[bcrosby95]

You're just using the channel as a future.

None of this is really problematic at the top level view of things. But when you need to compose libraries or applications that make use of these things - yes, even channels in Go - you can start running into problems.

Especially if you don't actually control the process you're running in. This is why promises and async/await really exist. E.g. if you have code you need to fork off the main UI thread so you don't block it, but need to re-capture the UI thread so you can call UI update code when you're done with your long running task. async/await is so much cleaner here.

Async/await allow for much more complex control of flow than simple goroutines and channels. Sometimes it's necessary. Sometimes it isn't. It was necessary in nodejs. It's extremely useful in applications where you have a "main thread" that drives your application that you don't want to unnecessarily block. Go doesn't solve this problem out-the-box. There's a reason why c# adopted async/await despite having futures and all sorts of other tools.

[philosopher1234]

I don’t see how futures can be more flexible than go routines. Could you explain that more? And why couldn’t you just spawn a goroutine to avoid blocking your main thread?

[bcrosby95]

The point of async/await is to make code that exits and returns to some kind of execution context - without blocking either context - read like plain, synchronous code.

A simple example of where this might be useful is in UI code. Every UI framework I've worked in has a single UI thread, where all UI changes must go - e.g. adding a button, adding text to the UI, etc. At the same time, you don't want to block the UI thread, because that will cause the UI to become unresponsive.

A common thing you might do in a UI is: on button click, make an API call, then update the UI with that data.

The on button click will be called from the UI thread. You don't want to make the API call there though because that would block the UI thread. So you spin it off into a worker thread. But after that worker finishes, you need to regain control of the UI thread so you can update the UI.

The way you traditionally do this is you have some kind of main loop which is running the UI thread, which has (among other things) some kind of queue of functions it should call (I assume it would be a channel in Go). So your worker thread will hold onto a reference to this queue. When it finishes, it pushes a function call onto the queue. The main UI loop occasionally checks this queue and calls all functions in it. So eventually it gets called, allowing you to update the UI in the UI thread.

This can be fine for simple scenarios. But if you have deeply nested or complex interactions between multiple threads, the code can get confusing and turn into "callback hell". This is the problem that was ran into in early versions of nodejs. This is the problem async/await was intended to solve. It's a bigger problem in nodejs due to its design, but it can still be useful in other languages that don't share that design depending upon the application you're writing.

[jayd16]

Sometimes you want to block the main thread, or at least finish what you were doing. With async/await and cooperative concurrency you can be explicit about what will run on a thread. You retain control of the thread until you yield or await. You can ask tasks to complete on other threads or post back to the main thread. You have a lot of control. Its easy to write code without locks that runs concurrently on the main thread but is still able to build a UI in a threaded way.

I don't really know how go UI frameworks work. How do you have multiple, preemptively scheduled goroutines on the UI thread but without critical sections? You have to use channels and message passing back to a main thread manager to handle this, yes?

I think Java's Loom would have the same issue but again, I don't really know. Perhaps worrying about a UI thread is 'fighting the last war' and we should work on new UI paradigms in these new language features.

[throwaway34241]

I'm working on a UI app in Go, yes I think you'd use channels and message passing but it doesn't look all that bad in practice.

First you'd probably call runtime.LockOSThread() to tie a goroutine to an OS thread if the native API you're coding against needs that (like Cocoa, OpenGL, etc).

To perform work on the main thread using closures is probably the most convenient way. So you just have a RunOnMainThread(func(){...}) that puts the closure on a channel to run on the main thread (or uses some similar feature from the underlying native framework).

It's not terribly inconvenient - it's similar to the old Cocoa / UIKit performSelectorOnMainThread: method except that you have closures to make things simpler.

There's probably a little syntactic overhead compared to if you had several async/await functions running concurrently on the main thread. But on the other hand it's probably a bit easier to reason about, since the flow of execution on the main thread is very straightforward (if you have multiple async/await functions running at the same time on the main thread, it seems like every time they await a result they'd have to worry about other code being run on the main thread, and make sure they release any locks, etc).

[anonymoushn]

You can spawn a goroutine that immediately waits on a channel, so that it will not actually do anything until you want it to. This seems at least as expressive as a single-threaded switch() primitive. I think it can also express the threaded async pattern you want, but I'm not sure.

[jayd16]

Are there any popular, idiomatic Go UI frameworks I could explore?

[oefrha]

You can try your luck with https://github.com/avelino/awesome-go#gui

I explored the landscape earlier this year when I was building a GUI version of a CLI tool written in Go. I was throughly disappointed by all the “native Go” and non-webview options — narrow selection of widgets with basic functionality missing, UIs ranging from lack of polish to horrendous looking (that makes Java GUIs look like godsend), lots of bugs, etc. I ended up using the Qt binding which, despite its own share of problems, at least worked fairly reliably and didn’t constantly get in my way in every way imaginable: https://github.com/therecipe/qt

[kjksf]

A channel can be used as future / promise but that's not what it is and that's not how it's used by majority of Go programs.

Channel is what it says it is: a way to send data between goroutines.

Also, Go works just fine for UI code, out of the box. See https://github.com/lxn/walk for one of many examples.

You just lock main goroutine with runtime.LockOSThread() to its thread and that's your UI thread and marshall code that touches UI to UI thread. Which is the same thing you must do in C# (or any other language). See https://github.com/golang/go/wiki/LockOSThread