| .. | ||
| context_test.go | ||
| context.go | ||
| gen_sym.go | ||
| id_pool.go | ||
| LICENSE | ||
| README.md | ||
| stack_tags.go | ||
gls
Goroutine local storage
Huhwaht? Why?
Every so often, a thread shows up on the golang-nuts asking for some form of goroutine-local-storage, or some kind of goroutine id, or some kind of context. There are a few valid use cases for goroutine-local-storage, one of the most prominent being log line context. One poster was interested in being able to log an HTTP request context id in every log line in the same goroutine as the incoming HTTP request, without having to change every library and function call he was interested in logging.
This would be pretty useful. Provided that you could get some kind of goroutine-local-storage, you could call log.SetOutput with your own logging writer that checks goroutine-local-storage for some context information and adds that context to your log lines.
But alas, Andrew Gerrand's typically diplomatic answer to the question of goroutine-local variables was:
We wouldn't even be having this discussion if thread local storage wasn't useful. But every feature comes at a cost, and in my opinion the cost of threadlocals far outweighs their benefits. They're just not a good fit for Go.
So, yeah, that makes sense. That's a pretty good reason for why the language won't support a specific and (relatively) unuseful feature that requires some runtime changes, just for the sake of a little bit of log improvement.
But does Go require runtime changes?
How it works
Go has pretty fantastic introspective and reflective features, but one thing Go doesn't give you is any kind of access to the stack pointer, or frame pointer, or goroutine id, or anything contextual about your current stack. It gives you access to your list of callers, but only along with program counters, which are fixed at compile time.
But it does give you the stack.
So, we define 16 special functions and embed base-16 tags into the stack using the call order of those 16 functions. Then, we can read our tags back out of the stack looking at the callers list.
We then use these tags as an index into a traditional map for implementing this library.
What are people saying?
"Wow, that's horrifying."
"This is the most terrible thing I have seen in a very long time."
"Where is it getting a context from? Is this serializing all the requests? What the heck is the client being bound to? What are these tags? Why does he need callers? Oh god no. No no no."
Docs
Please see the docs at http://godoc.org/github.com/jtolds/gls