Asynchronous vs. Synchronous Programming: Key Similarities and Differences
In computer programming, synchronous and asynchronous models are essential. The terms offer a clue about what each programming model does and the differences between them. Synchronous tasks happen in order — you must finish task one before moving on to the next. Asynchronous tasks can be executed in any order, or even simultaneously. How can this be understood in terms of programming?
What is the difference between asynchronous and synchronous programming?
Synchronous, sometimes referred to as “sync,” and asynchronous, also known as “async,” are two types of programming models.
Understanding how these two models differ is critical in building application programming interfaces (APIs), creating event-based architectures, and deciding how to handle long-running tasks.
But before deciding which method to use and when, it’s important to know a few quick facts about synchronous programming and asynchronous programming.
Asynchronous programming is a multithreaded model that’s most applicable to networking and communications. Asynchronous is a non-blocking architecture, which means it doesn’t block further execution while one or more operations are in progress.
With asynchronous programming, multiple related operations can run concurrently without waiting for other tasks to complete. During asynchronous communication, parties receive and process messages when it’s convenient or possible, rather than responding immediately upon receipt.
Texting is an asynchronous communication method. One person can send a text message, and the recipient can respond at their leisure. In the meantime, the sender may do other things while waiting for a response.
Another example of asynchronous programming is low-code app development. In a low-code platform, multiple developers can work on projects at the same time, which helps accelerate the process of delivering apps.
Synchronous is known as a blocking architecture and is ideal for programming reactive systems. As a single-thread model, it follows a strict set of sequences, which means that operations are performed one at a time, in perfect order. While one operation is being performed, other operations’ instructions are blocked. The completion of the first task triggers the next, and so on.
To illustrate how synchronous programming works, think of a telephone conversation. While one person speaks, the other listens. When the first person finishes, the second tends to respond immediately.
Asynchronous vs. synchronous programming
Ultimately, the choice comes down to operational dependencies. Do you want the start of an operation to be dependent on the completion of another operation, or do you want it to run independently?
Asynchronous is a non-blocking architecture, so the execution of one task isn’t dependent on another. Tasks can run simultaneously. Synchronous is a blocking architecture, so the execution of each operation is dependent on the completion of the one before it. Each task requires an answer before moving on to the next iteration.
The differences between asynchronous and synchronous include:
- Async is multi-thread, which means operations or programs can run in parallel. Sync is single-thread, so only one operation or program will run at a time.
- Async is non-blocking, which means it will send multiple requests to a server. Sync is blocking — it will only send the server one request at a time and will wait for that request to be answered by the server.
- Async increases throughput because multiple operations can run at the same time. Sync is slower and more methodical.
Differences aside, asynchronous and synchronous methods both offer advantages, but for different stakeholders: Async for users and sync for developers.
Asynchronous programming enhances a user’s experience by decreasing the lag time between when a function is called and when the value of that function is returned. In the real world, this translates to a faster, more seamless flow.
For example, users want their apps to run fast, but it takes time to fetch data from an application programming interface (API). In these cases, asynchronous programming helps the app screen load faster, improving the user experience.
Synchronous programming, on the other hand, is advantageous for developers. Quite simply, synchronous programming is much easier to code. It’s well supported among all programming languages, and as the default programming method, developers don’t have to spend time learning something new that could open the door to bugs.
Programming makes our digital world run, but without the right pairing of programs and operations, chaos and poor user experiences would ensue. If operations are inappropriately relying on asynchronous programming, our digital world could spin into a mad, hyperactive frenzy. And if operations are inappropriately relying on synchronous programming, our digital world could come to a screeching halt. It’s imperative to understand when to use each type of programming.
When to use async
Asynchronous programming should only be used in programming independent tasks, where it plays a critical role. For instance, asynchronous programs are ideal for development projects with a large number of iterations. Because steps don’t have to follow a fixed sequence, asynchronous programming keeps development moving forward.
Responsive UI is a great use case for asynchronous planning. Take, for example, a shopping app. When a user pulls up their order, the font size should increase. Instead of first waiting to load the history and update the font size, asynchronous programming can make both actions happen simultaneously.
When to use sync
Asynchronous programming is relatively complex. It can overcomplicate things and make code difficult to read. Synchronous programming, on the other hand, is fairly straightforward; its code is easier to write and doesn’t require tracking and measuring process flows (as async does). Because tasks depend on each other, there’s a need to know if they could run independently without interrupting each other.
Synchronous programming could also be appropriate for a shopping app, for example. When checking out online, a user wants to buy all of their items together, not individually. Instead of completing an order every time the user adds something to their cart, synchronous programming ensures that the payment method and shipping destination for all items are selected at the same time.
How to choose between asynchronous and synchronous programming
When deciding which approach to take, it may be helpful to think of asynchronous programming as adaptable, and synchronous programming as strict. Asynchronous programming is the multitasker, moving from one to-do to the other and alerting the system when each one is complete. Synchronous programming functions as a one-track mind, checking off one task at a time in a rigid sequence.
Asynchronous programming allows more things to be done at the same time and is typically used to enhance the user experience by providing an effortless, quick-loading flow.
Synchronous programming is best utilized in reactive systems. While it is simpler for developers to code and is recognized by every programming language, sync is resource-intensive and can slow things down.