package Tie::File;
require 5.005;
-use Carp;
+use Carp ':DEFAULT', 'confess';
use POSIX 'SEEK_SET';
-use Fcntl 'O_CREAT', 'O_RDWR', 'LOCK_EX', 'O_WRONLY', 'O_RDONLY';
+use Fcntl 'O_CREAT', 'O_RDWR', 'LOCK_EX', 'LOCK_SH', 'O_WRONLY', 'O_RDONLY';
sub O_ACCMODE () { O_RDONLY | O_RDWR | O_WRONLY }
-$VERSION = "0.93";
+
+$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, "-$_" => 1}
- qw(memory dw_size mode recsep discipline autodefer autochomp);
+my %good_opt = map {$_ => 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{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};
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};
+ $rec;
}
# Chomp many records in-place; return nothing useful
}
if ($#{$self->{offsets}} < $n) {
- return if $self->{eof};
+ 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
- unless ($self->{eof}) {
- while (defined ($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->{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;
}
$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);
$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 {
+ $self->{cache}->remove($_);
+ }
}
- }
-
- # If we're about to splice out the end of the offsets table...
- if ($pos + $nrecs >= @{$self->{offsets}}) {
- $self->{eof} = 0; # ... the table is no longer complete
- }
- splice(@{$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}};
- # If the file got longer, the offsets table is no longer complete
- $self->{eof} = 0 if @data > $nrecs;
-
-
- # Perhaps the following cache foolery could be factored out
- # into a bunch of mor opaque cache functions. For example,
- # it's odd to delete a record from the cache and then remove
- # it from the LRU queue later on; there should be a function to
- # do both at once.
-
- # update the read cache, part 1
- # modified records
- for ($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}->ckeys;
- 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 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.
+ $self->_cache_flush;
+}
+
# If a record does not already end with the appropriate terminator
# string, append one.
sub _fixrecs {
defined($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
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
# 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}) {
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);
@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
# 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;
"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 0.93
+ # 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:
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>.
+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>
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
Similarly, C<-E<gt>autodefer(1)> re-enables autodeferment, and
C<-E<gt>autodefer()> recovers the current value of the autodefer setting.
-=head1 CAVEATS
-(That's Latin for 'warnings'.)
+=head1 CONCURRENT ACCESS TO FILES
-=over 4
+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.
-=item *
+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
-This is BETA RELEASE SOFTWARE. It may have bugs. See the discussion
-below about the (lack of any) warranty.
+(That's Latin for 'warnings'.)
-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.
+=over 4
=item *
=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 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.
-
-Profiling suggests that these defects are probably minor; in any
-event, they will be fixed in a future version of the module.
-
-=item *
-
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
-tried to take it.
+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 LICENSE
-C<Tie::File> version 0.93 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 0.93 comes with ABSOLUTELY NO WARRANTY.
+C<Tie::File> version 0.95 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 /
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 /
-Juerd Wallboer
+Tels (again) /
+Juerd Waalboer
=head1 TODO
-More tests. (The cache and heap modules need more unit tests.)
-
-Improve SPLICE algorithm to use deferred writing machinery.
-
-Cleverer strategy for flushing deferred writes.
-
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.
+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