multithreadinglockingpython-multithreadingpython-3.10sentence-transformers

import sentence_transformers hangs on macOS with [mutex.cc] RAW: Lock blocking error

I'm encountering a persistent issue where importing the sentence_transformers library on macOS causes my Python script to hang indefinitely. When the script hangs, the only output I see is a low-level mutex lock error. The script becomes unkillable (Ctrl+C does not work), and I have to force-quit the terminal or process.

The error message is: [mutex.cc : 452] RAW: Lock blocking 0x11b3e1888 @

Background

This problem began after I was experimenting with running sentence-transformers tasks concurrently using Python's asyncio library. My code structure was similar to this:

import asyncio
# from sentence_transformers import SentenceTransformer # This import is now problematic

# model = SentenceTransformer('all-MiniLM-L6-v2') # Example model loading

async def process_with_tracking(org_data):
    # Some processing logic that would eventually use the model
    # e.g., model.encode(org_data['text'])
    pass

async def main():
    orgs = [...] # A list of data objects
    tasks = []
    
    # Create tasks for each org
    for org in orgs:
        task = asyncio.create_task(process_with_tracking(org))
        tasks.append(task)

    # Wait for all tasks to complete
    if tasks:
        await asyncio.gather(*tasks, return_exceptions=True)

# asyncio.run(main())

My hypothesis is that a previous concurrent execution created a deadlock or corrupted a shared resource/cache file used by sentence-transformers or one of its dependencies (like Hugging Face Transformers or PyTorch).

The Core Problem

The issue is now system-wide and persists even when I am not using asyncio or any form of concurrency. A minimal script with just the import statement is enough to trigger the hang:

test_import.py

print("Attempting to import sentence_transformers...")
import sentence_transformers
print("Import successful!") # This line is never reached

When I run python test_import.py, the script hangs after the first print statement, and I see the [mutex.cc] error.

What I've Tried So Far

  1. Restarting my computer: The issue persists across reboots.
  2. Reinstalling the library: I have run pip uninstall sentence-transformers and pip install sentence-transformers multiple times.
  3. Running in a simple script: Confirmed the hang occurs with a single import line, ruling out my specific asyncio code as the immediate trigger.

My Questions

  1. What could be causing this kind of persistent lock that survives reinstallation and reboots?
  2. Where does sentence-transformers or Hugging Face transformers store cache, configuration, or lock files on macOS that I could manually inspect or delete? (e.g., ~/.cache/huggingface/)
  3. Are there any known issues with the underlying tokenizer parallelism (tokenizers) on macOS that could lead to this state? How can I reset it?

Environment

Solution

  • I found that downgrading Python from 3.13 to 3.12.7 worked for me to get the sentence_transformer library to run without the multi-threading issues. It must be a bug with the newer release of Python.