Perl Multiple Subroutines

Question

It may be a simple question for a perl expert -

I am trying to run a script which should logically do this>

Main
{
 While (true)
  Call Sub A
  Call Sub B
  Call Sub C
}

Sub A
{
Go execute a method A for whatever it needs to do ---
before next time method A runs it need to wait atleast 60 seconds but i still want to call method B in these 60 seconds.
}

Sub B
{
  Go execute a method B for whatever it needs to do ---
before next time method b runs it need to wait atleast 60 seconds but i still want to call method C in these 60 seconds in mean time.

}

Sub C
{
  Go execute a method C for whatever it needs to do ---
before next time method C runs it need to wait atleast 60 seconds at this moment control should be back in Main and wait for first 60 seconds of A to expire so that Sub A can be called
}

My question: Q: what is best and optimized way can i do this -?

Q: If i put sleep 60 in each sub then next sub will not be called even till 60 seconds expire and it will delay overall processing.

Q: I want 3 subs called every 60 seconds in a sequential order

Q Lastly if i need to call 2 subs in every 60 seconds and last sub every hour - how do i do it?

Comment - my thought was to take UTC as a variable and store it in a variable and keep checking time if time expires than call individual subs but not sure if it optimum way of running code.

Do the subroutines each take multiple seconds? Is the sum always less than 60 seconds? If A has completed inside 60 seconds but B has not completed, should A be run again? What about C? Can you use multiple threads, so there's an A-thread that runs A at no greater frequency that once every 60 seconds, and a B-thread for B and a C-thread for C? — Jonathan Leffler
– Jonathan Leffler, Commented Mar 6, 2014 at 8:17
Using threads is probably the way to go here, but keep in mind, if your subs mingle with common global variables (global as in not only in the respective sub) you will have to make sure that no two threads try to modify the same variable at the same time. That is not a trivial task. — DeVadder
– DeVadder, Commented Mar 6, 2014 at 8:19
So in theory none should take more than few seconds (these are SOAP calls) and my testing shows it may take very less seconds and definitely sum will not be equal to or greate than 60 seconds. But again i want to take best practice and not rely on my thoughts.....so i am ok to use multi threading program (i dont know how?) i need some pseudo code help if possible in perl. and explaination how it will work...thanks and appreciate your response. — Nik
– Nik, Commented Mar 6, 2014 at 8:21
perldoc.perl.org/perlthrtut.html If you do not understand something in there, ask. — DeVadder
– DeVadder, Commented Mar 6, 2014 at 8:27
do you want to call B before A finishes? the threads answer assumes that, but it sounds to me like you want them to be sequential, which means you don't want to use threads. — ysth
– ysth, Commented Mar 6, 2014 at 8:47

amon · Accepted Answer · 2014-03-06 08:19:11Z

3

Inside the subroutine record the time when it last ran, then wait if necessary on the next execution:

use feature 'state';

my $sleep_duration = 60; # seconds

sub foo {
   state $last_execution = 0;
   my $remaining = $last_execution + $sleep_duration - time;
   sleep $remaining if $remaining > 0;
   $last_execution = time;

   ...; # normal processing for this sub
}

answered Mar 6, 2014 at 8:19

amon

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Comments

René Nyffenegger · Accepted Answer · 2014-03-06 08:25:33Z

1

You probably want to use threads. The following snippet might give you a starting point. Since you have four Qs instead of one, I won't go into detail for each of them.

#!/usr/bin/perl

use warnings;
use strict;
use threads;

my @t = (
  threads->create(\&A),
  threads->create(\&B),
  threads->create(\&C)
);

$t[0] -> join();
$t[1] -> join();
$t[2] -> join();

sub A {
  for my $i (1 .. 10) {
     print "A $i\n";
     sleep 60;
  }
}

sub B {
  for my $i (1 .. 20) {
     print "B $i\n";
     sleep 60;
  }
}

sub C {
  for my $i (1 .. 3) {
     print "C $i\n";
     sleep 60;
  }
}

edited Mar 6, 2014 at 8:25

answered Mar 6, 2014 at 8:16

René Nyffenegger

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1 Comment

Nik Over a year ago

So basically each thread in your example will be child thread started from main thread and will be independent and have sleep duration which do not overlap or affect others.

mpapec · Accepted Answer · 2014-03-06 08:31:48Z

1

Using Amon idea, but with sleeping logic outside functions,

sub get_sleeper {

  my ($sleep_duration) = @_;

  my $last_execution = 0;
  return sub {
    my $remaining = $last_execution + $sleep_duration - time();
    sleep $remaining if $remaining >0;
    $last_execution = time();
  };
}

my ($sleepA, $sleepB, $sleepC) = map get_sleeper(60), 1..3;
while (1) {
  $sleepA->(); SubA();
  $sleepB->(); SubB();
  $sleepC->(); SubC();
}

answered Mar 6, 2014 at 8:31

mpapec

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Comments

DeVadder · Accepted Answer · 2014-03-06 08:25:53Z

0

Both answers are good but a sort of middle way would be: (stolen from the answer by amon)

use feature 'state';

my $sleep_duration = 60; # seconds

sub foo {
   state $last_execution = 0;
   my $remaining = $last_execution + $sleep_duration - time;
   if ($remaining > 0)
   {
       return "Waiting";  # Make sure main checks for this to know whether the sub ran.
   }

   ...; # normal processing for this sub
}

This will allow you to run the next sub while this one wait without needing more than one thread. But of course, it means that this sub will run only after the other two had their chance. This means you mix up the order and depending on subs, take longer than 60 seconds till the next call.

answered Mar 6, 2014 at 8:25

DeVadder

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3 Comments

Nik Over a year ago

ok make sense any caveats of using Threads other than i need to be careful with Global Variables

DeVadder Over a year ago

@Nik Not really. Sometimes it is a little fiddly. But if you plan to keep programing, learning to use and understand multithreading is important and good anyways. So i would say, doing so in a script you know and with a limited complexity like this problem is probably a great opportunity to dive in. The concepts are mostly similar in all languages. Even if getting it to work like you want with threads takes you a few hours longer, that is absolutely worth it, so go ahead. And come back if you encounter something that just wont work as expected (what is likely to happen at first ^^)

Nik Over a year ago

Agree and thanks everyone - i will give it a shot probably a good learning opportunity for me to write clean code.

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