Units of Work

The problem with the threading model described earlier is that for the average programmer, writing error-free, multithreaded code is nearly impossible. This is not meant as a critique of our industry or of the average programmer's abilities; it's simply an observation. The complex interactions you must account for in your code when synchronizing data and actions across multiple threads are really just too much for most people to tackle. Imagine that 5% of all people have the capacity to write software at all. Only a small fraction of those 5% are really up to the task of writing heavy-duty multithreaded applications. Even people who have done it successfully will often advise others to not follow their example!

Fortunately, all hope is not lost. It is possible to implement some concurrency without too much low-level thread-twisting. Just as we have the ability to display data on the screen without directly poking bits into video RAM, and to read data from disk without interfacing directly with disk controllers, software abstractions exist that let us run our code on multiple threads without requiring us to do much directly with the threads.