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Everton Freire
Everton Freire

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Java Virtual Threads vs Kotlin Coroutines


In this article, we will compare two different ways of implementing concurrency in the JVM: Java Virtual Threads and Kotlin Coroutines. We will see what are the main differences, advantages and disadvantages of each approach.

What are Virtual Threads and Coroutines?

Virtual Threads and Coroutines are both techniques to achieve concurrency without creating too many system threads. System threads are expensive to create and maintain, and they can cause performance problems if there are too many of them. Virtual Threads and Coroutines allow us to create many lightweight tasks that can run concurrently on a smaller number of system threads, reducing the overhead of context switching and memory usage.

Virtual Threads are a feature of Project Loom, which is an experimental project to add new concurrency features to Java. Virtual Threads are also known as fibers or continuations. They are similar to regular threads, but they are managed by the JVM instead of the operating system. The JVM can schedule many virtual threads on a single system thread, and switch between them as needed. Virtual Threads can also suspend and resume their execution without blocking the system thread, which allows for non-blocking IO operations.

Coroutines are a feature of Kotlin, which is a modern programming language that runs on the JVM. Coroutines are also similar to threads, but they are implemented as library functions instead of language features. Coroutines can be created using special keywords like suspend, launch or async, and they can also suspend and resume their execution without blocking the system thread. Coroutines can use different dispatchers to control how they are scheduled on system threads, and they can also communicate with each other using channels or shared variables.

How do they compare?

Virtual Threads and Coroutines have some similarities and some differences. Let’s see some of them:

  • Performance: Both Virtual Threads and Coroutines are generally more efficient and can utilize resources more effectively than regular threads. However, the actual performance benefits will depend on the specific use case and implementation. Some benchmarks have shown that Go Goroutines, which are similar to Virtual Threads, have better performance than Kotlin Coroutines1. However, other benchmarks have shown that Kotlin Coroutines have better performance than Java Virtual Threads. Therefore, it is hard to say which one is faster or better in general.
  • Syntax: Virtual Threads use the same syntax as regular threads in Java, which means that they are easy to use and integrate with existing code. However, this also means that they inherit some of the limitations and complexities of regular threads, such as synchronization, locking, or exception handling. Coroutines use a different syntax than regular threads in Kotlin, which means that they require some learning and adaptation. However, this also means that they offer some advantages and simplifications over regular threads, such as structured concurrency, cancellation, or error handling.
  • Maturity: Virtual Threads are still an experimental feature of Project Loom, which is not yet part of the official Java release. Therefore, they are not stable or widely supported by tools or libraries. They may also change or evolve in the future. Coroutines are a stable feature of Kotlin since version 1.3, which was released in 2018. Therefore, they are more reliable and well-supported by tools or libraries. They have also been tested and improved over time.


In conclusion, Virtual Threads and Coroutines are both interesting and promising ways of achieving concurrency in the JVM. They both offer better performance and resource utilization than regular threads, but they also have some trade-offs and challenges. Depending on the situation and preference, one may choose one or the other for their concurrent programming needs.

Top comments (1)

emmysteven profile image
Emmy Steven

The good news is that virtual threads are going to be part of Java 21 LTS.