When you break up your application up as a set of tasks, which GAE pretty much requires, it's hard to execute them in any sort of order. Your program is not executing sequentially so there aren't any while loops and if-then statements to make sure calculations happen in a certain sequence. So you need a higher level kind system that can order everything. Node.js which is a similar sort of event driven system, but not distributed, has a number of similar libraries https://github.com/ry/node/wiki/modules under Flow control / Async goodies.
