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From: Dan Drew on 7 Apr 2010 11:03
No problem, glad I could help
Dan


From: Nathan
Sent: Wednesday, April 07, 2010 10:57 AM
To: ruby-talk ML
Subject: Re: modifying a Hash in one process when .each is running in another


Dan, many thanks for this. Method 2 looks like it'll suite me
perfectly. As I've explained in reply to Brian's post, I don't want to
test objects which are no longer on the most up-to-date list, and, if
I've understood correctly, method 1 would still do that, but method 2
wouldn't. So that looks like the solution.
Thanks,
Nathan

On Apr 7, 3:32 pm, "Dan Drew" <d...(a)brilliantsoftware.ca> wrote:
> Depending on how memory efficient you want to be you could also try.
>
> 1) Memory hog method... this will have potentially two copies of your data at a given time
>
> Thread 1:
> lock_shared # using whatever mechanism you want such as a mutex
> testHash = sharedHash
> unlock_shared
> # iterate and test
>
> Thread 2
> newHash = generate_hash()
> lock_shared
> sharedHash = newHash
> unlock_shared
>
> 2) Memory efficient but more contention
>
> Thread 1
> lock_shared
> test_keys = sharedHash.keys
> unlock_shared
> test_keys.each do |k|
> lock_shared
> v = sharedHash[k]
> unlock_shared
> test(v) if v
> end
>
> Thread 2
> # for each item as it's loaded from the network
> generate_index do |k,v|
> next if sharedHash[k] == v # Optional to avoid unnecessary contention
> lock_shared
> if v
> sharedHash[k] = v
> else
> sharedHash.delete(k)
> end
> unlock_shared
> end
>
> Dan
>
> From: Matthew K. Williams
> Sent: Wednesday, April 07, 2010 10:02 AM
> To: ruby-talk ML
> Subject: Re: modifying a Hash in one process when .each is running in another
>
> On Wed, 7 Apr 2010, Nathan wrote:
> > Thanks for the clarification... My application is network based, and
> > some operations take several seconds. generate_list_of_objects takes
> > anything between 2 and 15 seconds, so I wouldn't like to have my whole
> > program on hold while that's happening. Each test process takes a few
> > seconds too, so if the object is no longer on the list, it isn't a
> > particularly bad thing if test tries to run, but it'll take up a lot
> > of time unnecessarily.
>
> > I'm trying to work out if there's another way of doing it then.
> > Perhaps I'll modify the test method so that it knows if the current
> > object is on the list, and only runs the test if it is.
> > Nathan
>
> Might a messaging queue work better? That way you don't have the
> concurrency issues, as well as the issues with changing a hash in the
> middle of iteration.
>
> Matt


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