Greetings,
I'm a former hardware guy (embedded C & C++ experience mainly) trying to get up to speed with Java and Perl for a set of graduate courses.

I've written up a Perl script that simulates a scheduling algorithm, the script consists of two primary loops the first to parse process/event info from a file, the second to schedule each event. The first loop executes fine, but I'm having issues getting the script to run with my second loop - since I'm doing this in Perl (with no main block) I'm concerned it may have something to do with the scope of my vars (my three primary data structures are a 2d array used as an array of stacks, and two hashes used to reference event dependencies.

I am using Eclipse/EPIC/ActiveState Perl 5.8.6 to debug my script. I'm a noob at this, although I've had some experience using regular expressions/Perl in a Unix environment, admittedly at the moment I'm completely stuck...
Parse loop (appears to work fine): 

foreach $line (<FILE>)
{    
    chomp $line;
    
    if ($line =~ m/(\d)-(\d)->(\d)-(\d)/)
    {    
        #create local sender and receiver vars 
        my $sp = "$1-$2";
        my $rp = "$3-$4";
        
        #update sender and receiver hashes
        $sender{$sp} = $rp;
        $receiver{$rp} = $sp;    
        
        print "enter $sender{$sp}->$receiver{$rp} in dependency hashes
+\n";
    }
    elsif($line =~ m/(\d)-(\d)/)
    {
        #create local process var
        my $p = "$1-$2";
    
        #queue process on @p_s multi-dimensional array
        unshift (@{$p_s[$1]},$p); 
        print "unshift $p_s[$1][0] onto process array\n";
        $numevents++;
    }
    else
    {
        print "\nunmatched line: $line \n";
        chomp($line); #remove empty newlines in input file
    }
}

[download]

Scheduling loop (script produces no output with this included) 

while($timestamp <= $numevents)
{
    print "\ntimestamp: $timestamp, numevents: $numevents\n";
    foreach $pid (@p_s) 
    {
        my $p_e = 0, $p_t = 0;
        
          #for every process pop the first event and examine it
          if($p_e = pop @{$p_s[$pid]})
          {

              #if process-event has receiver-dependency then push it b
+ack on the stack
              if($receiver{$p_e})
              {
                  push (@{$p_s[$pid]},$p_e);
              }
              else
              {
                  my $s_o = 0;
                  #else if process-event has sender-obligation then up
+date sender and reciever hashes
                  if($s_o = $sender{$p_e})
                  {
                      delete $sender{$p_e};
                      delete $receiver{$s_o};
                  }
                  
                  #and then enqueue process-event with process-timesta
+mp in schedule hash
                  if($p_e =~ m/(\d)-(\d)/)
                  {
                      $p_t = "$timestamp.$1"
                  }
                  else
                  {
                      print "\nerror parsing processor-event signature
+\n";
                  }
                  
                  $schedule{$p_e} = $p_t;
                  unshift (@totalorder, $p_t);
              }
          }
    }
    $timestamp++;
}

[download]

Since the timestamp of each event is it's occurance relative to every other event, I don't need any abosolute means of stamping each event, and I can say that my $timestamp < $numevents always. I do need to output the total order of events, as well as each event and it's timestamp, hence I create a third and fourth hash and array respectively, %schedule and @totalorder. I have created a subroutine check_data() that outputs all of the data stored in all of my major data structures, the definition for this is located after all of the code I have in what would be my main() block in C/C++.

Sorry for the lengthy description - anyone here have an idea why the first loop would execute but not the second?

Do I need to initialize my vars prior to use, ex: 

$pid = 0; #process index
@p_s = (); #2d process array/stack
%sender = (); #sending event hash
%receiver = (); #receiving event hash
$numevents = 0; #total number of events in all processes 
$timestamp = 0; #timestamp for event scheduler
%schedule = (); #hash of each event with timestamp
@totalorder = (); #final order of each event

[download]

Should be declared before the first loop (I've tried this already w/o success but maybe I'm missing something)?

Will vars declared on the fly in the first loop be visible in the second loop?

I will append the full script at the end of this post for the reference of the more experienced perl-sons who are hopefully perusing this forum... 


###################
#Lamport.pl
###################

#!/usr/bin/perl -w
#begin main routine

#$pid = 0; #process index
#@p_s = (); #process stack
#%sender = (); #sending event hash
#%receiver = (); #receiving event hash
#$numevents = 0; #total number of events in all processes 
#$timestamp = 0; #timestamp for event scheduler
#%schedule = (); #= Tie::IxHash->new();
#@totalorder = ();

#read process/event input from file
open FILE, $ARGV[0]
      or die "$ARGV[0] can't be opened:\n$!";
    #local $/;   # Set input to "slurp" mode.

#initialize process/event stack/hash from input file 
print "\nbegin Lamport's algorithm for input file $ARGV[0]\n";

foreach $line (<FILE>)
{    
    chomp $line;
    
    if ($line =~ m/(\d)-(\d)->(\d)-(\d)/)
    {    
        #create local sender and receiver vars 
        my $sp = "$1-$2";
        my $rp = "$3-$4";
        
        #update sender and receiver hashes
        $sender{$sp} = $rp;
        $receiver{$rp} = $sp;    
        
        print "enter $sender{$sp}->$receiver{$rp} in dependency hashes
+\n";
    }
    elsif($line =~ m/(\d)-(\d)/)
    {
        #create local process var
        my $p = "$1-$2";
    
        #queue process on @p_s multi-dimensional array
        unshift (@{$p_s[$1]},$p); 
        print "unshift $p_s[$1][0] onto process array\n";
        $numevents++;
    }
    else
    {
        print "\nunmatched line: $line \n";
        chomp($line); #remove empty newlines in input file
    }
}

print "\ncompleted $ARGV[0] parsing\n";
close FILE;

check_data();

#schedule process events according to Lamport's algorithm
while($timestamp <= $numevents)
{
    print "\ntimestamp: $timestamp, numevents: $numevents\n";
    foreach $pid (@p_s) 
    {
        my $p_e = 0, $p_t = 0;
        
          #for every process pop the first event and examine it
          if($p_e = pop @{$p_s[$pid]})
          {

              #if process-event has receiver-dependency then push it b
+ack on the stack
              if($receiver{$p_e})
              {
                  push (@{$p_s[$pid]},$p_e);
              }
              else
              {
                  my $s_o = 0;
                  #else if process-event has sender-obligation then up
+date sender and reciever hashes
                  if($s_o = $sender{$p_e})
                  {
                      delete $sender{$p_e};
                      delete $receiver{$s_o};
                  }
                  
                  #and then enqueue process-event with process-timesta
+mp in schedule hash
                  if($p_e =~ m/(\d)-(\d)/)
                  {
                      $p_t = "$timestamp.$1"
                  }
                  else
                  {
                      print "\nerror parsing processor-event signature
+\n";
                  }
                  
                  $schedule{$p_e} = $p_t;
                  unshift (@totalorder, $p_t);
              }
          }
    }
    $timestamp++;
}

check_data();

#create "totalorder" copy of schedule hash

#pop totalorder as stack and print

#sort and print schedule hash

#end MAIN routine

#begin subroutine definitions

sub check_data
{
    #print "numprocs = $numprocs\n";
    print "\ntimestamp = $timestamp\n";
    print "numevents = $numevents\n";
    
    print "\ncontents of process stack:\n";
    foreach my $r (@p_s) 
    {
       my $j=0;
       foreach my $c (@{$r}) 
       {
          print "P$i j: $j Value: $c\n";
          $j++;
       }
       $i++;
       print "\n";
    }
    
    print "\nsender key/value pairs:\n";
    foreach my $k (sort keys %sender) 
    {
        print "$k => $sender{$k}\n";
    }
    
    print "\nreceiver key/value pairs:\n";
    foreach my $k (sort keys %receiver) 
    {
        print "$k => $receiver{$k}\n";
    }
    
    print "\nschedule key/value pairs:\n";
    foreach my $k (sort keys %schedule) 
    {
        print "$k => $schedule{$k}\n";
    }
    
    print "\ncontents of totalorder queue:\n";
    foreach my $r (@totalorder)
    {
        print "$r, ";
    }
    
    print "\n\n";
}

[download]

In reply to simple script question scope/structure for Perl noob by scotchfx

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