GeezerVison

Calling terminate() on a Worker that is ending on its own at the same moment, for example through its own close(), can make the parent thread interrupt the worker's isolate after the worker thread has already disposed it. A parent that terminates its child workers during its own shutdown races the same way. Separately, terminate() cannot stop a worker that called close() and kept running, so close(); while (true) {} spins forever.

WorkerWrapper::Terminate reads workerIsolate_ and then calls TerminateExecution() and the event-loop lookup on it with no lock, while BackgroundLooper clears the pointer and disposes the isolate during teardown. Nothing makes the worker thread wait for a Terminate that has already read the pointer. Terminate now holds a mutex across the read and the use, and the worker thread takes the same mutex when it clears the pointer, before disposing the isolate: a terminate that already read it finishes with it first, and a later one finds null. This is the same fix as NativeScript/ios#478 on iOS.

close() only ends the worker once its running callback returns, and Terminate returned early for a closing worker. It no longer returns early for a closing worker, which matches the iOS runtime, so it interrupts one that is still running.

The isolate race window is a few instructions wide, so it has no spec. With a sleep injected between the read and the use, a worker that closes itself while terminate() runs is already disposed when the parent touches its isolate on main, and stays alive until the parent is done with this change. The new spec for a worker spinning after close() fails on main and passes here, and the full device suite passes.

Summary by CodeRabbit

• Bug Fixes
  • Workers that have called close() but continue running can now be terminated reliably. Their ongoing activity stops after termination is requested.
• Tests
  • Added coverage verifying that termination stops a closing worker’s ongoing activity. The test checks that its shared counter remains unchanged after termination.