Re^3: Threading: Invalid value for shared scalar

You can share nested hash, as long as the internal hashes are also marked as shared. Let's say your non-shared code to populate the hash looked like this:

#non shared hash version
my %abc;

my @parents = qw( a b c );
my @children = qw( 1 2 3 4 );

for my $parent ( @parents )
{
  for my $child ( @children )
  {
      $abc{ $parent }{ $child } = 1;
  }
}
[download]

Changing the implicit hash creation to explicit hash creation will fix the problem. the perl thread model is predicated on non-shared data by default. This forces us to deliberately share all the structures. (It is a pain).

# shared hash version.
my %abc : shared ;

my @parents = qw( a b c );
my @children = qw( 1 2 3 4 );

for my $parent ( @parents )
{
  unless (exists $abc{$parent})
  {
    my %p : shared;
    $abc{ $parent } = \%p;
  }
  
  for my $child ( @children )
  {
      unless ( exists $abc{$parent}{$child} )
      {
        my %c : shared;
        $abc{$parent}{$child}=\%c;
      }
      $abc{ $parent }{ $child } = 1;
  }
}
[download]

The lexical scopes for %p and %c will go away, but the references will remain in the hash, preventing garbage collection.

Comment on Re^3: Threading: Invalid value for shared scalar Select or Download Code

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Re^4: Threading: Invalid value for shared scalar by hexcoder (Curate) on Jul 03, 2015 at 12:05 UTC
Very good explanation, thanks! But in the second example this `... unless ( exists $abc{$parent}{$child} ) { my %c : shared; $abc{$parent}{$child}=\%c; } ...` [download] looks like an superficial assignment of `$abc{ $parent }{ $child }` since immediately thereafter the reference `\%c` is overwritten by a scalar. For two levels of hashing two shared hashes should be enough (`%abc` and `%p`). So for this example the following minimal version should work as well: `# shared hash version. my %abc : shared ; my @parents = qw( a b c ); my @children = qw( 1 2 3 4 ); for my $parent ( @parents ) { unless (exists $abc{$parent}) { my %p : shared; $abc{ $parent } = \%p; } for my $child ( @children ) { $abc{ $parent }{ $child } = 1; } }` [download] For all Perl people who got a bit confused by the example code like I was...	[reply] [d/l] [select]
Re^5: Threading: Invalid value for shared scalar by BrowserUk (Patriarch) on Jul 03, 2015 at 12:42 UTC
Or just: `my @parents = qw( a b c ); my @children = qw( 1 2 3 4 ); my %abc :shared; %{ $abc{ $_ } //= &share({}) } = map{ $_ => 1 } @children for @parents +; pp \%abc;` [download] Which prints: `do { my $a = { # tied threads::shared::tie a => { # tied threads::shared::tie 1 => 1, 2 => 1, 3 => 'fix', 4 => 'fix', }, b => { # tied threads::shared::tie 1 => 1, 2 => 1, 3 => 'fix', 4 => 'fix', }, c => { # tied threads::shared::tie 1 => 1, 2 => 1, 3 => 'fix', 4 => 'fix', }, }; $a->{a}{3} = $a->{a}{1}; $a->{a}{4} = $a->{a}{2}; $a->{b}{3} = $a->{b}{1}; $a->{b}{4} = $a->{b}{2}; $a->{c}{3} = $a->{c}{1}; $a->{c}{4} = $a->{c}{2}; $a; }` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. I'm with torvalds on this Agile (and TDD) debunked I told'em LLVM was the way to go. But did they listen!	[reply] [d/l] [select]
Re^4: Threading: Invalid value for shared scalar by Anonymous Monk on Feb 26, 2015 at 13:10 UTC
This method tested work, thanks a lot.	[reply]