ignore events during grace period after task start

[Canop]

When some file events are received:

• the task child process waits for 5ms before starting the real task
• during the same period, file events are discarded

The goal is to prevent

• the cargo job from running with not all changes
• a bunch of quasi-simultaneous file changes from triggerring more than one cargo execution

Downside is that you have to wait for 5ms more before the computation result is displayed after a save.

The delay can be removed or modified in the preferences. Eg grace_period="15ms" or grace_period="none".

May fix #222

[narpfel]

Thanks, this works well for me.

• the task child process waits for 5ms before starting the real task

I’m not sure if that’s really necessary. Yes, there technically is a race between the text editor writing the file and the triggered job reading the file, however I’d expect that in the vast majority of cases, the text editor is faster. Just starting cargo through the rustup shim takes ~50ms (rust-lang/rustup#2626), so the sleep here

bacon/src/exec/executor.rs

Lines 111 to 116 in b8cb636

	// before starting the command, we wait some time, so that a bunch
	// of quasi-simultaneous file events can be finished before the command
	// starts (during this time, no other command is started by bacon in app.rs)
	if !grace_period.is_zero() {
	thread::sleep(grace_period.duration);
	}

is probably not necessary. On the other hand, a couple of milliseconds are probably not noticeable.

[Canop]

I first pushed the PR without this sleep, then I decided I didn't want to have race conditions when cargo becomes faster and I'm sure nobody will be annoyed by those 5 or 10 ms.