bartblast
What is the bullet-proof way to get notified when any module in a Phoenix application gets recompiled?
I’m working on a bullet-proof live reload mechanism in Hologram, and I need a reliable way to be notified when any module in a Phoenix application gets recompiled and its .beam file gets updated.
From my research, I’ve discovered that there may be a few ways to approach this:
- Watching for
.beamfile changes - Set up a file system watcher to monitor changes to.beamfiles - Hook into compilation tracers - Use Elixir’s compilation tracers somehow
What do you recommend? Is there another, more reliable approach that I’m missing?
I’m looking for a solution that’s as robust as possible, with minimal chances of missing any module recompilations, even in edge cases. Importantly, I want a mechanism that is not dependent on any Phoenix-related internals, just a pure Elixir way of doing this.
Thanks for your insights!
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garrison
For my styled components library I used a Mix compiler to hook the compilation and then regenerate the compiled CSS from all of the modules. I didn’t do any checking of which modules were recompiled or anything, though. Figured I could do some diffing down the line if needed but I’ve yet to run into any performance problems. I think I stole most of the approach from Surface, which did roughly the same thing 
Looking at those docs now I see they’ve added some new stuff (related to the LSP work, I believe). I’ll have to look into that!
jstimps
Is this what you’re looking for?
jstimps
I meant to link :beam_lib.cmp_dirs/2 directly. I guess the Discourse magic didn’t pull that into the preview.
In any case, cmp_dirs will tell you which beams have differing code between two dirs. For example you can compare a release dir on the system with a release dir in a fresh clone to decide which modules have changed. I have used this in the past to do targeted reloads of specific modules in running production systems, without a restart and without relup. (Of course you have to know a priori that the module you’re loading is safe, and does not change any assumptions about runtime state)
I realize it’s not exactly what you’re looking for but maybe a piece of the puzzle.
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