For many years I’ve been comfortable knowing that programming is build on just four pillars. These are all you need to develop anything you want and these would be:

• Statements, or basically all the actions that need to perform.
• Conditions, which determines in which direction the code will flow.
• Loops for situations where actions need to be repeated.
• Structures to organize both code and data into logical units like records and classes, databases with indices and even protocols so two applications can communicate with one another.

But as I’m developing more and more asynchronous code where you just trigger an action and later wait for the response, I start wondering if there should be a fifth one. So, should there be a fifth one?

• Parallel tasks, where two or more flows run concurrently.

It’s a tricky one and if you learned to use flow charts and Nassi–Shneiderman diagrams to design applications then you’ll discover that these diagrams don’t have any popular option to represent parallel tasks in any way. Well, except in the way I just said, by triggering an external event and ignore the result until you need it.

Well, Nassi-Shneiderman does have this type for concurrent execution:

And flowcharts also have a fork-join model to represent concurrent execution. So these diagrams do provide some way to indicate parallel execution. But the representation is one that suggests several different tasks are executed at the same time. But what if you have an array of records and need to execute the same task on every record in a parallel way instead?

Parallel execution is quite old yet I never found a satisfying way to display concurrency in these kinds of diagrams. Which makes sense as they are meant to define a single flow while parallel execution results in multiple, simultaneous flows. And parallel execution can make things quite complex as you might just want to cancel all these flows if one of them results in an error.

But it is possible to represent them in diagrams for a long time already even though their usage was rare in the past. But in modern times where computers have numerous cores and multithreading has become a mainstream development technique, it has become clear that parallel or concurrent execution is becoming an important standard in programming.

So it’s time to recognize that there’s a fifth pillar to programming now. But mainly because it has become extremely common nowadays to split the flow of execution only to join things at a later moment.

But this will bring many challenges. Especially because forking can result in similar tasks being executed while they don’t have to join all at once either. It basically adds a complete new dimension to programming and while it’s an old technique, it isn’t until recently that mainstream developers have started using it. The diagrams are still limited in how it can be executed while developers can be extremely creative.

Of course, there’s also a thing like thread pools as computers still have limits to how many threads can be executed simultaneously. You might trigger 50 threads at once yet add limitations so only 20 will run at the same time while the rest will wait for one of those threads to finish.

It becomes even more complex when two or more threats start sending signals to one another while they continue running. This is basically a start for event-driven programming, which doesn’t really fit inside the old diagram styles. You could use UML for various of these scenarios but it won’t fit in a single diagram anymore. A sequence diagram could be used to display parallel execution with interprocess communications but this focuses only on communication between processes. Not the flow of a single process. Then again, UML doesn’t even have those kinds of flow diagrams.

So, while programming might have a fifth pillar, it also seems it breaks the whole system due to the added complexity. It also makes programming extremely different, especially for beginners. When you start to learn programming then the four pillars should teach you what you need to know. But once you start on the fifth pillar, everything will turn upside down again…

So maybe I should even forget about my four pillars theory? Or add the fifth one and ignore the added complexity?