Python multiprocessing on windows: Can't pickle SyncManager, works on linux

8 months ago

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The issue you're encountering with multiprocessing and the SyncManager on Windows is due to the way the multiprocessing module in Python works on different platforms. Windows has a different process forking mechanism compared to Unix-like systems, which can cause some issues with certain objects that need to be pickled.

The SyncManager is used to create synchronized objects that can be shared between processes. However, when you try to use a SyncManager in Windows, you might encounter a "Can't pickle SyncManager" error because some objects used by the manager can't be pickled due to Windows' process spawning mechanism.

To work around this issue, you can try the following:

Use the "spawn" Start Method:
When creating the multiprocessing context, you can specify the "spawn" start method. This method creates new processes using the spawn method instead of fork, which is more compatible with Windows.
```
python
import multiprocessing



if __name__ == '__main__':

    multiprocessing.set_start_method('spawn')

    # Your multiprocessing code here
```

Avoid Using SyncManager:
If possible, avoid using the SyncManager and choose other synchronization mechanisms that work better on Windows, such as multiprocessing.Queue or multiprocessing.Event.

python
from multiprocessing import Process, Queue



def worker(q):

    q.put("Hello from worker!")



if __name__ == '__main__':

    q = Queue()

    p = Process(target=worker, args=(q,))

    p.start()

    p.join()

    print(q.get())

Use Multiprocessing for Unix, Separate Code for Windows:
If your code needs to work on both Unix-like systems and Windows, you might need to structure your code in a way that handles the platform differences. You can use conditional statements to choose different synchronization mechanisms based on the platform.
```
python
import multiprocessing

import sys



if sys.platform.startswith('win'):

    # Use Windows-specific synchronization mechanisms

else:

    # Use Unix-like synchronization mechanisms
```

Keep in mind that the multiprocessing behavior can be different on Windows and Unix-like systems due to the underlying operating system differences. It's important to thoroughly test your code on both platforms to ensure that it behaves as expected.