just observed that there seems to exist a race whe...
# developmentc
curved-television-6568
04/21/2023, 9:57 PMjust observed that there seems to exist a race when a process result is cached and the digest for the files involved is captured. 🧵
curved-television-6568
04/21/2023, 9:58 PMI’m not sure how to investigate this so I’ll just dump some facts first, see what comes out if anything…
curved-television-6568
04/21/2023, 10:00 PMhacking on pants code base I have some
NameErrorcurved-television-6568
04/21/2023, 10:00 PManyone have any ideas or thoughts here?
e
enough-analyst-54434
04/21/2023, 10:33 PMWell, we use file watching in pantsd and that sounds like a missed event, which can always happen. I believe across OSs these systems are designed lossy with a ringbuffer to fend against badly performing watch clients. So this should all boil down to how we handle missed events, which I can't recall, but should give you a narrow area in the codebase to look.
enough-analyst-54434
04/21/2023, 10:34 PMBut, just on the surface this problem sounds fundamentally racy. Did this just happen once?
enough-analyst-54434
04/21/2023, 10:43 PMSo we invalidate all files on ring buffer overflow: https://github.com/pantsbuild/pants/blob/2983f166e18b1c1a480b85bf722d16d514b41b17/src/rust/engine/watch/src/lib.rs#L260-L262
But not all OSes support that event.
c
curved-television-6568
04/22/2023, 12:11 PMI’ve seen this before, but rarely, I think there’s a very narrow window for when the file mutation must take place in order to exhibit this behaviour.
curved-television-6568
04/22/2023, 12:11 PMI’m not sure I follow the reasoning why a missed file watching event would explain this. I would expect the failed process to use the fingerprint of the file prior to my saving the fixed version of the file; which was used to launch the process, rather than the fingerprint of the fixed version as it were when the process failed.
But I guess that’s a narrow enough code path described to actually dig into…