52 ms·

I was under the impression that goroutines were cooperative but that they yield pretty aggressively (on blocking channel operations, disk and network I/O, cgo c

• masklinn 3y ago
  New implicit yield points started getting added from 1.2, which added a yield point in the function prologue (so any function call, even with no IO whatsoever, could yield). I think later releases also added yield points on allocation and stack growth. This culminated in 1.14, which made the runtime preemptive on most platforms (https://go.dev/doc/go1.14#runtime https://go.dev/doc/go1.14#runtime) in order to fix the last sticking point where a goroutine might not yield: a tight numerical loop might never yield. This was an issue, because the GC relied on scheduling to slip in its STW pauses, so the GC would trigger STW, progressively pause every goroutine reaching a yield point, but would be unable to ever pause the last goroutine, and the program would pretty much grind to a halt until it was done. There are ways to handle this (e.g. insert trapping reads in various control structures), but ultimately preemption was considered a better and more useful solution.