Errors when running hg commit with clang-format extension enabled on Windows 10

Dave Justice@LAPTOP-NA0Q0G86 /c/mozilla-build/mozilla-central
$ hg commit
Processing 5 file(s)...
Process PoolWorker-1:
Traceback (most recent call last):
  File "c:\mozilla-build\python\lib\multiprocessing\process.py", line 267, in _bootstrap
    self.run()
  File "c:\mozilla-build\python\lib\multiprocessing\process.py", line 114, in run
    self._target(*self._args, **self._kwargs)
  File "c:\mozilla-build\python\lib\multiprocessing\pool.py", line 102, in worker
Process PoolWorker-2:
Traceback (most recent call last):
   File "c:\mozilla-build\python\lib\multiprocessing\process.py", line 267, in _bootstrap
   task = get()
  File "c:\mozilla-build\python\lib\multiprocessing\queues.py", line 376, in get
     self.run()
   return recv()
  File "c:\mozilla-build\python\lib\multiprocessing\process.py", line 114, in run
I    self._target(*self._args, **self._kwargs)
mportError: No module named 4b8aac71360011e98d4600e18ca3ea22
P rocess PoolWorker-3:
 File "c:\mozilla-build\python\lib\multiprocessing\pool.py", line 102, in worker
Traceback (most recent call last):
     task = get()
 File "c:\mozilla-build\python\lib\multiprocessing\process.py", line 267, in _bootstrap
  File "c:\mozilla-build\python\lib\multiprocessing\queues.py", line 376, in get
    self.run()
  File "c:\mozilla-build\python\lib\multiprocessing\process.py", line 114, in run
    self._target(*self._args, **self._kwargs)
  File "c:\mozilla-build\python\lib\multiprocessing\pool.py", line 102, in worker
    return recv()
 I   task = get()
mportError: No module named 4b8aac71360011e98d4600e18ca3ea22
  File "c:\mozilla-build\python\lib\multiprocessing\queues.py", line 376, in get
    return recv()
ImportError: No module named 4b8aac71360011e98d4600e18ca3ea22

A little more context for this:

I had gotten my repo up to date with latest from upstream and had about 3 local commits that I used hg strip to get rid of before committing my changes which triggered this error.

Andi will have a look as I don't know much about windows

Bug 1529415 looks related, maybe a duplicate/unrelated to the clang-format hg extension itself.

This is a regression caused by this patch.

Andi, if this is too complex, we could just disable parallel execution on windows until we have a fix.

1. A sheriff is going to revert b59977d42a4d
2. I will redo this after we have the backout using futures since multiprocessing is broken on windows.

Aryx, Dluca, can you please backout changeset b59977d42a4d?

Changeset b59977d42a4d has been reverted here : https://hg.mozilla.org/mozilla-central/rev/121bbaec1b30e7e0a4cf1b9db1db2bd8898306e6

Parts of this patch were taken from the original work of :bbouvier in Bug 1521772.
We needed to revert Bug 1521772 since it broken Windows compatibility.

https://hg.mozilla.org/mozilla-central/rev/add98afa5f0c

https://hg.mozilla.org/integration/autoland/rev/add98afa5f0ca1ca17aa87eaa045442a3e1fa07a