Responsive and real-time. If you’re an application developer, you likely hear these words a lot. Whether you build business or customer-facing applications, your users expect the same experience no matter what device they use. Many want applications to offer instant information and real-time interactions.
So, how do you fulfill these expectations? Start by incorporating async functions into your applications. In other words, add some asynchronous APIs!
What are asynchronous functions?
Asynchronous (async) functions allow code to execute non-blocking operations, meaning operations can run simultaneously without waiting for other tasks to complete. Asynchronous functions can be on the client side or the server side.
Client-side async functions
Async functions on the client side (typically web and mobile browsers) involve completing API operations concurrently. These functions allow browsers to process shorter operations while waiting for longer ones to complete. By creating non-blocking operations with async functions, you can build fast and responsive user interfaces.
Server-side async functions
On the server side, async functions enable the server to coordinate requests. By running these requests simultaneously via a thread pool, the server can optimize resource use and improve application throughput. You can also use server-side code to make API endpoints asynchronous, handling multiple non-blocking requests.
These functions allow you to implement asynchronous APIs in various applications and environments.
The benefits of asynchronous APIs
Async APIs are a category that includes streaming, message queues, and event logs, as well as APIs that specify async processing. These can run simultaneous non-blocking operations themselves — no added server-side code. You can implement nearly all APIs to support asynchronous operations, and the benefits are significant:
- Greater responsiveness — Applications respond to user inputs while processing operations in the background.
- Improved user experience — Users see faster, more reliable performance from applications — no freezing or slowness when pages render or UI components load.
- More efficient resource usage — Applications use system resources more efficiently with no need for multiple disparate processes or threads.
- Higher scalability — Applications can handle multiple requests concurrently without the server overloading, enabling them to perform well when traffic increases.
Async APIs: Core components
Now that you know the benefits of async APIs, we’ll cover two essential components: communication protocols and mechanisms.
Communication protocols
These non-blocking APIs use various protocols for communication, such as:
- Advanced Message Queuing Protocol (AMQP) — AMPQ enables asynchronous communication between producers and consumers.
- Message Queuing Telemetry Transport (MQTT) — MQTT is a protocol for sending data to and from devices and networks with limited bandwidth. It uses the pub/sub messaging model and is ideal for small sensors and mobile devices.
- WebSockets — A WebSocket is a bidirectional communication protocol that sends and receives data in real time between the client and the server. It sends information using a single Transmission Control Protocol (TCP) connection.
- Server-Sent Events (SSE) — With SSE, the server sends or pushes automatic updates to the client in real time via an HTTP connection.
Mechanisms
Async APIs use mechanisms to specify what should happen once asynchronous operations have been completed:
- Callbacks — Callbacks are functions passed to other functions as arguments when an asynchronous operation is done. Developers often avoid using many callbacks when implementing async APIs to prevent “callback hell” or the “pyramid of doom.” Instead, they rely on promises to handle callbacks.
- Promises — A promise is an object that represents the current state of an operation: pending, fulfilled, and rejected. It is returned upon the completion or failure of an asynchronous operation. With a promise, you attach callbacks instead of passing them into a function.
- Futures — Futures are read-only objects representing potential future values resulting from asynchronous operations or computations. Most languages support callbacks and promises, but only some support futures, such as Python, Scala, Rust, and Dart.
These components are core to how async APIs work. You need to combine them carefully to ensure that your application performs well.
Synchronous vs. asynchronous APIs
You can use both synchronous and asynchronous APIs to build applications that perform tasks in real time. The trick is knowing when to use asynchronous APIs, synchronous APIs, or a combination. Here’s a quick compare-and-contrast exercise:
| Synchronous APIs | Asynchronous APIs | |
| Blocking | The client must wait for the API to respond before executing other tasks (blocking). | The client can perform other tasks while waiting for the API to respond (non-blocking). |
| Execution | Requests are handled one at a time in order (sequential). | Multiple requests are handled simultaneously (concurrent). |
| Implementation | Linear, predictable execution. Generally simpler to implement and manage than async APIs. | Typically involve event loops and callbacks or promises. More complex to implement and maintain than synchronous APIs. |
| Performance | Tend to run slower when handling long-running tasks, compared to async APIs. | Usually perform better than synchronous APIs, especially when performing multiple asynchronous requests. |
| Scalability | Each request is handled separately instead of concurrently, limiting scalability. | Can process multiple requests concurrently, facilitating scalability. |
| Use cases | Ideal for quick and simple tasks. Great for tasks that require immediate feedback and low latency. | Ideal for long-running tasks and high-traffic scenarios. Great for applications that require real-time updates and can tolerate high latency. |
The snapshot comparison above provides plenty of guidance to get you started, but how do you decide on which type of API to incorporate into your application? Let’s get into some use cases.
When to use synchronous APIs
If you plan to develop an application where users expect quick and immediate responses, consider using synchronous APIs. Let’s look at an airline booking application.
Applications for airline bookings direct customers through an ordered process. The process starts with searching for and selecting an available flight. It ends with booking and paying for the flight and then getting an immediate booking notification.
Typically, a synchronous API performs each operation before moving on to the next. This simple, predictable process makes it easier for developers to understand the flow and debug the application. It also simplifies error handling — when an error occurs, the system communicates it immediately to the client so the latter can resolve it quickly or send a notification.
When to use asynchronous APIs
If you’re building an application where some tasks will take an unpredictable amount of time, asynchronous APIs will serve you better. With async APIs, the application can complete tasks while others are processing.
Take audio and video processing applications. These need to process files of varying sizes. Using async functions in an API allows the application to return processed data faster. The processing time for audio and video files doesn’t scale linearly with size, so small files process quicker than large ones. Async API endpoints let the application process small files and return data while large files continue processing in the background.
With async APIs, you can ensure your application can perform tasks even when others require more time to complete.
Building better real-time applications
Synchronous and asynchronous APIs can help you build amazing and reliable real-time applications. However, they achieve real-time functionality in different ways. Your choice of API depends on your use case, the expectations of your users, and knowing how these APIs work.
Once you understand these factors, you can decide whether synchronous or asynchronous APIs will work for you — or perhaps both!
