Simplify the qmlextensionplugins example a bit

[lu-fennell]

... by using a channel to shut down the timer thread, instead of a
condvar.

I was a little distracted by the verbose handling of the condvar when looking at the example. This is my attempt to make it a bit clearer. Maybe you like it.

[lu-fennell]

Note: I used the channel from std::sync::mpsc which I guess is not really recommended, as it seem to have bugs. So maybe it's better to switch to crossbeam's channel.

[ogoffart]

To me, the two are equal in term of complexity. Although yours has less lines of code.

I wouldn't want to pull a crossbeam dependency just for that.

Anyway, the change looks good to me.

@ratijas what's your opinion?

[lu-fennell]

To me, the two are equal in term of complexity.

Fair enough :)

Fwiw, I, personally, find that the channel version has less subtleties to be aware of. In particular, it took me a little while to realize (resp. read up on) the interaction between condvars and mutexes and why spurious wake-ups aren't a problem here. But that's just me, I guess.

Anyhow, in case you prefer the original condvar version, it would be good to replace thread: Option<(JoinHandle<()>, Arc<AbortCondVar>)> with thread: Option<Arc<AbortCondVar>>; the JoinHandle<()> part is never used...