[sf-perl] Perl references to arrays vs. references to shared arrays

[David Christensen]

On 2020-08-11 16:55, David Christensen wrote:

> I have been working with nested data structures.

> To detect circular loops ... stringify a reference

> But the technique fails for data structures built from shared variables.


The solution is to use shared::threads::is_shared:

     https://metacpan.org/pod/threads::shared


In the example below, I used Scalar::Util::refaddr for consistency:


2020-08-13 18:00:18 dpchrist at tinkywinky ~/sandbox/perl
$ cat circular-arrayref-vs-shared-arrayref.pl
#!perl

use strict;
use warnings;
use threads;
use threads::shared;

use Scalar::Util		qw( refaddr );

my @a0;
my @a1;

my @sa0 :shared;
my @sa1 :shared;

sub d {
     no warnings 'uninitialized';
     printf "%i %s=[%21s] %s=[%21s]\n",
	(caller)[2],
        	refaddr(\@a0), refaddr($a0[0]),
        	refaddr(\@a1), refaddr($a1[0]);
}

sub e {
     no warnings 'uninitialized';
     printf "%i %s=[%21s] %s=[%21s]\n",
	(caller)[2],
        	is_shared(@sa0), is_shared($sa0[0]),
        	is_shared(@sa1), is_shared($sa1[0]);
}

print "\nArrays with circular references:\n";
				d; d; d;
$a0[0]  = \@a1;			d; d; d;
$a1[0]  = \@a0;			d; d; d;

print "\nShared arrays with circular references:\n";
				e; e; e;
$sa0[0] = \@sa1;		e; e; e;
$sa1[0] = \@sa0;		e; e; e;

2020-08-13 18:00:22 dpchrist at tinkywinky ~/sandbox/perl
$ perl circular-arrayref-vs-shared-arrayref.pl

Arrays with circular references:
33 93884874649056=[                     ] 93884874649128=[ 
       ]
33 93884874649056=[                     ] 93884874649128=[ 
       ]
33 93884874649056=[                     ] 93884874649128=[ 
       ]
34 93884874649056=[       93884874649128] 93884874649128=[ 
       ]
34 93884874649056=[       93884874649128] 93884874649128=[ 
       ]
34 93884874649056=[       93884874649128] 93884874649128=[ 
       ]
35 93884874649056=[       93884874649128] 93884874649128=[ 
93884874649056]
35 93884874649056=[       93884874649128] 93884874649128=[ 
93884874649056]
35 93884874649056=[       93884874649128] 93884874649128=[ 
93884874649056]

Shared arrays with circular references:
38 93884875574272=[                     ] 93884875574296=[ 
       ]
38 93884875574272=[                     ] 93884875574296=[ 
       ]
38 93884875574272=[                     ] 93884875574296=[ 
       ]
39 93884875574272=[       93884875574296] 93884875574296=[ 
       ]
39 93884875574272=[       93884875574296] 93884875574296=[ 
       ]
39 93884875574272=[       93884875574296] 93884875574296=[ 
       ]
40 93884875574272=[       93884875574296] 93884875574296=[ 
93884875574272]
40 93884875574272=[       93884875574296] 93884875574296=[ 
93884875574272]
40 93884875574272=[       93884875574296] 93884875574296=[ 
93884875574272]


David