Intuitive Python

Approach Concurrency with Caution

Running your code concurrently sounds appealing—who doesn’t want to run more code? Unfortunately, running code concurrently can create problems that you didn’t realize even existed. Before diving into concurrency, we’ll start this chapter with a brief forewarning.

One class of problems caused by concurrency are called race conditions. In a classic race condition example, two concurrent banking operations accidentally allow a customer to overdraw his bank account:

1. Customer David has $8 in his bank account.
2. Process A reads David’s balance of $8.
3. Process B reads David’s balance of $8.
4. Process A allows David to withdraw $6.
5. Process A updates David’s balance to $8 - $6 = $2.
6. Process A ends.
7. Process B allows David to withdraw ...