• What are virtual threads?
  Lightweight threads introduced in Java 19/21, managed by the JVM.
• Why are they useful?
  They allow running millions of concurrent tasks efficiently, especially for I/O-heavy applications.
• How are they different from platform (OS) threads?
  Virtual threads are cheaper to block and resume, making blocking I/O operations inexpensive.
• How do they help developers?
  They simplify concurrent programming—no need for complex callbacks or reactive code.
• How to create them?
  Use:
  • Executors.newVirtualThreadPerTaskExecutor()
  • Thread.startVirtualThread()
• Best use case:
  Ideal for I/O-bound workloads with many concurrent tasks.
• Not suitable for:
  CPU-intensive tasks—use platform threads instead.
• Thread limits:
  Don’t limit thread count. Instead, use resource controls like semaphores to avoid overloading systems.
• Avoid “pinning”:
  Some operations (like synchronized blocks) can force virtual threads to stick to one carrier thread, reducing concurrency.
• Performance tip:
  A single JVM with virtual threads often performs better than multiple JVMs for I/O-heavy workloads.
• JVM lifecycle note:
  Virtual threads are daemon threads, so make sure the JVM stays alive when needed.
• Overall benefit:
  Combines massive concurrency with simple, readable code, improving scalability and developer productivity.

Virtual Threads v/s Platform (Normal) Threads

Aspect	Virtual Threads	Platform Threads
Thread Type	Lightweight, managed by JVM, multiplexed on few OS threads	Heavyweight, directly mapped to OS threads
Creation Cost	Very low; can create millions	High; limited by OS and memory
Blocking Behavior	Cheap; JVM suspends and reuses carrier threads	Expensive; blocks OS thread
Best Use Case	I/O-bound, high concurrency tasks	CPU-bound or low concurrency tasks
Performance	Scales well with many blocking tasks	Better for CPU-intensive workloads
Stack Storage	Stored on heap; shallow stacks	Stored on OS thread stack; deeper stacks
Scheduling	JVM schedules on carrier threads	OS handles scheduling
Short-circuiting & State	Supports complex stateful operations	Limited to basic thread behavior
Daemon Thread Support	Always daemon; doesn’t keep JVM alive	Can be daemon or user thread

Single JVM Process with Virtual Threads v/s Multiple JVM Processes with Virtual Threads

Aspect	Single JVM with Virtual Threads	Multiple JVMs with Virtual Threads
Resource Sharing	Shares memory (heap), garbage collector, and thread scheduler—more efficient	Each JVM has its own memory and GC—more isolated but duplicates resources
I/O Concurrency	Scales better and handles many I/O tasks efficiently	More overhead, less efficient for high I/O concurrency
CPU-bound Tasks	May face issues like GC pauses and thread contention	Better isolation for CPU-heavy tasks, reducing interference
Management Complexity	Easier to deploy, monitor, and manage	Harder to manage due to multiple JVMs running separately
Fault Isolation	One JVM crash affects all tasks	Crashes are isolated to individual JVMs
I/O Performance	Generally faster due to shared scheduling and lightweight threads	Slower due to overhead from multiple JVMs