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A shutdown hook is simply an initialized but unstarted thread. When the virtual machine begins its shutdown sequence it will start all registered shutdown hooks in some unspecified order and let them run concurrently.
Shutdown Hooks are a special construct that allows developers to plug in a piece of code to be executed when the JVM is shutting down. This comes in handy in cases where we need to do special clean up operations in case the VM is shutting down.
We can use java. lang. Runtime. addShutdownHook(Thread t) method to add a shutdown hook in the JVM.
To shutdown computer in Java programming, you have to use the command shutdown -s. You can also specify the time in seconds, after which you want to turn off or shutdown the PC, using shutdown -s -t seconds.
You could do the following:
.interrupt the working threads if they wait for data in some blocking call)writeBatch in your case) to finish, by calling the Thread.join() method on the working threads.Some sketchy code:
static volatile boolean keepRunning = true;
In run() you change to
for (int i = 0; i < N && keepRunning; ++i)
writeBatch(pw, i);
In main() you add:
final Thread mainThread = Thread.currentThread();
Runtime.getRuntime().addShutdownHook(new Thread() {
public void run() {
keepRunning = false;
mainThread.join();
}
});
That's roughly how I do a graceful "reject all clients upon hitting Control-C" in terminal.
From the docs:
When the virtual machine begins its shutdown sequence it will start all registered shutdown hooks in some unspecified order and let them run concurrently. When all the hooks have finished it will then run all uninvoked finalizers if finalization-on-exit has been enabled. Finally, the virtual machine will halt.
That is, a shutdown hook keeps the JVM running until the hook has terminated (returned from the run()-method.
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