[Haskell-iPhone] Thread model questions

[Stephen Blackheath [to GHC-iPhone]]

David,

The GHC-iPhone port is no different to any other platform with regard to 
threading.

What we (iPwn Studios) do with the video game is this:  We have a main.m 
that feeds some command-line arguments (RTS options) into Haskell_main. 
  The Haskell main function then forkIOs and forkOSs some Haskell 
threads for its own purposes and then calls back to C on the main 
thread.  The C code then calls the iOS UIApplicationMain function.

To delegate processing to the main thread (required by iOS for GUI 
calls), we then use this code that I got from somewhere:

void DelegateToMain__(void* appController, Closure* closure)
{
     AppController* ac = (AppController*)appController;
     NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
     [ac performSelectorOnMainThread:@selector(delegateToMain:)
         withObject:[NSValue valueWithPointer:closure] waitUntilDone:NO];
     [pool release];
}

- (void) delegateToMain:(NSValue*)closureValue
{
     Closure* closure = (Closure*)[closureValue pointerValue];
     closure->run();
}

Since we ran the iOS event loop from the Haskell main, and since 'main' 
always starts on a bound thread (see haddocks for Control.Concurrent), 
it would be perfectly safe to use the above technique to run Haskell code.

 > Given the 5 second rule about an iOS app getting shut down... if there
 > are Haskell threads doing Haskell-y kind of work, is there a way of
 > notifying those threads en masse about the shutdown?

Greg already gave you lots of links, so take a look at those.  There are 
two ways: co-operatively, or using killThread.  To do it co-operatively, 
you'll need to just read up.  killThread may be simpler.  It's important 
to note that GHC does something that no other language I know of can do: 
  It can kill a thread safely.

This is explained in section 3.3 of Simon Marlow's parallel Haskell 
tutorial (Greg gave this link too):

http://community.haskell.org/~simonmar/par-tutorial.pdf


Steve

On 11/06/11 06:12, David Pollak wrote:
> Howdy,
>
> I've got a question about threading and thread models in ghc-iphone.
>
> My understanding is that Haskell has its own threading model that under
> the covers uses OS threads, but allows for significantly more active
> threads.  Is this a correct understanding?  If so, how does the Haskell
> threading model work on the iPhone?  Is it that iOS is close enough to
> OS X/Darwin that it "just works"?
>
> If it "just works", then how does one marshal an event back onto the iOS
> "UI thread" so that the display or draw or whatever command can take
> place on the UI thread?  Is there a convention or recipe for doing so?
> Would it be possible to put an event on the UI event queue that applies
> an Haskell closure such that the Haskell code that contains the computed
> value (I'd force the computation before marshaling the event to minimize
> the actual delay on the UI thread) then mutates the UI based on the
> computed value?
>
> Given the 5 second rule about an iOS app getting shut down... if there
> are Haskell threads doing Haskell-y kind of work, is there a way of
> notifying those threads en masse about the shutdown?
>
> Thanks,
>
> David
>
> --
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