Re^4: Timed event within a script

Thanks for your input. I have been trying to wrap my head around the best way to do this. The problem I have is that even though there has not been a message from the device for hours it doesn't mean there is actually a problem, it is more likely that there is NOT a problem in that case. It would be nice if there was a periodic "keep alive" type message from the device but I am not that lucky.

Simply put, the device shoots out a message on a IP port whenever there is an error event and only then. It does not care if there is 1 or 100 devices monitoring the port either

Comment on Re^4: Timed event within a script

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Re^5: Timed event within a script by Marshall (Canon) on Mar 10, 2017 at 21:29 UTC
Geez. One can only hope that this "emergency message" doesn't mean something like "reactor coolant low"! To make this into a single process, you will need to determine whether or not the socket for the device has a line for you to process in it or not. I think that you will need IO::Socket. This sort of thing would be done in what is called a "select server". Don't read from the socket unless you know that it has something to say. I think this psuedo code would be fine in your application. `# open file handles for reading and reporting # set $since_report_secs (seconds) = 0 while (sleep (1)) { my $emergency = check_for_emergency(); if ($emergency) { do something; } report_awake_status(); } sub check_for_emergency { while (device port ready to read) { read line and check it for "emergency" return 1 if emergency; } return 0; # "no error"; } sub report_awake_status { $last_report_time++; if (more than 30 minutes) { send awake message, set counter back to zero } }` [download] The above code essentially sets up a "polling loop". This is not as efficient as it "could be". But the logic for a simple single process is simple and I think that you will find that code like this doesn't take much CPU time.	[reply] [d/l]

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Re^5: Timed event within a script
by Marshall (Canon) on Mar 10, 2017 at 21:29 UTC

To make this into a single process, you will need to determine whether or not the socket for the device has a line for you to process in it or not. I think that you will need IO::Socket. This sort of thing would be done in what is called a "select server". Don't read from the socket unless you know that it has something to say.

I think this psuedo code would be fine in your application.

# open file handles for reading and reporting
# set $since_report_secs (seconds) = 0

while (sleep (1))
{
   my $emergency = check_for_emergency();
   if ($emergency)
   {
      do something; 
   }
   
   report_awake_status();
}


sub check_for_emergency
{
   while (device port ready to read)
   {
      read line and check it for "emergency"
      return 1 if emergency;
   }
   return 0; # "no error"; 
}

sub report_awake_status 
{
    $last_report_time++;
    if (more than 30 minutes)
    {
       send awake message, set counter back to zero
    }
}
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[d/l]