1. What is the advantage of persistent data structure? all data in the same block of memory,fast speed? It is suitable for what kind of needs?

2. If not use nfreeze, I mean, just use

It is quite hard to answer those questions without seeing their actual use in context.

On the face of it, it doesn't make a lot of sense to freeze a hash in order to return it from a subroutine.

The only possible (tentative) clue I can glean from the snippet you've posted comes from the name %testresults. It is possible that the code goes on to compare those results with a pre-frozen, known good results hash; in which case the author might be relying upon doing a binary compare of the frozen hashes rather than having to do a looping, possibly recursive traversal to compare them. If so, it might be cleverly efficient; or just obscurely dangerous.

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.

In reply to Re^5: parallel process on remote machines,read results and hanle timeout of those process by BrowserUk
in thread parallel process on remote machines,read results and hanle timeout of those process by x12345

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.