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fix: address PR review — per-palace lock, MCP server path, hook timeout, tests

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Addresses the six Copilot review comments on the initial commit.

1) #6 (critical) — mcp_server.py `_get_collection` bypassed ChromaBackend

   The MCP server creates its palace collection directly via
   `chromadb.PersistentClient.get_or_create_collection` in `_get_collection`,
   not through `ChromaBackend.get_collection`. That path was missing the
   `hnsw:num_threads=1` metadata, so the primary crash surface for #974
   and #965 was untouched by the original patch. Fixed by passing
   `hnsw:num_threads=1` at the mcp_server create site too. Documented
   in a code comment that the setting is only honored at creation
   time — existing palaces created before this fix still need a
   `mempalace nuke` + re-mine to gain the protection.

2) #3 — mine_global_lock over-serialized mines across unrelated palaces

   Replaced the single global lock file `mine_global.lock` with a
   per-palace lock keyed by `sha256(os.path.abspath(palace_path))`
   (`mine_palace_<hash>.lock`). Mines against the same palace still
   collapse to a single runner (the correctness boundary), but mines
   against *different* palaces are now free to run in parallel.
   `mine_global_lock` is kept as a backward-compatible alias for
   `mine_palace_lock` so any external callers that imported the
   previous name keep working.

3) #1 — hook_precompact swallowed OSError but not subprocess.TimeoutExpired

   `subprocess.run(..., timeout=60)` raises `TimeoutExpired` on slow
   palaces. The previous `except OSError` clause didn't catch it, so
   the hook could raise and fail to emit any JSON decision — leaving
   the harness without a block/passthrough signal. Fixed by catching
   `(OSError, subprocess.TimeoutExpired)` together and always falling
   through to the block decision so the hook reliably emits a response.

4) #2 + #4 — tests

   - tests/test_hooks_cli.py: added
     `test_precompact_first_two_attempts_block`,
     `test_precompact_passes_through_after_cap`, and
     `test_precompact_counter_is_per_session` to lock in the #955
     deadlock fix.
   - tests/test_palace_locks.py (new): covers `mine_palace_lock`
     single-acquire, reuse-after-release, cross-process serialization
     on the same palace, non-interference across different palaces,
     path normalization, and the `mine_global_lock` back-compat alias.

5) #5 — known limitation, documented but not auto-fixed

   Copilot suggested detecting collections missing `hnsw:num_threads=1`
   and calling `collection.modify(metadata=...)` to retrofit existing
   palaces. Verified against chromadb 1.5.7: `modify(metadata=...)`
   replaces metadata rather than merging, and re-passing
   `hnsw:space="cosine"` then raises `ValueError: Changing the
   distance function of a collection once it is created is not
   supported currently.` The HNSW runtime configuration
   (`configuration_json`) also does not expose `num_threads` in
   chromadb 1.5.x, so the flag appears to be read only at creation
   time. Rather than paper over the limitation with a best-effort
   `modify` that silently drops `hnsw:space`, documented in the
   mcp_server comment that pre-existing palaces need a
   `mempalace nuke` + re-mine to gain the protection. Fresh palaces
   are always protected.

Testing
- pytest tests/test_palace_locks.py tests/test_hooks_cli.py
  tests/test_backends.py tests/test_cli.py → **98 passed, 0 failed**.
- Runtime validation with two concurrent `mempalace mine` calls:
  - Different palaces → both complete in parallel ✓
  - Same palace     → one completes, the other exits with
    "another `mine` is already running against <palace> — exiting
    cleanly." ✓
This commit is contained in:
Felipe Truman
2026-04-17 16:03:07 -03:00
committed by Igor Lins e Silva
parent 7e18a70796
commit 99b820cb42
5 changed files with 245 additions and 58 deletions
Download Patch File Download Diff File Expand all files Collapse all files
tests/test_palace_locks.py
+130 -43
View File
@@ -1,59 +1,146 @@
"""Tests for mine_global_lock: non-blocking cross-process lock semantics."""
import threading
"""Tests for mine_palace_lock — the per-palace non-blocking mine guard.
Covers the fix for the runaway mine fan-out described alongside issues
#974 and #965: if N copies of `mempalace mine` are spawned concurrently
against the same palace, they must collapse to a single runner rather
than queue as waiters that will drive parallel HNSW inserts. Mines
against *different* palaces must still be free to run in parallel.
"""
from __future__ import annotations
import multiprocessing
import os
import time
import pytest
from mempalace.palace import MineAlreadyRunning, mine_global_lock
from mempalace.palace import (
MineAlreadyRunning,
mine_global_lock,
mine_palace_lock,
)
def test_mine_global_lock_acquired(tmp_path, monkeypatch):
"""Lock is acquired and released without error."""
# ---------------------------------------------------------------------------
# Helpers
# ---------------------------------------------------------------------------
def _hold_lock(palace_path: str, ready_flag: str, release_flag: str) -> int:
"""Acquire mine_palace_lock, signal readiness, wait for release flag.
Returns 0 if we acquired the lock, 1 if MineAlreadyRunning was raised.
Runs in a child process for true cross-process locking semantics.
"""
try:
with mine_palace_lock(palace_path):
# Tell the parent we hold the lock
open(ready_flag, "w").close()
# Wait until parent tells us to release
for _ in range(500):
if os.path.exists(release_flag):
return 0
time.sleep(0.01)
return 0
except MineAlreadyRunning:
return 1
# ---------------------------------------------------------------------------
# Tests
# ---------------------------------------------------------------------------
def test_single_acquire_succeeds(tmp_path, monkeypatch):
monkeypatch.setenv("HOME", str(tmp_path))
with mine_global_lock():
with mine_palace_lock(str(tmp_path / "palace")):
pass # should not raise
def test_mine_global_lock_second_acquire_raises(tmp_path, monkeypatch):
"""Concurrent second acquire raises MineAlreadyRunning."""
def test_lock_reusable_after_release(tmp_path, monkeypatch):
monkeypatch.setenv("HOME", str(tmp_path))
results: list[str] = []
with mine_global_lock():
# While this lock is held, spawn a thread that tries to acquire.
def try_acquire():
try:
with mine_global_lock():
results.append("acquired")
except MineAlreadyRunning:
results.append("blocked")
t = threading.Thread(target=try_acquire)
t.start()
t.join(timeout=5)
assert results == ["blocked"]
def test_mine_global_lock_reusable_after_release(tmp_path, monkeypatch):
"""Lock can be re-acquired after the context manager exits."""
monkeypatch.setenv("HOME", str(tmp_path))
with mine_global_lock():
pass # first acquire + release
# Second acquire must succeed; MineAlreadyRunning would propagate as failure.
with mine_global_lock():
palace = str(tmp_path / "palace")
with mine_palace_lock(palace):
pass
# Re-acquire must succeed now that the previous holder released
with mine_palace_lock(palace):
pass
def test_mine_global_lock_exception_still_releases(tmp_path, monkeypatch):
"""Lock is released even when the body raises."""
def test_same_palace_serializes_across_processes(tmp_path, monkeypatch):
"""Two processes contending for the same palace: second must be rejected."""
monkeypatch.setenv("HOME", str(tmp_path))
palace = str(tmp_path / "palace")
ready = str(tmp_path / "ready")
release = str(tmp_path / "release")
with pytest.raises(ValueError):
with mine_global_lock():
raise ValueError("boom")
ctx = multiprocessing.get_context("fork")
holder = ctx.Process(target=_hold_lock, args=(palace, ready, release))
holder.start()
try:
# Wait for the holder to acquire
for _ in range(500):
if os.path.exists(ready):
break
time.sleep(0.01)
assert os.path.exists(ready), "holder failed to acquire lock in time"
# Must be acquirable again after the exception.
with mine_global_lock():
pass
# From the parent, we must not be able to acquire the same palace lock
with pytest.raises(MineAlreadyRunning):
with mine_palace_lock(palace):
pytest.fail("second acquire of same palace should have raised")
finally:
open(release, "w").close()
holder.join(timeout=5)
assert holder.exitcode == 0
def test_different_palaces_dont_conflict(tmp_path, monkeypatch):
"""Mines against different palaces must NOT block each other."""
monkeypatch.setenv("HOME", str(tmp_path))
palace_a = str(tmp_path / "palace_a")
palace_b = str(tmp_path / "palace_b")
ready = str(tmp_path / "ready_a")
release = str(tmp_path / "release_a")
ctx = multiprocessing.get_context("fork")
holder = ctx.Process(target=_hold_lock, args=(palace_a, ready, release))
holder.start()
try:
for _ in range(500):
if os.path.exists(ready):
break
time.sleep(0.01)
assert os.path.exists(ready), "holder failed to acquire lock in time"
# Different palace — must succeed even while palace_a is held
with mine_palace_lock(palace_b):
pass # no exception expected
finally:
open(release, "w").close()
holder.join(timeout=5)
def test_palace_path_is_normalized(tmp_path, monkeypatch):
"""Relative and absolute forms of the same path must use the same lock."""
monkeypatch.setenv("HOME", str(tmp_path))
monkeypatch.chdir(tmp_path)
os.makedirs(tmp_path / "palace", exist_ok=True)
absolute = str(tmp_path / "palace")
relative = "palace"
# Hold the lock with the absolute form; attempting to re-acquire with
# the relative form (which resolves to the same absolute path) must fail.
with mine_palace_lock(absolute):
with pytest.raises(MineAlreadyRunning):
with mine_palace_lock(relative):
pytest.fail("normalized path collision should have raised")
def test_mine_global_lock_is_alias_for_back_compat(tmp_path, monkeypatch):
"""Old callers of `mine_global_lock` should still work."""
monkeypatch.setenv("HOME", str(tmp_path))
assert mine_global_lock is mine_palace_lock
with mine_global_lock(str(tmp_path / "palace")):
pass # the alias accepts the same palace_path argument