Re: run NSApllication in an other thread

[Richard Frith-Macdonald]

On 17 Feb 2009, at 20:36, Julien Isorce wrote:

> Hi,
>
> I can read in NSApplication's documentation that it must be called  
> in the main thread.
>
> I am in a case where there is an other main loop (in C) that I  
> cannot managed.
> The code I can access is an interface and its implementation that  
> leads to a shared library loaded by the main application where there  
> is this C main loop.
> Well, in the implementation (that I have to make) threre is 3  
> functions.
> One for initialization, one for deinitialization, and the last one  
> is called periodically.
> In the init function I create an NSWindow. Then this window has to  
> be updated in the function called periodically.
>
> In no cocoa env I usually create a thread in the init function. This  
> thread runs the specific window main loop (X loop or gdi32 loop).  
> And it works pretty good.
> I want to do the same thing in a cocoa env. I mean, i would like to  
> run the cocoa main loop in a thread created in the init function.
>
> Even if I read that NSApplicationMain (or [NSApp run] ) must be  
> called in the main thread, I  tried to call it in a different thread.
> But I am getting an acces violation in the main thread.
> Then if a replace the [NSApp run] from the second thread, by a while  
> an a sleep,  I have an access violation in the main thread only I do  
> not call [NSApp run] in the main thread.
> (but I cannot call [NSApp run] in the main thread because the  
> function must be called periodically, I must not block the main  
> thread)
>
> I am creating the thread with:
>
>  [NSThread detachNewThreadSelector: @selector(start:)
>         toTarget: [AppThread class]
>         withObject: nil];
>
> (like I could see in the gnu step examples)
>
> I am still on win32.
>
> Any suggestion ?

I wouldn't do it that way round.
Why not create an object to manage the C event loop, and run that in a  
secondary thread.

eg.

@interface LoopHandler : NSObject
- (void) callback;
- (void) run;
@end

@implementation LoopHandler

static LoopHandler      *instance = nil;

static void
periodicLoopCallback()
{
  [instance performSelectorInMainThread: @selector(callback)  
withObject: nil waitUntilDone: YES];
}

- (void) callback
{
  /* perform callback handling here.
   * this will be executed in the main thread whenever the
   * C loop in the secondary thread calls preiodicLoopCallback
   */
}

- (id) init
{
  instance = self;
  return self;
}

- (void) run
{
   // initialise C loop and tell it to use the callback function  
periodically
   // run the C loop
}
@end

Then you would call

  [NSThread detachNewThreadSelector: @selector(run) toTarget:  
[LoopHandler new] withObject: nil];

in your application startup code, and have all the GNUstep stuff  
working normally