Fix diagnostics reading live NOMUTEX reader connections#156
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resqlite_db_status_total skips readers marked in_use, but that flag has been dead code since exp 030 moved workers to dedicated reader assignment — Database.diagnostics() was calling sqlite3_db_status on reader connections actively executing queries on their worker threads. Connections are NOMUTEX, and SQLITE_DBSTATUS_SCHEMA_USED measures memory via the connection's pnBytesFreed dry-run mechanism; toggling it under a mid-query reader corrupts that reader's allocation accounting (observed as a flaky reader-isolate SEGV in sqlite3VdbeDelete once exp 160's detached admission reads made readers reliably busy at diagnostics-poll time, ~1-in-30 stream_test runs). Read workers now bracket each request with resqlite_reader_set_busy (atomic store, two leaf FFI calls per request), making the existing busy guard real; diagnostics reports those readers as a partial snapshot exactly as the existing in_use contract intended. The sacrifice path clears the bracket before Isolate.exit since exit skips finally. Validated on the exp 160 branch: crash reproduced pre-fix, 100/100 clean stress iterations and 8/8 full-suite runs post-fix. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
danReynolds
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Jun 10, 2026
The rebase onto main (which landed the diagnostics race fix via #156) re-applied the function on top of main's copy. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Problem
resqlite_db_status_totalskips readers markedin_use— but that flag has been dead code since exp 030 gave workers dedicated readers (exp 051 documented the acquire path as dead).Database.diagnostics()was therefore callingsqlite3_db_statuson live NOMUTEX reader connections from the main isolate.SCHEMA_USEDmeasures memory by toggling the connection'spnBytesFreeddry-run mechanism; doing that under a mid-query reader corrupts the reader's allocation accounting — a latent heap-corruption race on main, observed as a flaky reader-isolate SEGV (sqlite3VdbeDelete→ allocation-size read at null) at ~1-in-30 stream_test runs once exp 160's detached admission reads made readers reliably busy at diagnostics-poll time.Fix
Read workers bracket each request with
resqlite_reader_set_busy(atomic store, two ~ns leaf FFI calls per request), making the existing busy guard real — diagnostics reports busy readers as a partial snapshot exactly as thein_usecontract always intended. The sacrifice path clears the bracket beforeIsolate.exit(exit skipsfinally).Split out of #155 so the crash fix lands on main independently of the IVM review; the investigation record (bisection, crash trace, stress validation) lives in that PR's experiment doc.
Test plan
dart analyzeclean; stream/diagnostics/database tests pass🤖 Generated with Claude Code