The blocking is a result of "Pop" running before "Push". The input to timethese is a hashref which might imply that their relative ordering is unknown (that was my first guess... that an unordered "keys" was used). However, looking at timethese(), you can see that the incoming keys are sorted. So the Pop timing happens before the Push timing: 
sub timethese{
    my($n, $alt, $style) = @_;
    die usage unless ref $alt eq 'HASH';

    my @names = sort keys %$alt;
    $style = "" unless defined $style;
    ...

[download]

In reply to Re: Benchmark does timethese() in parallell? by darrellb
in thread Benchmark does timethese() in parallell? by johnnywang

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.