From: Rick DeNatale <rick.denatale@...>
Date: 2009-04-02T16:57:33+09:00
Subject: Re: Nilling for GC

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On Thu, Apr 2, 2009 at 3:19 AM, Paganoni <noway@fakenullvoid.com> wrote:

> Hi, I've read that
> http://whytheluckystiff.net/articles/theFullyUpturnedBin.html.
> I have a background script that runs continuously and threads some tasks
> on demand. I keep track of the launched tasks but, by keeping those
> tracks, I certainly prevent tasks classes instances and threads
> instances to be discarded by the garbage collector.
>
> Data are stored like that :
>
> @workers[:one_category] = []
> @workers[:one_category] << {:started_at => Time.now, :thread => th}
>
> So, I'm trying to setup a cleaner that would nil old references but I'm
> lost in maps :
>
> @semaphore.synchronize do
>  @workers.map{|k,v| v.map{|worker| (Time.now - worker[:started_at] > 5
> && worker[:thread].status == false) ? (cleaned +=1; nil) : worker}}
> end
>
> When condition is true, cleaned is incremented but the nil does not
> replace @workers entry.
>
> So, I did another test :
> hs = {}
> hs[:toto] = []
> hs[:toto] << {:kk => 28, :so => 'yes'}
> hs[:toto] << {:kk => 30}
> hs[:tata] = []
> hs[:tata] << {:kk => 2}
>
> hs = hs.map{|k,v| v.map {|a| a[:kk] > 28 ? nil : a} }
> pp hs displays
> [[{:kk=>28, :so=>"yes"}, nil], [{:kk=>2}]]
>
> This one works right, for each hs entry, array is nilled if :kk value is
>
>> to 28
>>
>
> Obviously there is a mistake somewhere in the first code source but I don't
> find it.
>
> Any help appreciated, thank you
>

@workers.map{|k,v| v.map{|worker| (Time.now - worker[:started_at] > 5  #
...

vs.

hs = hs.map{|k,v| v.map {|a| a[:kk] > 28 ? nil : a} }

In the first case you create a new array from the nested map calls and then
THROW IT AWAY, @workers still refers to the old array.

In the second you compute a new array and assign it to hs.

-- 
Rick DeNatale

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