virtual-threads-bridge

This library allows you to use Java21's Virtual Threads API in Java8+. You could then more easily write code that is compatible with both Java21 virtual threads and pre-Java21 platform threads.

For example, you might have your own Java8 or pre-Java21 library, and you want it to take advantage of virtual threads if your library is run on Java21 JVM. With virtual-threads-bridgem you can write code like this:

ExecutorService executor = ExecutorTool.hasVirtualThreads()
    ? ExecutorTool.newVirtualThreadPerTaskExecutor()
    : Executors.newCachedThreadPool();

ExecutorService concurrencyLimitedExecutor = ExecutorTool.hasVirtualThreads()
    ? ExecutorTool.newSempahoreVirtualExecutor(10)
    : Executors.newFixedThreadPool(10);

Thread thread = ThreadTool.hasVirtualThreads()
    ? ThreadTool.unstartedVirtualThread(myRunnable)
    : new Thread(myRunnable);

Of course, it's dangerous to blindly create excessive number of (platform) threads in Java8+/preJava21 without checking if virtual threads are available:

void processQueueMessage(...) {
   ThreadTool.startVirtualThread(this::process);  // dangerous in Java8+/preJava21
}

You can configure the library to throw exception if attempt is made to create virtual threads in Java8+/preJava21 (as opposed to creating in Java21):

public static void main(String ...) {
    // on app startup, configure library to throw exception if
    // startVirtualThread() is called in Java8+/preJava21
    ThreadTool.getConfig().throwExceptionWhen(START_VIRTUAL_THREAD);
}

void processQueueMessage(...) {
   ThreadTool.startVirtualThread(this::process);  // exception thrown here
}

The following Java21 APIs are bridged:

Java21	Bridge
Thread.isVirtual()	ThreadTool.isVirtual(Thread)
Thread.ofPlatform()	ThreadTool.ofPlatform()
Thread.ofVirtual()	ThreadTool.ofVirtual()
Thread.startVirtualThread(Runnable)	ThreadTool.startVirtualThread(Runnable)
Executors.newThreadPerTaskExecutor(ThreadFactory)	ExecutorTool.newThreadPerTaskExecutor(ThreadFactory)
Executors.newVirtualThreadPerTaskExecutor()	ExecutorTool.newVirtualThreadPerTaskExecutor()

Usage

Add the library to maven pom.xml (or the equivalent in your build system):

<dependency>
    <groupId>io.github.thunkware</groupId>
    <artifactId>virtual-threads-bridge</artifactId>
    <version>0.0.3</version>
</dependency>

License

This library is Open Source software released under the MIT license.