threadId

Thread ID traits:

Unique during thread lifetime.

May be re-used after thread is closed. In the JVM, `Thread.currentThread().threadId()` returns a **unique identifier** for the thread during its lifetime, but **this ID is not guaranteed to remain unique across the lifetime of the JVM**. Specifically:
  • During the thread's lifetime: The thread ID is unique. No two threads that exist concurrently will share the same thread ID.
  • After the thread is terminated: The JVM may reuse the thread ID for a new thread. There is no guarantee that thread IDs are never reused once a thread has completed its execution and has been garbage collected.

This behavior is defined in the Java documentation for Thread.threadId():

The thread ID is a positive long value generated when the thread is created. The thread ID is unique and remains unchanged during its lifetime. When a thread is terminated, this thread ID may be reused.

Key Takeaways:

  • Thread IDs are unique while the thread exists.
  • Thread IDs may be reused after the thread has terminated.
  • If you need a globally unique identifier that remains distinct for all threads, including terminated ones, you should consider using a different mechanism, such as a UUID.