hs.network.ping.ping blocks callback function of timer about hammerspoon

[jamesb93]

Thanks for this – it makes sense to me. I'll assign them to some variables.

[jamesb93]

It worked. Thank you.

[Rhys-T]

The short version is that you need to save the objects returned by hs.timer.doEvery(...) and hs.network.ping(...) so that they don't get garbage-collected before they can do their job.

One quirk of Hammerspoon that often trips people up is that a lot of its objects have visible side effects when they are garbage-collected. Timers stop running, canvases and webviews close, event taps stop intercepting events, etc. To prevent that, you have to save a reference to the object somewhere, like a global variable, the return value of a required module, or a table inside one of those. hs.timer.doEvery, .doAfter, and hs.network.ping need the same treatment, even though their names sound more like 'do something' than 'create something'.

What makes this more annoying is that garbage collection in Lua is non-deterministic: Objects aren't guaranteed to get GC'd immediately when the last reference goes away, but can stick around for a while until Lua decides it needs to free up some memory. So a doEvery timer might seem to be working, then randomly stop itself some time later. I'm actually surprised it's failing that consistently for you. I run a GC pass at the very end of my config to make sure things break as quickly and consistently as possible.

See also: https://github.com/asmagill/hammerspoon/wiki/Variable-Scope-and-Garbage-Collection