Before this change the cancelFunc could be called twice, once while
handling the interrupt (CTRL-C) and once while unwinding the stack if
the function happened to finish.
This change ensure the cancelFunc is only called once by wrapping it
in a sync.Once
When rclone received a SIGINT (Ctrl+C) or SIGTERM signal while an atexit
function is registered it always terminated with status code 0. Unix
convention is to exit with a non-zero status code. Often it's
`128 + int(signum), but at least not zero.
With this change fatal signals handled by the `atexit` package cause
a non-zero exit code. On Unix systems it's `128 + int(signum)` while
on other systems, such as Windows, it's always 2 ("error not otherwise
categorised").
Resolves#5437.
Signed-off-by: Michael Hanselmann <public@hansmi.ch>
Before this change CTRL-C could come in to exit rclone which would
start the atexit actions running. The Fuse unmount then signals rclone
to exit which wasn't waiting for the already running atexit actions to
complete.
This change makes sure that if the atexit actions are started they
should be completed.
When running `rclone mount`, there were 2 signal handlers for `os.Interrupt`.
Those handlers would run concurrently and in some cases cause either unmount or `atexit.Run()` being skipped.
In addition `atexit.Run()` will get called in `resolveExitCode` to ensure cleanup on errors.
