Alter how periodic session caching works

[fractalwrench]

Goal

Embrace periodicially caches sessions on disk to handle the case that a crash might lead to data loss. While this is something we ultimately want to move away from, for now I've refactored the existing implementation so that it handles backpressure more gracefully.

Previously we were using a ScheduledExecutorService that executes a runnable at a fixed interval. This works fine for most purposes, but if the device is under severe strain then the executor service is unlikely to keep up, and will have a large queue of jobs to churn through (ironically causing more strain). Historically we had the same problem with ANR data capture.

I've therefore refactored the logic so that after each cache a new job is scheduled for the given interval.

Testing

Relied on existing test coverage & manually verified that cached sessions make it through to the dash. I also checked that the interval is more or less the same:

2023-11-09 14:20:51.419  4868-4868  [Embrace] Periodic cache of session
2023-11-09 14:20:53.420  4868-4950  [Embrace] Periodic cache of session
2023-11-09 14:20:55.435  4868-4950  [Embrace] Periodic cache of session
2023-11-09 14:20:57.438  4868-4950  [Embrace] Periodic cache of session
2023-11-09 14:20:59.443  4868-4950  [Embrace] Periodic cache of session
2023-11-09 14:21:01.448  4868-4950  [Embrace] Periodic cache of session
2023-11-09 14:21:03.450  4868-4950  [Embrace] Periodic cache of session
2023-11-09 14:21:05.454  4868-4950  [Embrace] Periodic cache of session
2023-11-09 14:21:07.463  4868-4950  [Embrace] Periodic cache of session
2023-11-09 14:21:09.466  4868-4950  [Embrace] Periodic cache of session
2023-11-09 14:21:11.470  4868-4950  [Embrace] Periodic cache of session

[codecov]

Codecov Report

Merging #51 (9f72815) into master (ea815e8) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #51   +/-   ##
=======================================
  Coverage   74.67%   74.67%           
=======================================
  Files         308      308           
  Lines       10095    10095           
  Branches     1448     1448           
=======================================
  Hits         7538     7538           
  Misses       1982     1982           
  Partials      575      575           

Files	Coverage Δ
...brace/android/embracesdk/session/SessionHandler.kt	85.92% <100.00%> (ø)

[bidetofevil]

Sweet. I was just looking at this today and if we have big session payloads, it could lead to a tonne of GC and lmkd kills once we background!

[bidetofevil]

LGTM. If need re-start the caching, we should probably just not shutdown the executor.

[fractalwrench]

@bidetofevil I made a few changes based on your comments to use scheduleWithFixedDelay instead as that simplifies the implementation & avoids the need to shutdown an executor.

[bidetofevil]

Nice. LGTM