RFR: 8378268: Thread.join can wait on Thread, allows joinNanos to be removed

[Jaikiran Pai]

On Fri, 20 Feb 2026 09:26:52 GMT, Alan Bateman <alanb at openjdk.org> wrote:

> Thread.join was historically implemented with a loop of Object.wait conditioned on isAlive. We couldn't for this virtual threads because it would pin a virtual thread invoking join to it carrier.  Now that Object.wait preempts, it means the special implementation of join for virtual threads can be removed. Where possible, the notifyAll is elided as it adds to the cost of termination.
> 
> The implNote of the join methods is restored (this is implNote text, not spec, so no CSR required).
> 
> Testing: tier1-5

src/java.base/share/classes/java/lang/VirtualThread.java line 188:

> 186: 
> 187:     // termination object when joining, created lazily if needed
> 188:     private volatile CountDownLatch termination;

Nit - I suspect the CountDownLatch import can be removed too?

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PR Review Comment: https://git.openjdk.org/jdk/pull/29839#discussion_r2857064073