Project Loom: Threads Vs Virtual Threads

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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());
      }
   };
   thread.start();
   System.out.println(thread.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 Threads – They 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.