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Comment by weberc2 | Hacker News Reader

> Once you use async/await it's hard to go back, since the code is as easy to write as synchronous code.

Wait until you try goroutines :)

I don't think anyone would enjoy going back to goroutines (threads) after async/await. Multithreaded code is actually much harder to write and deal with. Go is inappropriate example here.

Goroutines are not threads: https://rcoh.me/posts/why-you-can-have-a-million-go-routines...

https://en.wikipedia.org/wiki/Thread_(computing)#M:N_(hybrid...

Goroutines are probably closer to Fibers which D also has:

https://en.wikipedia.org/wiki/Fiber_(computer_science)

They used to be closer to fibers years ago, when they were running on a single thread by default. Now they behave exactly like normal threads with the same problems. And fibers are threads anyway.

Care to share a reference to them no longer being lightweight?

They still start with tiny stacks, if that's what you are asking. I believe it's somewhere around 2 KB nowadays.

goroutines are anything but threads.

Here's a 40min talk explaining how Go's scheduler works:

https://youtu.be/YHRO5WQGh0k

No, they are threads. It doesn't matter if they start with tiny growing stacks and whether blocking syscall wrappers call into the scheduler. Those are just implementation details.

I mean, sure, but they have all the same problems as threads for most / application-level developers. They're indeed quite different when you get into calling out to C or other kinds of FFI, but relatively few developers need to do so directly. For everyone else, they come with very nearly exactly the same semantics as threads.

I have used both and its hard to argue that goroutines and channels are as easy to use as async/await.

On the surface, perhaps, but when you factor in the gotchas of both approaches and the debugging difficulty, I much prefer goroutines. In particular, I’ve never witnessed someone DOS a fleet of servers in Go by scheduling a task was making a sync call under the covers, by doing an intensive computation in the event loop, or by scheduling tens of thousands of tiny events. We also have a lot of bugs involving accidentally putting the task/coroutine into a variable instead of the result of the task because the programmer forgot the “await” keyword, but that’s a dynamic typing problem.

Goroutines are not threads. Async await behind the scenes uses threads.

Does it? https://blog.stephencleary.com/2013/11/there-is-no-thread.ht...

In that case and in some others it doesn’t, but in general it does: https://stackoverflow.com/questions/17661428/async-stay-on-t... Probably it makes sense to say that async await can try to use a continuation passing style or run on a different thread because there is no actual guarantee that it will use one or the other.

After I used Go channels (https://go101.org/article/channel-use-cases.html), I feel async/await is much like a rigid toy. :)

Can use System.Threading.Channels https://docs.microsoft.com/en-us/dotnet/api/system.threading... if you like that programming model

Do those channels support async? Since C# is built around async/await for scaling to large numbers of connections / tasks, they wouldn't be very useful if they didn't support async, but I'm not familiar enough with modern C# to figure out if they do or not.

Yes. It's a library that is fully async. We process millions of records/second using these.

Do you happen to have any public information on this approach, it sounds interesting but I'm not up on the C# world like I used to be.

This is the best overview article so far: https://ndportmann.com/system-threading-channels/

Thank you.

Yeah you have a triple for different use cases; the sync call is `TryRead` so its non-blocking; `ReadAsync` for async reading and `WaitToReadAsync` to wait for data to be available without reading (likely then followed by the non-blocking `TryRead` in usage)

Does it support select? Almost half of concurrrent programming use cases in Go are select related.

Yeah, at a guess you'd combine the multiple `WaitToReadAsync` with `await Task.WhenAny`; then use `TryRead` to run though the bunch of channels in a non-blocking way.

Could even use the return `await Task.WhenAny` to tell you the specific one to check. Shouldn't be a very hard construct to make; to make it more select like.

good. It looks it is much like the reflect.Select (https://golang.org/pkg/reflect/#Select) in Go.

It has the benefit that any number of tasks can be selected, but the efficiency is not good as hard-coded select blocks.

But it looks C# Task.WhenAny has much less use case variants than Go select block.

aka "threading without thread handles". no thanks.

It works out okay for the most part, but fair point.

The thing about Go is that you're always writing preemptively threaded code, with all of its issues.

The holy grail is cooperative multitasking and always-on, opt-out async [0] if you ask me.

[0] https://gitlab.com/sifoo/snigl#tasks

I guess I think of that as a feature, but I also write threadsafe code by default. It’s not an issue compared to our async python code. Someone calling a library that makes sync calls under the hood can block the event loop until the load balancer kills it. Same thing with CPU intensive tasks or just a lot of tasks on the event loop. Never mind the problems of async code in a dynamic language.

> Never mind the problems of async code in a dynamic language.

Such as?

Forgetting the “await” keyword and trying to use a variable which now actually holds a future/coroutine as though it were the awaited future. We write tests to cover those cases.

An interesting point. But this could be mitigated in a fairly obvious way by requiring an equivalent of "await" that is basically an identity transform for future-returning function calls (i.e. if a call is returning a future, you must always either explicitly indicate that you're awaiting it, or else explicitly indicate that you want the raw future - a naked call is an error).

That wouldn't solve the problem at all--at best I'm getting a marginally clearer error message. It doesn't help me (the programmer) remember (before runtime) that my expression is evaluating to an async function and not a sync function. Whether I get the runtime error, "invalid call to async function" or "future has no property 'status_code'" is of little consequence.

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