[DCJ-457] Stairway can be built with a provided ThreadPoolTaskExecutor

[okotsopoulos]

Addresses

Partially addresses https://broadworkbench.atlassian.net/browse/DCJ-457

PRs will need to be merged in the following order:

1. This PR
2. [DCJ-457] Register a ThreadPoolTaskExecutor for Stairway as a Bean terra-common-lib#187
3. A forthcoming TDR PR to update its TCL version

Summary of changes

This PR allows calling services to bring their own instrumented executor to serve as their Stairway's threadpool.

If unspecified in StairwayBuilder, a DefaultThreadPoolTaskExecutor will be constructed and used.

DefaultThreadPoolTaskExecutor is a public class: calling services may elect to instantiate it themselves (e.g. a Spring Boot service would register this as a Bean for automatic actuator instrumentation).

Testing Strategy

Expanded unit tests.

Verified end-to-end behavior manually:

• Publishing Stairway and TCL to my local Maven repository
• Booting up TDR, with and without maxParallelFlights specified
• Observed that stairwayExecutor metrics were automatically flowing through TDR's Actuator endpoint
• Initiated a Stairway flight which succeeded. Executor occupancy was reflected in actuator metrics.

Example where TDR configured its maxParallelFlights to be 120, has one actively running flight, and one completed flight:

(base) okotsopo@wm111-e35 jade-data-repo % curl http://localhost:8080/actuator/prometheus | grep 'stairwayExecutor'
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 87022  100 8executor_pool_core_threads{name="stairwayExecutor",} 120.0   0
7022    0     0  10.1M      0 --:--:-- --:--:-- --:--:-- 10.3M
executor_queue_remaining_tasks{name="stairwayExecutor",} 2.147483647E9
executor_completed_tasks_total{name="stairwayExecutor",} 1.0
executor_pool_size_threads{name="stairwayExecutor",} 2.0
executor_queued_tasks{name="stairwayExecutor",} 0.0
executor_pool_max_threads{name="stairwayExecutor",} 120.0
executor_active_threads{name="stairwayExecutor",} 1.0

[okotsopoulos]

(Only marked as "ready for review" to see if that helps with checks not running… but it seems that GitHub is experiencing issues: https://www.githubstatus.com/incidents/9vwllhs2w1kj)

[rtitle]

This looks good to me -- I like the approach of decoupling StairwayThreadPool from the executor (instead of inheriting from it).

[nmalfroy]

This looks great! The reason I put in request changes is about some questions. All minor but probably worthy of calling out

[nmalfroy]

You've answered all the questions I had :). Looks great!

[sonarcloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud