I Ditched Async/Await: 5 Virtual Thread Wins for 2025

Introduction: The Async/Await Era and Its Discontents

For years, the `async/await` pattern has been the undisputed champion of concurrency for I/O-bound applications. From JavaScript to C# and Python, we were taught that to achieve high throughput, we had to embrace asynchronicity. We learned to wrap our heads around Promises, Futures, and a syntax that cleaved our code into two distinct worlds: the synchronous and the asynchronous. It worked, but at a cost.

The mental overhead was significant. We battled with "function coloring," where an `async` function infects its entire call stack. Debugging became a journey through fragmented stack traces, and simple, sequential business logic was contorted to fit the non-blocking model. I lived in this world for a long time, believing it was the only way to build scalable services.

Then came Java's Project Loom, which delivered virtual threads as a production-ready feature in JDK 21. After initial skepticism, I took the plunge. I refactored a microservice, ditching `CompletableFuture` and the reactive mindset for this new model. The results were so profound that I can say with confidence: for backend Java development in 2025, I've ditched `async/await`, and I'm never looking back. Here are the five wins that convinced me.

A Quick Primer: What Are Virtual Threads?

Before we dive into the wins, let's clarify what virtual threads are. Unlike traditional "platform threads," which are heavy wrappers around OS threads, virtual threads are lightweight threads managed by the Java Virtual Machine (JVM) itself. You can create millions of them without breaking a sweat.

The magic is how they handle blocking operations (like a database query or an HTTP call). When a virtual thread blocks, the JVM doesn't block the underlying OS thread. Instead, it suspends the virtual thread and uses the OS thread to run another one. When the blocking operation completes, the JVM resumes the original virtual thread. This gives you the scalability of non-blocking I/O with the simplicity of traditional, blocking, thread-per-request code. It’s the best of both worlds.

Win 1: Code That Breathes - The Return of Readability

The most immediate and satisfying victory is the dramatic simplification of your code. Business logic is almost always sequential: fetch user data, then get their order history, then update their status. Writing this with `async/await` (or Java's `CompletableFuture`) forces you into a chain of callbacks or `thenApply`/`thenCompose` calls.

Code Comparison: Before and After

Consider a simple operation to fetch a user and their recent posts.

Before (using `CompletableFuture`):

public CompletableFuture<UserWithPosts> getUserAndPosts(UUID userId) {
    return userClient.fetchUser(userId)
        .thenCompose(user -> 
            postsClient.fetchPostsForUser(user.getId())
                .thenApply(posts -> new UserWithPosts(user, posts))
        );
}

After (using Virtual Threads):

public UserWithPosts getUserAndPosts(UUID userId) {
    // Each call blocks the virtual thread, but not the OS thread!
    User user = userClient.fetchUser(userId);
    List<Post> posts = postsClient.fetchPostsForUser(user.getId());
    return new UserWithPosts(user, posts);
}

The virtual thread version is plain, simple, sequential Java. It's instantly understandable to any developer, regardless of their experience with concurrency models. It’s boring, and in software engineering, boring is beautiful. This linear code is easier to write, review, and maintain.

Win 2: Eradicating the “Function Coloring” Plague

One of the most insidious problems with `async/await` is what's known as "function coloring." In this model, functions are either "blue" (synchronous, returning a direct value) or "red" (asynchronous, returning a Promise/Future). The rule is simple and brutal: a red function can call a blue function, but a blue function cannot easily call a red one without becoming red itself.

This "redness" is viral. Once you make one low-level I/O function `async`, you're forced to make its caller `async`, and its caller's caller, all the way up your stack. This creates an artificial and rigid division in your codebase.

Virtual threads eliminate this problem entirely. There are no colored functions. All code is written in the same, simple, synchronous style. A method that performs I/O looks and behaves just like a method that calculates a sum. This freedom simplifies architecture, promotes code reuse, and removes a whole category of frustrating design constraints.

Win 3: Effortless Scalability Without the Complexity

The original promise of `async` was scalability. By not blocking precious OS threads, a server could handle thousands of concurrent connections. This is true, but it came with the code complexity we've discussed.

Virtual threads deliver the same, if not better, scalability. Because they are so lightweight, you can follow the simple "thread-per-request" model without fear. A new web request comes in? Spin up a new virtual thread. Need to make three parallel API calls? Spin up three virtual threads and `join()` them.

try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
    Supplier<DataA> dataASupplier = scope.fork(() -> apiClientA.fetchData());
    Supplier<DataB> dataBSupplier = scope.fork(() -> apiClientB.fetchData());

    scope.join();
    scope.throwIfFailed();

    // Both tasks are complete, results are available
    return new CombinedData(dataASupplier.get(), dataBSupplier.get());
}

This example using Java 21's Structured Concurrency is both easy to read and incredibly performant. The JVM handles the efficient scheduling of these virtual threads onto a small pool of OS threads. You get massive throughput with code that looks like it was written for a single-user desktop app.

Win 4: Debugging and Profiling Made Sane Again

If you've ever tried to debug an issue in a reactive or `async` codebase, you know the pain. Stack traces are a mess. They either point to the reactive framework's scheduler or are broken into disconnected fragments, making it nearly impossible to trace the logical flow of your code.

With virtual threads, this nightmare is over. Because your code is sequential, the stack traces are too. When an exception is thrown, you get a clean, deep, and understandable trace that shows the exact sequence of calls leading to the error, just like in a traditional application. This applies to debuggers and profilers as well. Standard tools work out of the box, allowing you to step through your code and analyze performance without needing special plugins or mental gymnastics to piece the story together.

Win 5: Unlocking the Entire Java Ecosystem, Instantly

This might be the most underrated benefit. The Java ecosystem is vast, with decades of robust, battle-tested libraries for everything from database access (JDBC) to messaging. The vast majority of these libraries are written in a simple, blocking style.

In the `async` world, you couldn't use them efficiently. You had to wait for the library maintainer to release a separate, non-blocking, `async` version of the driver or client. This led to a split ecosystem and forced developers to choose libraries based on their concurrency model rather than their features.

Virtual threads solve this problem elegantly. Since blocking a virtual thread is cheap, you can use any standard, blocking library (like a JDBC driver) inside a virtual thread, and it will behave as a non-blocking component from the application's perspective. Your application remains scalable and responsive. There's no need to rewrite or replace your favorite libraries. The entire existing Java ecosystem is now supercharged for modern, high-throughput applications.

Virtual Threads vs. Async/Await: A Head-to-Head Comparison

Conclusion: A Clear Path Forward for 2025

The shift from `async/await` to virtual threads isn't just an incremental improvement; it's a paradigm shift that reclaims simplicity without sacrificing performance. For years, we accepted complexity as the price of scalability. Project Loom proves that this is a false dichotomy.

By providing readable code, eliminating function coloring, offering effortless scalability, simplifying debugging, and unlocking the entire existing library ecosystem, virtual threads represent a massive leap forward in developer experience and productivity. For new backend services in Java, the choice is clear. It's time to ditch the complexity of `async/await` and embrace the elegant power of virtual threads. Your codebase—and your sanity—will thank you.