Beefy Boxes and Bandwidth Generously Provided by pair Networks
The stupid question is the question not asked
 
PerlMonks  

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
your example does not use an external lock file...i'll just leave it at that.
...one other thing i noticed with the original poster's code is that it's closing the counter file and then opening it again, which is just plain asking for trouble, as it all should be done under one lock. anyway, i got the camel book out:
use Fcntl qw(:DEFAULT :flock); $lockfile = "counter.lck"; sysopen(COUNTERLOCK, $lockfile, O_RDONLY | O_CREAT) or die "can't open + $lockfile: $!"; flock(COUNTERLOCK, O_EXCL) or die "can't lock $lockfile: $!";
....here open your counter file in read/write mode using same locking semantics as per the lockfile...then seek to 0, read the integer, add 1, seek to 0, write new value, close counter file, close lockfile, output new value to screen. don't unlock the counterfile/lockfile, just close them. this flushes the buffers and releases locks and closes in a fairly atomic fashion....that's another bug in the original code. Just remember that all this locking is only advisory, and programs not written to respect the locks will clobber it. Also, don't try to lock files over any network file systems, such as NFS,SMBFS.

In reply to Re: Re: Re: Mysterious Disapperance of file contents by aquarium
in thread Mysterious Disapperance of file contents by Gorby

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 meditating upon the Monastery: (4)
    As of 2020-06-06 21:28 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?
      Do you really want to know if there is extraterrestrial life?



      Results (41 votes). Check out past polls.

      Notices?