Hello to all! I have studied posts here for a while now, trying to improve my meagre Perl coding skills, but seemingly to little avail so far! I've been toying with alarms, in order to build a slideshow script. This thing will display random images, images in sequence forward or backwards or pause indefinitely on an image. If the user does not press a key within the timmeout period, the script repeats the last action. Sadly for reasons I don't understand, it works 99% of the time, and occasionally craps out with the following error message: 
panic: leave_scope inconsistency at slideshow.pl line xx.
panic: leave_scope inconsistency.

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This corresponds to the "eval {" line in the code fragment below. Can anybody help explain what I've clearly failed to grasp? 
do
  {
    $SIG{CHLD} = 'IGNORE';
    undef $pid;

    die "fork: $!" unless defined ($pid = fork);

    if ($pid)
      {
        eval {
          local $SIG{ALRM} = sub { die "alarm\n" };
          alarm $timeout;

          do {
            # Wait for a keypress
            # Take appropriate action
            SWITCHKEY:
              {
                if ($key eq "q")
                  { $continue = 0; last SWITCHKEY; };
                if ($key eq "n")
                  { $action = $key; $index++ ; last SWITCHKEY; };
                if ($key eq "b")
                  { $action = $key; $index-- ; last SWITCHKEY; };
                if ($key eq ".")
                  { alarm 0 ; last SWITCHKEY; };
                $action = "r";
                $index = int rand @files;
              }

          }
          until $key ne ".";
          alarm 0;

          # Close the current image window (by killing the child)
          kill TERM => $pid;

        };
        if ($@) {
          # Timed out
          die unless $@ eq "alarm\n";
          kill TERM => $pid;
          SWITCHACTION:
            {
              # n -> next image
              if ($action eq "n")
                { $index++;  last SWITCHACTION; };

              # b -> previous image
              if ($action eq "b")
                { $index--; last SWITCHACTION; };

              # r -> random image
              if ($action eq "r")
                { $index = int rand @files; last SWITCHACTION; };
            }
        }
      }
    else
      { # This is the child process 
        # exec an image viewer over the child process...
        exec("/usr/bin/ee '$file'");
      }
  }
until not $continue;

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Minds are like parachutes; they only work when open. (Sir James Dewar)

In reply to Why does my parent panic when comitting serial infanticide? by emptynet

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