Creating GF fails if done from a separate thread

[semjon00]

Hello! Thank you for this nice library! Here is a bug report:

Currently, the databases are accessed using a singleton cursor. Due to the way the cursor is created, the database disallows accessing it from a thread that does not match the thread in which it was created. This may cause the creation of fields to fail if they are created from different threads.

Here is a code that reproduces the issue:

from threading import Thread
from galois import GF

if __name__ == '__main__':
    field = GF(7)

    t = Thread(target=lambda: GF(11), args=())
    t.start()
    t.join()

A possible fix would be to substitute the
cls.conn = sqlite3.connect(cls.file)
with
cls.conn = sqlite3.connect(cls.file, check_same_thread=False)
inside the constructor of galois._databases._interface.DatabaseInterface.
I believe that this is a safe thing to do, since there are no write operations to the database.

[mhostetter]

Thanks for the report. This looks good to me. If you'd like to submit a PR, we can get it merged. Otherwise, I can apply the patch.

[semjon00]

It turns out there are more issues that could arise due to using multiple threads.