[darion-yaphet]

Destroying a KeyTable may run a user-provided TLS destructor. The destructor can wait for another bthread or access the same pool.

Previously, pool destruction deleted cached KeyTables while holding both the pool write lock and ThreadLocal's internal mutex. A user destructor could therefore wait for a bthread that needs one of these locks, causing a deadlock.

The cleanup now works in two phases:

1. Under the cache locks, mark the pool destroyed and detach cached KeyTables into a local list.
2. Release the locks, then destroy the detached KeyTables and run their TLS destructors.

Summary

Pool destruction currently deletes cached KeyTables while holding both the pool write lock and ThreadLocal's internal mutex. TLS destructors can execute user code, which may wait for or interact with tasks that need these locks.

Detach KeyTable chains while the cache locks protect the pool structure, then destroy the detached KeyTables after releasing both locks. Delete the now-empty thread-local cache container afterward.

Add a regression test that attempts to acquire both locks from a TLS destructor. The test fails before the fix and verifies that both locks are available after it.

Testing

• cmake --build build --target bthread_key_unittest -j6
• bthread_key_unittest --gtest_filter=KeyTest.* — 12 tests passed.
• KeyTest.pooled_destructor_runs_outside_cache_locks repeated 30 times — passed.

Risk and Rollback

The change preserves the pool shutdown sequence while moving user destructor execution outside cache-management locks. It does not change public APIs.

[Copilot]

🟢 Approval recommended

The focused cleanup change preserves shutdown synchronization and has targeted regression coverage, with no blocking issues identified.

No open issues 🎉

What changed in this PR

This PR addresses a bthread keytable-pool shutdown deadlock by moving TLS destructor execution outside cache-management locks, without changing public APIs.

Changes:

• Detach cached KeyTable chains under the locks, then destroy them after releasing both locks.
• Add a regression test that verifies TLS destructors can acquire both cache-management locks.

File	Description
test/​bthread_key_unittest.cpp	Adds regression coverage for lock availability during pooled TLS destruction.
src/​bthread/​key.cpp	Separates cache detachment from KeyTable destruction during pool shutdown.

_{Review effort: Balanced}