I like this idea but I'm having trouble get a 2 pass solution to work nicely. In the first pass I identify which line numbers need to be removed. But then I'll need to mung that list into some convenient form to use while reading the file again in the second pass...

I don't understand your difficulty. Pass #1 records line numbers, pass #2 writes all the lines that haven't been recorded. Here's some code based on your original but with a few tweaks: 

#!/usr/bin/perl

use strict; use warnings;
sub Log;

die "Usage:     $0 <filename>\n" unless @ARGV == 1;
my $logfile = shift;

# Pass #1 : gather line numbers to be deleted.
my %locks;                      # Hash of currently open locks.
my @unlock_lines;               # lines to rid ourselves of
open(LOGFILE,$logfile) or die "Can't read $logfile - $!\n";
while (<LOGFILE>) {
  Log 2, "Analysing line $.";
  next unless /Mutex\((.*?)\)::(\w+)/;
  my ($address,$action) = ($1,$2);
  if ($action eq 'locking') {
    Log 2, "Address $address locked at line $.";
    if (defined $locks{$address}) {
      Log 0, "ERROR: Address $address locked at line $., but already l
+ocked at line $locks{$address}.";
    }
    $locks{$address} = $.;
  }

  if ($action eq 'unlocked') {
    Log 2, "Address $address unlocked at line $.";
    unless (defined $locks{$address}) {
       Log 0, "ERROR: Address $address not locked, but unlocked at lin
+e $..";
    } else {
        push @unlock_lines, $., delete $locks{$address};
    }
  }
}
close LOGFILE;

# Sort the lines numbers that we've accumulated because we put them in
# unordered. This allows us to make just one more pass through the fil
+e
# to remove the lines.
@unlock_lines = sort { $a <=> $b } @unlock_lines;

# Pass #2: output all but the lines we're not interested in.
my $rmline = shift @unlock_lines;
open(LOGFILE,$logfile) or die "Can't read $logfile - $!\n";
while (<LOGFILE>) {
   if (defined $rmline && $. == $rmline) {
      $rmline = shift @unlock_lines;
      next;
   }
   print;
}
close LOGFILE;

[download]

duff

In reply to Re^3: Reducing memory usage while matching log entries by duff
in thread Reducing memory usage while matching log entries by matt.tovey

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