A Deep Dive into Java Project Loom

What is Project Loom?

In today’s software, applications frequently need to manage many operations at the same time. This is called concurrency. Consider an e-commerce platform handling many customer requests, or a data system processing large data sets. The capability to execute concurrent operations efficiently is very important for application responsiveness and scalability.

Java has been a fundamental technology for building robust and scalable applications for a long time. However, as system requirements have increased, certain parts of Java’s traditional concurrency model have shown limitations. This is the main challenge Project Loom aims to solve.

Project Loom is a significant initiative within OpenJDK. Its primary goal is to fundamentally improve how Java handles concurrent programming. This aims to simplify the development, maintenance, and scaling of applications that process many tasks simultaneously.

The central feature of Project Loom is the introduction of virtual threads. This represents a notable change in how Java applications manage numerous concurrent operations. Loom seeks to overcome the limitations of the traditional “thread-per-request” model, leading to Java applications that are simpler, more efficient, and more scalable.

Why Old Threads Were a Problem (and How Virtual Threads Fix It)

Java’s traditional concurrency model largely depends on operating system (OS) kernel threads. When a Java application creates a new thread, it usually maps directly to an OS thread. This approach has functioned, but it brings specific overheads and limitations, especially when applications must scale to handle thousands or millions of concurrent tasks.

Here are the key issues with traditional Java threads:

• Resource Usage: Each OS thread needs a significant amount of memory, mostly for its stack. Creating a large number of these threads can result in high memory consumption and potential memory errors. Also, the OS must manage these threads, which uses CPU due to context switching.
• Blocking Operations: Many common application operations are “blocking”. When a Java thread performs an I/O operation (for example, getting data from a database, making a network call, reading a file), the thread stops execution and waits for the operation to complete. During this waiting time, the OS thread is allocated but does no useful work. This leads to inefficient use of resources.
• Asynchronous Complexity: To reduce the blocking problem and achieve better scalability, developers often use complex asynchronous programming methods (like CompletableFuture or reactive frameworks). While effective for scaling, these solutions can make code more complicated, debugging harder, and the application’s business logic less clear.

Project Loom directly addresses these issues with virtual threads:

• Lightweight Design: Virtual threads are managed by the Java Virtual Machine (JVM), not directly by the OS. They require very little memory. This allows for millions of concurrent virtual threads to run on a small number of OS threads.
• Efficient Context Switching: When a virtual thread encounters a blocking operation, the JVM “parks” it. This immediately frees the underlying OS thread to execute other virtual threads. When the blocking operation finishes, the virtual thread is “unparked” and resumes execution. This JVM-level management results in much faster context switching compared to OS threads.
• Simplified Concurrency: Virtual threads allow developers to write direct, blocking-style code while still achieving the high scalability traditionally associated with complex asynchronous programming. This brings back the idea that “threads are cheap,” enabling developers to focus on application logic without complex concurrency setup.

More Cool Features Beyond Virtual Threads

While virtual threads are the main innovation of Project Loom, the initiative includes other important improvements for Java’s overall concurrency model. These features support virtual threads, making it even simpler to develop robust and understandable concurrent applications.

One important concept that works well with virtual threads is Structured Concurrency. In the past, managing the lifecycle of multiple concurrent tasks could be difficult. Developers often needed to manually ensure tasks finished or were terminated correctly, especially if errors happened. Structured concurrency introduces a more organized, hierarchical approach to concurrent operations. It enables developers to group-related concurrent tasks. If one task in a group fails, or the parent task is cancelled, the entire group can be managed together. This greatly simplifies error handling, task cancellation, and understanding the flow of concurrent operations, making them behave more like sequential code within a defined boundary.

Another valuable addition from Project Loom is Scoped Values. For many years, Java developers have used ThreadLocal for sharing immutable data within a thread. However, ThreadLocal has limitations, such as potential memory leaks if not managed carefully, and sometimes performance issues. Scoped Values offer a modern, more efficient, and safer alternative. They provide a way to implicitly share immutable data within a specific execution scope. Designed to work well with virtual threads and structured concurrency, Scoped Values smoothly follow virtual threads across underlying OS threads without performance problems or the risks linked to ThreadLocal  inheritance. This makes it cleaner to pass context information (like a request ID or security context) down a method call chain across multiple operations without explicit parameter passing.

Also, Project Loom is optimizing existing Java APIs to be “fiber-friendly”. This means that core libraries used for networking, file I/O, and other blocking operations are being adapted to work efficiently with virtual threads. Developers will generally not need to rewrite much existing code, their current blocking calls will simply become efficient in terms of resource usage when run on virtual threads. This offers a smooth transition and maximizes the benefits of this new concurrency model.

Applying Project Loom in Commercial Apps

So, where can we use Project Loom? It is simple: anywhere you need many tasks at the same time and to use computer resources very well. In our world today, this is almost everywhere.

Project Loom is very good for microservices and API gateways. These systems handle many requests at once. Often, they wait for other services or databases. With a light virtual thread for each request, these systems can work much faster and use less memory. This means less cost for servers and better work result.

Also, web servers and application servers (like Spring Boot) will be much better. They can now handle more users at same time without hard programming. Applications that use databases a lot will also gain because waiting for database(s) will not hold up important OS threads.

In simple words, any application that waits a lot – for network, disk, or other systems – is good for Project Loom. This includes processing big data, running background jobs, and event systems.

At the end, Project Loom helps developers write code that is simpler, easy to read, and easy to keep. This code looks like it runs one step at time, but it can handle many, many things. It is not just a small update: it is a big change for building Java applications that work very well. It promises to make development easier and bring new levels of good performance to businesses.

If you need the right technology partner to help your business succeed, contact Swan Software Solutions to schedule a free assessment.