🚀 go-pugleaf

On Sun, 07 Jul 2002 16:18:50 -0400, Alan Shiers wrote:

> This tells me it is waiting itself for a signal to shut the
> program down.  How does it know when CTRL+C has been pressed?

The Java shutdown hook has nothing to do with keystrokes.  It is 
triggered when the virtual machine is shut down.  That can happen
as the result of a number of events, including a System.exit() call
in your code or closing a Frame that has a DefaultCloseOperation of 
EXIT_ON_CLOSE.

Another way this can happen is for the operating system to tell it 
to shut down.  On Windows, if you press Ctrl-C from the console of 
a console application, it will send a signal to the process telling 
it to shut down.  Unix has a similar mechanism, the INT signal.  By 
default this is triggered by a DEL, but on many Linux systems it is 
a Ctrl-C.  You can also use the "kill" command to send that signal.

The operating system might also kill the Java VM in such a way that it 
does not have the opportunity to shut down gracefully.  On Unix 
systems, if you issue a "kill -9" command, the JVM is terminated 
immediately and shutdown hooks will not run.

> While it was running I tried pressing CTRL+C on the keyboard, 
> but nothing happens!  I was thinking that the Runtime class
> was monitoring for this activity.  I guess not...

As I said, the conditions under which the shutdown hooks are run are 
operating system dependent.  If I run a Java program as a Console 
Application on Windows or from a RH Linux terminal window, Ctrl-C will 
run the shutdown hooks.

What operating system are you running this on?  What command do you use 
to run the Java application?

-- 
Regards,

John McGrath [TeamB]

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