To avoid the problem of processes exiting before cleaning up, one could do the following: after the child has created its PID file, the child should lock the PID file. The lock will be gone as soon as the process exits - no matter what the reason of exiting is (well, I'm assuming a UNIX OS, I've no idea how other OSses work). To check whether a previous child is still running, open the PID files, and try to get a lock. If you can get a lock, the process is no longer running. Only if the file exists, and it's still locked, the process is still running.

It also solves the problem of PID reuse.

In reply to Re^2: Keeping track of children from previous runs of a script by JavaFan
in thread Keeping track of children from previous runs of a script by ajwood

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.