TestUDPConcurrent closed its UDP connection as soon as the send loop
finished, and then required that at least one reply had arrived. With
GOMAXPROCS=1 the send loop runs to completion before the proxy's relay
goroutines are scheduled at all, so the close discarded every response.
The test failed on all 20 runs of "go test -race -count=20 -cpu=1".
Wait for the first reply, with a 10 second timeout, before closing the
connection.
This also makes the test catch the race it was written for more often.
With the fix in 0301c7493 reverted, "-cpu=2" reports the race where it
previously reported none.
Fixes#21182
Signed-off-by: Brendan Creane <bcreane@gmail.com>
Brendan Creane
f48358288c