        for n := range in {
            select {
            case out <- n * n:
            case <-done:
                return
            }
        }
    }()
    return out
}

You pass a done channel to all the goroutines, and you close it when you want them all to stop processing. If you do this a lot, you may find the golang.org/x/net/context package useful, which formalizes this pattern, and adds some extra features (like timeout).