Re: [MacRuby-devel] some gcd issues

4 Jun 2010

      Hi Bernd,

On Jun 4, 2010, at 1:28 AM, B. Ohr wrote:
...
Hi,
yesterday I did my first steps with GCD: parsing a very big CSV-file, processing and filtering it and displaying the result in a table view. Before GCD the UI was blocked for more than a minute, now the user can continue working instantly. Hey that’s really, really great!
:-)
...
There are some issues I don’t understand:
:-(
...
1. @job.group.notify(Dispatch::Queue.main) {}  # gives an error...
  @job.group.notify(Dispatch::Queue.concurrent) {} # …..while is working
2. @job.group.notify(Dispatch::Queue.concurrent) {}  # the block is called twice or more times
Hmm, you should NOT need to call "group" on the @job for normal usage.  

Could you just use "@job.join" to get the behavior you want?
...
3. the proxy object does not work here (I’m not sure, that I am using it correctly)
Yeah, the "+=" thing actually replaces the -variable- instead of mutating the object, so it won't do what you want. Look at the README.rdoc for more details:

http://github.com/masterkain/macruby/tree/master/lib/dispatch/

Sorry about the formatting...

-- Ernie P.
...
I made a small Xcode project demo out my project and attached it to this mail. (you can multi-click on the job button)
- Bernd
######
require 'dispatch'
class AppController
attr_accessor :calculations, :running
def initialize
  self.calculations = []
  @prefix = 1
  @job = Dispatch::Job.new
  #the main queue is used here because the UI is bound to the calculations array 
  @calc_queue = Dispatch::Queue.main
end
def calc_sync &block
  @calc_queue.async { block.call }
end
def nextPrefix
  prefix = @prefix
  @prefix += 1
  prefix
end
def calc1
  # @calc_proxy = Dispatch::Proxy.new(self.calculations,@job.group,@calc_queue)
  @job.add do
    prefix = nextPrefix
    10.times do |i|
      dur = rand / 4 + 0.2
      sleep(dur)
      c = Calculation.new("#{prefix}:#{i}",dur)
      calc_sync { self.calculations += [c] }
      # proxy does not work here:
      # @calc_proxy += [c]
    end
    #NSLog self.calculations.inspect
  end
  # why can the notify block be called twice ore more?
  # if true
  if !running
    self.running = true
    # notifying on the main queue is crashing here:
    # @job.group.notify(@calc_queue) { NSLog "notify“; self.running = false }
    @job.group.notify(Dispatch::Queue.concurrent) { NSLog "notify"; self.running = false }
  end
end
def jobAction sender
  calc1
end
def clearAction sender
  self.calculations = []
end
end
<gcd_demo.zip>
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Re: [MacRuby-devel] some gcd issues

Ernest N. Prabhakar, Ph.D.