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#!perl
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# ########################################################################## #
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# Title: Batch-of-rows processor
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# Creation date: 2007-03-05
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# Author: Michael Zedeler
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# Henrik Andreasen
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# Description: Process batches of rows in a data stream
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# Data Stream class
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# Data transformer
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# Buffers rows
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# File: $Source: /data/cvs/lib/DSlib/lib/DS/Transformer/Buffer.pm,v $
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# Repository: kronhjorten
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# State: $State: Exp $
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# Documentation: inline
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# Recepient: -
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# ########################################################################## #
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package DS::Transformer::Buffer;
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1
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1
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1053
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use base qw{ DS::Transformer::TypePassthrough };
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3
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1
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687
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1
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1
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7
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use strict;
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1
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30
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1
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1
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5
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use Carp;
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2
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1
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53
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25
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1
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1
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7
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use Carp::Assert;
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1
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2
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1
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6
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26
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our ($VERSION) = $DS::VERSION;
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our ($REVISION) = '$Revision: 1.1 $' =~ /(\d+\.\d+)/;
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# new
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#
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# Class constructor
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#
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sub new {
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1
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1
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1
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1304
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my( $class, $source, $target ) = @_;
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1
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my $self = $class->SUPER::new( $source, $target );
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40
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1
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$self->{buffer} = []; # Holds copies (?) of the currently buffered rows (stream is N elements long, indexed 0 .. N-1)
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1
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4
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$self->{first} = 0; # Range: [0..N] Inv: Always at first buffered element (one past "last" when buffer is empty)
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1
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4
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$self->{last} = -1; # Range: [-1..N-1] Inv: Always at last element (one before "first" when buffer is empty)
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1
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2
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$self->{current} = -1; # Range: [-1..N] Inv: Always at current element, initially -1, finally N (past end)
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45
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1
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5
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return $self;
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}
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48
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# receive_row
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#
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# Processes a row in stream.
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# Returns undef when no more rows are available.
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# It is allowed to call fetch after the stream has ended, each call returning undef.
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#
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sub process {
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15
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15
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1
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my ($self, $row) = @_;
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56
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15
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49
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$self->push( $row );
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57
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15
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36
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return $self->shift;
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58
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}
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59
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60
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sub shift {
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15
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15
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0
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21
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my( $self ) = @_;
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63
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15
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25
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my $last = $self->{last};
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15
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22
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my $current = $self->{current};
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65
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15
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18
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my $result = undef;
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66
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67
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# Find and return the "next" element, if any
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15
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100
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37
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++$current if ($current <= $last);
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15
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100
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38
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$result = ${$self->{buffer}}[$current] if ($current <= $last);
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13
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25
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70
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71
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15
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$self->{current} = $current;
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73
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15
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61
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return $result;
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}
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76
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sub push {
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15
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15
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0
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my( $self, $row ) = @_;
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79
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15
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24
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my $last = $self->{last};
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81
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# Put row in buffer if not EOF or EOF not already registered in buffer
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15
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100
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100
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45
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if ( $row or ${$self->{buffer}}[$last] ) {
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5
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27
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83
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11
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++$last;
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11
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100
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$row = {%$row} if $row; # Make a copy if not EOF
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11
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2430
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${$self->{buffer}}[$last] = $row;
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11
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33
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86
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}
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87
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88
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15
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$self->{last} = $last;
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90
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15
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29
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return;
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}
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93
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# fetch
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#
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# Re-fetches rows that has been unfetched.
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# It is a fatal error to try fetching beyond last row in the buffer
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#TODO Implement some kind of end of stream indicator that will allow fetch to return undef indicating end of stream
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sub fetch {
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10
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10
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0
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4383
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my ($self) = @_;
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101
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10
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20
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my $last = $self->{last};
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10
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20
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my $current = $self->{current};
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10
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15
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my $result = undef;
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105
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# Make sure we're not beyond end of buffer
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10
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100
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26
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if( $current < $last ) {
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# Find and return the "next" element
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6
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9
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++$current;
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109
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6
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10
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$result = ${$self->{buffer}}[$current];
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6
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18
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110
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} else {
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111
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4
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1105
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croak("Can't fetch past buffer end.");
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}
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113
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114
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6
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12
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$self->{last} = $last;
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115
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6
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11
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$self->{current} = $current;
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116
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117
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6
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30
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return $result;
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}
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119
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120
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121
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# unreceive_row
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#
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123
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# Moves the "current" position one step backwards within the buffered rows.
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# It is a fatal error to try to move before the start of the currently buffered rows.
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#
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126
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sub unfetch {
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127
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13
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13
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0
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4306
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my ($self) = @_;
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128
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129
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13
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25
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my $first = $self->{first};
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130
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13
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22
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my $last = $self->{last};
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131
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13
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18
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my $current = $self->{current};
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132
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133
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# Validate the request
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134
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13
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100
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44
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if ($current < $first) {
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100
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135
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3
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21
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die "Cannot unfetch beyond buffer start (frame starts at row number $first and current record is $current)\n";
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136
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} elsif( $current > $last ) {
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137
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# If EOF reached, return to the element that contains EOF
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138
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1
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10
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assert( $current == $last + 1, '$current must never be more than one past $last' );
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139
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1
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5
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--$current;
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140
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}
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141
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142
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# Move back one step
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143
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10
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12
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--$current;
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144
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145
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10
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18
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$self->{current} = $current;
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146
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10
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23
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return 1;
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147
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}
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148
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149
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150
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# flush
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151
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#
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152
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# Clears the buffered rows up to and including the given point.
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153
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# If the "current" position is flush, it is moved forward such that it will
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154
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# return the first available element at next fetch, if any.
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155
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# It is a fatal error to flush non-existent rows.
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156
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#
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157
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sub flush {
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158
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2
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2
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0
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3105
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my ($self, $point) = @_;
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159
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160
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2
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5
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my $first = $self->{first};
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161
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2
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5
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my $last = $self->{last};
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162
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2
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5
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my $current = $self->{current};
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163
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164
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# Use current position to flush in no point provided
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165
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2
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66
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13
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$point ||= $current;
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166
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167
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# Validate the request
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168
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2
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50
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33
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15
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if ($point < $first || $point > $last) {
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169
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0
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0
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croak("Cannot flush non-existent elements. ($point is not within valid range: $first .. $last)");
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170
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}
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171
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172
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# Delete buffer elements and adjust pointers
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173
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2
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8
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for (my $i = $first; $i <= $point; ++$i) {
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174
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3
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4
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delete ${$self->{buffer}}[$i];
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3
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18
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175
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}
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176
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2
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5
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$self->{first} = $point + 1;
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177
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2
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100
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8
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$self->{current} = $point if ($self->{current} < $point);
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178
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179
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2
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5
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return 1;
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180
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}
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181
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182
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1;
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