Project Loom: Threads Vs Virtual Threads

java concurrency
Reading Time: 2 minutes

If you’d like to create a large number of processes in a cheap way, these processes must run in a concurrent way so that a scale is achieved for a large number of requests processing. To understand in which scenario the Thread needs to scale, let us look at an example below.

Concurrency Example

  • HTTP requests
  • processing messages from the queue
  • integrating external services
  • orchestrating workflows
  • background jobs

Thread – a current unit of concurrency

Thread thread = new Thread("My Thread") {
      public void run(){
        System.out.println("run by: " + getName());

Currently, the basic unit of concurrency is a THREAD

  • Problems with Thread
    • expensive to create
    • expensive to switch
    • limited in number results in limited concurrency
  • Solutions
    • created upfront
      • Problems with Thread Pooling
        • expensive to switch
        • limited in number results in limited concurrency
    • CompletableFuture – Run tasks in a separate thread and notify the main thread about the progress
      • Advantage with CompletableFuture
        • cheap to create
        • cheap to switch
        • unlimited in number results in unlimited concurrency (heap memory)
      • Problems with CompletableFuture
        • lost control flow
        • lost context
        • viral

What is Project Loom

Project Loom aims to provide a lightweight concurrency tool in Java through virtual threads abstraction.

Virtual ThreadsThey are just like threads with the difference that they are not exactly a physical OS thread.

  • An instance of java.lang
  • Multiple virtual threads can run their java code on the same OS thread
Thread t = Thread.startVirtualThread(t) -> { ... };

Creating a Virtual Thread

Thread.startVirtualThread(() -> {
    System.out.println("Hello World");

Difference between Thread and Virtual Thread

  • Thread is managed by OS, Virtual threads are managed by the virtual machine, There we can call that there is no 1-to-1 correspondence between the number of virtual threads you are spawning and how they mapped to actual physical threads behind the scene. It is just providing you with a basic unit of concurrency provided by an actual thread at the JVM level. Now, this can be revolutionary when it comes to creating a very large number of concurrent compute units and scaling to a million without worrying about the resources.


  • For more info regarding differences, you can refer to the link
  • For Basics of project loom: link

1 thought on “Project Loom: Threads Vs Virtual Threads2 min read

Comments are closed.