Mention when to create own scheduler in binding development docs

[rkoshak]

Based on a tricky problem analyzed here: https://community.openhab.org/t/oh-stops-properly-processing-changes/165147/88 we discovered that the Chromecast and Exec bindings were both using the default scheduler provided by BasicThingHandler to run their execution methods.

This should only be done in cases where that execution function will always run fast. But in the case of these two bindings that is not guaranteed and the result was the Chromecast binding was causing a significant delay when Exec binding commands were processed.

A few sentences should be added to the developer docs to make sure developers know of this limitation.

I can take a cut at that but I'm not a developer so I might get the wording wrong or put it in the wrong place. I'll need help to make sure it's worded correctly.

[openhab-bot]

This issue has been mentioned on openHAB Community. There might be relevant details there:

https://community.openhab.org/t/oh-stops-properly-processing-changes/165147/97

[stefan-hoehn]

I have looped in @lolodomo as he was part of the community conversation

[andrewfg]

a tricky problem analyzed here

Note that we have in the meantime also introduced two PRs in core to make the analysis less tricky in future.

openhab/openhab-core#4948
openhab/openhab-core#4969

[rkoshak]

The number of changes going on and in work is why I've held off on starting anything here. Changes to the developer docs may become moot or might become more involved when the root problem gets addressed.

[andrewfg]

Agreed.