Catching user interrupts

I would like to be able to catch a user interrupt or, if not possible,
some other user action like a key stroke or mouse action much like
one catches an Error.  Ideally my code would look something like:

[some code]  on:  Interrupt  do:  [process Interrupt].

Of course there is no class Interrupt and even if there was
my guess is that user interrupts are handled at a low enough
level that the above code wouldn't work anyway.
For example, for the code:

  [some code]  on:  Error  do:  [process Interrupt].

The user interrupt is generated while  "some code" is running
so the  "process Interrupt" code has no chance of running.

A simple question.  I'm guessing the answer is not so simple
and perhaps not so safe.

I hope others find this question interesting.

Regards,

Ralph Boland


--
Quantum Theory cannot save us from the tyranny of a deterministic
universe but it does give God something to do

Hi Ralph -

The answer to your question depends a little on why you're trying to do
what you're doing. Generally speaking, there's a #userInterruptWatcher
process that waits until the interrupt semaphore is signaled and then
does whatever it is instructed to do. It could easily interrupt the UI
process with an exception for example, in which case your code (if run
from the UI process) would work.

On the other hand, if what you're really trying to do is to seal an
image for production purposes you can just kill the interrupt watcher
process and no interrupt handler will ever be run. Or, you can do what
we do in our production images - use the interrupt watcher to signal the
UI to pop up a password box which will allow you to break into the
running app if you enter the correct password.

So there's a bunch of options depending on what you're trying to do.

Cheers,
   - Andreas

On 5/20/2010 3:10 PM, Ralph Boland wrote:

Thanks for the info.  It was very helpful.
I looked up who implements #userInterruptWatcher and InputSensor does.
I can figure out what I need to do from what InputSensor does.

Sorry for not stating my objective more clearly in my original post.
What I am trying to do is catch a user interrupt or some other
signal from the user and then shut a particular process down cleanly.
The user is able to restart the process whereupon it starts approximately
at the point it was interrupted but at a clean restart point.
What I will do now is one of your solutions. That is, generate some error when
I catch the interrupt and then catch the error using a block where I clean up
as described in the original post.  i.e.

arrange to watch for user interrupts and generate an InterruptGeneratedError
when a user interrupt is generated.
 [some code]  on:  InterruptGeneratedError  do:
        [shutdown process cleanly and restore system userInterruptWatcher].

Regards,

Ralph Boland

> Hi Ralph -

> The answer to your question depends a little on why you're trying to do
> what you're doing. Generally speaking, there's a #userInterruptWatcher
> process that waits until the interrupt semaphore is signaled and then
> does whatever it is instructed to do. It could easily interrupt the UI
> process with an exception for example, in which case your code (if run
> from the UI process) would work.

> On the other hand, if what you're really trying to do is to seal an
> image for production purposes you can just kill the interrupt watcher
> process and no interrupt handler will ever be run. Or, you can do what
> we do in our production images - use the interrupt watcher to signal the
> UI to pop up a password box which will allow you to break into the
> running app if you enter the correct password.

> So there's a bunch of options depending on what you're trying to do.

> Cheers,
>   - Andreas