Provide explicit ways to prevent concurrency

[p.colbert]

@junderhill

we should work to prevent those problems intruding into the orderly world of Python

This is precisely what we’re trying to accomplish. The title reflects the fact that we currently have some uncontrolled concurrency, and we would like to have clean, simple ways to limit or eliminate it, as shown here:

@hugetim

Please add an app-wide option to instead have all functions behave like uninterrupted subroutines and make this the default for new apps, particularly for new users.

Emphasis mine. The goal is to prevent concurrency, by default – except where the developer (or the task) demands otherwise.

We hope that the latter case will be rare. However, when it does happen, we should at least be able to prevent concurrency for critical areas of code, i.e., via the in-memory equivalent of (nestable) transactions.