Beefy Boxes and Bandwidth Generously Provided by pair Networks
Welcome to the Monastery
 
PerlMonks  

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
This is exactly the situation where flock makes sense. But I think you need LOCK_EX. EX stands for "exclusive" while SH stands for "shared". If you had lots of data to read before the write it might make sense to first use LOCK_SH (prevents others to get LOCK_EX, but doesn't prevent the LOCK_SH of other readers). But since you do a quick test+optional write, LOCK_SH probably wastes more time than it saves on simultaneous reads.

So my advice: Just do your operation between a LOCK_EX and a LOCK_UN.

Linux and most other unixes work with flock, but you should avoid nfs-mounted partitions. It is probably best to include a test in your code if you anticipate the program to use different OSes

UPDATE: the seek in your example code seeks to the end of the file. Not a good idea if you want to read it or rewrite it, only good for appending.


In reply to Re: Atomic operation by jethro
in thread Atomic operation by willjones

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, 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, 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.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others lurking in the Monastery: (6)
    As of 2020-06-05 03:14 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?
      Do you really want to know if there is extraterrestrial life?



      Results (35 votes). Check out past polls.

      Notices?