Re: [9fans] "Blocks" in C

[David Leimbach <leimy2k@gmail.com>]

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On Fri, Sep 4, 2009 at 12:11 AM, Bakul Shah
<bakul+plan9@bitblocks.com<bakul%2Bplan9@bitblocks.com>
> wrote:

> On Thu, 03 Sep 2009 22:35:35 PDT David Leimbach <leimy2k@gmail.com>
>  wrote:
> >
> >
> > Actually, reading on a bit more they deal with the "variable capture"
> > talking about const copies.
> >
> > Automatic storage variables not marked with __block are imported as
> > const copies.
> >
> > The simplest example is that of importing a variable of type int.
> >
> >    int x = 10;
> >    void (^vv)(void) = ^{ printf("x is %d\n", x); }
> >    x = 11;
> >    vv();
> >
> > would be compiled
> >
> > struct __block_literal_2 {
> >     void *isa;
> >     int flags;
> >     int reserved;
> >     void (*invoke)(struct __block_literal_2 *);
> >     struct __block_descriptor_2 *descriptor;
> >     const int x;
> > };
> >
> > void __block_invoke_2(struct __block_literal_2 *_block) {
> >     printf("x is %d\n", _block->x);
> > }
> >
> > static struct __block_descriptor_2 {
> >     unsigned long int reserved;
> >     unsigned long int Block_size;
> > } __block_descriptor_2 = { 0, sizeof(struct __block_literal_2) };
> >
> > and
> >
> >   struct __block_literal_2 __block_literal_2 = {
> >       &_NSConcreteStackBlock,
> >       (1<<29), <uninitialized>,
> >       __block_invoke_2,
> >       &__block_descriptor_2,
> >         x
> >    };
> >
> > In summary, scalars, structures, unions, and function pointers are
> > generally imported as const copies with no need for helper functions.
>
> Just read this after posting my last message.
>
> But this has no more to do with parallelism than any other
> feature of C. If you used __block vars in a block, you'd
> still need to lock them when the block is called from
> different threads.
>
>
I just wrote a prime sieve with terrible shutdown synchronization you can
look at here:

http://paste.lisp.org/display/86549

Dave

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