Hello,
We were having a discussion at work about passing around references to
sync.WaitGroup. I said it was a bad idea, because if a goroutine launched a
goroutine of its own and called sync.WaitGroup.Add() after a goroutine
called sync.WaitGroup.Wait(), but before the count dropped to 0, your code
would panic. The comments seem to support this:
"If a WaitGroup is reused to wait for several independent sets of events,
new Add calls must happen after all previous Wait calls have returned."
And the WaitGroup source code for Add has lines like this:
if w != 0 && delta > 0 && v == int32(delta) {
panic("sync: WaitGroup misuse: Add called concurrently with Wait")
}
But a co-worker wrote this code, and it runs without a
panic: https://play.golang.org/p/NjqK_YoqHeH
I thought that this code might only be working because the playground is
single-threaded, but when this code is run locally, it also completes
without panics. Running it with the race flag also works properly.
How do you trigger those panics in the WaitGroup codebase?
Thanks,
Jon
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