Bug Report: MONAI Import Hangs on macOS with Apple Silicon (MPS)

[Slangevar]

Describe the bug

Importing MONAI causes a complete hang with a mutex lock error on macOS 15.7.3 (Apple Silicon). The process becomes unresponsive and must be force-terminated. The error message displayed is:

[mutex.cc : 452] RAW: Lock blocking 0x<address>   @

To Reproduce

Steps to reproduce the behavior:

1. Environment Setup:

   • macOS 15.7.3 (Build 24G419) on Apple Silicon
   • Python 3.12.11
   • Install MONAI 1.5.1 with PyTorch 2.6.0

2. Installation:

   pip install monai==1.5.1
   pip install torch==2.6.0

3. Run the minimal reproduction:

   python3.12 -c "import monai; print('Monai imported')"

4. Observe: The command hangs indefinitely with the mutex lock error message.

Expected behavior

The import should complete successfully and print "Monai imported" without hanging.

Environment

Since import monai hangs, I cannot run monai.config.print_debug_info(). Here's the environment information:

ProductName:            macOS
ProductVersion:         15.7.3
BuildVersion:           24G419
Python:                 3.12.11

Package Versions:
monai                         1.5.1
torch                         2.6.0
numpy                         2.3.2
pytorch-lightning             2.5.2

Additional context

• The issue occurs immediately upon import monai, before any MONAI functionality is used
• The same environment can successfully import and use PyTorch with MPS acceleration for training
• Setting PYTORCH_ENABLE_MPS_FALLBACK=1 does not resolve the issue
• Attempting to force CPU-only mode before import also fails
• The issue persists across both MONAI 1.5.0 and 1.5.1
• Other PyTorch-based libraries (pytorch-lightning, segmentation-models-pytorch) work correctly in the same environment
• The mutex lock appears to be related to multiprocessing/threading initialization within MONAI's dependencies

Workaround Attempted

Tried updating from MONAI 1.5.0 to 1.5.1 - issue persists.

Impact

This completely blocks the use of MONAI on Apple Silicon Macs with macOS 15.7.3