I am confused over how Go handles non-blocking I/O. Go's APIs look mostly synchronous to me, and when watching presentations on Go, it's not uncommon to hear comments like "and the call blocks".
Is Go using blocking I/O when reading from files or the network? Or is there some kind of magic that re-writes the code when used from inside a goroutine?
Coming from a C# background, this feels very unintuitive, as in C# we have the await keyword when consuming async APIs, which clearly communicates that the API can yield the current thread and continue later inside a continuation.
TLDR; will Go block the current thread when doing I/O inside a goroutine?, or will it be transformed into a C# like async/await state machine using continuations?
Go has a scheduler that lets you write synchronous code, and does context switching on its own and uses async I/O under the hood. So if you're running several goroutines, they might run on a single system thread, and when your code is blocking from the goroutine's view, it's not really blocking. It's not magic, but yes, it masks all this stuff from you.
The scheduler will allocate system threads when they're needed, and during operations that are really blocking (file I/O is blocking, for example, or calling C code). But if you're doing some simple http server, you can have thousands and thousands of goroutines using actually a handful of "real threads".
You can read more about the inner workings of Go here.