[Rubycocoa-talk] Thread scheduling

[Jonathan P. <jp...@dc...>]

Hi,

I've been trying to do some Ruby processing in the background (parsing 
a large XML file with REXML upon opening a document) while letting the 
Cocoa GUI still be responsive.

I've tried a number of techniques to achieve this, and was wondering if 
anybody had any comments or suggestions - particularly to do with how 
Ruby threads are expected to work in RubyCocoa.

I have a document window, and during loading I'm posting a sheet with 
an indeterminate progress bar in it. I want the progress bar to animate 
(and other windows/menus to be responsive) while doing the REXML 
parsing.

(1) I've tried calling the run loop in a loop from a Ruby thread to get 
events processed whilst REXML works on the main Ruby thread. For some 
reason I haven't figured out, no events were processed. This may be 
because I was calling the run loop from within an existing run loop 
invocation.

(2) I've tried doing the REXML processing in a Ruby thread and calling 
NSApplication endSheet.

Both of these techniques suffered from the problem of invoking Cocoa 
methods from a non-main Ruby thread. Largely things would be okay, but 
occasionally AppKit would get unhappy because the per-NSThread 
exception handler list (NS_DURING etc) becomes invalid when Ruby 
switches the C stack between its threads.

This is unfortunate, because it means we can't even call normally 
thread-safe Foundation methods because Cocoa exception handlers are 
used in RubyCocoa.

Any ideas how to get around this?

Thanks.
Jonathan

Below are some code fragments describing (1) and (2).

(1)

   OSX::NSApplication.sharedApplication.beginSheet_...(@sheet,...)

   done = false
   rl = OSX::NSApplication.sharedApplication.currentRunLoop
   t = Thread.new do
	rl.runMode_beforeDate(OSX::NSDefaultRunLoopMode, OSX::NSDate.date) 
until done
   end

   @doc = REXML::Document.new(big_xml_string)
   ## code here to populate GUI from contents of @doc

   done = true
   t.join
   OSX::NSApplication.sharedApplication.endSheet(@sheet)

(2)

   OSX::NSApplication.sharedApplication.beginSheet_...(@sheet,...)
   Thread.new do
      @doc = REXML::Document.new(big_xml_string)
      ## code here to populate GUI from contents of @doc
      OSX::NSApplication.sharedApplication.endSheet(@sheet)
   end