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

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

No source file or test is identified. First reproduce the hang with the documented Python 3.12/macOS Apple Silicon environment using the minimal import monai command, then trace MONAI's import-time dependency or threading initialization. Done means the command completes and prints "Monai imported" without hanging.