WaitGroup.Wait should not be concurrently called WaitGroup.Add.
In other words, we should not start new goroutines after shutodwn is called.
Thus, add a conditional to check that shutdown has not been called
before starting off a new waitAndDelete goroutine.
Updates tailscale/corp#14772
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
File resumption requires keeping partial files around for some time,
but we must still eventually delete them if never resumed.
Thus, we implement asynchronous file deletion, which could
spawn a background goroutine to delete the files.
We also use the same mechanism for deleting files on Windows,
where a file can't be deleted if there is still an open file handle.
We can enqueue those with the asynchronous file deleter as well.
Updates tailscale/corp#14772
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
Joe Tsai