In software development, one of the most critical responsibilities of a class managing persistent data is ensuring synchronization between its in-memory representation and the external storage mechanism (in this case the file system, but this could apply to any external persistent storage). It’s not enough to trust that everything will align itself magically — you need to design with intention. As I said during a mentoring session: “You need to design a way to have the least possible chance that the file contents will get out of sync with the in-memory contents.” This article walks you through practical strategies to achieve just that, minimizing risk while maintaining clarity in your code.

The Root of Synchronization Issues

Synchronization problems often stem from having too many “moving parts” in your code. As I explained: “The fewer moving parts possible, the better, because any additional place that’s manipulating the state introduces a chance for errors.” This means your goal should be to centralize responsibility — designating one area to handle file writes and another to handle reads. If multiple methods directly manipulate the file and memory, you’re inviting subtle bugs that can surface in the most inconvenient ways. Take, for example, a class managing an in-memory list and its file-based counterpart. If you allow multiple methods to write to the file independently, you risk data inconsistencies. I call this creating an “exclusive club,” where only select methods have permission to write or synchronize state.

Best Practices for Synchronization

  1. Isolate File I/O Keep all file-writing operations confined to a single method. When reviewing code with my mentee, I asked: “How many places are we writing to the file? Let’s search for all instances of file.write in this class.” The goal is to reduce these instances to one. By centralizing file operations, you reduce complexity and improve maintainability.

  2. Synchronize on State Changes

Whenever your in-memory state changes in a way that must be remembered, persist it immediately. I likened this to saving a term paper: “Why would you wait until the very end before saving something critical? It’s like writing a 982-page term paper and hitting save only after the final sentence.”

  1. Design with Intentionality

Think of the class you’re designing as if it’s the only thing in the universe. This means ensuring it meets its own requirements without relying on external assumptions. As I told my mentee: “You can’t make assumptions that this other component will handle synchronization for you. Every component must take care of its own responsibilities.”

  1. Avoid Implicit Dependencies

Side effects — such as relying on a specific member variable to trigger synchronization — can make code unpredictable. Instead, pass explicit parameters to ensure synchronization logic is always applied intentionally. As I noted, “When methods have inputs and outputs, you can trust them to behave predictably. Side effects, on the other hand, are inherently less reliable.”

Iterative Improvements: The Path to Better Synchronization

No design is perfect the first time, and that’s okay. As I mentioned: “You might make a design choice that seems best at the time, but two weeks later, you realize it could be better. That’s the nature of iterative design.” Synchronization is no exception. Over time, you’ll refine your methods to better align with the evolving needs of your application.

For example, in the session, we discussed whether to save state at the end of a class’s lifecycle or after each meaningful operation. By revisiting this question, we uncovered inconsistencies in how and when data was written to the file. This led to a simpler, more robust approach where synchronization happened immediately after key updates.

Conclusion

Effective synchronization between in-memory data and persistent storage isn’t just about technical correctness — it’s about building trust in your application’s reliability. By isolating file I/O, synchronizing on state changes, designing with intentionality, and avoiding implicit dependencies, you can significantly reduce the risk of desynchronization.

Remember: “Your goal is to minimize the number of places in that exclusive club allowed to write to the file. That’s your guiding principle.” By adhering to this philosophy, you’ll create software that’s not only functional but maintainable and resilient. So, next time you’re designing a synchronization mechanism, keep these principles in mind — they just might save you from writing a metaphorical 982-page term paper that vanishes before you hit save.