How to write native Java methods which respond to Thread.interrupt()

This is a tutorial project, demonstrating how to hook a Java thread's interrupt() method to cancel a long-running native method.

Problem

For all the Java methods which block, such as Thread.sleep() or Object.wait(), it's possible to interrupt the action by calling Thread.interrupt().

What happens if you implement your own blocking procedure? Well, this isn't possible in Java because you don't get much in the way of blocking calls, you have to build on top of one of the existing mechanisms. But, if you're providing Java bindings for some native code which does its own I/O, then it becomes a concern.

In particular, the question really is, "how do I receive a notification when Thread.interrupt() is called, so I can wake up my native code?"

The solution uses a class which unfortunately has rather few hits on Google, hence this writeup: java.nio.channels.spi.AbstractSelector.

How do you get a notification from Thread.interrupt()?

Inside the Sun Java (and OpenJDK), there is a hook whereby an object can register itself as the thread's current blocking operation, but the method is private so there's no way to get at it directly.

Using the sun.misc.SharedSecrets class lets other parts of the JVM get access to the notification from the Thread. If you're happy to grub around itside the semi-private JRE implementation, you can call JavaLangAccess.blockedOn() to get what you want.

As far as I can tell, there's only one way to get public access to that functionality, as of Java 1.7: using NIO selectors.

The java.nio.channels.Selector interface is probably something that Sun didn't expect many people to to have to implement themselves, and on its own it's not very useful, but thankfully they created a partial implementation of it in the form of AbstractSelector which does the cheeky hooking using SharedSecrets for you.

This sample code

This sample is tutorial/example code which shows how to extend AbstractSelector appropriately. I couldn't find any other examples of this, so I hope I'm doing it the right way!

Building

Windows

mkdir bld; cd bld
cmake -G "Visual Studio 12 2013 Win64" .. # Or whichever version of VS you have
# Build using VS...
sh java.sh

Mac/Linux

mkdir bld; cd bld
cmake ..
make
sh java.sh