From: Eric Hodel <drbrain@...7.net>
Date: 2005-10-10T05:20:49+09:00
Subject: Re: using lambda/Proc can prevent a lot of garbage collection

On Oct 9, 2005, at 8:20 AM, David A. Black wrote:

> Hi --
>
> On Sun, 9 Oct 2005, Eric Mahurin wrote:
>
>> Here is an example where a Proc can cause a memory leak:
>>
>> ruby -e '
>> n=2**13;squares=(1..n).map{|i|a=(1..i).to_a;lambda{i*i}};
>> IO.readlines("/proc/#{Process.pid}/status").grep(/VmSize/).display'
>> VmSize:   169312 kB
>>
>> You wouldn't expect each of these lambda's to need the local
>> "a", but the binding holds it.  Right now, the programmer needs
>> to specifically think about this and clear these unexpected
>> object references by hand:
>>
>> ruby -e ' n=2**13;squares =
>> (1..n).map{|i|a=(1..i).to_a;f=lambda{i*i};a=nil;f};
>> IO.readlines("/proc/#{Process.pid}/status").grep(/VmSize/).display'
>> VmSize:    10644 kB
>
> That's an interesting illustration, but I don't think I'd call it a
> memory leak, since it's working as advertised.  (At least, "memory
> leak" to me implies something going wrong under the hood, so to
> speak.)

A closure should only enclose the variables needed for its execution.  
This is actually not very difficult but unfortunately eval('a') 
prevents Ruby from excluding unbound variables in closures.

This is a (unfortunate IMO) feature of Ruby.