...hmmm... and now we may have an argument for using microtime...

If you've moved away from staying pure Perl, for a source of an unguessable counter, I'd use the Time Stamp Counter.

Given that this changes by anything ranging from 1/2 a million to 10s of millions between successive calls in a tight loop, the odds of collisions even if you have 16 concurrent cores are negligible:

#! perl -slw
use strict;
use Inline C => Config => BUILD_NOISY => 1;
use Inline C => <<'END_C',  NAME => 'rdtsc', CLEAN_AFTER_BUILD => 0;

SV *rdtsc() {
    return newSVuv( (UV)__rdtsc() );
}

END_C

my( $last, $this ) = ( 0, 0 );
print( $this = rdtsc(), ' ', $this - $last ), $last = $this  for 1 .. 
+20;

__END__
C:\test>rdtsc
95054001389914 95054001389914
95054002276396 886482
95054003052862 776466
95054004698944 1646082
95054006658865 1959921
95054008588537 1929672
95054010420586 1832049
95054012410180 1989594
95054014268572 1858392
95054016253981 1985409
95054018070946 1816965
95054050803874 32732928
95054051382070 578196
95054053061884 1679814
95054054901610 1839726
95054056870252 1968642
95054058682825 1812573
95054060659909 1977084
95054062399501 1739592
95054064304702 1905201

[download]

Indeed, used alone with some suitable modulus operations, it would form the basis of a pretty damn good cryptographic rand() all by itself.

Even if the bad guys had an identical system -- hardware and software -- it would be impossible to predict the next number coming from it. It is affected by every single thing that happens on the system -- interrupts from your nic; mouse movements; thermal loading; every piece of software running in the systems.

Even if you put two totally identical systems side by side and synchronised them, I bet they would not stay in step for more than a few milliseconds.

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.

The start of some sanity?

In reply to Re^3: How do I get a unique Perl Interpreter ID? by BrowserUk
in thread How do I get a unique Perl Interpreter ID? by wrog

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