CODEWITHSUNDEEP
go
the_big_blackbox
the_big_blackbox

Reputation: 1196

Receiving from a channel into nowhere

Too often, reading at Go source code, I encounter this pattern where a value is received from a channel, something such as <-doneC, it does not save the result to a variable.

I don't understand what it does.

doneC, _, err := rest.XReceive(eHandler, errHandler)
if err != nil {
    fmt.Println("Error",err)
    return
}
<-doneC

Upvotes: 3

Views: 582

Answers (1)

rustyx
rustyx

Reputation: 85481

That's an idiomatic way to implement an asynchronous wait in Go.

A function starts a new goroutine and returns a "done" channel to the caller.

The caller then does <-doneC which is basically an attempt to receive from the channel, ignoring the result.

The goroutine, when finished, can then either send a dummy value to doneC or, better yet, simply close it. That acts as the signal for <-doneC to resume execution.

The added benefit of closing doneC instead of sending a dummy value is that (1) multiple calls to <-doneC can be unblocked at the same time, and (2) if none are waiting, the sending will block, but close won't.

Upvotes: 6

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