What does java.lang.Thread.interrupt() do?
java, multithreading
Solution
`Thread.interrupt()` sets the interrupted status/flag of the target thread. Then code running in that target thread MAY poll the interrupted status and handle it appropriately. Some methods that block such as `Object.wait()` may consume the interrupted status immediately and throw an appropriate exception (usually `InterruptedException`)
Interruption in Java is not pre-emptive. Put another way both threads have to cooperate in order to process the interrupt properly. If the target thread does not poll the interrupted status the interrupt is effectively ignored.
Polling occurs via the `Thread.interrupted()` method which returns the current thread's interrupted status AND clears that interrupt flag. Usually the thread might then do something such as throw InterruptedException.
EDIT (from Thilo comments): Some API methods have built in interrupt handling. Of the top of my head this includes.
- `Object.wait()`, `Thread.sleep()`, and `Thread.join()`
- Most `java.util.concurrent` structures
- Java NIO (but not java.io) and it does NOT use `InterruptedException`, instead using `ClosedByInterruptException`.
EDIT (from @thomas-pornin's answer to exactly same question for completeness)
Thread interruption is a gentle way to nudge a thread. It is used to give threads a chance to exit cleanly, as opposed to `Thread.stop()` that is more like shooting the thread with an assault rifle.
Problem
Could you explain what `java.lang.Thread.interrupt()` does when invoked?