feat(python): warn on fork (#2258)

Closes #768

docs/src/troubleshooting.md

@@ -8,6 +8,10 @@ For trouble shooting, the best place to ask is in our Discord, under the relevan
 language channel. By asking in the language-specific channel, it makes it more
 likely that someone who knows the answer will see your question.
 
+## Common issues
+
+* Multiprocessing with `fork` is not supported. You should use `spawn` instead.
+
 ## Enabling logging
 
 To provide more information, especially for LanceDB Cloud related issues, enable

python/python/lancedb/__init__.py

@@ -7,6 +7,7 @@ import os
 from concurrent.futures import ThreadPoolExecutor
 from datetime import timedelta
 from typing import Dict, Optional, Union, Any
+import warnings
 
 __version__ = importlib.metadata.version("lancedb")
 
@@ -213,3 +214,13 @@ __all__ = [
     "RemoteDBConnection",
     "__version__",
 ]
+
+
+def __warn_on_fork():
+    warnings.warn(
+        "lance is not fork-safe. If you are using multiprocessing, use spawn instead.",
+    )
+
+
+if hasattr(os, "register_at_fork"):
+    os.register_at_fork(before=__warn_on_fork)