Introduction to Async Programming in Swift

Async programming is a technique that allows developers to write non-blocking code, which improves the performance of the application. It is particularly useful in Vapor development when you need to perform long-running operations such as database queries, file I/O, or network operations. In this tutorial, we will take a closer look at using async programming in Swift.

The async/await Syntax in Swift

Swift 5.5 introduced a new feature called async/await, which simplifies the process of writing async code. With async/await, you can write asynchronous code that looks almost identical to synchronous code. Here's an example of using async/await syntax to make an API call:

func fetchData() async throws -> [Post] {
    let url = URL(string: "https://jsonplaceholder.typicode.com/posts")!
    let (data, _) = try await URLSession.shared.data(from: url)
    return try JSONDecoder().decode([Post].self, from: data)
}

In this example, we're using the `async` keyword to specify that the function is asynchronous. We're also using the `await` keyword to indicate that we're waiting for the result of the API call before continuing execution.

Improving Performance with Async Programming

By using async programming, we can improve the performance of our Vapor web application. For example, let's say we have a route that needs to fetch user data from a database:

app.get("users") { req -> [User] in
    let users = try User.query(on: req.db).all().wait()
    return users
}

In this example, we're using the `wait()` function to block execution until the query is complete. However, this can cause a significant performance hit if the query takes a long time to complete. By using async programming, we can rewrite this route to avoid blocking the thread:

app.get("users") { req async throws -> [User] in
    let users = try await User.query(on: req.db).all()
    return users
}

In this example, we're using the `async` keyword to indicate that the function is asynchronous. We're also using the `await` keyword to wait for the query to complete without blocking the thread. This allows the thread to continue executing other operations while the query is running.

Conclusion

Async programming is an advanced Swift feature that can greatly improve the performance of your Vapor web application. With async/await syntax, you can write non-blocking code that looks almost identical to synchronous code. By using async programming, you can free up your app's resources to continue executing other operations while waiting for long-running operations to complete.