Re: Screen Saver Question

I've reproduced the SysPref freeze problem :-). I have a suggestion about the cause (see below).

During debugging I found a bug in the .m file; there is a -release method which looks intended to free resources. The trick with ObjC is to free resources in the -dealloc method, like this:

- (void) dealloc {

    NSLog(@"Deallocating Saver3View");

    [messageRect release];

    [self clearVMArgs];

    [super dealloc];

}

-release decrements the reference-count on an object. When the ref-count reaches zero ObjC's runtime will call dealloc for you. When I made the change I see a rotating green line in screensaver's preview window.

For examples see:   http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/index.html?http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/Introduction/chapter_1_section_1.html

And the freeze-problem? I used NSLog to print debug messages to the Console:

2005-07-28 12:11:25.402 System Preferences[5789] Saver3View:initWithFrame

2005-07-28 12:11:25.455 System Preferences[5789] startVM ...

2005-07-28 12:11:25.455 System Preferences[5789] clearVMArgs ...

2005-07-28 12:11:26.061 System Preferences[5789] started VM ok

2005-07-28 12:11:26.787 System Preferences[5789] all ok so far

2005-07-28 12:11:26.838 System Preferences[5789] Apple AWT Couldn't start headless. SetApplicationIsDaemon returned -50

Look at this message        ^^^^^^^^^^^^

<animateOneframe is called many times to display your message ...>

2005-07-28 12:11:35.969 System Preferences[5789] stopVM ...

'-stopVM' attempts to destroy the Java VM you created. Note the JNI VM unload information below

from   http://java.sun.com/j2se/1.4.2/docs/guide/jni/spec/invocation.html#wp16553

" Unloading the VM

The main thread cannot detach itself from the VM. Instead, it must call DestroyJavaVM() to unload the entire VM.

The VM waits until the main thread is the only user thread before it actually unloads. User threads include both Java threads and attached native threads. This restriction exists because a Java thread or attached native thread may be holding system resources, such as locks, windows, and so on. The VM cannot automatically free these resources. By restricting the main thread to be the only running thread when the VM is unloaded, the burden of releasing system resources held by arbitrary threads is on the programmer."

Is it possible resources are being held and the VM is waiting to unload? Because of the wait, System Preferences appears to freeze?

Rob