Re: Grand Central

[Jamie Ramone]

This "block thingy" looks interesting. Oh, while we're on the topic of
multi-processors, I've invented an algorithm that allows parallel
lock-less insertions on a linked list. Could be useful for
NSConnections, as it's WAY more efficient than anything else I've ever
seen (and, yes, I am including NSMutableArray methods here). It does
come at a price: it requires an atomic swap operation i.e. assembly.
The good news is that only one instruction is needed so the
portability issue isn't at the "I feel like kissing the barrel of a
shotgun". I'll submit the paper for it as soon as Ive finished
polishing it, shoulda been this week (I am so fuckin' lazy...and
studying...and trying to work, don't ask).

On Sun, Jun 14, 2009 at 10:27 AM, Jens Ayton<address@hidden> wrote:
> On Jun 14, 2009, at 14:53, Pete French wrote:
>>
>>>
>>> http://images.apple.com/macosx/technology/docs/GrandCentral_TB_brief_20090608.pdf
>>
>> Interesting - that ^{ syntax to describe a block is somewhat ugly, and it
>> doesnt
>> give any deats of how you associate data with a block (which is necessary
>> if
>> you want to get rid of locks).
>
> There are two ways to pass data into blocks: constant copies from the parent
> scope, and mutable access to "block variables" in the parent scope (the
> latter makes blocks true closures). Here is a simple example:
>
> typedef int (^IntIntBlock)(int);
>
> IntIntBlock MakeExampleThing(int initial, int delta)
> {
>    __block int accum = initial;
>    int (^block)(int) = ^(int i) { return accum += i + delta; };
>    return Block_copy(block);
> }
>
>
> In the block created above, accum is a block variable, and delta is a const
> copy. If MakeExampleThing() is called twice, they get separate copies of
> accum, so there's your data associated with the block. If two blocks were
> created in the same function, both referring to accum, they would share it.
>
> int main(void)
> {
>    int (^a)(int) = MakeExampleThing(5, 2);
>    int (^b)(int) = MakeExampleThing(1, 0);
>
>    printf("%i\n", a(3));  // prints 10
>    printf("%i\n", b(1));  // prints 2
>
>    Block_release(a);
>    Block_release(b);
>    return 0;
> }
>
>
> The block runtime is set up to allow blocks to be ObjC objects, so that
> Block_copy() and Block_release() can be replaced with retain and release
> messages. (Block_copy() is conceptually a retain operation, although it
> actually does copy in the above example because the block is initially
> created on the stack.)
>
> In case the new syntax and manual memory management overhead gets in the way
> in the above code, here's a Javascript equivalent:
>
> function MakeExampleThing(initial, delta)
> {
>    return function(i)
>    {
>        return initial += i + delta;
>    }
> }
>
>
>> I can't work out if GCD is supposed to be an extension for OSX or an
>> extension
>> to Objective-C itself. Obviously the block syntax requiures a language
>> extension,
>> but how do the bits fit together from there onward ?
>
> Other than blocks, as far as I can see (I don't have Snow Leopard seeds)
> it's "just" a library and an optimized thread scheduler.
>
>
> --
> Jens Ayton
>
>
>
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>



-- 
Besos, abrazos, confeti y aplausos.
Jamie Ramone
"El Vikingo"