bootstrap spawns dozens of python processes simultaneously, enough to freeze a computer for a few seconds

[cyrilbouvier]

Steps To Reproduce

Run make

Expected Behavior

My machine should still be usable while SageMath is building

Actual Behavior

At the beginning of the make command, my machine becomes unresponsive for a few seconds. If I run top while running, I can clearly see dozens and dozens of python processes all appearing at the same time.

Additional Information

I think this come from the last line of src/doc/bootstrap :

sage-package list --has-file SPKG.rst | OUTPUT_DIR=$OUTPUT_DIR OUTPUT_RST=1 xargs -P 99 -n 1 sage-spkg-info

which will call sage-spkg-info 99 times simultaneously.
I think it should be -P 1 or, if possible, the user could overwrite this value (with 1 as default).

Environment

• OS: Debian 11
• Sage Version: 10.5.beta6

Checklist

• I have searched the existing issues for a bug report that matches the one I want to file, without success.
• I have read the documentation and troubleshoot guide