Virtual threads let us keep ordinary blocking code while many more requests wait concurrently. Under load, however, that brings three critical questions into focus:How much work do we admit? Cheap threads can still build an expensive queue. What belongs inside a lock? A sleeping lock holder still makes everyone else wait. Who stops abandoned work? A caller's timeout does not cancel its task.The examples below isolate these questions with separate before-and-after programs. Each program is complete: save its code block under the filename shown and run the accompanying command, without arguments. All you need is JDK 25. They use its compact source-file syntax, so no class declaration, build tool, external library, or preview flag is required.