Add --smoothing parameter for watchmedo --command to smooth over / ignore multiple triggering events.

[nuket]

No description provided.

[nuket]

Changes relate to Issue #136, which relates to a problem I was having with a software development IDE. Whenever the IDE makes changes to a source file, it generates more than a single filesystem event, and triggers multiple automatic builds.

Using a --smoothing=<seconds> parameter will cause the first triggering event to be fired after <seconds> have passed, and after the extra/interim-detected filesystem events have been cleared out of the api.py::dispatch_events::event_queue.

[tamland]

HI. I'm not sure there's any need for this in the core api. Can you not add it in ShellCommandTrick or other tricks? If I've understood #136 correctly, people just want all events that occur during the execution of shell command to be skipped. There shouldn't be any need for delays or anything to be added to the python api.

[tamland]

possible race condition here

[nuket]

I can give it a shot. The reason I believed I needed to add the smoothing parameter to drain the event_queue all the way down in the API level is because I've tried using --wait and --no-parallel on the ShellCommandTrick, and it doesn't work as I would expect.

i.e. Using both parameters at the same time would lead me to believe that the command would "avoid multiple simultaneous instances" and "ignore events that happen while the previous process is still running". So it should run the command a single time, and ignore events that happen while that command is running.

But what I see instead is the command being run serially multiple times when I do a touch * on a watched directory's contents.

[tamland]

On second thought: doesn't --no-parallel actually implement this? (awful name). https://github.com/gorakhargosh/watchdog/blob/master/src/watchdog/tricks/__init__.py#L94 returns immediately while the command is running. Author notes "This causes events that arrive while a process is still running to be silently ignored".

Don't use --wait and --no-parallel simultaneously though. Then I think you have misunderstood. --wait will just wait for the command to finish before processing the next event (conflicting with --no-parallel).

[nuket]

Ok, yes, that works. Meaning Issue #136 can be closed. But yeah, not the best naming.