* fix: run PBKDF2 in thread pool to prevent event loop freeze
Problem: Event loop freezes for 100-500ms during secret decryption, blocking
all HTTP requests and async operations. The diagnostic monitor detected the
main thread stuck in PBKDF2 HMAC SHA256 computation at:
apps/core/letta/helpers/crypto_utils.py:51 (_derive_key)
apps/core/letta/schemas/secret.py:161 (get_plaintext)
Root cause: PBKDF2 with 100k iterations is intentionally CPU-intensive for
security, but running it synchronously on the main thread blocks the event loop.
Stack trace showed:
Thread 1 (Main): PBKDF2HMAC -> SHA256_Final -> sha256_block_data_order_avx2
Event loop watchdog: Detected freeze at 01:11:44 (request started 01:12:03)
Solution:
1. Run PBKDF2 in ThreadPoolExecutor to avoid blocking event loop
2. Add async versions of encrypt/decrypt methods
3. Add LRU cache for derived keys (deterministic results)
4. Add async get_plaintext_async() method to Secret class
Changes:
- apps/core/letta/helpers/crypto_utils.py:
- Added ThreadPoolExecutor for crypto operations
- Added @lru_cache(maxsize=256) to _derive_key_cached()
- Added _derive_key_async() using loop.run_in_executor()
- Added encrypt_async() and decrypt_async() methods
- Added warnings to sync methods about blocking behavior
- apps/core/letta/schemas/secret.py:
- Added get_plaintext_async() method
- Added warnings to get_plaintext() about blocking behavior
Benefits:
- Event loop no longer freezes during secret decryption
- HTTP requests continue processing while crypto runs in background
- Derived keys are cached, reducing CPU usage for repeated operations
- Backward compatible - sync methods still work for non-async code
Performance impact:
- Before: 100-500ms event loop block per decryption
- After: 100-500ms in thread pool (non-blocking) + LRU cache hits ~0.1ms
Next steps (follow-up PRs):
- Migrate all async callsites to use get_plaintext_async()
- Add metrics to track sync vs async usage
- Consider reducing PBKDF2 iterations if security allows
* update
* test
---------
Co-authored-by: Letta Bot <jinjpeng@gmail.com>
bce1749408