renodino has asked for the wisdom of the Perl Monks concerning the following question:

Is there any direct way to test if a variable is threads::shared ? I can't find anything in the threads::shared docs, nor in perlthrtut, nor in a Google search, nor in a search here. Currently, my only solution is this bit of code: 
sub shared_test {
    my $var_ref = shift;
    return undef unless ref $var_ref;
    my $safety : shared;

    eval {
        $safety = $var_ref;
    };
    return !$@;
}

my $shared : shared = 1;
my $private = 2;

shared_test(\$shared);
shared_test(\$private);

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...which is a pretty expensive operation for something which should be a simple test. Any help much appreciated.

Replies are listed 'Best First'.
Re: Testing if variable is threads::shared ?
by jdhedden (Deacon) on Aug 30, 2005 at 18:32 UTC
    Use threads::shared::_id(\$var), as in: 
      use threads;
  use threads::shared;

  my $var : shared;

  if (threads::shared::_id($var)) {
      print("'\$var' is shared\n");
  }

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    It returns a true value (a memory address) if $var is shared, and undef if not.

    NOTE: This is not documented, and the underscore in the name indicates its internal use nature. This function is found in ext/threads/shared/shared.xs in the Perl source code distribution.

    UPDATE: Corrected as per below. Thanks pg.


    Remember: There's always one more bug.
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      The posted code returned:

      Undefined subroutine &threads::shared::_id called at math1.pl line 5.

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      Testing is done with 5.8.4 on windows XP.

      Update: The above code could be fixed like this:

      use threads; #added
use threads::shared;

  my $var : shared;

  if (threads::shared::_id($var)) {#pass the var not the ref
      print("'\$var' is shared\n");
  }

      [download]
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      Groovy! Many thanks.

      Couple of things:

      1) Any chance this will be exported into a public method someday ?

      2) FYI: When I tried directly testing a ref operator (e.g., threads::shared::_id(\@ary)), it choked. I had to explicitly assign the ref to another variable, then it reports shared (which is the important bit for me).

      For the record, here's a bit more complete test:

      use threads;
use threads::shared;

package Dweeble;

sub new {
    my $class = shift;
    
    my %obj : shared = (
        cow => 'bossy'
    );
    return bless \%obj, $class;
}

sub holycow {
    print "Holy Cow!\n";
}

1;

package main;

my $hope : shared = 27;

my @ary : shared = (1,2,3,4,5);

my $aryref = \@ary;

my %hash : shared = ( one => 1, two => 2 );

my $hashref = \%hash;

my $cow;

my $krelboin = Dweeble->new();

print "hope is ", (threads::shared::_id($hope) ? "shared\n" : "private
+\n");

print "cow is ", (threads::shared::_id($cow) ? "shared\n" : "private\n
+");

print "ary is ", (threads::shared::_id($aryref) ? "shared\n" : "privat
+e\n");

print "hash is ", (threads::shared::_id($hashref) ? "shared\n" : "priv
+ate\n");

print "krelboin is ", (threads::shared::_id($krelboin) ? "shared\n" : 
+"private\n");

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[reply]
[d/l]
        1) Any chance this will be exported into a public method someday?
        Most likely not. However, it probably isn't going to go away either. It's still in the blead code.

        Remember: There's always one more bug.
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