Re: Threads, Distributed Objects, and NSUndoManager

FROM : m
DATE : Sun Oct 17 00:50:47 2004

On Oct 16, 2004, at 12:40 PM, John C. Daub wrote:

> Now I have refactored my application a bit so that while the work is 
> going
> on I display a progress sheet with progress bar and Stop button. To do 
> this,
> I had to put my work into a thread. But from what I was reading about
> threads, since I'm going to need to have the thread collect my data 
> then
> pass the data back to the main thread, I need to use something like
> distributed objects to pass that data back.


[snip]

> My guess is because the data object I'm
> actually given isn't the real data object but instead an NSProxy 
> version of
> the object...


I think your guess is right on.

You don't need to use DO, though it is sometimes more convenient. You 
just need to ensure that your threads aren't accessing your data object 
at "at the same time".

Here's a strategy: have your main thread allocate the data object and 
pass it to your worker thread (without retaining a reference to it), 
then you can just have the worker thread hand it back when it's done 
(perhaps by calling 
performSelectorOnMainThread:withObject:waitUntilDone: on some suitable 
selctor).

something like this (typed in mail, not tested, obviously)

- (void) kickOffLongOperation
{
   [NSThread detachNewThreadSelector:@(longOperation:) toTarget:self 
withObject:[[MyDataThing alloc]init]];
}

- (void) hereIsTheResult:(MyDataThing*)dataThing
{
   // pop the data thing on the undo stack
   ....
}

- (void) longOperation:(MyDataThing*) dataObject
{
   ...
   while (stillComputing)
   {
       [dataObject addData:moreData];
   }

   // all done, transfer object to main thread
   [objectInMainThread 
performSelectorOnMainThread:@selector(hereIsTheResult:)withObject:
dataObject     waitUntilDone:NO];
   ...
}

_murat