Java ExecutorService.shutdownNow() is a method in the Java ExecutorService interface that attempts to stop all actively executing tasks and halts the processing of waiting tasks. It returns a list of the tasks that were waiting to be executed. Introduced in Java 2004 with Java 5, shutdownNow() is typically used when a thread pool needs to be terminated immediately, for instance in response to an error or during application shutdown.

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html