Use virtual threads in high-throughput concurrent applications, especially those that consist of a great number of concurrent tasks that spend much of their time waiting. Server applications are examples of high-throughput applications because they typically handle many client requests that perform blocking I/O operations such as fetching resources.

Virtual threads are not faster threads; they do not run code any faster than platform threads. They exist to provide scale (higher throughput), not speed (lower latency).

Here’s a breakdown of the key benefits:

1. High Scalability and Throughput

Platform threads (the traditional java.lang.Thread) are wrappers around operating system (OS) threads. OS threads are a scarce and expensive resource, consuming significant memory (often 1MB or more per thread) and having high overhead for context switching. This limits the number of platform threads you can create, typically to a few thousand at most.

• Virtual threads are lightweight threads managed entirely by the Java Virtual Machine (JVM), not the OS. They are extremely cheap, requiring very little memory, allowing you to create millions of them.
• The JVM multiplexes these millions of virtual threads onto a small, fixed pool of platform threads.
• This model allows a server application to adopt the simple and readable “thread-per-request” style, even when handling a massive number of concurrent connections, which was previously only possible with complex asynchronous or reactive programming.

2. Efficient Handling of Blocking Operations (I/O-Bound Workloads)

The core problem virtual threads solve is the inefficiency of platform threads during blocking operations, such as waiting for a database query, a network call, or a file I/O to complete.

• Platform Thread: When a platform thread performs a blocking I/O operation, it is tied up and sits idle, doing no work for a long time. This is known as thread blocking and wastes an expensive OS resource, limiting the application’s overall concurrency.
• Virtual Thread: When a virtual thread executes a blocking I/O operation, the JVM suspends the virtual thread and unmounts it from its carrier platform thread. This action is very fast and cheap. The now-free platform thread immediately becomes available to run another virtual thread.
  • Once the I/O operation is complete, the virtual thread is resumed and mounted onto any available carrier platform thread (not necessarily the same one) to finish its task.

This process ensures that the limited pool of platform threads remains busy doing actual work instead of waiting, dramatically increasing throughput for I/O-bound applications (which covers most modern server applications).

3. Simplified Programming Model

Virtual threads allow developers to write simple, sequential, and imperative code using the standard Thread API, even for highly concurrent tasks.

• This is a massive benefit over older solutions like reactive programming (e.g., Reactor or RxJava), which were introduced to achieve high concurrency without thread blocking but required complex, non-sequential code that was difficult to read, debug, and maintain.
• With virtual threads, you get the scalability of the asynchronous model with the simplicity of the synchronous model.