package Tie::File;
require 5.005;
-use Carp;
+use Carp ':DEFAULT', 'confess';
use POSIX 'SEEK_SET';
-use Fcntl 'O_CREAT', 'O_RDWR', 'LOCK_EX';
+use Fcntl 'O_CREAT', 'O_RDWR', 'LOCK_EX', 'LOCK_SH', 'O_WRONLY', 'O_RDONLY';
+sub O_ACCMODE () { O_RDONLY | O_RDWR | O_WRONLY }
+
-$VERSION = "0.90";
+$VERSION = "0.97_01";
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, "-$_" => 1}
- qw(memory dw_size mode recsep discipline autodefer autochomp);
+my %good_opt = map {$_ => 1, "-$_" => 1}
+ qw(memory dw_size mode recsep discipline
+ autodefer autochomp autodefer_threshhold concurrent);
sub TIEARRAY {
if (@_ % 2 != 0) {
}
}
+ if ($opts{concurrent}) {
+ croak("$pack: concurrent access not supported yet\n");
+ }
+
unless (defined $opts{memory}) {
# 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{deferred_s} = 0; # count of total bytes in ->{deferred}
$opts{deferred_max} = -1; # empty
- # the cache is a hash instead of an array because it is likely to be
- # sparsely populated
- $opts{cache} = Tie::File::Cache->new($opts{memory});
+ # What's a good way to arrange that this class can be overridden?
+ $opts{cache} = Tie::File::Cache->new($opts{memory});
# autodeferment is enabled by default
$opts{autodefer} = 1 unless defined $opts{autodefer};
$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')) {
unless (seek $file, 1, SEEK_SET) {
croak "$pack: your filehandle does not appear to be seekable";
}
- seek $file, 0, SEEK_SET # put it back
+ seek $file, 0, SEEK_SET; # put it back
$fh = $file; # setting binmode is the user's problem
} elsif (ref $file) {
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;
+ # $fh = \do { local *FH }; # XXX this is buggy
+ if ($] < 5.006) {
+ # perl 5.005 and earlier don't autovivify filehandles
+ require Symbol;
+ $fh = Symbol::gensym();
+ }
+ sysopen $fh, $file, $opts{mode}, 0666 or return;
binmode $fh;
+ ++$opts{ourfh};
}
{ my $ofh = select $fh; $| = 1; select $ofh } # autoflush on write
if (defined $opts{discipline} && $] >= 5.006) {
my $rec;
# check the defer buffer
- if ($self->_is_deferring && exists $self->{deferred}{$n}) {
- $rec = $self->{deferred}{$n};
- } else {
- $rec = $self->_fetch($n);
- }
+ $rec = $self->{deferred}{$n} if exists $self->{deferred}{$n};
+ $rec = $self->_fetch($n) unless defined $rec;
- $self->_chomp1($rec);
+ # inlined _chomp1
+ substr($rec, - $self->{recseplen}) = ""
+ if defined $rec && $self->{autochomp};
+ $rec;
}
# Chomp many records in-place; return nothing useful
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;
# 20020324 Wait, but this DOES alter the cache. TODO BUG?
my $oldrec = $self->_fetch($n);
- if (defined($self->{cache}->lookup($n))) {
- $self->{cache}->update($n, $rec);
- }
-
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 {
sub FETCHSIZE {
my $self = shift;
- my $n = $#{$self->{offsets}};
- # 20020317 Change this to binary search
- while (defined ($self->_fill_offsets_to($n+1))) {
- ++$n;
- }
+ 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;
$#{$self->{offsets}} = $len;
# $self->{offsets}[0] = 0; # in case we just chopped this
- $self->{cache}->remove(grep $_ >= $len, $self->{cache}->keys);
+ $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:
+ # $self->FETCHSIZE; # because av.c takes care of this for me
}
sub POP {
sub EXISTS {
my ($self, $n) = @_;
return 1 if exists $self->{deferred}{$n};
- $self->_fill_offsets_to($n); # I think this is unnecessary
$n < $self->FETCHSIZE;
}
my $self = shift;
$self->flush if $self->_is_deferring;
$self->{cache}->delink if defined $self->{cache}; # break circular link
+ if ($self->{fh} and $self->{ourfh}) {
+ delete $self->{ourfh};
+ close delete $self->{fh};
+ }
}
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;
+ }
}
$self->_fixrecs(@data);
# compute length of data being removed
for ($pos .. $pos+$nrecs-1) {
- $self->_fill_offsets_to($_);
+ last unless defined $self->_fill_offsets_to($_);
my $rec = $self->_fetch($_);
last unless defined $rec;
push @result, $rec;
# Why don't we just use length($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($rec) is the length of the record to be *written*,
- # not the length of the actual record in the file. But the offsets are
- # still true. 20020322
+ # and in this case length($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];
}
+ $self->_fill_offsets_to($pos+$nrecs);
# 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[$_]);
+ $self->_mtwrite($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 {
+ $self->{cache}->remove($_);
+ }
}
- }
- 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;
- }
- # 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.
-
- # 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 {
- $self->{cache}->remove($_);
+
+ # 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);
}
- }
- # 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}->keys;
- my @newkeys = map $_-$nrecs+@data, @oldkeys;
- $self->{cache}->rekey(\@oldkeys, \@newkeys);
+ # 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
$readpos += $br;
$writepos += length $data;
$data = $next_block;
- } while $more_data; # BUG XXX TODO how could this have worked?
+ } while $more_data;
$self->_seekb($writepos);
$self->_write_record($next_block);
$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 accommodate 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.
+#
+# Undefined $len means 'until the end of the file'
+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;
+ my $last_read_was_short = length($old) < $readsize;
+ $data .= $old;
+ my $writable;
+ if ($last_read_was_short) {
+ # If last read was short, then $data now contains the entire rest
+ # of the file, so there's no need to write only one block of it
+ $writable = $data;
+ $data = "";
+ } else {
+ $writable = substr($data, 0, $readsize, "");
+ }
+ last if $writable eq "";
+ $self->_seekb($pos);
+ $self->_write_record($writable);
+ last if $last_read_was_short && $data eq "";
+ $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);
+# $self->{_written} += length($rec);
}
sub _read_record {
my $fh = $self->{fh};
$rec = <$fh>;
}
- $self->{_read} += length($rec) if defined $rec;
+ return unless defined $rec;
+ if (substr($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;
}
sub _rw_stats {
+ my $self = shift;
@{$self}{'_read', '_written'};
}
# 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
#
# 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;
}
}
-# If autodferring was enabled, cut it out and discard the history
+# If autodeferring was enabled, cut it out and discard the history
sub _stop_autodeferring {
my $self = shift;
if ($self->{autodeferring}) {
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;
_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 $.");
+ }
+ }
+ if (@{$self->{offsets}} > $.+1) {
+ $good = 0;
+ my $n = @{$self->{offsets}};
+ _ci_warn("The offset table has $n items, but the file has only $.");
}
my $deferring = $self->_is_deferring;
- for my $n ($self->{cache}->keys) {
+ for my $n ($self->{cache}->ckeys) {
my $r = $self->{cache}->_produce($n);
$cached += length($r);
next if $n+1 <= $.; # checked this already
}
}
+ # That cache has its own set of tests
$good = 0 unless $self->{cache}->_check_integrity;
# Now let's check the deferbuffer
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 {
if (defined $n) {
$self->[HASH]{$k} = $n;
} else {
- delete $self->[HASH]{$k};
+ delete $self->[HASH]{$k};
}
}
}
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);
$self->[HEAP]->insert($key, $val);
}
$self->[BYTES] += length($val);
- $self->flush;
+ $self->flush if $self->[BYTES] > $self->[MAX];
}
sub expire {
sub remove {
my ($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]{$key});
my ($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]{$key});
} else {
%{$self->[HASH]} = ();
$self->[BYTES] = 0;
$self->[HEAP]->empty;
+# @{$self->[STAT]} = ();
+# $self->[MISS] = 0;
+# $self->[REQ] = 0;
}
sub is_empty {
local *_;
croak "missing argument to ->update" unless defined $key;
if (length($val) > $self->[MAX]) {
- my $oldval = $self->remove($key);
+ 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);
}
}
-sub keys {
+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->is_empty || $self->[BYTES] <= $max) {
- $self->expire;
+ until ($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 $self = shift;
- until ($self->is_empty || $self->[BYTES] <= $self->[MAX]) {
- $self->expire;
- }
+ $self->reduce_size_to($self->[MAX]) if $self->[BYTES] > $self->[MAX];
}
# For internal use only
$self->[HEAP]->expire_order;
}
-sub _check_integrity {
+BEGIN { *_ci_warn = \&Tie::File::_ci_warn }
+
+sub _check_integrity { # For CACHE
my $self = shift;
- $self->[HEAP]->_check_integrity;
+ 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 {
$self->[0][0] = 0; # might as well reset the sequence numbers
}
-# notify the parent cache objec tthat we moved something
+# notify the parent cache object that we moved something
sub _heap_move {
my $self = shift;
$self->_cache->_heap_move(@_);
my $i = @$self;
$i = int($i/2) until defined $self->[$i/2];
$self->[$i] = $item;
- $self->_heap_move($self->[$i][KEY], $i);
+ $self->[0][1]->_heap_move($self->[$i][KEY], $i);
$self->_nelts_inc;
}
# If $i is omitted, default to 1 (the top element.)
sub _insert {
my ($self, $item, $i) = @_;
- $self->_check_loc($i) if defined $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]);
- $self->_heap_move($self->[$i][KEY], $i);
+ $self->[0][1]->_heap_move($self->[$i][KEY], $i);
}
# If either is undefined, go that way. Otherwise, choose at random
my $dir;
$i = 2*$i + $dir;
}
$self->[$i] = $item;
- $self->_heap_move($self->[$i][KEY], $i);
+ $self->[0][1]->_heap_move($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 the removed item. Return undef if there was no item at node $i.
sub remove {
my ($self, $i) = @_;
$i = 1 unless defined $i;
}
$self->[$i] = $self->[$ii]; # Promote child to fill vacated spot
- $self->_heap_move($self->[$i][KEY], $i);
+ $self->[0][1]->_heap_move($self->[$i][KEY], $i);
$i = $ii; # Fill new vacated spot
}
- $self->_heap_move($top->[KEY], undef);
+ $self->[0][1]->_heap_move($top->[KEY], undef);
undef $self->[$i];
$self->_nelts_dec;
return $top->[DAT];
# bottom.
sub promote {
my ($self, $n) = @_;
- $self->_check_loc($n);
+# $self->_check_loc($n);
$self->[$n][SEQ] = $self->_nseq;
my $i = $n;
while (1) {
}
@{$self}[$i, $dir] = @{$self}[$dir, $i];
for ($i, $dir) {
- $self->_heap_move($self->[$_][KEY], $_) if defined $self->[$_];
+ $self->[0][1]->_heap_move($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);
+# $self->_check_loc($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);
+# $self->_check_loc($n);
my $oval = $self->[$n][DAT];
$self->[$n][DAT] = $val;
$self->promote($n);
# alter the heap's record of the hash key
sub rekey {
my ($self, $n, $new_key) = @_;
- $self->_check_loc($n);
+# $self->_check_loc($n);
$self->[$n][KEY] = $new_key;
}
sub _check_loc {
my ($self, $n) = @_;
- unless (defined $self->[$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")}) {
- print "# Element 0 of heap corrupt\n";
+ _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]) {
- print "# Element $i of heap defined, but parent $p isn't\n";
+ _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;
}
my $c = $n*2 + $_;
next unless defined $self->[$c];
if ($self->[$n][SEQ] >= $self->[$c]) {
- print "# Node $n of heap does not predate node $c\n";
+ _ci_warn "Node $n of heap does not predate node $c";
$good = 0 ;
}
$good = 0 unless $self->_satisfies_heap_condition($c);
($self->[$i], $self->_nodes($i*2), $self->_nodes($i*2+1));
}
-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 0.90
+ # This file documents Tie::File version 0.97
+ 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<"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.)
+
+Note that Tie::File will only close any filehandles that it opened
+internally. If you passed it a filehandle as above, you "own" the
+filehandle, and are responsible for closing it after you have untied
+the @array.
=head1 Deferred Writing
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
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. In the example above, 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.
+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
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. Other
+optimizations performed internally by this module are also
+incompatible with concurrent access. A future version of this module will
+support a C<concurrent =E<gt> 1> option that enables safe concurrent access.
+
+Previous versions of this documentation suggested using C<memory
+=E<gt> 0> for safe concurrent access. This was mistaken. Tie::File
+will not support safe concurrent access before version 0.98.
+
=head1 CAVEATS
(That's Latin for 'warnings'.)
=item *
-This is BETA RELEASE SOFTWARE. It may have bugs. See the discussion
-below about the (lack of any) warranty.
-
-In particular, this means that the interface may change in
-incompatible ways from one version to the next, without warning. That
-has happened at least once already. The interface will freeze before
-Perl 5.8 is released, probably sometime in April 2002.
-
-=item *
-
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
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
=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.
-
-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.
-
-These defects are probably minor; in any event, they will be fixed in
-a future version of the module.
-
-=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 bookkeeping following a C<splice>
-operation.
+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.
=item *
transactions, with C<flush> as C<commit> and C<discard> as
C<rollback>, but it isn't, so don't.
+=item *
+
+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.
+
+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 SUBCLASSING
=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 *
+People sometimes point out that L<DB_File> will do something similar,
+and ask why C<Tie::File> module is necessary.
-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.
-
-=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 0.90 is copyright (C) 2002 Mark Jason Dominus.
+C<Tie::File> version 0.97 is copyright (C) 2003 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 0.90 comes with ABSOLUTELY NO WARRANTY.
+C<Tie::File> version 0.97 comes with ABSOLUTELY NO WARRANTY.
For details, see the license.
=head1 THANKS
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 /
+Tom Christiansen /
Gerrit Haase /
+Gurusamy Sarathy /
+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
-More tests. (_twrite should be tested separately, because there are a
-lot of weird special cases lurking in there.)
-
-Improve SPLICE algorithm to use deferred writing machinery.
-
More tests. (Stuff I didn't think of yet.)
Paragraph mode?
Maybe an autolocking mode?
+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 the module might support an undo
log and get real transactions. What a tour de force that would be.
-Cleverer strategy for flushing deferred writes.
+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).
-oMore tests.
+More tests.
=cut
-
-
-
-
-
-
projects / p5sagit/p5-mst-13.2.git / blobdiff