在channel.Consume（）上使用channel.Get（）有缺点吗？

Question

I'm using streadway's amqp library to connect with a rabbitmq server. The library provides a channel.Consume() function which returns a "<- chan Delivery". It also provides a channel.Get() function which returns a "Delivery" among other things.

I've to implement a pop() functionality, and I'm using channel.Get(). However, the documentation says:

"In almost all cases, using Channel.Consume will be preferred."

Does the preferred here means recommended? Are there any disadvantages of using channel.Get() over channel.Consume()? If yes, how do I use channel.Consume() to implement a Pop() function?

Answer 1

As far as I can tell from the docs, yes, "preferred" does mean "recommended".

It seems that channel.Get() doesn't provide as many features as channel.Consume(), as well as being more readily usable in concurrent code due to it's returning a chan of Delivery, as opposed to each individual Delivery separately.

The extra features mentioned are exclusive, noLocal and noWait, as well as an optional Table of args "that have specific semantics for the queue or server."

To implement a Pop() function using channel.Consume() you could, to link to some code fragments from the amqp example consumer, create a channel using the Consume() function, create a function to handle the chan of Delivery which will actually implement your Pop() functionality, then fire off the handle() func in a goroutine.

The key to this is that the channel (in the linked example) will block on sending if nothing is receiving. In the example, the handle() func uses range to process the entire channel until it's empty. Your Pop() functionality may be better served by a function that just receives the last value from the chan and returns it. Every time it's run it will return the latest Delivery.

EDIT: Example function to receive the latest value from the channel and do stuff with it (This may not work for your use case, it may be more useful if the function sent the Delivery on another chan to another function to be processed. Also, I haven't tested the code below, it may be full of errors)

func handle(deliveries <-chan amqp.Delivery, done chan error) {
    select {
    case d = <-deliveries:
        // Do stuff with the delivery
        // Send any errors down the done chan. for example:
        // done <- err
    default:
        done <- nil
    }
}