Understanding the “suspend” Keyword in Kotlin Coroutines and Why It Matters for Android Development

If you’ve been developing Android apps with Kotlin, you’ve likely come across the term “suspend” when diving into coroutines. At first, it might seem like just another keyword in Kotlin, but it’s actually very useful when working with tasks that take time, like downloading data from the internet.

In this post, I’ll walk you through what the “suspend” keyword is, why we need it, and how it simplifies our Android development workflow.

What is a “suspend” function?

A suspend function is a special type of function in Kotlin that can pause and resume its execution at a later point in time without blocking the current thread. In other words, it allows you to run long-running operations (like network calls or database transactions) in a non-blocking way, making sure your UI stays responsive.

Now, you might be thinking: “Why can’t I just use regular functions?”

The key reason we use suspend functions is to avoid blocking the main thread, which is responsible for handling UI updates. If the main thread gets blocked for even a short time, the user experiences lag, freezing, or unresponsiveness in the app. That’s a quick way to get bad reviews, and nobody wants that.

Why do we need “suspend” functions in Android?

Let’s say you’re building an app where users can search for products, and to get that data, you need to fetch it from a remote API. Traditionally, you’d either use a background thread or an AsyncTask (remember those?). While this worked, it led to some messy code, difficult error handling, and often, memory leaks.

But with Kotlin’s coroutines and suspend functions, you can write your asynchronous code almost as if it were synchronous, without any of the complexity.

Here’s an example of how this looks:

suspend fun fetchProductData(): Product {
    return apiService.getProduct() // Simulate a network call
}

In this snippet, fetchProductData() is a suspend function. The word suspend tells Kotlin that this function will execute some long-running operation, and during that time, the function can "suspend" itself and free up the main thread.

Once the data is available (or the operation is complete), the function resumes where it left off. All this happens behind the scenes, making your code easier to read and maintain.

The Power of “suspend” with Coroutines

Coroutines, combined with suspend, allow us to write asynchronous code that looks straightforward and readable. You no longer have to deal with callbacks, nested code, or the complexity that comes with older asynchronous solutions.

Let’s compare two examples. One using callbacks and the other using suspend functions and coroutines:

With Callbacks:

fun fetchDataWithCallback() {
    apiService.getProduct(callback = { product ->
        updateUI(product)
    })
}

Looks simple, right? But imagine if you had to do multiple network calls one after the other. You’d end up with deeply nested callbacks (also known as callback hell). Managing this can get messy fast.

With Coroutines and “suspend”:

suspend fun fetchData() {
    val product = apiService.getProduct()
    updateUI(product)
}

This approach is much cleaner and easier to manage. With suspend, you no longer need to worry about managing callbacks or threads manually. The coroutine framework does it for you.

When to use “suspend” functions?

You should use suspend functions whenever you’re dealing with long-running tasks, such as:

• Network requests (API calls)
• Reading from or writing to a database
• File I/O operations
• Heavy computations

Essentially, whenever you perform any task that could block the main thread, it’s a good candidate for a suspend function.

Conclusion

The suspend keyword in Kotlin is like a magic wand that makes asynchronous programming much easier in Android development. By allowing functions to pause and resume without blocking the main thread, you can create a smoother, more responsive user experience.

The real power of suspend comes when combined with coroutines, making your code cleaner, more readable, and easier to manage.

If you’re just getting started with Kotlin Coroutines, try experimenting with suspend functions in your Android projects. You’ll quickly realize how much simpler your code can become and why this keyword is so essential in modern Android development.