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Re: Avoiding memory loss...

by LanX (Canon)
on Dec 27, 2012 at 21:53 UTC ( #1010586=note: print w/ replies, xml ) Need Help??


in reply to Avoiding memory loss...

Hi

first, you don't need to intialize an array, perl does the allocation automatically when you do the push.

#if (! exists $cTable{$cID}{raw}) { # $cTable{$cID}{raw}=[]; #} push @{$Table{$cID}{raw}}, $currentVal;

> and, periodically wanting to delete the hash.

delete $cTable{$cID}
> My question is, do I first need to do something to remove the array or is that cleaned up automatically for me?

depends, garbage collections cleans up variables with an empty reference count.

so as long as you don't have any $copies = $Table{$cID} somewhere else in the code the hash will be automatically destroyed when deleting the last reference.

The same for all nested substructures/elements like the array $Table{$cID}{raw}, if there are no other references they will be destroyed, too.

in other words: no reference left <=> no memory used

for details see: perlref

Cheers Rolf


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Re^2: Avoiding memory loss...
by J.Perl.Man (Novice) on Dec 27, 2012 at 22:37 UTC

    Excellent -- I hoped my read of the memory cleanup stuff was accurate. There are no copies, so I should be good to go I guess!

    Regarding the allocation, in this case, we're talking pointer to an array. Normally, I wouldn't create an empty array, but was pretty sure that I had to have the reference in place before the push, yes?

    Thanks!

      > Regarding the allocation, in this case, we're talking pointer to an array.

      yes, reference to an array (pointers are in C memory addresses but references are more complicated).

      But it doesn't matter @array and $array_ref=\@array are just two different ways to represent the same array.

      > Normally, I wouldn't create an empty array, but was pretty sure that I had to have the reference in place before the push, yes?

      As I told you: No!

      You are pushing to a variable starting with @. If the array doesn't exist already it will be allocated. If it exists but it's incompatible to push (like a hash) you,'ll get an error.

      DB<107> ref $a => "" DB<108> push @$a,1..3 => 3 DB<109> ref $a => "ARRAY" DB<110> $b={} => {} DB<111> push @$b,1..3 Not an ARRAY reference at (eval 44)[multi_perl5db.pl:644] line 2. DB<112> ref $b => "HASH"
      In newer versions of Perl you are even allowed to push directly to $array_refs.

      Cheers Rolf

        Greatly appreciated, cleaned up the code!

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