What is the JVM’s safepoint and why does Stop-the-World GC require all threads to reach one?

Question

Java Professional — Hard

What is the JVM’s safepoint and why does Stop-the-World GC require all threads to reach one?

Accepted Answer

The JVM's safepoint is a point in execution where thread state is fully known and consistent, allowing the JVM to safely inspect or modify the heap. Stop-the-World GC requires all threads to reach a safepoint to freeze them while relocating or marking objects without interference.