Thank you, syphilis for this thread. I did not realize this is broken. PDL overriding "srand" and not "rand" also breaks parallel code. The results are not repeatable.

use v5.030;
use PDL;
use MCE;

srand(3);

MCE->new(
  max_workers => 4, user_func => sub {
    MCE->say(MCE->wid, " ", rand());
  }
)->run;

[download]
$ perl ex.pl | sort
1 0.455586975281225
2 0.224720416431413
3 0.993853857581602
4 0.76298729873179

$ perl ex.pl | sort
1 0.778804464106546
2 0.547937905256735
3 0.317071346406923
4 0.0862047875571115

$ perl ex.pl | sort
1 0.49638699840671
2 0.265520439556898
3 0.0346538807070864
4 0.803787321857275

[download]
This requires a workaround in MCE. Ditto for MCE::Child and MCE::Hobo. 
# The PDL module 2.062 ~ 2.089 exports its own srand() function, that
# silently clobbers Perl's srand function, and does not seed Perl's
# pseudo-random generator. https://perlmonks.org/?node_id=11159773
      
if ( $INC{'PDL/Primitive.pm'} && PDL::Primitive->can('srand') ) {
   # Call PDL's random() function if exported i.e. use PDL.
         
   my $caller = caller(); local $@;
   $caller = caller(1) if ( $caller =~ /^MCE/ );
   $caller = caller(2) if ( $caller =~ /^MCE/ ); 
   $caller = caller(3) if ( $caller =~ /^MCE/ );
      
   $self->{_seed} = eval "$caller->can('random')"
      ? int(PDL::Primitive::random() * 1e9)
      : int(CORE::rand() * 1e9);
}  
else {
   $self->{_seed} = int(CORE::rand() * 1e9);
}

[download]

Edit 1: MCE v1.894, MCE::Shared v1.889

if ( $INC{'PDL/Primitive.pm'} ) {
   ...
}

[download]

Edit 2: MCE configures an internal seed. It turns out that MCE may not know the srand or setter used by the application. Releasing MCE 1.895 and MCE::Shared 1.890. I updated the demonstration to process a sequence of numbers (lesser memory consumption). See also, Predictability Summary.

Reverting back to the following. 
$self->{_seed} = int(CORE::rand() * 1e9);

[download]

In reply to Re^2: PDL and srand puzzle - support needed in MCE by marioroy
in thread PDL and srand puzzle by syphilis

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