MySQL Bugs: #99796: Python multiprocessing not working

Bug #99796	Python multiprocessing not working
Submitted:	7 Jun 2020 12:07	Modified:	28 Sep 2022 15:22
Reporter:	Jesper Wisborg Krogh	Email Updates:
Status:	Closed	Impact on me:	None
Category:	Shell General / Core Client	Severity:	S2 (Serious)
Version:	8.0.20	OS:	Windows
Assigned to:		CPU Architecture:	Any

Description:
If you try to use the multiprocessing module in Python mode in MySQL Shell, an error occurs when you try to start the processes:

py> proc.start()
C:\Program Files\MySQL\MySQL Shell 8.0\bin\mysqlsh.exe: unknown option -c

How to repeat:
py> import multiprocessing

py> def run_proc():
 ->     print(f'Hello World')
 ->

py> proc = multiprocessing.Process(target=run_proc)

py> proc.start()
C:\Program Files\MySQL\MySQL Shell 8.0\bin\mysqlsh.exe: unknown option -c

py> proc.join

py> proc.close()

Suggested fix:
If it is deemed impossible to support multiprocessing, at least remove the module, so it is clear that it is not supported.

The workaround is to use the threading module (and the queue module if you need queues) instead.

Dear Jesper,

Thank you for the report and feedback.

regards,
Umesh

Posted by developer:
 
The test case is wrong as it doesn't work in plain python either.
This is a correct test case:

$ cat /tmp/a.py 
import multiprocessing
def run_proc():
    print(f'Hello World')

if __name__ == "__main__":
        proc = multiprocessing.Process(target=run_proc)

        proc.start()
        proc.join()
        proc.close()

$ python3 /tmp/a.py 
Hello World

That said, this bug can be fixed.

Posted by developer:
 
Added the following note to the MySQL Shell 8.0.31 release notes:

Support was added for Python modules which invoke the Python interpreter, such as multiprocessing.