Hi, I'm Ayan Dutta, a Software Architect, Instructor, and Content Creator.
I create practical, hands-on courses on Java, Spring Boot, Debugging, Git, Python, and more.

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This repository contains all the demo code for the Udemy course: Java Virtual Threads & Structured Concurrency w/ Spring Boot

• JDK 21+ (stable virtual threads)
• JDK 19/20 also supported with --enable-preview
• IntelliJ IDEA or Eclipse (recommended)
• Maven 3.9+ for building projects

Clone the repository and navigate to the project directory:

git clone https://github.com/j2eeexpert2015/virtual-threads-structured-concurrency.git
cd virtual-threads-structured-concurrency

Build the project:

mvn clean compile

Add --add-exports (and preview where needed) at compile and runtime.

Go to Settings → Build, Execution, Deployment → Compiler → Java Compiler → "Additional command line parameters":

--enable-preview --add-exports=java.base/jdk.internal.vm=ALL-UNNAMED

Go to Run/Debug Configurations → your app → VM options:

--enable-preview --add-exports=java.base/jdk.internal.vm=ALL-UNNAMED

You should already have set:

• Project SDK = Java 21
• Language level = 21 (Preview) for both Project and Modules

Keep these settings as they are.

After completing the setup above, you can run any demo directly from IntelliJ.

Run Basic Virtual Thread Demo:

mvn clean compile exec:java -Dexec.mainClass="com.example.virtualthreadcreation.BasicVirtualThreadCreation"

Run Virtual Thread Builder Demo:

mvn exec:java -Dexec.mainClass="com.example.virtualthreadcreation.VirtualThreadCreationWithBuilder"

Run Structured Concurrency Demo:

mvn exec:java -Dexec.mainClass="com.example.structuredconcurrency.ProductPageWithStructuredConcurrency"

Run Continuation Demo:

mvn exec:java -Dexec.mainClass="com.example.continuation.SimpleContinuationDemo" -Dexec.args="--add-exports java.base/jdk.internal.vm=ALL-UNNAMED --enable-preview"

For debugging jdk.internal.vm.Continuation and other internal APIs:

1. Go to Run/Debug Configurations
2. Click Modify options
3. Select Add additional command line parameters
4. Add the same VM options:

   --add-exports java.base/jdk.internal.vm=ALL-UNNAMED --enable-preview
   

This enables the IntelliJ debugger to step into Continuation methods and other internal JDK classes.

src/main/java/com/example/
├── virtualthreadcreation/     # Basic virtual thread creation examples
├── structuredconcurrency/     # Structured concurrency demonstrations  
├── scopedvalue/              # ScopedValue vs ThreadLocal examples
├── continuation/             # Low-level Continuation API examples
├── pinning/                 # Virtual thread pinning detection
├── mountandunmount/         # Thread mounting behavior
└── util/                   # Utility classes (JFR, profiling, etc.)

• BasicVirtualThreadCreation.java - Simple VT creation patterns
• VirtualThreadCreationWithBuilder.java - Builder API usage
• VirtualThreadCreationWithThreadFactory.java - Factory patterns

• ProductPageWithStructuredConcurrency.java - Real-world scenarios
• ProductAvailabilityWithShutdownOnSuccess.java - Success patterns
• StructuredVsUnstructuredDemo.java - Side-by-side comparison

• ScopedValueExample.java - Modern context handling
• ThreadLocalInheritanceProblem.java - Legacy issues demonstration

• VirtualThreadMountUnmount.java - Mount/unmount behavior
• VirtualThreadPinning.java - Pinning detection and prevention
• MillionVirtualThreads.java - Scalability demonstrations

JDK Version Compatibility:

• --enable-preview is only required for JDK 19/20
• On JDK 21+, virtual threads are stable - you can omit --enable-preview unless using other preview features
• Structured Concurrency requires --enable-preview on all JDK versions (still in preview as of JDK 21)

Internal API Access:

• --add-exports java.base/jdk.internal.vm=ALL-UNNAMED is required for Continuation examples
• This exports internal JDK APIs that are normally encapsulated by the module system
• ⚠️ Warning: Internal APIs can change without notice - use only for learning purposes

Issue: IllegalAccessError with Continuation examples
Solution: Ensure VM options include --add-exports java.base/jdk.internal.vm=ALL-UNNAMED

Issue: ClassNotFoundException for preview features
Solution: Add --enable-preview flag and ensure using compatible JDK version

Issue: Maven exec plugin not finding main class
Solution: Run mvn clean compile first to ensure classes are built

This repository is designed to complement the "Java Virtual Threads & Structured Concurrency w/ Spring Boot" Udemy course. Each demo corresponds to specific course sections and lectures for hands-on learning.

For production Spring Boot examples with monitoring and observability, check out the companion repository: sample-retail-app

Happy Learning! 🚀