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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
mempalace/mcp_server.py
+8 -1
View File
@@ -217,9 +217,16 @@ def _get_collection(create=False):
try:
client = _get_client()
if create:
# hnsw:num_threads=1 disables ChromaDB's multi-threaded ParallelFor
# HNSW insert path, which has a race in repairConnectionsForUpdate /
# addPoint (see issues #974, #965). The setting is only honored at
# collection creation time — pre-existing palaces created before
# this fix keep the unsafe default; users must `mempalace nuke` +
# re-mine to get the protection on legacy palaces.
_collection_cache = ChromaCollection(
client.get_or_create_collection(
_config.collection_name, metadata={"hnsw:space": "cosine"}
_config.collection_name,
metadata={"hnsw:space": "cosine", "hnsw:num_threads": 1},
)
)
_metadata_cache = None
mempalace/miner.py
+4 -3
View File
@@ -25,8 +25,8 @@ from .palace import (
file_already_mined,
get_closets_collection,
get_collection,
mine_global_lock,
mine_lock,
mine_palace_lock,
purge_file_closets,
upsert_closet_lines,
)
@@ -1008,7 +1008,7 @@ def mine(
)
try:
with mine_global_lock():
with mine_palace_lock(palace_path):
return _mine_impl(
project_dir,
palace_path,
@@ -1021,7 +1021,8 @@ def mine(
)
except MineAlreadyRunning:
print(
"mempalace: another `mine` is already running — exiting cleanly.",
f"mempalace: another `mine` is already running against "
f"{palace_path} — exiting cleanly.",
file=sys.stderr,
)
return
mempalace/palace.py
+23 -11
View File
@@ -311,27 +311,33 @@ def mine_lock(source_file: str):
class MineAlreadyRunning(RuntimeError):
"""Raised when another `mempalace mine` process already holds the global lock."""
"""Raised when another `mempalace mine` already holds the per-palace lock."""
@contextlib.contextmanager
def mine_global_lock():
"""Process-wide non-blocking lock around the full `mine` pipeline.
def mine_palace_lock(palace_path: str):
"""Per-palace non-blocking lock around the full `mine` pipeline.
The per-file `mine_lock` only protects delete+insert interleave for a
single source; it does not prevent N copies of `mempalace mine <dir>`
from being spawned concurrently by hooks. When that happens, each copy
drives ChromaDB HNSW inserts in parallel, which (combined with
chromadb's multi-threaded ParallelFor) can corrupt the HNSW graph and
produce sparse link_lists.bin blowups.
drives ChromaDB HNSW inserts in parallel against the same palace,
which (combined with chromadb's multi-threaded ParallelFor) can
corrupt the HNSW graph and produce sparse link_lists.bin blowups.
This lock is non-blocking: if another `mine` is already running, we
The lock file is keyed by sha256(palace_path) so mines against
*different* palaces can still run in parallel — we only serialize
writes into the same palace, which is the correctness boundary.
Non-blocking: if another `mine` is already writing to this palace,
raise MineAlreadyRunning so the caller can exit cleanly instead of
piling up waiting workers.
piling up as a waiting worker.
"""
lock_dir = os.path.join(os.path.expanduser("~"), ".mempalace", "locks")
os.makedirs(lock_dir, exist_ok=True)
lock_path = os.path.join(lock_dir, "mine_global.lock")
resolved = os.path.abspath(os.path.expanduser(palace_path))
palace_key = hashlib.sha256(resolved.encode()).hexdigest()[:16]
lock_path = os.path.join(lock_dir, f"mine_palace_{palace_key}.lock")
lf = open(lock_path, "w")
acquired = False
@@ -344,7 +350,7 @@ def mine_global_lock():
acquired = True
except OSError as exc:
raise MineAlreadyRunning(
"another `mempalace mine` is already running"
f"another `mempalace mine` is already running against {resolved}"
) from exc
else:
import fcntl
@@ -354,7 +360,7 @@ def mine_global_lock():
acquired = True
except BlockingIOError as exc:
raise MineAlreadyRunning(
"another `mempalace mine` is already running"
f"another `mempalace mine` is already running against {resolved}"
) from exc
yield
finally:
@@ -373,6 +379,12 @@ def mine_global_lock():
lf.close()
# Backward-compatible alias (previous patch iteration used a single global
# lock). Kept so third-party callers that imported it continue to work; new
# code should use `mine_palace_lock(palace_path)` for per-palace scoping.
mine_global_lock = mine_palace_lock
def file_already_mined(collection, source_file: str, check_mtime: bool = False) -> bool:
"""Check if a file has already been filed in the palace.
tests/test_hooks_cli.py
+80
View File
@@ -9,6 +9,7 @@ from unittest.mock import MagicMock, patch
import pytest
from mempalace.hooks_cli import (
MAX_PRECOMPACT_BLOCK_ATTEMPTS,
SAVE_INTERVAL,
_count_human_messages,
_extract_recent_messages,
@@ -59,6 +60,85 @@ def test_sanitize_empty_returns_unknown():
assert _sanitize_session_id("!!!") == "unknown"
# --- hook_precompact attempt cap (regression for #955 deadlock fix) ---
def _call_precompact(session_id: str) -> dict:
"""Invoke hook_precompact with a deterministic session_id, capture stdout.
Returns the parsed JSON decision emitted by the hook.
"""
stdout = io.StringIO()
with contextlib.redirect_stdout(stdout):
hook_precompact({"session_id": session_id}, "claude-code")
raw = stdout.getvalue().strip()
return json.loads(raw) if raw else {}
def test_precompact_first_two_attempts_block(tmp_path, monkeypatch):
"""First MAX_PRECOMPACT_BLOCK_ATTEMPTS calls must block with a reason."""
monkeypatch.setenv("HOME", str(tmp_path))
monkeypatch.delenv("MEMPAL_DIR", raising=False)
import mempalace.hooks_cli as hooks_cli
monkeypatch.setattr(
hooks_cli, "STATE_DIR", tmp_path / "hook_state", raising=False
)
sid = "test-session-block"
for i in range(MAX_PRECOMPACT_BLOCK_ATTEMPTS):
decision = _call_precompact(sid)
assert decision.get("decision") == "block", (
f"attempt {i + 1}/{MAX_PRECOMPACT_BLOCK_ATTEMPTS}: expected block, "
f"got {decision}"
)
assert decision.get("reason") == PRECOMPACT_BLOCK_REASON
def test_precompact_passes_through_after_cap(tmp_path, monkeypatch):
"""After the cap is reached, the hook must stop blocking (fix for #955)."""
monkeypatch.setenv("HOME", str(tmp_path))
monkeypatch.delenv("MEMPAL_DIR", raising=False)
import mempalace.hooks_cli as hooks_cli
monkeypatch.setattr(
hooks_cli, "STATE_DIR", tmp_path / "hook_state", raising=False
)
sid = "test-session-passthrough"
for _ in range(MAX_PRECOMPACT_BLOCK_ATTEMPTS):
_call_precompact(sid) # exhaust the budget
# Next call must pass through (empty JSON decision)
decision = _call_precompact(sid)
assert decision == {}, (
f"after {MAX_PRECOMPACT_BLOCK_ATTEMPTS} attempts, hook must pass "
f"through to avoid deadlock; got {decision}"
)
def test_precompact_counter_is_per_session(tmp_path, monkeypatch):
"""A fresh session_id must get a fresh attempt budget."""
monkeypatch.setenv("HOME", str(tmp_path))
monkeypatch.delenv("MEMPAL_DIR", raising=False)
import mempalace.hooks_cli as hooks_cli
monkeypatch.setattr(
hooks_cli, "STATE_DIR", tmp_path / "hook_state", raising=False
)
sid_a = "session-a"
sid_b = "session-b"
# Exhaust session A
for _ in range(MAX_PRECOMPACT_BLOCK_ATTEMPTS):
_call_precompact(sid_a)
assert _call_precompact(sid_a) == {} # A is done blocking
# Session B must still block on its first call — isolation between sessions
assert _call_precompact(sid_b).get("decision") == "block"
# --- _count_human_messages ---
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