I couldn't really decide where to put this, but I figured Meditations would be best.
I was working with a script yesterday and realized that flock() doesn't do much by itself.
Using a simple flock FILEHANDLE, LOCK_EX; won't always succeed in locking a file.
So, I created a subroutine that attempts to lock a file several times, and if it cannot, there is definitely something wrong, and the user is presented with an error.

So here is the small subroutine:

sub lockfile {
my $file = pop();
for $i (1 .. 10) {
sleep .15;
$locked = 1 if (flock $file, LOCK_EX);
}
unless ($locked == 1) { print "\n\nFlock error: could not lock $file";
+ exit; }
}

[download]
There. Very easy subroutine that will try flocking a file 10 times before informing the user of an error.
I surprised myself by using pop()!
Anyway, this code is very easy to use:
lockfile (FILEHANDLE);

I could have also allowed an optional parameter that would allow the user to pass what kind of lock to use, rather than simply applying LOCK_EX, but I always use LOCK_EX, so...

Better not be an error in that post... ;-)

In reply to Flock Subroutine by mt2k

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.