Fix crash: guard executor submits against teardown race

[patrickrb]

Problem

The app crashes with RejectedExecutionException after a decode when the connection is reset/reconnected or the app is closing. Observed live on a FlexRadio network reconnect:

FATAL EXCEPTION: Thread-101
java.util.concurrent.RejectedExecutionException: Task ...GetQTHRunnable rejected from
   ThreadPoolExecutor[Terminated, pool size = 0 ...]
   at MainViewModel$4.afterDecode(MainViewModel.java:594)
   at FT8SignalListener$3.run(FT8SignalListener.java:189)

afterDecode() runs on the FT8 decode thread and submits a QTH/grid-lookup task to getQTHThreadPool after every pass. That pool — and sendWaveDataThreadPool — is shut down in MainViewModel.onCleared() when the ViewModel is destroyed (app close, connection reset/reconnect). A decode result that lands in the same instant the pool is shut down reaches ExecutorService.execute() on a terminated pool and throws on the decode thread, crashing the app.

Fix

Add ExecutorUtils.safeExecute(pool, task), which:

• skips submission when pool.isShutdown(), and
• catches the residual RejectedExecutionException for the narrow check-then-execute race,

dropping the follow-up task instead of crashing. The dropped work is non-essential (a grid lookup, or a TX-audio send during teardown).

Routed all three submit sites through it: the QTH lookup (line 594) and the two network/CAT TX-audio sends (lines 689, 717).

Test

ExecutorUtilsTest (pure JUnit4 + Truth, no runner needed): active pool runs the task and returns true; shut-down pool drops the task and returns false without throwing; null pool/task return false.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 11.51%. Comparing base (bc6c21e) to head (8dd0103).

Additional details and impacted files

@@            Coverage Diff            @@
##                dev     #324   +/-   ##
=========================================
  Coverage     11.51%   11.51%           
  Complexity      113      113           
=========================================
  Files            88       88           
  Lines         12466    12466           
  Branches       2230     2230           
=========================================
  Hits           1435     1435           
  Misses        10900    10900           
  Partials        131      131           

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[Copilot]

Pull request overview

This PR prevents a teardown race from crashing the decode thread by guarding ExecutorService.execute() submissions against executors that are concurrently being shut down during MainViewModel.onCleared().

Changes:

• Added ExecutorUtils.safeExecute(...) to skip submissions on shutdown pools and swallow RejectedExecutionException.
• Routed QTH/grid lookup and TX-audio send submissions in MainViewModel through safeExecute.
• Added unit tests validating safeExecute behavior for active/shutdown/null inputs.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
ft8af/app/src/main/java/com/k1af/ft8af/ExecutorUtils.java	Introduces safeExecute helper to avoid crashes from executor teardown races.
ft8af/app/src/main/java/com/k1af/ft8af/MainViewModel.java	Uses safeExecute for decode follow-up and TX-audio executor submissions.
ft8af/app/src/test/java/com/k1af/ft8af/ExecutorUtilsTest.java	Adds unit tests for safeExecute behavior across pool/task states.

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[patrickrb]

Consolidated into #329 (single combined PR) as requested.