fix(chroma): cap hnsw:num_threads to available CPU cores during collection load Closes langchain-ai/langchain#32678

libs/community/langchain_community/vectorstores/chroma.py

@@ -2,6 +2,7 @@
 
 import base64
 import logging
+import os
 import uuid
 from typing import (
     TYPE_CHECKING,
@@ -125,6 +126,15 @@ def __init__(
             )
 
         self._embedding_function = embedding_function
+        # --- BEGIN ADDED CPU GUARD LOGIC ---
+        if (
+            collection_metadata
+            and "hnsw:num_threads" in collection_metadata
+            and collection_metadata["hnsw:num_threads"] > os.cpu_count()
+        ):
+            collection_metadata["hnsw:num_threads"] = os.cpu_count()
+        # --- END ADDED LOGIC ---
+
         self._collection = self._client.get_or_create_collection(
             name=collection_name,
             embedding_function=None,

libs/community/tests/unit_tests/vectorstores/test_chroma.py

@@ -0,0 +1,80 @@
+"""Unit tests for Chroma vectorstore."""
+import os
+import unittest.mock
+import pytest
+from unittest.mock import patch, MagicMock
+
+from langchain_community.vectorstores import Chroma
+
+
+class TestChromaCPUGuard:
+    """Test CPU guard functionality in Chroma initialization."""
+
+    @patch('langchain_community.vectorstores.chroma.chromadb')
+    @patch('os.cpu_count')
+    def test_cpu_guard_caps_excessive_threads(self, mock_cpu_count, mock_chromadb):
+        """Test that hnsw:num_threads is capped to CPU count when excessive."""
+        mock_cpu_count.return_value = 4
+        mock_client = MagicMock()
+        mock_chromadb.Client.return_value = mock_client
+        mock_chromadb.config.Settings.return_value = MagicMock()
+
+        collection_metadata = {"hnsw:num_threads": 8}  # More than CPU count
+
+        Chroma(
+            collection_name="test_cpu_guard",
+            collection_metadata=collection_metadata
+        )
+
+        # Verify the metadata was modified
+        assert collection_metadata["hnsw:num_threads"] == 4
+
+    @patch('langchain_community.vectorstores.chroma.chromadb')
+    @patch('os.cpu_count')
+    def test_cpu_guard_preserves_valid_threads(self, mock_cpu_count, mock_chromadb):
+        """Test that valid thread counts are preserved."""
+        mock_cpu_count.return_value = 8
+        mock_client = MagicMock()
+        mock_chromadb.Client.return_value = mock_client
+        mock_chromadb.config.Settings.return_value = MagicMock()
+
+        collection_metadata = {"hnsw:num_threads": 4}  # Less than CPU count
+
+        Chroma(
+            collection_name="test_cpu_guard_valid",
+            collection_metadata=collection_metadata
+        )
+
+        # Verify the metadata was NOT modified
+        assert collection_metadata["hnsw:num_threads"] == 4
+
+    @patch('langchain_community.vectorstores.chroma.chromadb')
+    def test_cpu_guard_handles_none_metadata(self, mock_chromadb):
+        """Test that None collection_metadata doesn't cause issues."""
+        mock_client = MagicMock()
+        mock_chromadb.Client.return_value = mock_client
+        mock_chromadb.config.Settings.return_value = MagicMock()
+
+        # Should not raise any exceptions
+        Chroma(
+            collection_name="test_none_metadata",
+            collection_metadata=None
+        )
+
+    @patch('langchain_community.vectorstores.chroma.chromadb')
+    def test_cpu_guard_handles_missing_threads_key(self, mock_chromadb):
+        """Test metadata without hnsw:num_threads key."""
+        mock_client = MagicMock()
+        mock_chromadb.Client.return_value = mock_client
+        mock_chromadb.config.Settings.return_value = MagicMock()
+
+        collection_metadata = {"hnsw:space": "cosine"}  # No num_threads key
+
+        Chroma(
+            collection_name="test_missing_key",
+            collection_metadata=collection_metadata
+        )
+
+        # Should remain unchanged
+        assert "hnsw:num_threads" not in collection_metadata
+        assert collection_metadata["hnsw:space"] == "cosine"