>>kimi+(OP)
I think you mean <! and <!! - first one is parking take for use inside go blocks (lightweight threads) and second is blocking take for use outside them. I have sometimes wondered if they should have just called them, like, "take!" and "take!!" or even better "take-parking" and "take-blocking". Even if personally it was not hard for me to learn them, versus the whole model of async and the rules around go blocks.
I haven't heard complaints about the thread pool before, I thought it just matched your number of cores by default but could be configured. I do know if you do blocking takes (<!!) where you're supposed to do parking takes (<!) the lightweight threads block the entire parent "real" thread and you can get thread exhaustion, maybe it was that?