Waiting without busy waiting

[Evan8]

Hi all,

I have a question about waiting without busy waiting. I'm trying to create a small popup window to prompt the user for some information, and i'm wondering how to write one that will wait for the user to take some action without eating up all of the cpu cycles. In this way, i can create one of these in another part of my code, and have that code stop until the user is done entering his info.

A good example of this is the Java object JFileChooser. Example code from the Sun site looks like:

JFileChooser chooser = new JFileChooser();
int returnVal = chooser.showOpenDialog(parent);
if(returnVal == JFileChooser.APPROVE_OPTION) {
System.out.println("You chose to open this file: " +
chooser.getSelectedFile().getName());
}

You can see that the function "showOpenDialog()" somehow waits for the user to do something (click ok, or cancel), and returns a value after that. How is this done without busy waiting and taking up all the processing time?

Thanks very much!
-Evan

[bryce777]

Originally posted by Evan8
Hi all,

I have a question about waiting without busy waiting. I'm trying to create a small popup window to prompt the user for some information, and i'm wondering how to write one that will wait for the user to take some action without eating up all of the cpu cycles. In this way, i can create one of these in another part of my code, and have that code stop until the user is done entering his info.

A good example of this is the Java object JFileChooser. Example code from the Sun site looks like:

JFileChooser chooser = new JFileChooser();
int returnVal = chooser.showOpenDialog(parent);
if(returnVal == JFileChooser.APPROVE_OPTION) {
System.out.println("You chose to open this file: " +
chooser.getSelectedFile().getName());
}

You can see that the function "showOpenDialog()" somehow waits for the user to do something (click ok, or cancel), and returns a value after that. How is this done without busy waiting and taking up all the processing time?

Thanks very much!
-Evan

[bryce777]

bah hit the mouse wheel and it posted.

Anyhow, the filechooser is strictly modal, as far as I can tell.

Note that this does not mean it is busy waiting.

The current thread of execution blocks until you get a response, but all threads are not blocked. Usually GUI stuff is event driven, and anything you are running already will therefore continue runnig.

If not, you will have to spawn it in a seperate thread, but I doubt this is the case.

It is really only the focus that is affected - the user can't do other things without finishing the task.

Normally, this is what you want, but if you want a non modal file dialog you will have to create it yourself by extending JDialog, which would take a few hours to an afternoon, probably.

[Evan8]

Hey,

I took a look at the JDialog class, and found it very useful. I also stepped though the code of JFileChooser and did see that it blocks a thread. I'm new to multithreaded programming, so i'll use JDialog for now (might as well) and try to figure out how to block to wait for user input (just for my own programming knowledge).

Thanks!
-ev