Fix Brightway Multiprocessing Error on Windows 11

The issue you’re encountering with bw2io.import_ecoinvent_release() failing on Windows 11 when multiprocessing is enabled is a well-known problem related to Python’s multiprocessing behavior on Windows systems. This error occurs because Windows uses a different process spawning mechanism compared to Unix-like systems, requiring specific initialization to avoid bootstrapping conflicts.

Contents

• Understanding the Root Cause
• Solutions for Enabling Multiprocessing
  • Method 1: Proper Code Structure with freeze_support()
  • Method 2: Brightway-Specific Multiprocessing Configuration
  • Method 3: Alternative Multiprocessing Approach
• Troubleshooting Steps
• Preventative Measures
• When to Disable Multiprocessing

Understanding the Root Cause

The error RuntimeError: An attempt has been made to start a new process before the current process has finished its bootstrapping phase occurs because Windows doesn’t support the fork process creation method that Unix systems use. Instead, Windows uses spawn, which requires the entire Python interpreter to be restarted for each new process source.

When multiprocessing is enabled in Brightway’s import_ecoinvent_release(), it attempts to create worker processes to handle the large ecoinvent dataset. On Windows, this requires proper initialization to ensure the parent process has completed its bootstrapping phase before spawning child processes source.

Solutions for Enabling Multiprocessing

Method 1: Proper Code Structure with freeze_support()

The most reliable solution is to properly structure your code with the required Windows multiprocessing initialization:

if __name__ == '__main__':
    import bw2data as bd
    import bw2io as bi
    from multiprocessing import freeze_support
    
    freeze_support()  # Required for Windows multiprocessing
    
    bd.projects.set_current(<project_name>)
    bi.import_ecoinvent_release(
        version="3.11",
        system_model="cutoff",
        username=<username>,
        password=<password>)

The freeze_support() function is essential when using multiprocessing on Windows, especially when the code might be frozen into an executable source. This tells the multiprocessing module to support restarting the Python interpreter when needed.

Method 2: Brightway-Specific Multiprocessing Configuration

Brightway 2.5 introduced the use_mp parameter specifically for controlling multiprocessing behavior during ecoinvent imports source. Instead of completely disabling multiprocessing, you can configure it more robustly:

import bw2data as bd
import bw2io as bi
from multiprocessing import set_start_method

# Set the start method before importing brightway
try:
    set_start_method('spawn', force=True)
except RuntimeError:
    # Method already set
    pass

bd.projects.set_current(<project_name>)
bi.import_ecoinvent_release(
    version="3.11",
    system_model="cutoff",
    username=<username>,
    password=<password>,
    use_mp=True)  # Enable with proper configuration

This approach explicitly sets the multiprocessing start method to ‘spawn’, which is the Windows-compatible method source.

Method 3: Alternative Multiprocessing Approach

If the above methods don’t work, you can try using the lower-level Brightway importers with more control over multiprocessing:

import bw2data as bd
import bw2io as bi
from bw2io import SingleOutputEcospold2Importer

bd.projects.set_current(<project_name>)

# Download ecoinvent files first, then import with controlled multiprocessing
# Use the ecospold2 importer directly
importer = SingleOutputEcospold2Importer(
    dirpath='path/to/your/ecospold/files',
    db_name='ecoinvent_3.11_cutoff',
    use_mp=True  # Enable multiprocessing with direct control
)

importer.apply_strategies()
importer.write_database()

This method gives you more direct control over the multiprocessing process and can help avoid the bootstrapping issues source.

Troubleshooting Steps

If you’re still experiencing issues, follow these systematic troubleshooting steps:

1. Check Import Order: Ensure all multiprocessing-related imports happen at the very beginning of your script, even before Brightway imports:

   python

   # First line of your script
   from multiprocessing import freeze_support
   
   if __name__ == '__main__':
       freeze_support()
       
       # Then import brightway packages
       import bw2data as bd
       import bw2io as bi
   

2. Verify Conda Environment: Sometimes conda environments can have conflicting multiprocessing configurations. Try creating a completely fresh environment:

   bash

   conda create -n brightway_fix python=3.9
   conda activate brightway_fix
   conda install -c conda-forge brightway2
   

3. Check for Conflicting Software: Some security software or system utilities can interfere with Windows process spawning. Temporarily disable such software during the import process.

4. Update Python and Brightway: Ensure you’re using compatible versions. Research suggests Python 3.9-3.11 work best with Brightway 2.5 on Windows source.

Preventative Measures

To avoid future multiprocessing issues:

1. Always use the proper structure:

   python

   if __name__ == '__main__':
       from multiprocessing import freeze_support
       freeze_support()
       # Your code here
   

2. Consider using a wrapper script that handles the multiprocessing initialization separately from your main analysis code.

3. Monitor system resources during import, as Windows multiprocessing can be more resource-intensive than on Unix systems.

4. Test multiprocessing functionality with smaller datasets before attempting large ecoinvent imports.

When to Disable Multiprocessing

While you want to enable multiprocessing for performance, there are legitimate cases where use_mp=False is the better choice:

1. Limited system resources: If your system has minimal RAM or CPU cores
2. Debugging scenarios: When you need to trace import issues step by step
3. Very large datasets: Sometimes the overhead of multiprocessing outweighs benefits for extremely large imports
4. Inconsistent environments: When working across different Windows configurations

The fact that use_mp=False works correctly on your system suggests that the multiprocessing functionality itself is properly implemented in Brightway, but your specific Windows environment has configuration conflicts that need to be resolved source.

Sources

1. Python multiprocessing RuntimeError on Windows - Stack Overflow
2. RuntimeError with multiprocessing bootstrapping - DEAP GitHub
3. Brightway ecoinvent import documentation
4. Windows multiprocessing FAQ - MineRL documentation
5. Brightway2 multiprocessing issues - GitHub
6. Configurable multiprocessing for large data import - Brightway2-io GitHub
7. Importing ecoinvent with Brightway - Stack Overflow

Conclusion

The multiprocessing issues you’re experiencing with bw2io.import_ecoinvent_release() on Windows 11 are solvable without permanently disabling multiprocessing. The key solutions are:

1. Use proper Windows multiprocessing initialization with if __name__ == '__main__': freeze_support()
2. Explicitly set the multiprocessing start method to ‘spawn’ before importing Brightway
3. Consider alternative import approaches using lower-level Brightway importers
4. Ensure proper import order with multiprocessing-related imports at the script’s beginning

By implementing these solutions, you should be able to leverage multiprocessing for faster ecoinvent imports while avoiding the bootstrapping phase errors that occur on Windows systems. If you continue to experience issues, the use_mp=False parameter remains a reliable fallback option that maintains full functionality without multiprocessing benefits.