Threadscope fails to read partially written file

[pacak]

If ghc compiled program was launched with option to write eventlog and then was interrupted by Ctrl-C then eventlog file will be partially written.

Actual behaviour: Threadscope fails to read such file complaining "There was a problem loading the eventlog", "too few bytes. Failed reading at byte position 4194995"

Expecting behaviour: threadscope displays an info box saying that file was damaged and only first XXXX bytes (YYY seconds) was recovered then it should work as if this file was finalized properly.

[MikolajKonarski]

That sounds reasonable and fits the far future work ideas to let ThreadScope? show the behaviour of a running program. As a first step, we might extend the eventlog validation that will appear in the next release of ghc-events to accept such partial eventlogs. Then comes your proposal, then comes continuous re-reading of logs that are being still written to.

For a short-medium term hack, we could have a flag that disables both the validation and the length check you stumbled upon. The same flag could later be used to signal to the validator that it's running on an incomplete log. Patches are welcome.

[MikolajKonarski]

For some related discussion, see

https://github.com/scpmw/ghc-events/commit/2a9a0364d4624ebacc51dd8636ad04fbcf333366#commitcomment-3000183