file watcher tidying
Use a sync mutex, which is sensible here.
(I was prompted to look at this because @wesleyac was having trouble with the .block_on()
impl in MockExecutor
. #1835 (closed). I wanted to experiment with what happens if we have Runtime
not impl BlockOn
. I'm not sure what the right direction is there, but I think this MR is good anyway: even if calling .block_on
continues to be possible here, it's not necessary and using an async mutex is overcomplicated.)