package Tie::File;
-use Carp;
-use POSIX 'SEEK_SET';
-use Fcntl 'O_CREAT', 'O_RDWR', 'LOCK_EX';
require 5.005;
+use Carp ':DEFAULT', 'confess';
+use POSIX 'SEEK_SET';
+use Fcntl 'O_CREAT', 'O_RDWR', 'LOCK_EX', 'LOCK_SH', 'O_WRONLY', 'O_RDONLY';
+sub O_ACCMODE () { O_RDONLY | O_RDWR | O_WRONLY }
-$VERSION = "0.50";
+
+$VERSION = "0.95";
my $DEFAULT_MEMORY_SIZE = 1<<21; # 2 megabytes
+my $DEFAULT_AUTODEFER_THRESHHOLD = 3; # 3 records
+my $DEFAULT_AUTODEFER_FILELEN_THRESHHOLD = 65536; # 16 disk blocksful
-my %good_opt = map {$_ => 1, "-$_" => 1}
- qw(memory dw_size mode recsep discipline autochomp);
+my %good_opt = map {$_ => 1, "-$_" => 1}
+ qw(memory dw_size mode recsep discipline
+ autodefer autochomp autodefer_threshhold);
sub TIEARRAY {
if (@_ % 2 != 0) {
# default is the larger of the default cache size and the
# deferred-write buffer size (if specified)
$opts{memory} = $DEFAULT_MEMORY_SIZE;
- $opts{memory} = $opts{dw_size}
+ $opts{memory} = $opts{dw_size}
if defined $opts{dw_size} && $opts{dw_size} > $DEFAULT_MEMORY_SIZE;
# Dora Winifred Read
}
$opts{defer} = 0 unless defined $opts{defer};
$opts{deferred} = {}; # no records are presently deferred
$opts{deferred_s} = 0; # count of total bytes in ->{deferred}
+ $opts{deferred_max} = -1; # empty
+
+ # What's a good way to arrange that this class can be overridden?
+ $opts{cache} = Tie::File::Cache->new($opts{memory});
- # the cache is a hash instead of an array because it is likely to be
- # sparsely populated
- $opts{cache} = {};
- $opts{cached} = 0; # total size of cached data
- $opts{lru} = []; # replace with heap in later version
+ # autodeferment is enabled by default
+ $opts{autodefer} = 1 unless defined $opts{autodefer};
+ $opts{autodeferring} = 0; # but is not initially active
+ $opts{ad_history} = [];
+ $opts{autodefer_threshhold} = $DEFAULT_AUTODEFER_THRESHHOLD
+ unless defined $opts{autodefer_threshhold};
+ $opts{autodefer_filelen_threshhold} = $DEFAULT_AUTODEFER_FILELEN_THRESHHOLD
+ unless defined $opts{autodefer_filelen_threshhold};
$opts{offsets} = [0];
$opts{filename} = $file;
$opts{autochomp} = 1 unless defined $opts{autochomp};
- my $mode = defined($opts{mode}) ? $opts{mode} : O_CREAT|O_RDWR;
+ $opts{mode} = O_CREAT|O_RDWR unless defined $opts{mode};
+ $opts{rdonly} = (($opts{mode} & O_ACCMODE) == O_RDONLY);
+ $opts{sawlastrec} = undef;
+
my $fh;
if (UNIVERSAL::isa($file, 'GLOB')) {
croak "usage: tie \@array, $pack, filename, [option => value]...";
} else {
$fh = \do { local *FH }; # only works in 5.005 and later
- sysopen $fh, $file, $mode, 0666 or return;
+ sysopen $fh, $file, $opts{mode}, 0666 or return;
binmode $fh;
}
{ my $ofh = select $fh; $| = 1; select $ofh } # autoflush on write
sub FETCH {
my ($self, $n) = @_;
- my $rec = exists $self->{deferred}{$n}
- ? $self->{deferred}{$n} : $self->_fetch($n);
- $self->_chomp1($rec);
+ my $rec;
+
+ # check the defer buffer
+ $rec = $self->{deferred}{$n} if exists $self->{deferred}{$n};
+ $rec = $self->_fetch($n) unless defined $rec;
+
+ # inlined _chomp1
+ substr($rec, - $self->{recseplen}) = ""
+ if defined $rec && $self->{autochomp};
+ $rec;
}
# Chomp many records in-place; return nothing useful
my ($self, $n) = @_;
# check the record cache
- { my $cached = $self->_check_cache($n);
+ { my $cached = $self->{cache}->lookup($n);
return $cached if defined $cached;
}
- unless ($#{$self->{offsets}} >= $n) {
+ if ($#{$self->{offsets}} < $n) {
+ return if $self->{eof}; # request for record beyond end of file
my $o = $self->_fill_offsets_to($n);
# If it's still undefined, there is no such record, so return 'undef'
return unless defined $o;
# }
# }
- $self->_cache_insert($n, $rec) if defined $rec;
+ $self->{cache}->insert($n, $rec) if defined $rec && not $self->{flushing};
$rec;
}
sub STORE {
my ($self, $n, $rec) = @_;
+ die "STORE called from _check_integrity!" if $DIAGNOSTIC;
$self->_fixrecs($rec);
- return $self->_store_deferred($n, $rec) if $self->{defer};
+ if ($self->{autodefer}) {
+ $self->_annotate_ad_history($n);
+ }
+
+ return $self->_store_deferred($n, $rec) if $self->_is_deferring;
+
# We need this to decide whether the new record will fit
# It incidentally populates the offsets table
# Note we have to do this before we alter the cache
+ # 20020324 Wait, but this DOES alter the cache. TODO BUG?
my $oldrec = $self->_fetch($n);
- if (my $cached = $self->_check_cache($n)) {
- my $len_diff = length($rec) - length($cached);
- $self->{cache}{$n} = $rec;
- $self->{cached} += $len_diff;
- $self->_cache_flush if $len_diff > 0 && $self->_cache_too_full;
- }
-
if (not defined $oldrec) {
# We're storing a record beyond the end of the file
$self->_extend_file_to($n+1);
$oldrec = $self->{recsep};
}
+# return if $oldrec eq $rec; # don't bother
my $len_diff = length($rec) - length($oldrec);
# length($oldrec) here is not consistent with text mode TODO XXX BUG
- $self->_twrite($rec, $self->{offsets}[$n], length($oldrec));
-
- # now update the offsets
- # array slice goes from element $n+1 (the first one to move)
- # to the end
- for (@{$self->{offsets}}[$n+1 .. $#{$self->{offsets}}]) {
- $_ += $len_diff;
- }
+ $self->_mtwrite($rec, $self->{offsets}[$n], length($oldrec));
+ $self->_oadjust([$n, 1, $rec]);
+ $self->{cache}->update($n, $rec);
}
sub _store_deferred {
my ($self, $n, $rec) = @_;
- $self->_uncache($n);
+ $self->{cache}->remove($n);
my $old_deferred = $self->{deferred}{$n};
+
+ if (defined $self->{deferred_max} && $n > $self->{deferred_max}) {
+ $self->{deferred_max} = $n;
+ }
$self->{deferred}{$n} = $rec;
- $self->{deferred_s} += length($rec);
- $self->{deferred_s} -= length($old_deferred) if defined $old_deferred;
+
+ my $len_diff = length($rec);
+ $len_diff -= length($old_deferred) if defined $old_deferred;
+ $self->{deferred_s} += $len_diff;
+ $self->{cache}->adj_limit(-$len_diff);
if ($self->{deferred_s} > $self->{dw_size}) {
$self->_flush;
} elsif ($self->_cache_too_full) {
my ($self, $n) = @_;
my $rec = delete $self->{deferred}{$n};
return unless defined $rec;
+
+ if (defined $self->{deferred_max}
+ && $n == $self->{deferred_max}) {
+ undef $self->{deferred_max};
+ }
+
$self->{deferred_s} -= length $rec;
+ $self->{cache}->adj_limit(length $rec);
}
sub FETCHSIZE {
my $self = shift;
- my $n = $#{$self->{offsets}};
- # 20020317 Change this to binary search
- while (defined ($self->_fill_offsets_to($n+1))) {
- ++$n;
- }
- for my $k (keys %{$self->{deferred}}) {
- $n = $k+1 if $n < $k+1;
- }
+ my $n = $self->{eof} ? $#{$self->{offsets}} : $self->_fill_offsets;
+
+ my $top_deferred = $self->_defer_max;
+ $n = $top_deferred+1 if defined $top_deferred && $n < $top_deferred+1;
$n;
}
sub STORESIZE {
my ($self, $len) = @_;
+
+ if ($self->{autodefer}) {
+ $self->_annotate_ad_history('STORESIZE');
+ }
+
my $olen = $self->FETCHSIZE;
return if $len == $olen; # Woo-hoo!
# file gets longer
if ($len > $olen) {
- if ($self->{defer}) {
+ if ($self->_is_deferring) {
for ($olen .. $len-1) {
$self->_store_deferred($_, $self->{recsep});
}
}
# file gets shorter
- if ($self->{defer}) {
+ if ($self->_is_deferring) {
+ # TODO maybe replace this with map-plus-assignment?
for (grep $_ >= $len, keys %{$self->{deferred}}) {
$self->_delete_deferred($_);
}
+ $self->{deferred_max} = $len-1;
}
$self->_seek($len);
$self->_chop_file;
$#{$self->{offsets}} = $len;
# $self->{offsets}[0] = 0; # in case we just chopped this
- my @cached = grep $_ >= $len, keys %{$self->{cache}};
- $self->_uncache(@cached);
+
+ $self->{cache}->remove(grep $_ >= $len, $self->{cache}->ckeys);
}
+### OPTIMIZE ME
+### It should not be necessary to do FETCHSIZE
+### Just seek to the end of the file.
sub PUSH {
my $self = shift;
$self->SPLICE($self->FETCHSIZE, scalar(@_), @_);
-# $self->FETCHSIZE; # av.c takes care of this for me
+
+ # No need to return:
+ # $self->FETCHSIZE; # because av.c takes care of this for me
}
sub POP {
}
sub CLEAR {
- # And enable auto-defer mode, since it's likely that they just
- # did @a = (...);
- #
- # 20020316
- # Maybe that's too much dwimmery. But stuffing a fake '-1' into the
- # autodefer history might not be too much. If you did that, you
- # could also special-case [ -1, 0 ], which might not be too much.
my $self = shift;
+
+ if ($self->{autodefer}) {
+ $self->_annotate_ad_history('CLEAR');
+ }
+
$self->_seekb(0);
$self->_chop_file;
- %{$self->{cache}} = ();
- $self->{cached} = 0;
- @{$self->{lru}} = ();
+ $self->{cache}->set_limit($self->{memory});
+ $self->{cache}->empty;
@{$self->{offsets}} = (0);
%{$self->{deferred}}= ();
$self->{deferred_s} = 0;
+ $self->{deferred_max} = -1;
}
sub EXTEND {
my ($self, $n) = @_;
# No need to pre-extend anything in this case
- return if $self->{defer};
+ return if $self->_is_deferring;
$self->_fill_offsets_to($n);
$self->_extend_file_to($n);
sub DELETE {
my ($self, $n) = @_;
+
+ if ($self->{autodefer}) {
+ $self->_annotate_ad_history('DELETE');
+ }
+
my $lastrec = $self->FETCHSIZE-1;
my $rec = $self->FETCH($n);
- $self->_delete_deferred($n) if $self->{defer};
+ $self->_delete_deferred($n) if $self->_is_deferring;
if ($n == $lastrec) {
$self->_seek($n);
$self->_chop_file;
$#{$self->{offsets}}--;
- $self->_uncache($n);
+ $self->{cache}->remove($n);
# perhaps in this case I should also remove trailing null records?
# 20020316
# Note that delete @a[-3..-1] deletes the records in the wrong order,
sub EXISTS {
my ($self, $n) = @_;
return 1 if exists $self->{deferred}{$n};
- $self->_fill_offsets_to($n); # I think this is unnecessary
$n < $self->FETCHSIZE;
}
sub SPLICE {
my $self = shift;
- $self->_flush if $self->{defer};
+
+ if ($self->{autodefer}) {
+ $self->_annotate_ad_history('SPLICE');
+ }
+
+ $self->_flush if $self->_is_deferring; # move this up?
if (wantarray) {
$self->_chomp(my @a = $self->_splice(@_));
@a;
sub DESTROY {
my $self = shift;
- $self->flush if $self->{defer};
+ $self->flush if $self->_is_deferring;
+ $self->{cache}->delink if defined $self->{cache}; # break circular link
}
sub _splice {
return unless @data;
$pos = $oldsize; # This is what perl does for normal arrays
}
+
+ # The manual is very unclear here
+ if ($nrecs < 0) {
+ $nrecs = $oldsize - $pos + $nrecs;
+ $nrecs = 0 if $nrecs < 0;
+ }
+
+ # nrecs is too big---it really means "until the end"
+ # 20030507
+ if ($nrecs + $pos > $oldsize) {
+ $nrecs = $oldsize - $pos;
+ }
}
$self->_fixrecs(@data);
my $oldlen = 0;
# compute length of data being removed
- # Incidentally fills offsets table
for ($pos .. $pos+$nrecs-1) {
+ last unless defined $self->_fill_offsets_to($_);
my $rec = $self->_fetch($_);
last unless defined $rec;
push @result, $rec;
- $oldlen += length($rec);
- }
-
- # Modify the file
- $self->_twrite($data, $self->{offsets}[$pos], $oldlen);
-
- # update the offsets table part 1
- # compute the offsets of the new records:
- my @new_offsets;
- if (@data) {
- push @new_offsets, $self->{offsets}[$pos];
- for (0 .. $#data-1) {
- push @new_offsets, $new_offsets[-1] + length($data[$_]);
- }
- }
- splice(@{$self->{offsets}}, $pos, $nrecs, @new_offsets);
- # update the offsets table part 2
- # adjust the offsets of the following old records
- for ($pos+@data .. $#{$self->{offsets}}) {
- $self->{offsets}[$_] += $datalen - $oldlen;
+ # Why don't we just use length($rec) here?
+ # Because that record might have come from the cache. _splice
+ # might have been called to flush out the deferred-write records,
+ # and in this case length($rec) is the length of the record to be
+ # *written*, not the length of the actual record in the file. But
+ # the offsets are still true. 20020322
+ $oldlen += $self->{offsets}[$_+1] - $self->{offsets}[$_]
+ if defined $self->{offsets}[$_+1];
}
- # If we scrubbed out all known offsets, regenerate the trivial table
- # that knows that the file does indeed start at 0.
- $self->{offsets}[0] = 0 unless @{$self->{offsets}};
-
- # Perhaps the following cache foolery could be factored out
- # into a bunch of mor opaque cache functions. For example,
- # it's odd to delete a record from the cache and then remove
- # it from the LRU queue later on; there should be a function to
- # do both at once.
+ $self->_fill_offsets_to($pos+$nrecs);
- # update the read cache, part 1
- # modified records
- # Consider this carefully for correctness
- for ($pos .. $pos+$nrecs-1) {
- my $cached = $self->{cache}{$_};
- next unless defined $cached;
- my $new = $data[$_-$pos];
- if (defined $new) {
- $self->{cached} += length($new) - length($cached);
- $self->{cache}{$_} = $new;
- } else {
- $self->_uncache($_);
- }
- }
- # update the read cache, part 2
- # moved records - records past the site of the change
- # need to be renumbered
- # Maybe merge this with the previous block?
- {
- my %adjusted;
- for (keys %{$self->{cache}}) {
- next unless $_ >= $pos + $nrecs;
- $adjusted{$_-$nrecs+@data} = delete $self->{cache}{$_};
+ # Modify the file
+ $self->_mtwrite($data, $self->{offsets}[$pos], $oldlen);
+ # Adjust the offsets table
+ $self->_oadjust([$pos, $nrecs, @data]);
+
+ { # Take this read cache stuff out into a separate function
+ # You made a half-attempt to put it into _oadjust.
+ # Finish something like that up eventually.
+ # STORE also needs to do something similarish
+
+ # update the read cache, part 1
+ # modified records
+ for ($pos .. $pos+$nrecs-1) {
+ my $new = $data[$_-$pos];
+ if (defined $new) {
+ $self->{cache}->update($_, $new);
+ } else {
+ $self->{cache}->remove($_);
+ }
}
- @{$self->{cache}}{keys %adjusted} = values %adjusted;
-# for (keys %{$self->{cache}}) {
-# next unless $_ >= $pos + $nrecs;
-# $self->{cache}{$_-$nrecs+@data} = delete $self->{cache}{$_};
-# }
- }
- # fix the LRU queue
- my(@new, @changed);
- for (@{$self->{lru}}) {
- if ($_ >= $pos + $nrecs) {
- push @new, $_ + @data - $nrecs;
- } elsif ($_ >= $pos) {
- push @changed, $_ if $_ < $pos + @data;
- } else {
- push @new, $_;
+ # update the read cache, part 2
+ # moved records - records past the site of the change
+ # need to be renumbered
+ # Maybe merge this with the previous block?
+ {
+ my @oldkeys = grep $_ >= $pos + $nrecs, $self->{cache}->ckeys;
+ my @newkeys = map $_-$nrecs+@data, @oldkeys;
+ $self->{cache}->rekey(\@oldkeys, \@newkeys);
}
- }
- @{$self->{lru}} = (@new, @changed);
- # Now there might be too much data in the cache, if we spliced out
- # some short records and spliced in some long ones. If so, flush
- # the cache.
- $self->_cache_flush;
+ # Now there might be too much data in the cache, if we spliced out
+ # some short records and spliced in some long ones. If so, flush
+ # the cache.
+ $self->_cache_flush;
+ }
# Yes, the return value of 'splice' *is* actually this complicated
wantarray ? @result : @result ? $result[-1] : undef;
}
+
# write data into the file
-# $data is the data to be written.
+# $data is the data to be written.
# it should be written at position $pos, and should overwrite
# exactly $len of the following bytes.
# Note that if length($data) > $len, the subsequent bytes will have to
my $bufsize = _bufsize($len_diff);
my ($writepos, $readpos) = ($pos, $pos+$len);
my $next_block;
+ my $more_data;
# Seems like there ought to be a way to avoid the repeated code
# and the special case here. The read(1) is also a little weird.
do {
$self->_seekb($readpos);
my $br = read $self->{fh}, $next_block, $bufsize;
- my $more_data = read $self->{fh}, my($dummy), 1;
+ $more_data = read $self->{fh}, my($dummy), 1;
$self->_seekb($writepos);
$self->_write_record($data);
$readpos += $br;
$self->_chop_file if $len_diff < 0;
}
+# _iwrite(D, S, E)
+# Insert text D at position S.
+# Let C = E-S-|D|. If C < 0; die.
+# Data in [S,S+C) is copied to [S+D,S+D+C) = [S+D,E).
+# Data in [S+C = E-D, E) is returned. Data in [E, oo) is untouched.
+#
+# In a later version, don't read the entire intervening area into
+# memory at once; do the copying block by block.
+sub _iwrite {
+ my $self = shift;
+ my ($D, $s, $e) = @_;
+ my $d = length $D;
+ my $c = $e-$s-$d;
+ local *FH = $self->{fh};
+ confess "Not enough space to insert $d bytes between $s and $e"
+ if $c < 0;
+ confess "[$s,$e) is an invalid insertion range" if $e < $s;
+
+ $self->_seekb($s);
+ read FH, my $buf, $e-$s;
+
+ $D .= substr($buf, 0, $c, "");
+
+ $self->_seekb($s);
+ $self->_write_record($D);
+
+ return $buf;
+}
+
+# Like _twrite, but the data-pos-len triple may be repeated; you may
+# write several chunks. All the writing will be done in
+# one pass. Chunks SHALL be in ascending order and SHALL NOT overlap.
+sub _mtwrite {
+ my $self = shift;
+ my $unwritten = "";
+ my $delta = 0;
+
+ @_ % 3 == 0
+ or die "Arguments to _mtwrite did not come in groups of three";
+
+ while (@_) {
+ my ($data, $pos, $len) = splice @_, 0, 3;
+ my $end = $pos + $len; # The OLD end of the segment to be replaced
+ $data = $unwritten . $data;
+ $delta -= length($unwritten);
+ $unwritten = "";
+ $pos += $delta; # This is where the data goes now
+ my $dlen = length $data;
+ $self->_seekb($pos);
+ if ($len >= $dlen) { # the data will fit
+ $self->_write_record($data);
+ $delta += ($dlen - $len); # everything following moves down by this much
+ $data = ""; # All the data in the buffer has been written
+ } else { # won't fit
+ my $writable = substr($data, 0, $len - $delta, "");
+ $self->_write_record($writable);
+ $delta += ($dlen - $len); # everything following moves down by this much
+ }
+
+ # At this point we've written some but maybe not all of the data.
+ # There might be a gap to close up, or $data might still contain a
+ # bunch of unwritten data that didn't fit.
+ my $ndlen = length $data;
+ if ($delta == 0) {
+ $self->_write_record($data);
+ } elsif ($delta < 0) {
+ # upcopy (close up gap)
+ if (@_) {
+ $self->_upcopy($end, $end + $delta, $_[1] - $end);
+ } else {
+ $self->_upcopy($end, $end + $delta);
+ }
+ } else {
+ # downcopy (insert data that didn't fit; replace this data in memory
+ # with _later_ data that doesn't fit)
+ if (@_) {
+ $unwritten = $self->_downcopy($data, $end, $_[1] - $end);
+ } else {
+ # Make the file longer to accomodate the last segment that doesn'
+ $unwritten = $self->_downcopy($data, $end);
+ }
+ }
+ }
+}
+
+# Copy block of data of length $len from position $spos to position $dpos
+# $dpos must be <= $spos
+#
+# If $len is undefined, go all the way to the end of the file
+# and then truncate it ($spos - $dpos bytes will be removed)
+sub _upcopy {
+ my $blocksize = 8192;
+ my ($self, $spos, $dpos, $len) = @_;
+ if ($dpos > $spos) {
+ die "source ($spos) was upstream of destination ($dpos) in _upcopy";
+ } elsif ($dpos == $spos) {
+ return;
+ }
+
+ while (! defined ($len) || $len > 0) {
+ my $readsize = ! defined($len) ? $blocksize
+ : $len > $blocksize ? $blocksize
+ : $len;
+
+ my $fh = $self->{fh};
+ $self->_seekb($spos);
+ my $bytes_read = read $fh, my($data), $readsize;
+ $self->_seekb($dpos);
+ if ($data eq "") {
+ $self->_chop_file;
+ last;
+ }
+ $self->_write_record($data);
+ $spos += $bytes_read;
+ $dpos += $bytes_read;
+ $len -= $bytes_read if defined $len;
+ }
+}
+
+# Write $data into a block of length $len at position $pos,
+# moving everything in the block forwards to make room.
+# Instead of writing the last length($data) bytes from the block
+# (because there isn't room for them any longer) return them.
+sub _downcopy {
+ my $blocksize = 8192;
+ my ($self, $data, $pos, $len) = @_;
+ my $fh = $self->{fh};
+
+ while (! defined $len || $len > 0) {
+ my $readsize = ! defined($len) ? $blocksize
+ : $len > $blocksize? $blocksize : $len;
+ $self->_seekb($pos);
+ read $fh, my($old), $readsize;
+ $data .= $old;
+ $self->_seekb($pos);
+ my $writable = substr($data, 0, $readsize, "");
+ last if $writable eq "";
+ $self->_write_record($writable);
+ $len -= $readsize if defined $len;
+ $pos += $readsize;
+ }
+ return $data;
+}
+
+# Adjust the object data structures following an '_mtwrite'
+# Arguments are
+# [$pos, $nrecs, @length] items
+# indicating that $nrecs records were removed at $recpos (a record offset)
+# and replaced with records of length @length...
+# Arguments guarantee that $recpos is strictly increasing.
+# No return value
+sub _oadjust {
+ my $self = shift;
+ my $delta = 0;
+ my $delta_recs = 0;
+ my $prev_end = -1;
+ my %newkeys;
+
+ for (@_) {
+ my ($pos, $nrecs, @data) = @$_;
+ $pos += $delta_recs;
+
+ # Adjust the offsets of the records after the previous batch up
+ # to the first new one of this batch
+ for my $i ($prev_end+2 .. $pos - 1) {
+ $self->{offsets}[$i] += $delta;
+ $newkey{$i} = $i + $delta_recs;
+ }
+
+ $prev_end = $pos + @data - 1; # last record moved on this pass
+
+ # Remove the offsets for the removed records;
+ # replace with the offsets for the inserted records
+ my @newoff = ($self->{offsets}[$pos] + $delta);
+ for my $i (0 .. $#data) {
+ my $newlen = length $data[$i];
+ push @newoff, $newoff[$i] + $newlen;
+ $delta += $newlen;
+ }
+
+ for my $i ($pos .. $pos+$nrecs-1) {
+ last if $i+1 > $#{$self->{offsets}};
+ my $oldlen = $self->{offsets}[$i+1] - $self->{offsets}[$i];
+ $delta -= $oldlen;
+ }
+
+# # also this data has changed, so update it in the cache
+# for (0 .. $#data) {
+# $self->{cache}->update($pos + $_, $data[$_]);
+# }
+# if ($delta_recs) {
+# my @oldkeys = grep $_ >= $pos + @data, $self->{cache}->ckeys;
+# my @newkeys = map $_ + $delta_recs, @oldkeys;
+# $self->{cache}->rekey(\@oldkeys, \@newkeys);
+# }
+
+ # replace old offsets with new
+ splice @{$self->{offsets}}, $pos, $nrecs+1, @newoff;
+ # What if we just spliced out the end of the offsets table?
+ # shouldn't we clear $self->{eof}? Test for this XXX BUG TODO
+
+ $delta_recs += @data - $nrecs; # net change in total number of records
+ }
+
+ # The trailing records at the very end of the file
+ if ($delta) {
+ for my $i ($prev_end+2 .. $#{$self->{offsets}}) {
+ $self->{offsets}[$i] += $delta;
+ }
+ }
+
+ # If we scrubbed out all known offsets, regenerate the trivial table
+ # that knows that the file does indeed start at 0.
+ $self->{offsets}[0] = 0 unless @{$self->{offsets}};
+ # If the file got longer, the offsets table is no longer complete
+ # $self->{eof} = 0 if $delta_recs > 0;
+
+ # Now there might be too much data in the cache, if we spliced out
+ # some short records and spliced in some long ones. If so, flush
+ # the cache.
+ $self->_cache_flush;
+}
+
# If a record does not already end with the appropriate terminator
# string, append one.
sub _fixrecs {
my $self = shift;
for (@_) {
+ $_ = "" unless defined $_;
$_ .= $self->{recsep}
unless substr($_, - $self->{recseplen}) eq $self->{recsep};
}
defined($o)
or confess("logic error: undefined offset for record $n");
seek $self->{fh}, $o, SEEK_SET
- or die "Couldn't seek filehandle: $!"; # "Should never happen."
+ or confess "Couldn't seek filehandle: $!"; # "Should never happen."
}
+# seek to byte $b in the file
sub _seekb {
my ($self, $b) = @_;
seek $self->{fh}, $b, SEEK_SET
# return the offset of record $n
sub _fill_offsets_to {
my ($self, $n) = @_;
+
+ return $self->{offsets}[$n] if $self->{eof};
+
my $fh = $self->{fh};
local *OFF = $self->{offsets};
my $rec;
until ($#OFF >= $n) {
- my $o = $OFF[-1];
$self->_seek(-1); # tricky -- see comment at _seek
$rec = $self->_read_record;
if (defined $rec) {
- push @OFF, tell $fh;
+ push @OFF, int(tell $fh); # Tels says that int() saves memory here
} else {
+ $self->{eof} = 1;
return; # It turns out there is no such record
}
}
# we have now read all the records up to record n-1,
# so we can return the offset of record n
- return $OFF[$n];
+ $OFF[$n];
+}
+
+sub _fill_offsets {
+ my ($self) = @_;
+
+ my $fh = $self->{fh};
+ local *OFF = $self->{offsets};
+
+ $self->_seek(-1); # tricky -- see comment at _seek
+
+ # Tels says that inlining read_record() would make this loop
+ # five times faster. 20030508
+ while ( defined $self->_read_record()) {
+ # int() saves us memory here
+ push @OFF, int(tell $fh);
+ }
+
+ $self->{eof} = 1;
+ $#OFF;
}
# assumes that $rec is already suitably terminated
sub _write_record {
my ($self, $rec) = @_;
my $fh = $self->{fh};
+ local $\ = "";
print $fh $rec
or die "Couldn't write record: $!"; # "Should never happen."
-
+# $self->{_written} += length($rec);
}
sub _read_record {
my $fh = $self->{fh};
$rec = <$fh>;
}
+ return unless defined $rec;
+ if (! $self->{sawlastrec} &&
+ substr($rec, -$self->{recseplen}) ne $self->{recsep}) {
+ # improperly terminated final record --- quietly fix it.
+# my $ac = substr($rec, -$self->{recseplen});
+# $ac =~ s/\n/\\n/g;
+ $self->{sawlastrec} = 1;
+ unless ($self->{rdonly}) {
+ local $\ = "";
+ my $fh = $self->{fh};
+ print $fh $self->{recsep};
+ }
+ $rec .= $self->{recsep};
+ }
+# $self->{_read} += length($rec) if defined $rec;
$rec;
}
-################################################################
-#
-# Read cache management
-
-# Insert a record into the cache at position $n
-# Only appropriate when no data is cached for $n already
-sub _cache_insert {
- my ($self, $n, $rec) = @_;
-
- # Do not cache records that are too big to fit in the cache.
- return unless length $rec <= $self->{memory};
-
- $self->{cache}{$n} = $rec;
- $self->{cached} += length $rec;
- push @{$self->{lru}}, $n; # most-recently-used is at the END
-
- $self->_cache_flush if $self->_cache_too_full;
-}
-
-# Remove cached data for record $n, if there is any
-# (It is OK if $n is not in the cache at all)
-sub _uncache {
+sub _rw_stats {
my $self = shift;
- for my $n (@_) {
- my $cached = delete $self->{cache}{$n};
- next unless defined $cached;
- @{$self->{lru}} = grep $_ != $n, @{$self->{lru}};
- $self->{cached} -= length($cached);
- }
+ @{$self}{'_read', '_written'};
}
-# _check_cache promotes record $n to MRU. Is this correct behavior?
-sub _check_cache {
- my ($self, $n) = @_;
- my $rec;
- return unless defined($rec = $self->{cache}{$n});
+################################################################
+#
+# Read cache management
- # cache hit; update LRU queue and return $rec
- # replace this with a heap in a later version
- # 20020317 This should be a separate method
- @{$self->{lru}} = ((grep $_ ne $n, @{$self->{lru}}), $n);
- $rec;
+sub _cache_flush {
+ my ($self) = @_;
+ $self->{cache}->reduce_size_to($self->{memory} - $self->{deferred_s});
}
sub _cache_too_full {
my $self = shift;
- $self->{cached} + $self->{deferred_s} > $self->{memory};
-}
-
-sub _cache_flush {
- my ($self) = @_;
- while ($self->_cache_too_full) {
- my $lru = shift @{$self->{lru}};
- my $rec = delete $self->{cache}{$lru};
- $self->{cached} -= length $rec;
- }
+ $self->{cache}->bytes + $self->{deferred_s} >= $self->{memory};
}
################################################################
my $pos = $self->{offsets}[-1];
# the offsets table has one entry more than the total number of records
- $extras = $n - $#{$self->{offsets}};
+ my $extras = $n - $#{$self->{offsets}};
# Todo : just use $self->{recsep} x $extras here?
while ($extras-- > 0) {
$self->_write_record($self->{recsep});
- push @{$self->{offsets}}, tell $self->{fh};
+ push @{$self->{offsets}}, int(tell $self->{fh});
}
}
# The result should be at least $n.
sub _bufsize {
my $n = shift;
- return 8192 if $n < 0;
+ return 8192 if $n <= 0;
my $b = $n & ~8191;
$b += 8192 if $n & 8191;
$b;
}
my $fh = $self->{fh};
$op = LOCK_EX unless defined $op;
- flock $fh, $op;
+ my $locked = flock $fh, $op;
+
+ if ($locked && ($op & (LOCK_EX | LOCK_SH))) {
+ # If you're locking the file, then presumably it's because
+ # there might have been a write access by another process.
+ # In that case, the read cache contents and the offsets table
+ # might be invalid, so discard them. 20030508
+ $self->{offsets} = [0];
+ $self->{cache}->empty;
+ }
+
+ $locked;
}
# Get/set autochomp option
}
}
+# Get offset table entries; returns offset of nth record
+sub offset {
+ my ($self, $n) = @_;
+
+ if ($#{$self->{offsets}} < $n) {
+ return if $self->{eof}; # request for record beyond the end of file
+ my $o = $self->_fill_offsets_to($n);
+ # If it's still undefined, there is no such record, so return 'undef'
+ return unless defined $o;
+ }
+
+ $self->{offsets}[$n];
+}
+
+sub discard_offsets {
+ my $self = shift;
+ $self->{offsets} = [0];
+}
+
################################################################
#
# Matters related to deferred writing
# Defer writes
sub defer {
my $self = shift;
+ $self->_stop_autodeferring;
+ @{$self->{ad_history}} = ();
$self->{defer} = 1;
}
#
# This could be better optimized to write the file in one pass, instead
# of one pass per block of records. But that will require modifications
-# to _twrite, so I should have a good _twite test suite first.
+# to _twrite, so I should have a good _twrite test suite first.
sub flush {
my $self = shift;
$self->{defer} = 0;
}
-sub _flush {
+sub _old_flush {
my $self = shift;
my @writable = sort {$a<=>$b} (keys %{$self->{deferred}});
-
+
while (@writable) {
# gather all consecutive records from the front of @writable
my $first_rec = shift @writable;
$self->_discard; # clear out defered-write-cache
}
+sub _flush {
+ my $self = shift;
+ my @writable = sort {$a<=>$b} (keys %{$self->{deferred}});
+ my @args;
+ my @adjust;
+
+ while (@writable) {
+ # gather all consecutive records from the front of @writable
+ my $first_rec = shift @writable;
+ my $last_rec = $first_rec+1;
+ ++$last_rec, shift @writable while @writable && $last_rec == $writable[0];
+ --$last_rec;
+ my $end = $self->_fill_offsets_to($last_rec+1);
+ if (not defined $end) {
+ $self->_extend_file_to($last_rec);
+ $end = $self->{offsets}[$last_rec];
+ }
+ my ($start) = $self->{offsets}[$first_rec];
+ push @args,
+ join("", @{$self->{deferred}}{$first_rec .. $last_rec}), # data
+ $start, # position
+ $end-$start; # length
+ push @adjust, [$first_rec, # starting at this position...
+ $last_rec-$first_rec+1, # this many records...
+ # are replaced with these...
+ @{$self->{deferred}}{$first_rec .. $last_rec},
+ ];
+ }
+
+ $self->_mtwrite(@args); # write multiple record groups
+ $self->_discard; # clear out defered-write-cache
+ $self->_oadjust(@adjust);
+}
+
# Discard deferred writes and disable future deferred writes
sub discard {
my $self = shift;
# Discard deferred writes, but retain old deferred writing mode
sub _discard {
my $self = shift;
- $self->{deferred} = {};
- $self->{deferred_s} = 0;
+ %{$self->{deferred}} = ();
+ $self->{deferred_s} = 0;
+ $self->{deferred_max} = -1;
+ $self->{cache}->set_limit($self->{memory});
+}
+
+# Deferred writing is enabled, either explicitly ($self->{defer})
+# or automatically ($self->{autodeferring})
+sub _is_deferring {
+ my $self = shift;
+ $self->{defer} || $self->{autodeferring};
+}
+
+# The largest record number of any deferred record
+sub _defer_max {
+ my $self = shift;
+ return $self->{deferred_max} if defined $self->{deferred_max};
+ my $max = -1;
+ for my $key (keys %{$self->{deferred}}) {
+ $max = $key if $key > $max;
+ }
+ $self->{deferred_max} = $max;
+ $max;
+}
+
+################################################################
+#
+# Matters related to autodeferment
+#
+
+# Get/set autodefer option
+sub autodefer {
+ my $self = shift;
+ if (@_) {
+ my $old = $self->{autodefer};
+ $self->{autodefer} = shift;
+ if ($old) {
+ $self->_stop_autodeferring;
+ @{$self->{ad_history}} = ();
+ }
+ $old;
+ } else {
+ $self->{autodefer};
+ }
+}
+
+# The user is trying to store record #$n Record that in the history,
+# and then enable (or disable) autodeferment if that seems useful.
+# Note that it's OK for $n to be a non-number, as long as the function
+# is prepared to deal with that. Nobody else looks at the ad_history.
+#
+# Now, what does the ad_history mean, and what is this function doing?
+# Essentially, the idea is to enable autodeferring when we see that the
+# user has made three consecutive STORE calls to three consecutive records.
+# ("Three" is actually ->{autodefer_threshhold}.)
+# A STORE call for record #$n inserts $n into the autodefer history,
+# and if the history contains three consecutive records, we enable
+# autodeferment. An ad_history of [X, Y] means that the most recent
+# STOREs were for records X, X+1, ..., Y, in that order.
+#
+# Inserting a nonconsecutive number erases the history and starts over.
+#
+# Performing a special operation like SPLICE erases the history.
+#
+# There's one special case: CLEAR means that CLEAR was just called.
+# In this case, we prime the history with [-2, -1] so that if the next
+# write is for record 0, autodeferring goes on immediately. This is for
+# the common special case of "@a = (...)".
+#
+sub _annotate_ad_history {
+ my ($self, $n) = @_;
+ return unless $self->{autodefer}; # feature is disabled
+ return if $self->{defer}; # already in explicit defer mode
+ return unless $self->{offsets}[-1] >= $self->{autodefer_filelen_threshhold};
+
+ local *H = $self->{ad_history};
+ if ($n eq 'CLEAR') {
+ @H = (-2, -1); # prime the history with fake records
+ $self->_stop_autodeferring;
+ } elsif ($n =~ /^\d+$/) {
+ if (@H == 0) {
+ @H = ($n, $n);
+ } else { # @H == 2
+ if ($H[1] == $n-1) { # another consecutive record
+ $H[1]++;
+ if ($H[1] - $H[0] + 1 >= $self->{autodefer_threshhold}) {
+ $self->{autodeferring} = 1;
+ }
+ } else { # nonconsecutive- erase and start over
+ @H = ($n, $n);
+ $self->_stop_autodeferring;
+ }
+ }
+ } else { # SPLICE or STORESIZE or some such
+ @H = ();
+ $self->_stop_autodeferring;
+ }
+}
+
+# If autodeferring was enabled, cut it out and discard the history
+sub _stop_autodeferring {
+ my $self = shift;
+ if ($self->{autodeferring}) {
+ $self->_flush;
+ }
+ $self->{autodeferring} = 0;
}
-# Not yet implemented
-sub autodefer { }
+################################################################
+
# This is NOT a method. It is here for two reasons:
# 1. To factor a fairly complicated block out of the constructor
# with the existing test suite.
sub _check_integrity {
my ($self, $file, $warn) = @_;
+ my $rsl = $self->{recseplen};
+ my $rs = $self->{recsep};
my $good = 1;
+ local *_; # local $_ does not work here
+ local $DIAGNOSTIC = 1;
+
+ if (not defined $rs) {
+ _ci_warn("recsep is undef!");
+ $good = 0;
+ } elsif ($rs eq "") {
+ _ci_warn("recsep is empty!");
+ $good = 0;
+ } elsif ($rsl != length $rs) {
+ my $ln = length $rs;
+ _ci_warn("recsep <$rs> has length $ln, should be $rsl");
+ $good = 0;
+ }
if (not defined $self->{offsets}[0]) {
_ci_warn("offset 0 is missing!");
$good = 0;
+
} elsif ($self->{offsets}[0] != 0) {
_ci_warn("rec 0: offset <$self->{offsets}[0]> s/b 0!");
$good = 0;
}
- local *_;
- local *F = $self->{fh};
- seek F, 0, SEEK_SET;
- local $/ = $self->{recsep};
- my $rsl = $self->{recseplen};
- local $. = 0;
-
- while (<F>) {
- my $n = $. - 1;
- my $cached = $self->{cache}{$n};
- my $offset = $self->{offsets}[$.];
- my $ao = tell F;
- if (defined $offset && $offset != $ao) {
- _ci_warn("rec $n: offset <$offset> actual <$ao>");
- $good = 0;
- }
- if (defined $cached && $_ ne $cached) {
- $good = 0;
- chomp $cached;
- chomp;
- _ci_warn("rec $n: cached <$cached> actual <$_>");
+ my $cached = 0;
+ {
+ local *F = $self->{fh};
+ seek F, 0, SEEK_SET;
+ local $. = 0;
+ local $/ = $rs;
+
+ while (<F>) {
+ my $n = $. - 1;
+ my $cached = $self->{cache}->_produce($n);
+ my $offset = $self->{offsets}[$.];
+ my $ao = tell F;
+ if (defined $offset && $offset != $ao) {
+ _ci_warn("rec $n: offset <$offset> actual <$ao>");
+ $good = 0;
+ }
+ if (defined $cached && $_ ne $cached && ! $self->{deferred}{$n}) {
+ $good = 0;
+ _ci_warn("rec $n: cached <$cached> actual <$_>");
+ }
+ if (defined $cached && substr($cached, -$rsl) ne $rs) {
+ $good = 0;
+ _ci_warn("rec $n in the cache is missing the record separator");
+ }
+ if (! defined $offset && $self->{eof}) {
+ $good = 0;
+ _ci_warn("The offset table was marked complete, but it is missing element $.");
+ }
}
- if (defined $cached && substr($cached, -$rsl) ne $/) {
- _ci_warn("rec $n in the cache is missing the record separator");
+ if (@{$self->{offsets}} > $.+1) {
+ $good = 0;
+ my $n = @{$self->{offsets}};
+ _ci_warn("The offset table has $n items, but the file has only $.");
}
- }
- my $cached = 0;
- while (my ($n, $r) = each %{$self->{cache}}) {
- $cached += length($r);
- next if $n+1 <= $.; # checked this already
- _ci_warn("spurious caching of record $n");
- $good = 0;
- }
- if ($cached != $self->{cached}) {
- _ci_warn("cache size is $self->{cached}, should be $cached");
- $good = 0;
- }
-
- my (%seen, @duplicate);
- for (@{$self->{lru}}) {
- $seen{$_}++;
- if (not exists $self->{cache}{$_}) {
- _ci_warn("$_ is mentioned in the LRU queue, but not in the cache");
+ my $deferring = $self->_is_deferring;
+ for my $n ($self->{cache}->ckeys) {
+ my $r = $self->{cache}->_produce($n);
+ $cached += length($r);
+ next if $n+1 <= $.; # checked this already
+ _ci_warn("spurious caching of record $n");
$good = 0;
}
- }
- @duplicate = grep $seen{$_}>1, keys %seen;
- if (@duplicate) {
- my $records = @duplicate == 1 ? 'Record' : 'Records';
- my $appear = @duplicate == 1 ? 'appears' : 'appear';
- _ci_warn("$records @duplicate $appear multiple times in LRU queue: @{$self->{lru}}");
- $good = 0;
- }
- for (keys %{$self->{cache}}) {
- unless (exists $seen{$_}) {
- _ci_warn("record $_ is in the cache but not the LRU queue");
+ my $b = $self->{cache}->bytes;
+ if ($cached != $b) {
+ _ci_warn("cache size is $b, should be $cached");
$good = 0;
}
}
+ # That cache has its own set of tests
+ $good = 0 unless $self->{cache}->_check_integrity;
+
# Now let's check the deferbuffer
# Unless deferred writing is enabled, it should be empty
- if (! $self->{defer} && %{$self->{deferred}}) {
+ if (! $self->_is_deferring && %{$self->{deferred}}) {
_ci_warn("deferred writing disabled, but deferbuffer nonempty");
$good = 0;
}
my $deferred_s = 0;
while (my ($n, $r) = each %{$self->{deferred}}) {
$deferred_s += length($r);
- if (exists $self->{cache}{$n}) {
+ if (defined $self->{cache}->_produce($n)) {
_ci_warn("record $n is in the deferbuffer *and* the readcache");
$good = 0;
}
- if (substr($r, -$rsl) ne $/) {
+ if (substr($r, -$rsl) ne $rs) {
_ci_warn("rec $n in the deferbuffer is missing the record separator");
$good = 0;
}
$good = 0;
}
+ # Stuff related to autodeferment
+ if (!$self->{autodefer} && @{$self->{ad_history}}) {
+ _ci_warn("autodefer is disabled, but ad_history is nonempty");
+ $good = 0;
+ }
+ if ($self->{autodeferring} && $self->{defer}) {
+ _ci_warn("both autodeferring and explicit deferring are active");
+ $good = 0;
+ }
+ if (@{$self->{ad_history}} == 0) {
+ # That's OK, no additional tests required
+ } elsif (@{$self->{ad_history}} == 2) {
+ my @non_number = grep !/^-?\d+$/, @{$self->{ad_history}};
+ if (@non_number) {
+ my $msg;
+ { local $" = ')(';
+ $msg = "ad_history contains non-numbers (@{$self->{ad_history}})";
+ }
+ _ci_warn($msg);
+ $good = 0;
+ } elsif ($self->{ad_history}[1] < $self->{ad_history}[0]) {
+ _ci_warn("ad_history has nonsensical values @{$self->{ad_history}}");
+ $good = 0;
+ }
+ } else {
+ _ci_warn("ad_history has bad length <@{$self->{ad_history}}>");
+ $good = 0;
+ }
+
$good;
}
+################################################################
+#
+# Tie::File::Cache
+#
+# Read cache
+
+package Tie::File::Cache;
+$Tie::File::Cache::VERSION = $Tie::File::VERSION;
+use Carp ':DEFAULT', 'confess';
+
+sub HEAP () { 0 }
+sub HASH () { 1 }
+sub MAX () { 2 }
+sub BYTES() { 3 }
+#sub STAT () { 4 } # Array with request statistics for each record
+#sub MISS () { 5 } # Total number of cache misses
+#sub REQ () { 6 } # Total number of cache requests
+use strict 'vars';
+
+sub new {
+ my ($pack, $max) = @_;
+ local *_;
+ croak "missing argument to ->new" unless defined $max;
+ my $self = [];
+ bless $self => $pack;
+ @$self = (Tie::File::Heap->new($self), {}, $max, 0);
+ $self;
+}
+
+sub adj_limit {
+ my ($self, $n) = @_;
+ $self->[MAX] += $n;
+}
+
+sub set_limit {
+ my ($self, $n) = @_;
+ $self->[MAX] = $n;
+}
+
+# For internal use only
+# Will be called by the heap structure to notify us that a certain
+# piece of data has moved from one heap element to another.
+# $k is the hash key of the item
+# $n is the new index into the heap at which it is stored
+# If $n is undefined, the item has been removed from the heap.
+sub _heap_move {
+ my ($self, $k, $n) = @_;
+ if (defined $n) {
+ $self->[HASH]{$k} = $n;
+ } else {
+ delete $self->[HASH]{$k};
+ }
+}
+
+sub insert {
+ my ($self, $key, $val) = @_;
+ local *_;
+ croak "missing argument to ->insert" unless defined $key;
+ unless (defined $self->[MAX]) {
+ confess "undefined max" ;
+ }
+ confess "undefined val" unless defined $val;
+ return if length($val) > $self->[MAX];
+
+# if ($self->[STAT]) {
+# $self->[STAT][$key] = 1;
+# return;
+# }
+
+ my $oldnode = $self->[HASH]{$key};
+ if (defined $oldnode) {
+ my $oldval = $self->[HEAP]->set_val($oldnode, $val);
+ $self->[BYTES] -= length($oldval);
+ } else {
+ $self->[HEAP]->insert($key, $val);
+ }
+ $self->[BYTES] += length($val);
+ $self->flush if $self->[BYTES] > $self->[MAX];
+}
+
+sub expire {
+ my $self = shift;
+ my $old_data = $self->[HEAP]->popheap;
+ return unless defined $old_data;
+ $self->[BYTES] -= length $old_data;
+ $old_data;
+}
+
+sub remove {
+ my ($self, @keys) = @_;
+ my @result;
+
+# if ($self->[STAT]) {
+# for my $key (@keys) {
+# $self->[STAT][$key] = 0;
+# }
+# return;
+# }
+
+ for my $key (@keys) {
+ next unless exists $self->[HASH]{$key};
+ my $old_data = $self->[HEAP]->remove($self->[HASH]{$key});
+ $self->[BYTES] -= length $old_data;
+ push @result, $old_data;
+ }
+ @result;
+}
+
+sub lookup {
+ my ($self, $key) = @_;
+ local *_;
+ croak "missing argument to ->lookup" unless defined $key;
+
+# if ($self->[STAT]) {
+# $self->[MISS]++ if $self->[STAT][$key]++ == 0;
+# $self->[REQ]++;
+# my $hit_rate = 1 - $self->[MISS] / $self->[REQ];
+# # Do some testing to determine this threshhold
+# $#$self = STAT - 1 if $hit_rate > 0.20;
+# }
+
+ if (exists $self->[HASH]{$key}) {
+ $self->[HEAP]->lookup($self->[HASH]{$key});
+ } else {
+ return;
+ }
+}
+
+# For internal use only
+sub _produce {
+ my ($self, $key) = @_;
+ my $loc = $self->[HASH]{$key};
+ return unless defined $loc;
+ $self->[HEAP][$loc][2];
+}
+
+# For internal use only
+sub _promote {
+ my ($self, $key) = @_;
+ $self->[HEAP]->promote($self->[HASH]{$key});
+}
+
+sub empty {
+ my ($self) = @_;
+ %{$self->[HASH]} = ();
+ $self->[BYTES] = 0;
+ $self->[HEAP]->empty;
+# @{$self->[STAT]} = ();
+# $self->[MISS] = 0;
+# $self->[REQ] = 0;
+}
+
+sub is_empty {
+ my ($self) = @_;
+ keys %{$self->[HASH]} == 0;
+}
+
+sub update {
+ my ($self, $key, $val) = @_;
+ local *_;
+ croak "missing argument to ->update" unless defined $key;
+ if (length($val) > $self->[MAX]) {
+ my ($oldval) = $self->remove($key);
+ $self->[BYTES] -= length($oldval) if defined $oldval;
+ } elsif (exists $self->[HASH]{$key}) {
+ my $oldval = $self->[HEAP]->set_val($self->[HASH]{$key}, $val);
+ $self->[BYTES] += length($val);
+ $self->[BYTES] -= length($oldval) if defined $oldval;
+ } else {
+ $self->[HEAP]->insert($key, $val);
+ $self->[BYTES] += length($val);
+ }
+ $self->flush;
+}
+
+sub rekey {
+ my ($self, $okeys, $nkeys) = @_;
+ local *_;
+ my %map;
+ @map{@$okeys} = @$nkeys;
+ croak "missing argument to ->rekey" unless defined $nkeys;
+ croak "length mismatch in ->rekey arguments" unless @$nkeys == @$okeys;
+ my %adjusted; # map new keys to heap indices
+ # You should be able to cut this to one loop TODO XXX
+ for (0 .. $#$okeys) {
+ $adjusted{$nkeys->[$_]} = delete $self->[HASH]{$okeys->[$_]};
+ }
+ while (my ($nk, $ix) = each %adjusted) {
+ # @{$self->[HASH]}{keys %adjusted} = values %adjusted;
+ $self->[HEAP]->rekey($ix, $nk);
+ $self->[HASH]{$nk} = $ix;
+ }
+}
+
+sub ckeys {
+ my $self = shift;
+ my @a = keys %{$self->[HASH]};
+ @a;
+}
+
+# Return total amount of cached data
+sub bytes {
+ my $self = shift;
+ $self->[BYTES];
+}
+
+# Expire oldest item from cache until cache size is smaller than $max
+sub reduce_size_to {
+ my ($self, $max) = @_;
+ until ($self->[BYTES] <= $max) {
+ # Note that Tie::File::Cache::expire has been inlined here
+ my $old_data = $self->[HEAP]->popheap;
+ return unless defined $old_data;
+ $self->[BYTES] -= length $old_data;
+ }
+}
+
+# Why not just $self->reduce_size_to($self->[MAX])?
+# Try this when things stabilize TODO XXX
+# If the cache is too full, expire the oldest records
+sub flush {
+ my $self = shift;
+ $self->reduce_size_to($self->[MAX]) if $self->[BYTES] > $self->[MAX];
+}
+
+# For internal use only
+sub _produce_lru {
+ my $self = shift;
+ $self->[HEAP]->expire_order;
+}
+
+BEGIN { *_ci_warn = \&Tie::File::_ci_warn }
+
+sub _check_integrity { # For CACHE
+ my $self = shift;
+ my $good = 1;
+
+ # Test HEAP
+ $self->[HEAP]->_check_integrity or $good = 0;
+
+ # Test HASH
+ my $bytes = 0;
+ for my $k (keys %{$self->[HASH]}) {
+ if ($k ne '0' && $k !~ /^[1-9][0-9]*$/) {
+ $good = 0;
+ _ci_warn "Cache hash key <$k> is non-numeric";
+ }
+
+ my $h = $self->[HASH]{$k};
+ if (! defined $h) {
+ $good = 0;
+ _ci_warn "Heap index number for key $k is undefined";
+ } elsif ($h == 0) {
+ $good = 0;
+ _ci_warn "Heap index number for key $k is zero";
+ } else {
+ my $j = $self->[HEAP][$h];
+ if (! defined $j) {
+ $good = 0;
+ _ci_warn "Heap contents key $k (=> $h) are undefined";
+ } else {
+ $bytes += length($j->[2]);
+ if ($k ne $j->[1]) {
+ $good = 0;
+ _ci_warn "Heap contents key $k (=> $h) is $j->[1], should be $k";
+ }
+ }
+ }
+ }
+
+ # Test BYTES
+ if ($bytes != $self->[BYTES]) {
+ $good = 0;
+ _ci_warn "Total data in cache is $bytes, expected $self->[BYTES]";
+ }
+
+ # Test MAX
+ if ($bytes > $self->[MAX]) {
+ $good = 0;
+ _ci_warn "Total data in cache is $bytes, exceeds maximum $self->[MAX]";
+ }
+
+ return $good;
+}
+
+sub delink {
+ my $self = shift;
+ $self->[HEAP] = undef; # Bye bye heap
+}
+
+################################################################
+#
+# Tie::File::Heap
+#
+# Heap data structure for use by cache LRU routines
+
+package Tie::File::Heap;
+use Carp ':DEFAULT', 'confess';
+$Tie::File::Heap::VERSION = $Tie::File::Cache::VERSION;
+sub SEQ () { 0 };
+sub KEY () { 1 };
+sub DAT () { 2 };
+
+sub new {
+ my ($pack, $cache) = @_;
+ die "$pack: Parent cache object $cache does not support _heap_move method"
+ unless eval { $cache->can('_heap_move') };
+ my $self = [[0,$cache,0]];
+ bless $self => $pack;
+}
+
+# Allocate a new sequence number, larger than all previously allocated numbers
+sub _nseq {
+ my $self = shift;
+ $self->[0][0]++;
+}
+
+sub _cache {
+ my $self = shift;
+ $self->[0][1];
+}
+
+sub _nelts {
+ my $self = shift;
+ $self->[0][2];
+}
+
+sub _nelts_inc {
+ my $self = shift;
+ ++$self->[0][2];
+}
+
+sub _nelts_dec {
+ my $self = shift;
+ --$self->[0][2];
+}
+
+sub is_empty {
+ my $self = shift;
+ $self->_nelts == 0;
+}
+
+sub empty {
+ my $self = shift;
+ $#$self = 0;
+ $self->[0][2] = 0;
+ $self->[0][0] = 0; # might as well reset the sequence numbers
+}
+
+# notify the parent cache object that we moved something
+sub _heap_move {
+ my $self = shift;
+ $self->_cache->_heap_move(@_);
+}
+
+# Insert a piece of data into the heap with the indicated sequence number.
+# The item with the smallest sequence number is always at the top.
+# If no sequence number is specified, allocate a new one and insert the
+# item at the bottom.
+sub insert {
+ my ($self, $key, $data, $seq) = @_;
+ $seq = $self->_nseq unless defined $seq;
+ $self->_insert_new([$seq, $key, $data]);
+}
+
+# Insert a new, fresh item at the bottom of the heap
+sub _insert_new {
+ my ($self, $item) = @_;
+ my $i = @$self;
+ $i = int($i/2) until defined $self->[$i/2];
+ $self->[$i] = $item;
+ $self->[0][1]->_heap_move($self->[$i][KEY], $i);
+ $self->_nelts_inc;
+}
+
+# Insert [$data, $seq] pair at or below item $i in the heap.
+# If $i is omitted, default to 1 (the top element.)
+sub _insert {
+ my ($self, $item, $i) = @_;
+# $self->_check_loc($i) if defined $i;
+ $i = 1 unless defined $i;
+ until (! defined $self->[$i]) {
+ if ($self->[$i][SEQ] > $item->[SEQ]) { # inserted item is older
+ ($self->[$i], $item) = ($item, $self->[$i]);
+ $self->[0][1]->_heap_move($self->[$i][KEY], $i);
+ }
+ # If either is undefined, go that way. Otherwise, choose at random
+ my $dir;
+ $dir = 0 if !defined $self->[2*$i];
+ $dir = 1 if !defined $self->[2*$i+1];
+ $dir = int(rand(2)) unless defined $dir;
+ $i = 2*$i + $dir;
+ }
+ $self->[$i] = $item;
+ $self->[0][1]->_heap_move($self->[$i][KEY], $i);
+ $self->_nelts_inc;
+}
+
+# Remove the item at node $i from the heap, moving child items upwards.
+# The item with the smallest sequence number is always at the top.
+# Moving items upwards maintains this condition.
+# Return the removed item. Return undef if there was no item at node $i.
+sub remove {
+ my ($self, $i) = @_;
+ $i = 1 unless defined $i;
+ my $top = $self->[$i];
+ return unless defined $top;
+ while (1) {
+ my $ii;
+ my ($L, $R) = (2*$i, 2*$i+1);
+
+ # If either is undefined, go the other way.
+ # Otherwise, go towards the smallest.
+ last unless defined $self->[$L] || defined $self->[$R];
+ $ii = $R if not defined $self->[$L];
+ $ii = $L if not defined $self->[$R];
+ unless (defined $ii) {
+ $ii = $self->[$L][SEQ] < $self->[$R][SEQ] ? $L : $R;
+ }
+
+ $self->[$i] = $self->[$ii]; # Promote child to fill vacated spot
+ $self->[0][1]->_heap_move($self->[$i][KEY], $i);
+ $i = $ii; # Fill new vacated spot
+ }
+ $self->[0][1]->_heap_move($top->[KEY], undef);
+ undef $self->[$i];
+ $self->_nelts_dec;
+ return $top->[DAT];
+}
+
+sub popheap {
+ my $self = shift;
+ $self->remove(1);
+}
+
+# set the sequence number of the indicated item to a higher number
+# than any other item in the heap, and bubble the item down to the
+# bottom.
+sub promote {
+ my ($self, $n) = @_;
+# $self->_check_loc($n);
+ $self->[$n][SEQ] = $self->_nseq;
+ my $i = $n;
+ while (1) {
+ my ($L, $R) = (2*$i, 2*$i+1);
+ my $dir;
+ last unless defined $self->[$L] || defined $self->[$R];
+ $dir = $R unless defined $self->[$L];
+ $dir = $L unless defined $self->[$R];
+ unless (defined $dir) {
+ $dir = $self->[$L][SEQ] < $self->[$R][SEQ] ? $L : $R;
+ }
+ @{$self}[$i, $dir] = @{$self}[$dir, $i];
+ for ($i, $dir) {
+ $self->[0][1]->_heap_move($self->[$_][KEY], $_) if defined $self->[$_];
+ }
+ $i = $dir;
+ }
+}
+
+# Return item $n from the heap, promoting its LRU status
+sub lookup {
+ my ($self, $n) = @_;
+# $self->_check_loc($n);
+ my $val = $self->[$n];
+ $self->promote($n);
+ $val->[DAT];
+}
+
+
+# Assign a new value for node $n, promoting it to the bottom of the heap
+sub set_val {
+ my ($self, $n, $val) = @_;
+# $self->_check_loc($n);
+ my $oval = $self->[$n][DAT];
+ $self->[$n][DAT] = $val;
+ $self->promote($n);
+ return $oval;
+}
+
+# The hask key has changed for an item;
+# alter the heap's record of the hash key
+sub rekey {
+ my ($self, $n, $new_key) = @_;
+# $self->_check_loc($n);
+ $self->[$n][KEY] = $new_key;
+}
+
+sub _check_loc {
+ my ($self, $n) = @_;
+ unless (1 || defined $self->[$n]) {
+ confess "_check_loc($n) failed";
+ }
+}
+
+BEGIN { *_ci_warn = \&Tie::File::_ci_warn }
+
+sub _check_integrity {
+ my $self = shift;
+ my $good = 1;
+ my %seq;
+
+ unless (eval {$self->[0][1]->isa("Tie::File::Cache")}) {
+ _ci_warn "Element 0 of heap corrupt";
+ $good = 0;
+ }
+ $good = 0 unless $self->_satisfies_heap_condition(1);
+ for my $i (2 .. $#{$self}) {
+ my $p = int($i/2); # index of parent node
+ if (defined $self->[$i] && ! defined $self->[$p]) {
+ _ci_warn "Element $i of heap defined, but parent $p isn't";
+ $good = 0;
+ }
+
+ if (defined $self->[$i]) {
+ if ($seq{$self->[$i][SEQ]}) {
+ my $seq = $self->[$i][SEQ];
+ _ci_warn "Nodes $i and $seq{$seq} both have SEQ=$seq";
+ $good = 0;
+ } else {
+ $seq{$self->[$i][SEQ]} = $i;
+ }
+ }
+ }
+
+ return $good;
+}
+
+sub _satisfies_heap_condition {
+ my $self = shift;
+ my $n = shift || 1;
+ my $good = 1;
+ for (0, 1) {
+ my $c = $n*2 + $_;
+ next unless defined $self->[$c];
+ if ($self->[$n][SEQ] >= $self->[$c]) {
+ _ci_warn "Node $n of heap does not predate node $c";
+ $good = 0 ;
+ }
+ $good = 0 unless $self->_satisfies_heap_condition($c);
+ }
+ return $good;
+}
+
+# Return a list of all the values, sorted by expiration order
+sub expire_order {
+ my $self = shift;
+ my @nodes = sort {$a->[SEQ] <=> $b->[SEQ]} $self->_nodes;
+ map { $_->[KEY] } @nodes;
+}
+
+sub _nodes {
+ my $self = shift;
+ my $i = shift || 1;
+ return unless defined $self->[$i];
+ ($self->[$i], $self->_nodes($i*2), $self->_nodes($i*2+1));
+}
+
"Cogito, ergo sum."; # don't forget to return a true value from the file
+__END__
+
=head1 NAME
Tie::File - Access the lines of a disk file via a Perl array
=head1 SYNOPSIS
- # This file documents Tie::File version 0.50
+ # This file documents Tie::File version 0.95
+ use Tie::File;
tie @array, 'Tie::File', filename or die ...;
push @array, new recs...;
my $r1 = pop @array;
unshift @array, new recs...;
- my $r1 = shift @array;
+ my $r2 = shift @array;
@old_recs = splice @array, 3, 7, new recs...;
untie @array; # all finished
What is a 'record'? By default, the meaning is the same as for the
C<E<lt>...E<gt>> operator: It's a string terminated by C<$/>, which is
-probably C<"\n">. (Minor exception: on dos and Win32 systems, a
+probably C<"\n">. (Minor exception: on DOS and Win32 systems, a
'record' is a string terminated by C<"\r\n">.) You may change the
definition of "record" by supplying the C<recsep> option in the C<tie>
call:
Curse these pesky flies!\n
-then the C<@array> would appear to have four elements:
+then the C<@array> would appear to have four elements:
"Curse th"
"e p"
emulated.
Records read from the tied array do not have the record separator
-string on the end; this is to allow
+string on the end; this is to allow
$array[17] .= "extra";
The result is that the contents of line 17 of the file will be
replaced with "Cherry pie"; a newline character will separate line 17
-from line 18. This means that in particular, this will do nothing:
+from line 18. This means that this code will do nothing:
chomp $array[17];
it is written back to the file. There is no way to create a file
whose trailing record separator string is missing.
-Inserting records that I<contain> the record separator string will
-produce a reasonable result, but if you can't foresee what this result
-will be, you'd better avoid doing this.
+Inserting records that I<contain> the record separator string is not
+supported by this module. It will probably produce a reasonable
+result, but what this result will be may change in a future version.
+Use 'splice' to insert records or to replace one record with several.
=head2 C<autochomp>
Setting the memory limit to 0 will inhibit caching; records will be
fetched from disk every time you examine them.
+The C<memory> value is not an absolute or exact limit on the memory
+used. C<Tie::File> objects contains some structures besides the read
+cache and the deferred write buffer, whose sizes are not charged
+against C<memory>.
+
+The cache itself consumes about 310 bytes per cached record, so if
+your file has many short records, you may want to decrease the cache
+memory limit, or else the cache overhead may exceed the size of the
+cached data.
+
+
=head2 C<dw_size>
(This is an advanced feature. Skip this section on first reading.)
-
+
If you use deferred writing (See L<"Deferred Writing">, below) then
data you write into the array will not be written directly to the
file; instead, it will be saved in the I<deferred write buffer> to be
=head1 Public Methods
-The C<tie> call returns an object, say C<$o>. You may call
+The C<tie> call returns an object, say C<$o>. You may call
$rec = $o->FETCH($n);
$o->STORE($n, $rec);
C<MODE> is optional; the default is C<LOCK_EX>.
+C<Tie::File> maintains an internal table of the byte offset of each
+record it has seen in the file.
+
+When you use C<flock> to lock the file, C<Tie::File> assumes that the
+read cache is no longer trustworthy, because another process might
+have modified the file since the last time it was read. Therefore, a
+successful call to C<flock> discards the contents of the read cache
+and the internal record offset table.
+
C<Tie::File> promises that the following sequence of operations will
be safe:
See L<"autochomp">, above.
-=head2 C<defer>, C<flush>, and C<discard>
+=head2 C<defer>, C<flush>, C<discard>, and C<autodefer>
See L<"Deferred Writing">, below.
+=head2 C<offset>
+
+ $off = $o->offset($n);
+
+This method returns the byte offset of the start of the C<$n>th record
+in the file. If there is no such record, it returns an undefined
+value.
+
=head1 Tying to an already-opened filehandle
If C<$fh> is a filehandle, such as is returned by C<IO::File> or one
Handles that were opened write-only won't work. Handles that were
opened read-only will work as long as you don't try to modify the
array. Handles must be attached to seekable sources of data---that
-means no pipes or sockets. If you supply a non-seekable handle, the
-C<tie> call will try to throw an exception. (On Unix systems, it
-B<will> throw an exception.)
+means no pipes or sockets. If C<Tie::File> can detect that you
+supplied a non-seekable handle, the C<tie> call will throw an
+exception. (On Unix systems, it can detect this.)
=head1 Deferred Writing
done in memory. Then, when you call C<-E<gt>flush>, the entire file
will be rewritten in a single pass.
+(Actually, the preceding discussion is something of a fib. You don't
+need to enable deferred writing to get good performance for this
+common case, because C<Tie::File> will do it for you automatically
+unless you specifically tell it not to. See L<"autodeferring">,
+below.)
+
Calling C<-E<gt>flush> returns the array to immediate-write mode. If
you wish to discard the deferred writes, you may call C<-E<gt>discard>
instead of C<-E<gt>flush>. Note that in some cases, some of the data
will have been written already, and it will be too late for
-C<-E<gt>discard> to discard all the changes.
+C<-E<gt>discard> to discard all the changes. Support for
+C<-E<gt>discard> may be withdrawn in a future version of C<Tie::File>.
Deferred writes are cached in memory up to the limit specified by the
C<dw_size> option (see above). If the deferred-write buffer is full
If the deferred-write buffer isn't yet full, but the total size of the
buffer and the read cache would exceed the C<memory> limit, the oldest
-records will be flushed out of the read cache until total usage is
+records will be expired from the read cache until the total size is
under the limit.
C<push>, C<pop>, C<shift>, C<unshift>, and C<splice> cannot be
is written to the file and the operation is performed immediately.
This may change in a future version.
-A soon-to-be-released version of this module may enabled deferred
-write mode automagically if it guesses that you are about to write
-many consecutive records. To disable this feature, use
+If you resize the array with deferred writing enabled, the file will
+be resized immediately, but deferred records will not be written.
+This has a surprising consequence: C<@a = (...)> erases the file
+immediately, but the writing of the actual data is deferred. This
+might be a bug. If it is a bug, it will be fixed in a future version.
+
+=head2 Autodeferring
+
+C<Tie::File> tries to guess when deferred writing might be helpful,
+and to turn it on and off automatically.
+
+ for (@a) {
+ $_ = "> $_";
+ }
+
+In this example, only the first two assignments will be done
+immediately; after this, all the changes to the file will be deferred
+up to the user-specified memory limit.
+
+You should usually be able to ignore this and just use the module
+without thinking about deferring. However, special applications may
+require fine control over which writes are deferred, or may require
+that all writes be immediate. To disable the autodeferment feature,
+use
(tied @o)->autodefer(0);
-(At present, this call does nothing.)
+or
+
+ tie @array, 'Tie::File', $file, autodefer => 0;
+
+
+Similarly, C<-E<gt>autodefer(1)> re-enables autodeferment, and
+C<-E<gt>autodefer()> recovers the current value of the autodefer setting.
+
+
+=head1 CONCURRENT ACCESS TO FILES
+
+Caching and deferred writing are inappropriate if you want the same
+file to be accessed simultaneously from more than one process. You
+will want to disable these features. You should do that by including
+the C<memory =E<gt> 0> option in your C<tie> calls; this will inhibit
+caching and deferred writing.
+
+You will also want to lock the file while reading or writing it. You
+can use the C<-E<gt>flock> method for this. A future version of this
+module may provide an 'autolocking' mode.
=head1 CAVEATS
=item *
-This is BETA RELEASE SOFTWARE. It may have bugs. See the discussion
-below about the (lack of any) warranty.
-
-=item *
-
-Every effort was made to make this module efficient. Nevertheless,
+Reasonable effort was made to make this module efficient. Nevertheless,
changing the size of a record in the middle of a large file will
always be fairly slow, because everything after the new record must be
moved.
defined. Similarly, if you have C<autochomp> disabled, then
# This DOES print "How unusual!" if 'autochomp' is disabled
- undef $a[10];
+ undef $a[10];
print "How unusual!\n" if $a[10];
Because when C<autochomp> is disabled, C<$a[10]> will read back as
C<"\n"> (or whatever the record separator string is.)
-There are other minor differences, but in general, the correspondence
-is extremely close.
+There are other minor differences, particularly regarding C<exists>
+and C<delete>, but in general, the correspondence is extremely close.
=item *
-Not quite every effort was made to make this module as efficient as
-possible. C<FETCHSIZE> should use binary search instead of linear
-search. The cache's LRU queue should be a heap instead of a list.
+I have supposed that since this module is concerned with file I/O,
+almost all normal use of it will be heavily I/O bound. This means
+that the time to maintain complicated data structures inside the
+module will be dominated by the time to actually perform the I/O.
+When there was an opportunity to spend CPU time to avoid doing I/O, I
+usually tried to take it.
-The performance of the C<flush> method could be improved. At present,
-it still rewrites the tail of the file once for each block of
-contiguous lines to be changed. In the typical case, this will result
-in only one rewrite, but in peculiar cases it might be bad. It should
-be possible to perform I<all> deferred writing with a single rewrite.
+=item *
-These defects are probably minor; in any event, they will be fixed in
-a future version of the module.
+You might be tempted to think that deferred writing is like
+transactions, with C<flush> as C<commit> and C<discard> as
+C<rollback>, but it isn't, so don't.
=item *
-The author has supposed that since this module is concerned with file
-I/O, almost all normal use of it will be heavily I/O bound, and that
-the time to maintain complicated data structures inside the module
-will be dominated by the time to actually perform the I/O. This
-suggests, for example, that an LRU read-cache is a good tradeoff,
-even if it requires substantial adjustment following a C<splice>
-operation.
+There is a large memory overhead for each record offset and for each
+cache entry: about 310 bytes per cached data record, and about 21 bytes per offset table entry.
-=item *
-You might be tempted to think that deferred writing is like
-transactions, with C<flush> as C<commit> and C<discard> as
-C<rollback>, but it isn't, so don't.
+The per-record overhead will limit the maximum number of records you
+can access per file. Note that I<accessing> the length of the array
+via C<$x = scalar @tied_file> accesses B<all> records and stores their
+offsets. The same for C<foreach (@tied_file)>, even if you exit the
+loop early.
=back
=head1 WHAT ABOUT C<DB_File>?
-C<DB_File>'s C<DB_RECNO> feature does something similar to
-C<Tie::File>, but there are a number of reasons that you might prefer
-C<Tie::File>. C<DB_File> is a great piece of software, but the
-C<DB_RECNO> part is less great than the rest of it.
-
-=over 4
-
-=item *
-
-C<DB_File> reads your entire file into memory, modifies it in memory,
-and the writes out the entire file again when you untie the file.
-This is completely impractical for large files.
-
-C<Tie::File> does not do any of those things. It doesn't try to read
-the entire file into memory; instead it uses a lazy approach and
-caches recently-used records. The cache size is strictly bounded by
-the C<memory> option. DB_File's C<-E<gt>{cachesize}> doesn't prevent
-your process from blowing up when reading a big file.
-
-=item *
-
-C<DB_File> has an extremely poor writing strategy. If you have a
-ten-megabyte file and tie it with C<DB_File>, and then use
-
- $a[0] =~ s/PERL/Perl/;
-
-C<DB_file> will then read the entire ten-megabyte file into memory, do
-the change, and write the entire file back to disk, reading ten
-megabytes and writing ten megabytes. C<Tie::File> will read and write
-only the first record.
-
-If you have a million-record file and tie it with C<DB_File>, and then
-use
-
- $a[999998] =~ s/Larry/Larry Wall/;
-
-C<DB_File> will read the entire million-record file into memory, do
-the change, and write the entire file back to disk. C<Tie::File> will
-only rewrite records 999998 and 999999. During the writing process,
-it will never have more than a few kilobytes of data in memory at any
-time, even if the two records are very large.
-
-=item *
-
-Since changes to C<DB_File> files only appear when you do C<untie>, it
-can be inconvenient to arrange for concurrent access to the same file
-by two or more processes. Each process needs to call C<$db-E<gt>sync>
-after every write. When you change a C<Tie::File> array, the changes
-are reflected in the file immediately; no explicit C<-E<gt>sync> call
-is required. (Or you can enable deferred writing mode to require that
-changes be explicitly sync'ed.)
-
-=item *
-
-C<DB_File> is only installed by default if you already have the C<db>
-library on your system; C<Tie::File> is pure Perl and is installed by
-default no matter what. Starting with Perl 5.7.3 you can be
-absolutely sure it will be everywhere. You will never have that
-surety with C<DB_File>. If you don't have C<DB_File> yet, it requires
-a C compiler. You can install C<Tie::File> from CPAN in five minutes
-with no compiler.
-
-=item *
-
-C<DB_File> is written in C, so if you aren't allowed to install
-modules on your system, it is useless. C<Tie::File> is written in Perl,
-so even if you aren't allowed to install modules, you can look into
-the source code, see how it works, and copy the subroutines or the
-ideas from the subroutines directly into your own Perl program.
-
-=item *
-
-Except in very old, unsupported versions, C<DB_File>'s free license
-requires that you distribute the source code for your entire
-application. If you are not able to distribute the source code for
-your application, you must negotiate an alternative license from
-Sleepycat, possibly for a fee. Tie::File is under the Perl Artistic
-license and can be distributed free under the same terms as Perl
-itself.
+People sometimes point out that L<DB_File> will do something similar,
+and ask why C<Tie::File> module is necessary.
-=back
+There are a number of reasons that you might prefer C<Tie::File>.
+A list is available at C<http://perl.plover.com/TieFile/why-not-DB_File>.
=head1 AUTHOR
=head1 LICENSE
-C<Tie::File> version 0.50 is copyright (C) 2002 Mark Jason Dominus.
+C<Tie::File> version 0.95 is copyright (C) 2002 Mark Jason Dominus.
This library is free software; you may redistribute it and/or modify
it under the same terms as Perl itself.
=head1 WARRANTY
-C<Tie::File> version 0.50 comes with ABSOLUTELY NO WARRANTY.
+C<Tie::File> version 0.95 comes with ABSOLUTELY NO WARRANTY.
For details, see the license.
=head1 THANKS
Special thanks to Craig Berry and Peter Prymmer (for VMS portability
help), Randy Kobes (for Win32 portability help), Clinton Pierce and
Autrijus Tang (for heroic eleventh-hour Win32 testing above and beyond
-the call of duty), and the rest of the CPAN testers (for testing
-generally).
+the call of duty), Michael G Schwern (for testing advice), and the
+rest of the CPAN testers (for testing generally).
+
+Special thanks to Tels for suggesting several speed and memory
+optimizations.
Additional thanks to:
Edward Avis /
+Mattia Barbon /
Gerrit Haase /
+Jarkko Hietaniemi (again) /
Nikola Knezevic /
+John Kominetz /
Nick Ing-Simmons /
Tassilo von Parseval /
H. Dieter Pearcey /
Slaven Rezic /
+Eric Roode /
+Peter Scott /
Peter Somu /
Autrijus Tang (again) /
-Tels
+Tels (again) /
+Juerd Waalboer
=head1 TODO
-Test DELETE machinery more carefully.
-
-More tests. (C<mode> option. _twrite should be tested separately,
-because there are a lot of weird special cases lurking in there.)
-
More tests. (Stuff I didn't think of yet.)
Paragraph mode?
-More tests.
-
-Fixed-length mode.
+Fixed-length mode. Leave-blanks mode.
Maybe an autolocking mode?
-Autodeferment.
+For many common uses of the module, the read cache is a liability.
+For example, a program that inserts a single record, or that scans the
+file once, will have a cache hit rate of zero. This suggests a major
+optimization: The cache should be initially disabled. Here's a hybrid
+approach: Initially, the cache is disabled, but the cache code
+maintains statistics about how high the hit rate would be *if* it were
+enabled. When it sees the hit rate get high enough, it enables
+itself. The STAT comments in this code are the beginning of an
+implementation of this.
-Record locking with fcntl()? Then you might support an undo log and
-get real transactions. What a coup that would be. All would bow
-before my might.
+Record locking with fcntl()? Then the module might support an undo
+log and get real transactions. What a tour de force that would be.
-Leave-blanks mode
+Keeping track of the highest cached record. This would allow reads-in-a-row
+to skip the cache lookup faster (if reading from 1..N with empty cache at
+start, the last cached value will be always N-1).
+
+More tests.
=cut
projects / p5sagit/p5-mst-13.2.git / blobdiff