From: Bakul Shah <bakul+plan9@bitblocks.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: Re: [9fans] "Blocks" in C
Date: Fri, 4 Sep 2009 08:58:25 -0700 [thread overview]
Message-ID: <20090904155826.1A9BC5B4B@mail.bitblocks.com> (raw)
In-Reply-To: Your message of "Fri, 04 Sep 2009 08:04:40 PDT." <3e1162e60909040804y67b4f85en589bb5410f11a7cc@mail.gmail.com>
On Fri, 04 Sep 2009 08:04:40 PDT David Leimbach <leimy2k@gmail.com> wrote:
> On Fri, Sep 4, 2009 at 7:41 AM, Bakul Shah
> <bakul+plan9@bitblocks.com<bakul%2Bplan9@bitblocks.com>
> > wrote:
>
> > On Fri, 04 Sep 2009 00:47:18 PDT David Leimbach <leimy2k@gmail.com>
> > wrote:
> > > On Fri, Sep 4, 2009 at 12:11 AM, Bakul Shah
> > > <bakul+plan9@bitblocks.com <bakul%2Bplan9@bitblocks.com><
> > bakul%2Bplan9@bitblocks.com <bakul%252Bplan9@bitblocks.com>>
> > > > wrote:
> > >
> > > > 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
> >
> > Not sure how your program invalidates what I said. Blocks do
> > provide more syntactic sugar but that "benefit" is independent
> > of GCD (grand central dispatch) or what have you. Given that
> > __block vars are shared, I don't see how you can avoid locking
> > if blocks get used in parallel.
> >
To be precise, I meant to write "avoid locking if blocks get
executed in parallel and access a __block variable".
> You've said it yourself. "if blocks get used in parallel". If the blocks
> are scheduled to the same non-concurrent queue, there shouldn't be a
> problem, unless you've got blocks scheduled and running on multiple serial
> queues. There are 3 concurrent queues, each with different priorities in
> GCD, and you can't create any more concurrent queues to the best of my
> knowledge, the rest are serial queues, and they schedule blocks in FIFO
> order.
>
> Given that you can arrange your code such that no two blocks sharing the
> same state can execute at the same time now, why would you lock it?
Consider this example:
int
main(int c, char**v)
{
int n = c > 1? atoi(v[1]) : 1000;
__block int x;
x = 0;
parallel_execute(n, ^{ for (int i = 0; i < n; i++) ++x; });
while (x != n*n)
sleep(1);
}
Where parallel_execute() spawns off n copies of the block and
tries to execute as many of them in parallel as possible.
Presumably this is implementable? Will this prorgam ever
terminate (for any value of n upto 2^15-1)? How would you
avoid sharing here except by turning parallel_execute() in
serial_execute()?
> I should note that for some reason my code falls apart in terms of actually
> working as I expected it after MAX is set to something over 700, so I'm
> probably *still* not doing something correctly, or I did something Apple
> didn't expect.
:-)
next prev parent reply other threads:[~2009-09-04 15:58 UTC|newest]
Thread overview: 117+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-02 8:04 Anant Narayanan
2009-09-02 9:43 ` Francisco J Ballesteros
2009-09-02 11:00 ` Philippe Anel
2009-09-02 11:13 ` Charles Forsyth
2009-09-03 9:52 ` Greg Comeau
2009-09-02 11:40 ` Eris Discordia
2009-09-02 12:32 ` Uriel
2009-09-02 14:20 ` Devon H. O'Dell
2009-09-03 9:52 ` Greg Comeau
2009-09-03 10:48 ` Akshat Kumar
2009-09-03 11:25 ` Charles Forsyth
2009-09-03 13:59 ` Greg Comeau
2009-09-03 15:15 ` Uriel
2009-09-03 15:44 ` David Leimbach
2009-09-03 16:01 ` Roman V Shaposhnik
2009-09-04 9:15 ` Greg Comeau
2009-09-04 16:49 ` Roman Shaposhnik
2009-09-03 16:02 ` erik quanstrom
2009-09-03 18:56 ` David Leimbach
2009-09-03 18:58 ` erik quanstrom
2009-09-03 19:13 ` David Leimbach
2009-09-03 19:36 ` erik quanstrom
2009-09-03 19:50 ` David Leimbach
2009-09-03 20:30 ` Iruata Souza
2009-09-06 22:35 ` Uriel
2009-09-07 0:41 ` David Leimbach
2009-09-03 21:08 ` Roman V Shaposhnik
2009-09-03 21:35 ` erik quanstrom
2009-09-03 21:45 ` David Leimbach
2009-09-03 21:49 ` David Leimbach
2009-09-03 21:51 ` David Leimbach
2009-09-03 22:36 ` Roman V Shaposhnik
2009-09-04 9:16 ` Greg Comeau
2009-09-03 22:10 ` Daniel Lyons
2009-09-03 22:07 ` Daniel Lyons
2009-09-04 9:15 ` Greg Comeau
2009-09-04 3:21 ` Anant Narayanan
2009-09-04 3:52 ` erik quanstrom
2009-09-04 4:18 ` David Leimbach
2009-09-04 4:44 ` erik quanstrom
2009-09-04 5:31 ` David Leimbach
2009-09-04 5:35 ` David Leimbach
2009-09-04 7:11 ` Bakul Shah
2009-09-04 7:47 ` David Leimbach
2009-09-04 14:41 ` Bakul Shah
2009-09-04 15:04 ` David Leimbach
2009-09-04 15:58 ` Bakul Shah [this message]
2009-09-04 12:14 ` erik quanstrom
2009-09-04 13:52 ` David Leimbach
2009-09-04 13:59 ` matt
2009-09-04 14:20 ` erik quanstrom
2009-09-04 14:56 ` David Leimbach
2009-09-06 23:03 ` Uriel
2009-09-07 0:45 ` David Leimbach
2009-09-04 16:50 ` Roman Shaposhnik
2009-09-04 6:45 ` Bakul Shah
2009-09-04 16:44 ` Roman Shaposhnik
2009-09-04 16:58 ` Iruata Souza
2009-09-04 17:09 ` Roman Shaposhnik
2009-09-04 17:42 ` erik quanstrom
2009-09-04 18:34 ` erik quanstrom
2009-09-04 21:54 ` Roman V Shaposhnik
2009-09-07 9:06 ` Greg Comeau
2009-09-07 9:05 ` Greg Comeau
2009-09-07 9:40 ` Uriel
2009-09-08 15:31 ` David Leimbach
2009-09-08 15:44 ` Uriel
2009-09-08 16:40 ` Bakul Shah
2009-09-11 18:15 ` Iruata Souza
2009-09-11 18:46 ` David Leimbach
2009-09-11 20:36 ` Roman V Shaposhnik
2009-09-11 21:28 ` David Leimbach
2009-09-14 16:07 ` Lawrence E. Bakst
2009-09-12 11:08 ` Anant Narayanan
2009-09-13 19:03 ` David Leimbach
2009-09-17 1:54 ` Lawrence E. Bakst
2009-09-17 8:43 ` Charles Forsyth
2009-09-17 9:12 ` Daniel Lyons
2009-09-17 15:56 ` David Leimbach
2009-09-17 17:38 ` Jack Norton
2009-09-17 20:23 ` Anant Narayanan
2009-09-17 20:26 ` erik quanstrom
2009-09-17 20:31 ` Anant Narayanan
2009-09-17 20:47 ` Akshat Kumar
2009-09-17 21:02 ` erik quanstrom
2009-09-17 22:26 ` Steve Simon
2009-09-17 22:32 ` Roman V Shaposhnik
2009-09-18 2:05 ` Daniel Lyons
2009-09-18 9:30 ` Charles Forsyth
2009-09-18 11:41 ` erik quanstrom
2009-09-17 21:03 ` Uriel
2009-09-03 9:52 ` Greg Comeau
2009-09-02 14:08 ` Rodolfo (kix)
2009-09-03 9:52 ` Greg Comeau
[not found] ` <C56117D7BD9A097270529AAE@192.168.1.2>
2009-09-02 15:07 ` David Leimbach
2009-09-02 15:26 ` Roman V Shaposhnik
2009-09-02 15:45 ` David Leimbach
2009-09-03 15:32 ` Uriel
2009-09-03 15:49 ` Roman V Shaposhnik
2009-09-03 15:54 ` erik quanstrom
2009-09-03 16:20 ` Roman V Shaposhnik
2009-09-03 16:44 ` erik quanstrom
2009-09-04 1:05 ` Roman V Shaposhnik
2009-09-04 1:30 ` Russ Cox
2009-09-04 1:32 ` erik quanstrom
2009-09-03 21:54 ` James Tomaschke
2009-09-06 22:26 ` Uriel
2009-09-04 9:04 ` Greg Comeau
2009-09-02 15:20 ` Roman V Shaposhnik
2009-09-02 17:51 ` Bakul Shah
2009-09-04 1:35 drivers
2009-09-04 1:52 ` erik quanstrom
2009-09-17 9:19 Andrew Simmons
2009-09-17 14:45 ` LiteStar numnums
2009-09-17 17:24 ` Daniel Lyons
2009-09-18 15:50 drivers
2009-09-18 15:56 ` erik quanstrom
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