Deadlock when running `pip_build.py`

[keras-team]

Deadlock when running `pip_build.py`

[mattdangerw]

@chenmoneygithub has also hit this issue, so figured this was worth tracking down.

We have both encountered this on ubuntu 22.04. Possibly this is os specific.

[fchollet]

This comes from the fact that:

• Importing torch triggers the issue when TF is imported
• pip build will try to import every file in the codebase, hence the torch import
• When torch backend is on, we import torch first, which fixes it
• Yes this is env specific

You could fix it by importing torch at the top of pip build script I bet.

[fchollet]

If that doesn't work let's set the KERAS_BACKEND env variable to torch at the start of the script.

[mattdangerw]

Fix works for me! Closing this.