Now in theory it could happen that you have an array of a handful elements and after 1 million combined push and shift operations it allocates megabytes of space while not logically growing. ... I doubt this happens

That's my position also. And I was bored, so here's the proof.

#!/usr/bin/env perl
#=====================================================================
+==========
#
#         FILE: fifo-mem.pl
#
#        USAGE: ./fifo-mem.pl  
#
#  DESCRIPTION: Test memory consumption of a push/shift FIFO
#               See https://www.perlmonks.org/?node_id=11157497
#
#=====================================================================
+==========

use strict;
use warnings;
use Memory::Usage;

my @fifo;

my $max = 100_000_000;

my $mu = Memory::Usage->new;

$mu->record ('start');

for my $count (1 .. $max) {
    push @fifo, 'dog';
    shift @fifo;
    $mu->record ("After $count iterations") unless $count % 10_000_000
+;
}

$mu->record ('finish');
$mu->dump;

[download]

And since not everyone can run this, here's the output:

$   time    vsz (  diff)    rss (  diff) shared (  diff)   code (  dif
+f)   data (  diff)
     0  10780 ( 10780)   6544 (  6544)   5448 (  5448)      4 (     4)
+   1356 (  1356) start
     3  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) After 10000000 iterations
     5  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) After 20000000 iterations
     8  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) After 30000000 iterations
    10  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) After 40000000 iterations
    12  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) After 50000000 iterations
    15  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) After 60000000 iterations
    17  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) After 70000000 iterations
    20  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) After 80000000 iterations
    22  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) After 90000000 iterations
    24  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) After 100000000 iterations
    24  10780 (     0)   6544 (     0)   5448 (     0)      4 (     0)
+   1356 (     0) finish
$

[download]

As expected, no leak whatsoever.

It could also be an issue if the OS doesn't "take back" released memory.

Of course, but so could any program doing anything. That doesn't constitute a leak.

🦛

In reply to Re^3: How to implement a Queue that doesn't leak memory? by hippo
in thread How to implement a Queue that doesn't leak memory? by Anonymous Monk

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