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Comment by cdelsolar | Hacker News Reader

Where's the evidence that Go can't handle large amounts of concurrency?

All over my profiler. Go can deal with something embarrassingly parallel, same as any other language, but try getting it to scale up to high core counts with small RPCs is impossible, for the reasons the OP mentioned: you can't avoid its global allocator and you don't control the scheduler either. You will spend all of your CPU time in runtime.findrunnable and runtime.mallocgc.

You will spend all of your CPU time in runtime.findrunnable

Profile your channel latency, then design around that. "Small RPCs?" With an 88 core server, should you be making that many remote procedure calls? Find the 20% most intensive code and take that out of the hands of the scheduler, as much as possible.

and runtime.mallocgc

Even with sync.Pool? Can you design those parts of the system to mostly use the stack?

Not for nothing but channels become a bottleneck pretty early when you start doing highly concurrent golang.

You can very carefully design around it using only channels but it quickly starts making more sense to just use a different concurrency abstraction.

My experience has been channels are a really good way to make highly concurrent code readable for people who hate concurrency (ymmv).

They aren't as efficient, but using them as a semaphore (i.e. only signaling) can facilitate fairly-efficient, easier-to-read shared memory. But I'm kind of proving the whole...

> You can very carefully design around it only channels

...part of your post.

Is there a Github issue for this problem? If not, would you consider filing one?

https://github.com/golang/go/issues

It should probably explain why one cannot "avoid its global allocator" by using pools and/or stack objects.

Stack is great, then you will spend more time in runtime.morestack because the Go authors have wisely decided that we are all too dumb to request specific stack sizes and we must rely on copying and doubling stacks larger than 2KiB even if we know in advance that 2KiB is not enough. This compares poorly with native threads where the stacks are dynamically allocated one page at a time without copying and we can specify the stack size _limit_ per thread if we need to. This is another place where the Go authors just arbitrarily decided that users cannot be trusted.

sync.Pool is fun but it has known scalability limits that are yet to be addressed in a released runtime (see https://go-review.googlesource.com/c/go/+/166960/ for example). You also can't use sync.Pool for anything that you need to be non-ephemeral, like CPU-local counters, because the GC can just blow them away at any time and the finalizers run at arbitrary future times or possibly never.

My point is that you should file a Github issue if there isn't one.

Why "should"? Nobody owes the writing of issues.

If you depend on an open source project, and can articulate a problem with it that can be fixed, then I do feel you should file an issue to contribute your insight.

The runtime.morestack issue is actually being tracked btw [0]. I'm also getting the impression that you want Go to be another C++, but I don't understand why.

All of your listed issues have additional details and discussions around them. It not "we don't add this stuff because you are too dumb to use it". It's more "we don't know how to add this currently so it would properly interact with other features and be non-confusing". There are some exceptions to this rule (time.Time issue comes to mind) but overall they tend to listen to the developer base. Also, keep in mind that there are also relatively few Core Go developers, so they have to be extremely careful about what they gonna add in the language. It's going to be them who is going to support it in years to come.

As for C++ - yes, nothing beats it in highly optimized cases. And there is nothing wrong with that. The problem is not only writing C++ for those highly optimized cases is an extremely hard task by itself. The problem is finding people who can actually do it with the resulting code which is going to be supportable in the future (I'm not talking about UB, races or memory leaks).

[0]: https://github.com/golang/go/issues/18138

Edit: wording

I guarantee you the "little bit of planning" you're doing in C++ is far greater than the equivalent planning in Go to avoid the global allocator in your goroutines (i.e., allocate on the stack, use object pools, etc). I'm sure you still won't get to the same performance ceiling that C++ allows, but it doesn't mean "Go is bad at concurrency".

The philosophy of Go, as far as I can tell, is opinionated simplicity. In this way, it is fantastic at concurrency.

It gives you a simplified fork in goroutines, a way to safely pass by value or signal between these through channels, and structures like select to psuedo randomly deal with race conditions.

That stuff is all awesome!

But when you are talking about performance, opinionated simplicity is a bad philosophy. You are going to want the finer grained control the poster is asking for, and which Go deliberately doesn't allow for. C, C++, and Rust will always have a speed advantage because they lack the overhead of the GC and were designed with allowing the developer minute control of the system, which is the space to make such optimizations.

That said, opininated simplicity means every Go codebase I drop into looks roughly the same. That is not true in the above langauges, precisely because they allow for more control.

To me, Go's ideal use case is the domains of Java, Python, NodeJS, and even Elixir -- where it has a performance edge in many cases and where its consistant style really shine.

All that to say, Go is bad at performance optimized concurrency, as designed.

Your post doesn’t address mine. I gave specific advice for addressing the GP’s issue. It’s much easier to move your allocs out of the hot path in Go than it is to do virtually anything in C++. I’m not claiming Go will compete with C++ on performance, only that his argument isn’t a good reason to write off Go. (I’ve written a lot of both languages).

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