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1 2 package Tie::File; 3 require 5.005; 4 use Carp ':DEFAULT', 'confess'; 5 use POSIX 'SEEK_SET'; 6 use Fcntl 'O_CREAT', 'O_RDWR', 'LOCK_EX', 'LOCK_SH', 'O_WRONLY', 'O_RDONLY'; 7 sub O_ACCMODE () { O_RDONLY | O_RDWR | O_WRONLY } 8 9 10 $VERSION = "0.97_02"; 11 my $DEFAULT_MEMORY_SIZE = 1<<21; # 2 megabytes 12 my $DEFAULT_AUTODEFER_THRESHHOLD = 3; # 3 records 13 my $DEFAULT_AUTODEFER_FILELEN_THRESHHOLD = 65536; # 16 disk blocksful 14 15 my %good_opt = map {$_ => 1, "-$_" => 1} 16 qw(memory dw_size mode recsep discipline 17 autodefer autochomp autodefer_threshhold concurrent); 18 19 sub TIEARRAY { 20 if (@_ % 2 != 0) { 21 croak "usage: tie \@array, $_[0], filename, [option => value]..."; 22 } 23 my ($pack, $file, %opts) = @_; 24 25 # transform '-foo' keys into 'foo' keys 26 for my $key (keys %opts) { 27 unless ($good_opt{$key}) { 28 croak("$pack: Unrecognized option '$key'\n"); 29 } 30 my $okey = $key; 31 if ($key =~ s/^-+//) { 32 $opts{$key} = delete $opts{$okey}; 33 } 34 } 35 36 if ($opts{concurrent}) { 37 croak("$pack: concurrent access not supported yet\n"); 38 } 39 40 unless (defined $opts{memory}) { 41 # default is the larger of the default cache size and the 42 # deferred-write buffer size (if specified) 43 $opts{memory} = $DEFAULT_MEMORY_SIZE; 44 $opts{memory} = $opts{dw_size} 45 if defined $opts{dw_size} && $opts{dw_size} > $DEFAULT_MEMORY_SIZE; 46 # Dora Winifred Read 47 } 48 $opts{dw_size} = $opts{memory} unless defined $opts{dw_size}; 49 if ($opts{dw_size} > $opts{memory}) { 50 croak("$pack: dw_size may not be larger than total memory allocation\n"); 51 } 52 # are we in deferred-write mode? 53 $opts{defer} = 0 unless defined $opts{defer}; 54 $opts{deferred} = {}; # no records are presently deferred 55 $opts{deferred_s} = 0; # count of total bytes in ->{deferred} 56 $opts{deferred_max} = -1; # empty 57 58 # What's a good way to arrange that this class can be overridden? 59 $opts{cache} = Tie::File::Cache->new($opts{memory}); 60 61 # autodeferment is enabled by default 62 $opts{autodefer} = 1 unless defined $opts{autodefer}; 63 $opts{autodeferring} = 0; # but is not initially active 64 $opts{ad_history} = []; 65 $opts{autodefer_threshhold} = $DEFAULT_AUTODEFER_THRESHHOLD 66 unless defined $opts{autodefer_threshhold}; 67 $opts{autodefer_filelen_threshhold} = $DEFAULT_AUTODEFER_FILELEN_THRESHHOLD 68 unless defined $opts{autodefer_filelen_threshhold}; 69 70 $opts{offsets} = [0]; 71 $opts{filename} = $file; 72 unless (defined $opts{recsep}) { 73 $opts{recsep} = _default_recsep(); 74 } 75 $opts{recseplen} = length($opts{recsep}); 76 if ($opts{recseplen} == 0) { 77 croak "Empty record separator not supported by $pack"; 78 } 79 80 $opts{autochomp} = 1 unless defined $opts{autochomp}; 81 82 $opts{mode} = O_CREAT|O_RDWR unless defined $opts{mode}; 83 $opts{rdonly} = (($opts{mode} & O_ACCMODE) == O_RDONLY); 84 $opts{sawlastrec} = undef; 85 86 my $fh; 87 88 if (UNIVERSAL::isa($file, 'GLOB')) { 89 # We use 1 here on the theory that some systems 90 # may not indicate failure if we use 0. 91 # MSWin32 does not indicate failure with 0, but I don't know if 92 # it will indicate failure with 1 or not. 93 unless (seek $file, 1, SEEK_SET) { 94 croak "$pack: your filehandle does not appear to be seekable"; 95 } 96 seek $file, 0, SEEK_SET; # put it back 97 $fh = $file; # setting binmode is the user's problem 98 } elsif (ref $file) { 99 croak "usage: tie \@array, $pack, filename, [option => value]..."; 100 } else { 101 # $fh = \do { local *FH }; # XXX this is buggy 102 if ($] < 5.006) { 103 # perl 5.005 and earlier don't autovivify filehandles 104 require Symbol; 105 $fh = Symbol::gensym(); 106 } 107 sysopen $fh, $file, $opts{mode}, 0666 or return; 108 binmode $fh; 109 ++$opts{ourfh}; 110 } 111 { my $ofh = select $fh; $| = 1; select $ofh } # autoflush on write 112 if (defined $opts{discipline} && $] >= 5.006) { 113 # This avoids a compile-time warning under 5.005 114 eval 'binmode($fh, $opts{discipline})'; 115 croak $@ if $@ =~ /unknown discipline/i; 116 die if $@; 117 } 118 $opts{fh} = $fh; 119 120 bless \%opts => $pack; 121 } 122 123 sub FETCH { 124 my ($self, $n) = @_; 125 my $rec; 126 127 # check the defer buffer 128 $rec = $self->{deferred}{$n} if exists $self->{deferred}{$n}; 129 $rec = $self->_fetch($n) unless defined $rec; 130 131 # inlined _chomp1 132 substr($rec, - $self->{recseplen}) = "" 133 if defined $rec && $self->{autochomp}; 134 $rec; 135 } 136 137 # Chomp many records in-place; return nothing useful 138 sub _chomp { 139 my $self = shift; 140 return unless $self->{autochomp}; 141 if ($self->{autochomp}) { 142 for (@_) { 143 next unless defined; 144 substr($_, - $self->{recseplen}) = ""; 145 } 146 } 147 } 148 149 # Chomp one record in-place; return modified record 150 sub _chomp1 { 151 my ($self, $rec) = @_; 152 return $rec unless $self->{autochomp}; 153 return unless defined $rec; 154 substr($rec, - $self->{recseplen}) = ""; 155 $rec; 156 } 157 158 sub _fetch { 159 my ($self, $n) = @_; 160 161 # check the record cache 162 { my $cached = $self->{cache}->lookup($n); 163 return $cached if defined $cached; 164 } 165 166 if ($#{$self->{offsets}} < $n) { 167 return if $self->{eof}; # request for record beyond end of file 168 my $o = $self->_fill_offsets_to($n); 169 # If it's still undefined, there is no such record, so return 'undef' 170 return unless defined $o; 171 } 172 173 my $fh = $self->{FH}; 174 $self->_seek($n); # we can do this now that offsets is populated 175 my $rec = $self->_read_record; 176 177 # If we happen to have just read the first record, check to see if 178 # the length of the record matches what 'tell' says. If not, Tie::File 179 # won't work, and should drop dead. 180 # 181 # if ($n == 0 && defined($rec) && tell($self->{fh}) != length($rec)) { 182 # if (defined $self->{discipline}) { 183 # croak "I/O discipline $self->{discipline} not supported"; 184 # } else { 185 # croak "File encoding not supported"; 186 # } 187 # } 188 189 $self->{cache}->insert($n, $rec) if defined $rec && not $self->{flushing}; 190 $rec; 191 } 192 193 sub STORE { 194 my ($self, $n, $rec) = @_; 195 die "STORE called from _check_integrity!" if $DIAGNOSTIC; 196 197 $self->_fixrecs($rec); 198 199 if ($self->{autodefer}) { 200 $self->_annotate_ad_history($n); 201 } 202 203 return $self->_store_deferred($n, $rec) if $self->_is_deferring; 204 205 206 # We need this to decide whether the new record will fit 207 # It incidentally populates the offsets table 208 # Note we have to do this before we alter the cache 209 # 20020324 Wait, but this DOES alter the cache. TODO BUG? 210 my $oldrec = $self->_fetch($n); 211 212 if (not defined $oldrec) { 213 # We're storing a record beyond the end of the file 214 $self->_extend_file_to($n+1); 215 $oldrec = $self->{recsep}; 216 } 217 # return if $oldrec eq $rec; # don't bother 218 my $len_diff = length($rec) - length($oldrec); 219 220 # length($oldrec) here is not consistent with text mode TODO XXX BUG 221 $self->_mtwrite($rec, $self->{offsets}[$n], length($oldrec)); 222 $self->_oadjust([$n, 1, $rec]); 223 $self->{cache}->update($n, $rec); 224 } 225 226 sub _store_deferred { 227 my ($self, $n, $rec) = @_; 228 $self->{cache}->remove($n); 229 my $old_deferred = $self->{deferred}{$n}; 230 231 if (defined $self->{deferred_max} && $n > $self->{deferred_max}) { 232 $self->{deferred_max} = $n; 233 } 234 $self->{deferred}{$n} = $rec; 235 236 my $len_diff = length($rec); 237 $len_diff -= length($old_deferred) if defined $old_deferred; 238 $self->{deferred_s} += $len_diff; 239 $self->{cache}->adj_limit(-$len_diff); 240 if ($self->{deferred_s} > $self->{dw_size}) { 241 $self->_flush; 242 } elsif ($self->_cache_too_full) { 243 $self->_cache_flush; 244 } 245 } 246 247 # Remove a single record from the deferred-write buffer without writing it 248 # The record need not be present 249 sub _delete_deferred { 250 my ($self, $n) = @_; 251 my $rec = delete $self->{deferred}{$n}; 252 return unless defined $rec; 253 254 if (defined $self->{deferred_max} 255 && $n == $self->{deferred_max}) { 256 undef $self->{deferred_max}; 257 } 258 259 $self->{deferred_s} -= length $rec; 260 $self->{cache}->adj_limit(length $rec); 261 } 262 263 sub FETCHSIZE { 264 my $self = shift; 265 my $n = $self->{eof} ? $#{$self->{offsets}} : $self->_fill_offsets; 266 267 my $top_deferred = $self->_defer_max; 268 $n = $top_deferred+1 if defined $top_deferred && $n < $top_deferred+1; 269 $n; 270 } 271 272 sub STORESIZE { 273 my ($self, $len) = @_; 274 275 if ($self->{autodefer}) { 276 $self->_annotate_ad_history('STORESIZE'); 277 } 278 279 my $olen = $self->FETCHSIZE; 280 return if $len == $olen; # Woo-hoo! 281 282 # file gets longer 283 if ($len > $olen) { 284 if ($self->_is_deferring) { 285 for ($olen .. $len-1) { 286 $self->_store_deferred($_, $self->{recsep}); 287 } 288 } else { 289 $self->_extend_file_to($len); 290 } 291 return; 292 } 293 294 # file gets shorter 295 if ($self->_is_deferring) { 296 # TODO maybe replace this with map-plus-assignment? 297 for (grep $_ >= $len, keys %{$self->{deferred}}) { 298 $self->_delete_deferred($_); 299 } 300 $self->{deferred_max} = $len-1; 301 } 302 303 $self->_seek($len); 304 $self->_chop_file; 305 $#{$self->{offsets}} = $len; 306 # $self->{offsets}[0] = 0; # in case we just chopped this 307 308 $self->{cache}->remove(grep $_ >= $len, $self->{cache}->ckeys); 309 } 310 311 ### OPTIMIZE ME 312 ### It should not be necessary to do FETCHSIZE 313 ### Just seek to the end of the file. 314 sub PUSH { 315 my $self = shift; 316 $self->SPLICE($self->FETCHSIZE, scalar(@_), @_); 317 318 # No need to return: 319 # $self->FETCHSIZE; # because av.c takes care of this for me 320 } 321 322 sub POP { 323 my $self = shift; 324 my $size = $self->FETCHSIZE; 325 return if $size == 0; 326 # print STDERR "# POPPITY POP POP POP\n"; 327 scalar $self->SPLICE($size-1, 1); 328 } 329 330 sub SHIFT { 331 my $self = shift; 332 scalar $self->SPLICE(0, 1); 333 } 334 335 sub UNSHIFT { 336 my $self = shift; 337 $self->SPLICE(0, 0, @_); 338 # $self->FETCHSIZE; # av.c takes care of this for me 339 } 340 341 sub CLEAR { 342 my $self = shift; 343 344 if ($self->{autodefer}) { 345 $self->_annotate_ad_history('CLEAR'); 346 } 347 348 $self->_seekb(0); 349 $self->_chop_file; 350 $self->{cache}->set_limit($self->{memory}); 351 $self->{cache}->empty; 352 @{$self->{offsets}} = (0); 353 %{$self->{deferred}}= (); 354 $self->{deferred_s} = 0; 355 $self->{deferred_max} = -1; 356 } 357 358 sub EXTEND { 359 my ($self, $n) = @_; 360 361 # No need to pre-extend anything in this case 362 return if $self->_is_deferring; 363 364 $self->_fill_offsets_to($n); 365 $self->_extend_file_to($n); 366 } 367 368 sub DELETE { 369 my ($self, $n) = @_; 370 371 if ($self->{autodefer}) { 372 $self->_annotate_ad_history('DELETE'); 373 } 374 375 my $lastrec = $self->FETCHSIZE-1; 376 my $rec = $self->FETCH($n); 377 $self->_delete_deferred($n) if $self->_is_deferring; 378 if ($n == $lastrec) { 379 $self->_seek($n); 380 $self->_chop_file; 381 $#{$self->{offsets}}--; 382 $self->{cache}->remove($n); 383 # perhaps in this case I should also remove trailing null records? 384 # 20020316 385 # Note that delete @a[-3..-1] deletes the records in the wrong order, 386 # so we only chop the very last one out of the file. We could repair this 387 # by tracking deleted records inside the object. 388 } elsif ($n < $lastrec) { 389 $self->STORE($n, ""); 390 } 391 $rec; 392 } 393 394 sub EXISTS { 395 my ($self, $n) = @_; 396 return 1 if exists $self->{deferred}{$n}; 397 $n < $self->FETCHSIZE; 398 } 399 400 sub SPLICE { 401 my $self = shift; 402 403 if ($self->{autodefer}) { 404 $self->_annotate_ad_history('SPLICE'); 405 } 406 407 $self->_flush if $self->_is_deferring; # move this up? 408 if (wantarray) { 409 $self->_chomp(my @a = $self->_splice(@_)); 410 @a; 411 } else { 412 $self->_chomp1(scalar $self->_splice(@_)); 413 } 414 } 415 416 sub DESTROY { 417 my $self = shift; 418 $self->flush if $self->_is_deferring; 419 $self->{cache}->delink if defined $self->{cache}; # break circular link 420 if ($self->{fh} and $self->{ourfh}) { 421 delete $self->{ourfh}; 422 close delete $self->{fh}; 423 } 424 } 425 426 sub _splice { 427 my ($self, $pos, $nrecs, @data) = @_; 428 my @result; 429 430 $pos = 0 unless defined $pos; 431 432 # Deal with negative and other out-of-range positions 433 # Also set default for $nrecs 434 { 435 my $oldsize = $self->FETCHSIZE; 436 $nrecs = $oldsize unless defined $nrecs; 437 my $oldpos = $pos; 438 439 if ($pos < 0) { 440 $pos += $oldsize; 441 if ($pos < 0) { 442 croak "Modification of non-creatable array value attempted, subscript $oldpos"; 443 } 444 } 445 446 if ($pos > $oldsize) { 447 return unless @data; 448 $pos = $oldsize; # This is what perl does for normal arrays 449 } 450 451 # The manual is very unclear here 452 if ($nrecs < 0) { 453 $nrecs = $oldsize - $pos + $nrecs; 454 $nrecs = 0 if $nrecs < 0; 455 } 456 457 # nrecs is too big---it really means "until the end" 458 # 20030507 459 if ($nrecs + $pos > $oldsize) { 460 $nrecs = $oldsize - $pos; 461 } 462 } 463 464 $self->_fixrecs(@data); 465 my $data = join '', @data; 466 my $datalen = length $data; 467 my $oldlen = 0; 468 469 # compute length of data being removed 470 for ($pos .. $pos+$nrecs-1) { 471 last unless defined $self->_fill_offsets_to($_); 472 my $rec = $self->_fetch($_); 473 last unless defined $rec; 474 push @result, $rec; 475 476 # Why don't we just use length($rec) here? 477 # Because that record might have come from the cache. _splice 478 # might have been called to flush out the deferred-write records, 479 # and in this case length($rec) is the length of the record to be 480 # *written*, not the length of the actual record in the file. But 481 # the offsets are still true. 20020322 482 $oldlen += $self->{offsets}[$_+1] - $self->{offsets}[$_] 483 if defined $self->{offsets}[$_+1]; 484 } 485 $self->_fill_offsets_to($pos+$nrecs); 486 487 # Modify the file 488 $self->_mtwrite($data, $self->{offsets}[$pos], $oldlen); 489 # Adjust the offsets table 490 $self->_oadjust([$pos, $nrecs, @data]); 491 492 { # Take this read cache stuff out into a separate function 493 # You made a half-attempt to put it into _oadjust. 494 # Finish something like that up eventually. 495 # STORE also needs to do something similarish 496 497 # update the read cache, part 1 498 # modified records 499 for ($pos .. $pos+$nrecs-1) { 500 my $new = $data[$_-$pos]; 501 if (defined $new) { 502 $self->{cache}->update($_, $new); 503 } else { 504 $self->{cache}->remove($_); 505 } 506 } 507 508 # update the read cache, part 2 509 # moved records - records past the site of the change 510 # need to be renumbered 511 # Maybe merge this with the previous block? 512 { 513 my @oldkeys = grep $_ >= $pos + $nrecs, $self->{cache}->ckeys; 514 my @newkeys = map $_-$nrecs+@data, @oldkeys; 515 $self->{cache}->rekey(\@oldkeys, \@newkeys); 516 } 517 518 # Now there might be too much data in the cache, if we spliced out 519 # some short records and spliced in some long ones. If so, flush 520 # the cache. 521 $self->_cache_flush; 522 } 523 524 # Yes, the return value of 'splice' *is* actually this complicated 525 wantarray ? @result : @result ? $result[-1] : undef; 526 } 527 528 529 # write data into the file 530 # $data is the data to be written. 531 # it should be written at position $pos, and should overwrite 532 # exactly $len of the following bytes. 533 # Note that if length($data) > $len, the subsequent bytes will have to 534 # be moved up, and if length($data) < $len, they will have to 535 # be moved down 536 sub _twrite { 537 my ($self, $data, $pos, $len) = @_; 538 539 unless (defined $pos) { 540 die "\$pos was undefined in _twrite"; 541 } 542 543 my $len_diff = length($data) - $len; 544 545 if ($len_diff == 0) { # Woo-hoo! 546 my $fh = $self->{fh}; 547 $self->_seekb($pos); 548 $self->_write_record($data); 549 return; # well, that was easy. 550 } 551 552 # the two records are of different lengths 553 # our strategy here: rewrite the tail of the file, 554 # reading ahead one buffer at a time 555 # $bufsize is required to be at least as large as the data we're overwriting 556 my $bufsize = _bufsize($len_diff); 557 my ($writepos, $readpos) = ($pos, $pos+$len); 558 my $next_block; 559 my $more_data; 560 561 # Seems like there ought to be a way to avoid the repeated code 562 # and the special case here. The read(1) is also a little weird. 563 # Think about this. 564 do { 565 $self->_seekb($readpos); 566 my $br = read $self->{fh}, $next_block, $bufsize; 567 $more_data = read $self->{fh}, my($dummy), 1; 568 $self->_seekb($writepos); 569 $self->_write_record($data); 570 $readpos += $br; 571 $writepos += length $data; 572 $data = $next_block; 573 } while $more_data; 574 $self->_seekb($writepos); 575 $self->_write_record($next_block); 576 577 # There might be leftover data at the end of the file 578 $self->_chop_file if $len_diff < 0; 579 } 580 581 # _iwrite(D, S, E) 582 # Insert text D at position S. 583 # Let C = E-S-|D|. If C < 0; die. 584 # Data in [S,S+C) is copied to [S+D,S+D+C) = [S+D,E). 585 # Data in [S+C = E-D, E) is returned. Data in [E, oo) is untouched. 586 # 587 # In a later version, don't read the entire intervening area into 588 # memory at once; do the copying block by block. 589 sub _iwrite { 590 my $self = shift; 591 my ($D, $s, $e) = @_; 592 my $d = length $D; 593 my $c = $e-$s-$d; 594 local *FH = $self->{fh}; 595 confess "Not enough space to insert $d bytes between $s and $e" 596 if $c < 0; 597 confess "[$s,$e) is an invalid insertion range" if $e < $s; 598 599 $self->_seekb($s); 600 read FH, my $buf, $e-$s; 601 602 $D .= substr($buf, 0, $c, ""); 603 604 $self->_seekb($s); 605 $self->_write_record($D); 606 607 return $buf; 608 } 609 610 # Like _twrite, but the data-pos-len triple may be repeated; you may 611 # write several chunks. All the writing will be done in 612 # one pass. Chunks SHALL be in ascending order and SHALL NOT overlap. 613 sub _mtwrite { 614 my $self = shift; 615 my $unwritten = ""; 616 my $delta = 0; 617 618 @_ % 3 == 0 619 or die "Arguments to _mtwrite did not come in groups of three"; 620 621 while (@_) { 622 my ($data, $pos, $len) = splice @_, 0, 3; 623 my $end = $pos + $len; # The OLD end of the segment to be replaced 624 $data = $unwritten . $data; 625 $delta -= length($unwritten); 626 $unwritten = ""; 627 $pos += $delta; # This is where the data goes now 628 my $dlen = length $data; 629 $self->_seekb($pos); 630 if ($len >= $dlen) { # the data will fit 631 $self->_write_record($data); 632 $delta += ($dlen - $len); # everything following moves down by this much 633 $data = ""; # All the data in the buffer has been written 634 } else { # won't fit 635 my $writable = substr($data, 0, $len - $delta, ""); 636 $self->_write_record($writable); 637 $delta += ($dlen - $len); # everything following moves down by this much 638 } 639 640 # At this point we've written some but maybe not all of the data. 641 # There might be a gap to close up, or $data might still contain a 642 # bunch of unwritten data that didn't fit. 643 my $ndlen = length $data; 644 if ($delta == 0) { 645 $self->_write_record($data); 646 } elsif ($delta < 0) { 647 # upcopy (close up gap) 648 if (@_) { 649 $self->_upcopy($end, $end + $delta, $_[1] - $end); 650 } else { 651 $self->_upcopy($end, $end + $delta); 652 } 653 } else { 654 # downcopy (insert data that didn't fit; replace this data in memory 655 # with _later_ data that doesn't fit) 656 if (@_) { 657 $unwritten = $self->_downcopy($data, $end, $_[1] - $end); 658 } else { 659 # Make the file longer to accommodate the last segment that doesn' 660 $unwritten = $self->_downcopy($data, $end); 661 } 662 } 663 } 664 } 665 666 # Copy block of data of length $len from position $spos to position $dpos 667 # $dpos must be <= $spos 668 # 669 # If $len is undefined, go all the way to the end of the file 670 # and then truncate it ($spos - $dpos bytes will be removed) 671 sub _upcopy { 672 my $blocksize = 8192; 673 my ($self, $spos, $dpos, $len) = @_; 674 if ($dpos > $spos) { 675 die "source ($spos) was upstream of destination ($dpos) in _upcopy"; 676 } elsif ($dpos == $spos) { 677 return; 678 } 679 680 while (! defined ($len) || $len > 0) { 681 my $readsize = ! defined($len) ? $blocksize 682 : $len > $blocksize ? $blocksize 683 : $len; 684 685 my $fh = $self->{fh}; 686 $self->_seekb($spos); 687 my $bytes_read = read $fh, my($data), $readsize; 688 $self->_seekb($dpos); 689 if ($data eq "") { 690 $self->_chop_file; 691 last; 692 } 693 $self->_write_record($data); 694 $spos += $bytes_read; 695 $dpos += $bytes_read; 696 $len -= $bytes_read if defined $len; 697 } 698 } 699 700 # Write $data into a block of length $len at position $pos, 701 # moving everything in the block forwards to make room. 702 # Instead of writing the last length($data) bytes from the block 703 # (because there isn't room for them any longer) return them. 704 # 705 # Undefined $len means 'until the end of the file' 706 sub _downcopy { 707 my $blocksize = 8192; 708 my ($self, $data, $pos, $len) = @_; 709 my $fh = $self->{fh}; 710 711 while (! defined $len || $len > 0) { 712 my $readsize = ! defined($len) ? $blocksize 713 : $len > $blocksize? $blocksize : $len; 714 $self->_seekb($pos); 715 read $fh, my($old), $readsize; 716 my $last_read_was_short = length($old) < $readsize; 717 $data .= $old; 718 my $writable; 719 if ($last_read_was_short) { 720 # If last read was short, then $data now contains the entire rest 721 # of the file, so there's no need to write only one block of it 722 $writable = $data; 723 $data = ""; 724 } else { 725 $writable = substr($data, 0, $readsize, ""); 726 } 727 last if $writable eq ""; 728 $self->_seekb($pos); 729 $self->_write_record($writable); 730 last if $last_read_was_short && $data eq ""; 731 $len -= $readsize if defined $len; 732 $pos += $readsize; 733 } 734 return $data; 735 } 736 737 # Adjust the object data structures following an '_mtwrite' 738 # Arguments are 739 # [$pos, $nrecs, @length] items 740 # indicating that $nrecs records were removed at $recpos (a record offset) 741 # and replaced with records of length @length... 742 # Arguments guarantee that $recpos is strictly increasing. 743 # No return value 744 sub _oadjust { 745 my $self = shift; 746 my $delta = 0; 747 my $delta_recs = 0; 748 my $prev_end = -1; 749 my %newkeys; 750 751 for (@_) { 752 my ($pos, $nrecs, @data) = @$_; 753 $pos += $delta_recs; 754 755 # Adjust the offsets of the records after the previous batch up 756 # to the first new one of this batch 757 for my $i ($prev_end+2 .. $pos - 1) { 758 $self->{offsets}[$i] += $delta; 759 $newkey{$i} = $i + $delta_recs; 760 } 761 762 $prev_end = $pos + @data - 1; # last record moved on this pass 763 764 # Remove the offsets for the removed records; 765 # replace with the offsets for the inserted records 766 my @newoff = ($self->{offsets}[$pos] + $delta); 767 for my $i (0 .. $#data) { 768 my $newlen = length $data[$i]; 769 push @newoff, $newoff[$i] + $newlen; 770 $delta += $newlen; 771 } 772 773 for my $i ($pos .. $pos+$nrecs-1) { 774 last if $i+1 > $#{$self->{offsets}}; 775 my $oldlen = $self->{offsets}[$i+1] - $self->{offsets}[$i]; 776 $delta -= $oldlen; 777 } 778 779 # # also this data has changed, so update it in the cache 780 # for (0 .. $#data) { 781 # $self->{cache}->update($pos + $_, $data[$_]); 782 # } 783 # if ($delta_recs) { 784 # my @oldkeys = grep $_ >= $pos + @data, $self->{cache}->ckeys; 785 # my @newkeys = map $_ + $delta_recs, @oldkeys; 786 # $self->{cache}->rekey(\@oldkeys, \@newkeys); 787 # } 788 789 # replace old offsets with new 790 splice @{$self->{offsets}}, $pos, $nrecs+1, @newoff; 791 # What if we just spliced out the end of the offsets table? 792 # shouldn't we clear $self->{eof}? Test for this XXX BUG TODO 793 794 $delta_recs += @data - $nrecs; # net change in total number of records 795 } 796 797 # The trailing records at the very end of the file 798 if ($delta) { 799 for my $i ($prev_end+2 .. $#{$self->{offsets}}) { 800 $self->{offsets}[$i] += $delta; 801 } 802 } 803 804 # If we scrubbed out all known offsets, regenerate the trivial table 805 # that knows that the file does indeed start at 0. 806 $self->{offsets}[0] = 0 unless @{$self->{offsets}}; 807 # If the file got longer, the offsets table is no longer complete 808 # $self->{eof} = 0 if $delta_recs > 0; 809 810 # Now there might be too much data in the cache, if we spliced out 811 # some short records and spliced in some long ones. If so, flush 812 # the cache. 813 $self->_cache_flush; 814 } 815 816 # If a record does not already end with the appropriate terminator 817 # string, append one. 818 sub _fixrecs { 819 my $self = shift; 820 for (@_) { 821 $_ = "" unless defined $_; 822 $_ .= $self->{recsep} 823 unless substr($_, - $self->{recseplen}) eq $self->{recsep}; 824 } 825 } 826 827 828 ################################################################ 829 # 830 # Basic read, write, and seek 831 # 832 833 # seek to the beginning of record #$n 834 # Assumes that the offsets table is already correctly populated 835 # 836 # Note that $n=-1 has a special meaning here: It means the start of 837 # the last known record; this may or may not be the very last record 838 # in the file, depending on whether the offsets table is fully populated. 839 # 840 sub _seek { 841 my ($self, $n) = @_; 842 my $o = $self->{offsets}[$n]; 843 defined($o) 844 or confess("logic error: undefined offset for record $n"); 845 seek $self->{fh}, $o, SEEK_SET 846 or confess "Couldn't seek filehandle: $!"; # "Should never happen." 847 } 848 849 # seek to byte $b in the file 850 sub _seekb { 851 my ($self, $b) = @_; 852 seek $self->{fh}, $b, SEEK_SET 853 or die "Couldn't seek filehandle: $!"; # "Should never happen." 854 } 855 856 # populate the offsets table up to the beginning of record $n 857 # return the offset of record $n 858 sub _fill_offsets_to { 859 my ($self, $n) = @_; 860 861 return $self->{offsets}[$n] if $self->{eof}; 862 863 my $fh = $self->{fh}; 864 local *OFF = $self->{offsets}; 865 my $rec; 866 867 until ($#OFF >= $n) { 868 $self->_seek(-1); # tricky -- see comment at _seek 869 $rec = $self->_read_record; 870 if (defined $rec) { 871 push @OFF, int(tell $fh); # Tels says that int() saves memory here 872 } else { 873 $self->{eof} = 1; 874 return; # It turns out there is no such record 875 } 876 } 877 878 # we have now read all the records up to record n-1, 879 # so we can return the offset of record n 880 $OFF[$n]; 881 } 882 883 sub _fill_offsets { 884 my ($self) = @_; 885 886 my $fh = $self->{fh}; 887 local *OFF = $self->{offsets}; 888 889 $self->_seek(-1); # tricky -- see comment at _seek 890 891 # Tels says that inlining read_record() would make this loop 892 # five times faster. 20030508 893 while ( defined $self->_read_record()) { 894 # int() saves us memory here 895 push @OFF, int(tell $fh); 896 } 897 898 $self->{eof} = 1; 899 $#OFF; 900 } 901 902 # assumes that $rec is already suitably terminated 903 sub _write_record { 904 my ($self, $rec) = @_; 905 my $fh = $self->{fh}; 906 local $\ = ""; 907 print $fh $rec 908 or die "Couldn't write record: $!"; # "Should never happen." 909 # $self->{_written} += length($rec); 910 } 911 912 sub _read_record { 913 my $self = shift; 914 my $rec; 915 { local $/ = $self->{recsep}; 916 my $fh = $self->{fh}; 917 $rec = <$fh>; 918 } 919 return unless defined $rec; 920 if (substr($rec, -$self->{recseplen}) ne $self->{recsep}) { 921 # improperly terminated final record --- quietly fix it. 922 # my $ac = substr($rec, -$self->{recseplen}); 923 # $ac =~ s/\n/\\n/g; 924 $self->{sawlastrec} = 1; 925 unless ($self->{rdonly}) { 926 local $\ = ""; 927 my $fh = $self->{fh}; 928 print $fh $self->{recsep}; 929 } 930 $rec .= $self->{recsep}; 931 } 932 # $self->{_read} += length($rec) if defined $rec; 933 $rec; 934 } 935 936 sub _rw_stats { 937 my $self = shift; 938 @{$self}{'_read', '_written'}; 939 } 940 941 ################################################################ 942 # 943 # Read cache management 944 945 sub _cache_flush { 946 my ($self) = @_; 947 $self->{cache}->reduce_size_to($self->{memory} - $self->{deferred_s}); 948 } 949 950 sub _cache_too_full { 951 my $self = shift; 952 $self->{cache}->bytes + $self->{deferred_s} >= $self->{memory}; 953 } 954 955 ################################################################ 956 # 957 # File custodial services 958 # 959 960 961 # We have read to the end of the file and have the offsets table 962 # entirely populated. Now we need to write a new record beyond 963 # the end of the file. We prepare for this by writing 964 # empty records into the file up to the position we want 965 # 966 # assumes that the offsets table already contains the offset of record $n, 967 # if it exists, and extends to the end of the file if not. 968 sub _extend_file_to { 969 my ($self, $n) = @_; 970 $self->_seek(-1); # position after the end of the last record 971 my $pos = $self->{offsets}[-1]; 972 973 # the offsets table has one entry more than the total number of records 974 my $extras = $n - $#{$self->{offsets}}; 975 976 # Todo : just use $self->{recsep} x $extras here? 977 while ($extras-- > 0) { 978 $self->_write_record($self->{recsep}); 979 push @{$self->{offsets}}, int(tell $self->{fh}); 980 } 981 } 982 983 # Truncate the file at the current position 984 sub _chop_file { 985 my $self = shift; 986 truncate $self->{fh}, tell($self->{fh}); 987 } 988 989 990 # compute the size of a buffer suitable for moving 991 # all the data in a file forward $n bytes 992 # ($n may be negative) 993 # The result should be at least $n. 994 sub _bufsize { 995 my $n = shift; 996 return 8192 if $n <= 0; 997 my $b = $n & ~8191; 998 $b += 8192 if $n & 8191; 999 $b; 1000 } 1001 1002 ################################################################ 1003 # 1004 # Miscellaneous public methods 1005 # 1006 1007 # Lock the file 1008 sub flock { 1009 my ($self, $op) = @_; 1010 unless (@_ <= 3) { 1011 my $pack = ref $self; 1012 croak "Usage: $pack\->flock([OPERATION])"; 1013 } 1014 my $fh = $self->{fh}; 1015 $op = LOCK_EX unless defined $op; 1016 my $locked = flock $fh, $op; 1017 1018 if ($locked && ($op & (LOCK_EX | LOCK_SH))) { 1019 # If you're locking the file, then presumably it's because 1020 # there might have been a write access by another process. 1021 # In that case, the read cache contents and the offsets table 1022 # might be invalid, so discard them. 20030508 1023 $self->{offsets} = [0]; 1024 $self->{cache}->empty; 1025 } 1026 1027 $locked; 1028 } 1029 1030 # Get/set autochomp option 1031 sub autochomp { 1032 my $self = shift; 1033 if (@_) { 1034 my $old = $self->{autochomp}; 1035 $self->{autochomp} = shift; 1036 $old; 1037 } else { 1038 $self->{autochomp}; 1039 } 1040 } 1041 1042 # Get offset table entries; returns offset of nth record 1043 sub offset { 1044 my ($self, $n) = @_; 1045 1046 if ($#{$self->{offsets}} < $n) { 1047 return if $self->{eof}; # request for record beyond the end of file 1048 my $o = $self->_fill_offsets_to($n); 1049 # If it's still undefined, there is no such record, so return 'undef' 1050 return unless defined $o; 1051 } 1052 1053 $self->{offsets}[$n]; 1054 } 1055 1056 sub discard_offsets { 1057 my $self = shift; 1058 $self->{offsets} = [0]; 1059 } 1060 1061 ################################################################ 1062 # 1063 # Matters related to deferred writing 1064 # 1065 1066 # Defer writes 1067 sub defer { 1068 my $self = shift; 1069 $self->_stop_autodeferring; 1070 @{$self->{ad_history}} = (); 1071 $self->{defer} = 1; 1072 } 1073 1074 # Flush deferred writes 1075 # 1076 # This could be better optimized to write the file in one pass, instead 1077 # of one pass per block of records. But that will require modifications 1078 # to _twrite, so I should have a good _twrite test suite first. 1079 sub flush { 1080 my $self = shift; 1081 1082 $self->_flush; 1083 $self->{defer} = 0; 1084 } 1085 1086 sub _old_flush { 1087 my $self = shift; 1088 my @writable = sort {$a<=>$b} (keys %{$self->{deferred}}); 1089 1090 while (@writable) { 1091 # gather all consecutive records from the front of @writable 1092 my $first_rec = shift @writable; 1093 my $last_rec = $first_rec+1; 1094 ++$last_rec, shift @writable while @writable && $last_rec == $writable[0]; 1095 --$last_rec; 1096 $self->_fill_offsets_to($last_rec); 1097 $self->_extend_file_to($last_rec); 1098 $self->_splice($first_rec, $last_rec-$first_rec+1, 1099 @{$self->{deferred}}{$first_rec .. $last_rec}); 1100 } 1101 1102 $self->_discard; # clear out defered-write-cache 1103 } 1104 1105 sub _flush { 1106 my $self = shift; 1107 my @writable = sort {$a<=>$b} (keys %{$self->{deferred}}); 1108 my @args; 1109 my @adjust; 1110 1111 while (@writable) { 1112 # gather all consecutive records from the front of @writable 1113 my $first_rec = shift @writable; 1114 my $last_rec = $first_rec+1; 1115 ++$last_rec, shift @writable while @writable && $last_rec == $writable[0]; 1116 --$last_rec; 1117 my $end = $self->_fill_offsets_to($last_rec+1); 1118 if (not defined $end) { 1119 $self->_extend_file_to($last_rec); 1120 $end = $self->{offsets}[$last_rec]; 1121 } 1122 my ($start) = $self->{offsets}[$first_rec]; 1123 push @args, 1124 join("", @{$self->{deferred}}{$first_rec .. $last_rec}), # data 1125 $start, # position 1126 $end-$start; # length 1127 push @adjust, [$first_rec, # starting at this position... 1128 $last_rec-$first_rec+1, # this many records... 1129 # are replaced with these... 1130 @{$self->{deferred}}{$first_rec .. $last_rec}, 1131 ]; 1132 } 1133 1134 $self->_mtwrite(@args); # write multiple record groups 1135 $self->_discard; # clear out defered-write-cache 1136 $self->_oadjust(@adjust); 1137 } 1138 1139 # Discard deferred writes and disable future deferred writes 1140 sub discard { 1141 my $self = shift; 1142 $self->_discard; 1143 $self->{defer} = 0; 1144 } 1145 1146 # Discard deferred writes, but retain old deferred writing mode 1147 sub _discard { 1148 my $self = shift; 1149 %{$self->{deferred}} = (); 1150 $self->{deferred_s} = 0; 1151 $self->{deferred_max} = -1; 1152 $self->{cache}->set_limit($self->{memory}); 1153 } 1154 1155 # Deferred writing is enabled, either explicitly ($self->{defer}) 1156 # or automatically ($self->{autodeferring}) 1157 sub _is_deferring { 1158 my $self = shift; 1159 $self->{defer} || $self->{autodeferring}; 1160 } 1161 1162 # The largest record number of any deferred record 1163 sub _defer_max { 1164 my $self = shift; 1165 return $self->{deferred_max} if defined $self->{deferred_max}; 1166 my $max = -1; 1167 for my $key (keys %{$self->{deferred}}) { 1168 $max = $key if $key > $max; 1169 } 1170 $self->{deferred_max} = $max; 1171 $max; 1172 } 1173 1174 ################################################################ 1175 # 1176 # Matters related to autodeferment 1177 # 1178 1179 # Get/set autodefer option 1180 sub autodefer { 1181 my $self = shift; 1182 if (@_) { 1183 my $old = $self->{autodefer}; 1184 $self->{autodefer} = shift; 1185 if ($old) { 1186 $self->_stop_autodeferring; 1187 @{$self->{ad_history}} = (); 1188 } 1189 $old; 1190 } else { 1191 $self->{autodefer}; 1192 } 1193 } 1194 1195 # The user is trying to store record #$n Record that in the history, 1196 # and then enable (or disable) autodeferment if that seems useful. 1197 # Note that it's OK for $n to be a non-number, as long as the function 1198 # is prepared to deal with that. Nobody else looks at the ad_history. 1199 # 1200 # Now, what does the ad_history mean, and what is this function doing? 1201 # Essentially, the idea is to enable autodeferring when we see that the 1202 # user has made three consecutive STORE calls to three consecutive records. 1203 # ("Three" is actually ->{autodefer_threshhold}.) 1204 # A STORE call for record #$n inserts $n into the autodefer history, 1205 # and if the history contains three consecutive records, we enable 1206 # autodeferment. An ad_history of [X, Y] means that the most recent 1207 # STOREs were for records X, X+1, ..., Y, in that order. 1208 # 1209 # Inserting a nonconsecutive number erases the history and starts over. 1210 # 1211 # Performing a special operation like SPLICE erases the history. 1212 # 1213 # There's one special case: CLEAR means that CLEAR was just called. 1214 # In this case, we prime the history with [-2, -1] so that if the next 1215 # write is for record 0, autodeferring goes on immediately. This is for 1216 # the common special case of "@a = (...)". 1217 # 1218 sub _annotate_ad_history { 1219 my ($self, $n) = @_; 1220 return unless $self->{autodefer}; # feature is disabled 1221 return if $self->{defer}; # already in explicit defer mode 1222 return unless $self->{offsets}[-1] >= $self->{autodefer_filelen_threshhold}; 1223 1224 local *H = $self->{ad_history}; 1225 if ($n eq 'CLEAR') { 1226 @H = (-2, -1); # prime the history with fake records 1227 $self->_stop_autodeferring; 1228 } elsif ($n =~ /^\d+$/) { 1229 if (@H == 0) { 1230 @H = ($n, $n); 1231 } else { # @H == 2 1232 if ($H[1] == $n-1) { # another consecutive record 1233 $H[1]++; 1234 if ($H[1] - $H[0] + 1 >= $self->{autodefer_threshhold}) { 1235 $self->{autodeferring} = 1; 1236 } 1237 } else { # nonconsecutive- erase and start over 1238 @H = ($n, $n); 1239 $self->_stop_autodeferring; 1240 } 1241 } 1242 } else { # SPLICE or STORESIZE or some such 1243 @H = (); 1244 $self->_stop_autodeferring; 1245 } 1246 } 1247 1248 # If autodeferring was enabled, cut it out and discard the history 1249 sub _stop_autodeferring { 1250 my $self = shift; 1251 if ($self->{autodeferring}) { 1252 $self->_flush; 1253 } 1254 $self->{autodeferring} = 0; 1255 } 1256 1257 ################################################################ 1258 1259 1260 # This is NOT a method. It is here for two reasons: 1261 # 1. To factor a fairly complicated block out of the constructor 1262 # 2. To provide access for the test suite, which need to be sure 1263 # files are being written properly. 1264 sub _default_recsep { 1265 my $recsep = $/; 1266 if ($^O eq 'MSWin32') { # Dos too? 1267 # Windows users expect files to be terminated with \r\n 1268 # But $/ is set to \n instead 1269 # Note that this also transforms \n\n into \r\n\r\n. 1270 # That is a feature. 1271 $recsep =~ s/\n/\r\n/g; 1272 } 1273 $recsep; 1274 } 1275 1276 # Utility function for _check_integrity 1277 sub _ci_warn { 1278 my $msg = shift; 1279 $msg =~ s/\n/\\n/g; 1280 $msg =~ s/\r/\\r/g; 1281 print "# $msg\n"; 1282 } 1283 1284 # Given a file, make sure the cache is consistent with the 1285 # file contents and the internal data structures are consistent with 1286 # each other. Returns true if everything checks out, false if not 1287 # 1288 # The $file argument is no longer used. It is retained for compatibility 1289 # with the existing test suite. 1290 sub _check_integrity { 1291 my ($self, $file, $warn) = @_; 1292 my $rsl = $self->{recseplen}; 1293 my $rs = $self->{recsep}; 1294 my $good = 1; 1295 local *_; # local $_ does not work here 1296 local $DIAGNOSTIC = 1; 1297 1298 if (not defined $rs) { 1299 _ci_warn("recsep is undef!"); 1300 $good = 0; 1301 } elsif ($rs eq "") { 1302 _ci_warn("recsep is empty!"); 1303 $good = 0; 1304 } elsif ($rsl != length $rs) { 1305 my $ln = length $rs; 1306 _ci_warn("recsep <$rs> has length $ln, should be $rsl"); 1307 $good = 0; 1308 } 1309 1310 if (not defined $self->{offsets}[0]) { 1311 _ci_warn("offset 0 is missing!"); 1312 $good = 0; 1313 1314 } elsif ($self->{offsets}[0] != 0) { 1315 _ci_warn("rec 0: offset <$self->{offsets}[0]> s/b 0!"); 1316 $good = 0; 1317 } 1318 1319 my $cached = 0; 1320 { 1321 local *F = $self->{fh}; 1322 seek F, 0, SEEK_SET; 1323 local $. = 0; 1324 local $/ = $rs; 1325 1326 while (<F>) { 1327 my $n = $. - 1; 1328 my $cached = $self->{cache}->_produce($n); 1329 my $offset = $self->{offsets}[$.]; 1330 my $ao = tell F; 1331 if (defined $offset && $offset != $ao) { 1332 _ci_warn("rec $n: offset <$offset> actual <$ao>"); 1333 $good = 0; 1334 } 1335 if (defined $cached && $_ ne $cached && ! $self->{deferred}{$n}) { 1336 $good = 0; 1337 _ci_warn("rec $n: cached <$cached> actual <$_>"); 1338 } 1339 if (defined $cached && substr($cached, -$rsl) ne $rs) { 1340 $good = 0; 1341 _ci_warn("rec $n in the cache is missing the record separator"); 1342 } 1343 if (! defined $offset && $self->{eof}) { 1344 $good = 0; 1345 _ci_warn("The offset table was marked complete, but it is missing element $."); 1346 } 1347 } 1348 if (@{$self->{offsets}} > $.+1) { 1349 $good = 0; 1350 my $n = @{$self->{offsets}}; 1351 _ci_warn("The offset table has $n items, but the file has only $."); 1352 } 1353 1354 my $deferring = $self->_is_deferring; 1355 for my $n ($self->{cache}->ckeys) { 1356 my $r = $self->{cache}->_produce($n); 1357 $cached += length($r); 1358 next if $n+1 <= $.; # checked this already 1359 _ci_warn("spurious caching of record $n"); 1360 $good = 0; 1361 } 1362 my $b = $self->{cache}->bytes; 1363 if ($cached != $b) { 1364 _ci_warn("cache size is $b, should be $cached"); 1365 $good = 0; 1366 } 1367 } 1368 1369 # That cache has its own set of tests 1370 $good = 0 unless $self->{cache}->_check_integrity; 1371 1372 # Now let's check the deferbuffer 1373 # Unless deferred writing is enabled, it should be empty 1374 if (! $self->_is_deferring && %{$self->{deferred}}) { 1375 _ci_warn("deferred writing disabled, but deferbuffer nonempty"); 1376 $good = 0; 1377 } 1378 1379 # Any record in the deferbuffer should *not* be present in the readcache 1380 my $deferred_s = 0; 1381 while (my ($n, $r) = each %{$self->{deferred}}) { 1382 $deferred_s += length($r); 1383 if (defined $self->{cache}->_produce($n)) { 1384 _ci_warn("record $n is in the deferbuffer *and* the readcache"); 1385 $good = 0; 1386 } 1387 if (substr($r, -$rsl) ne $rs) { 1388 _ci_warn("rec $n in the deferbuffer is missing the record separator"); 1389 $good = 0; 1390 } 1391 } 1392 1393 # Total size of deferbuffer should match internal total 1394 if ($deferred_s != $self->{deferred_s}) { 1395 _ci_warn("buffer size is $self->{deferred_s}, should be $deferred_s"); 1396 $good = 0; 1397 } 1398 1399 # Total size of deferbuffer should not exceed the specified limit 1400 if ($deferred_s > $self->{dw_size}) { 1401 _ci_warn("buffer size is $self->{deferred_s} which exceeds the limit of $self->{dw_size}"); 1402 $good = 0; 1403 } 1404 1405 # Total size of cached data should not exceed the specified limit 1406 if ($deferred_s + $cached > $self->{memory}) { 1407 my $total = $deferred_s + $cached; 1408 _ci_warn("total stored data size is $total which exceeds the limit of $self->{memory}"); 1409 $good = 0; 1410 } 1411 1412 # Stuff related to autodeferment 1413 if (!$self->{autodefer} && @{$self->{ad_history}}) { 1414 _ci_warn("autodefer is disabled, but ad_history is nonempty"); 1415 $good = 0; 1416 } 1417 if ($self->{autodeferring} && $self->{defer}) { 1418 _ci_warn("both autodeferring and explicit deferring are active"); 1419 $good = 0; 1420 } 1421 if (@{$self->{ad_history}} == 0) { 1422 # That's OK, no additional tests required 1423 } elsif (@{$self->{ad_history}} == 2) { 1424 my @non_number = grep !/^-?\d+$/, @{$self->{ad_history}}; 1425 if (@non_number) { 1426 my $msg; 1427 { local $" = ')('; 1428 $msg = "ad_history contains non-numbers (@{$self->{ad_history}})"; 1429 } 1430 _ci_warn($msg); 1431 $good = 0; 1432 } elsif ($self->{ad_history}[1] < $self->{ad_history}[0]) { 1433 _ci_warn("ad_history has nonsensical values @{$self->{ad_history}}"); 1434 $good = 0; 1435 } 1436 } else { 1437 _ci_warn("ad_history has bad length <@{$self->{ad_history}}>"); 1438 $good = 0; 1439 } 1440 1441 $good; 1442 } 1443 1444 ################################################################ 1445 # 1446 # Tie::File::Cache 1447 # 1448 # Read cache 1449 1450 package Tie::File::Cache; 1451 $Tie::File::Cache::VERSION = $Tie::File::VERSION; 1452 use Carp ':DEFAULT', 'confess'; 1453 1454 sub HEAP () { 0 } 1455 sub HASH () { 1 } 1456 sub MAX () { 2 } 1457 sub BYTES() { 3 } 1458 #sub STAT () { 4 } # Array with request statistics for each record 1459 #sub MISS () { 5 } # Total number of cache misses 1460 #sub REQ () { 6 } # Total number of cache requests 1461 use strict 'vars'; 1462 1463 sub new { 1464 my ($pack, $max) = @_; 1465 local *_; 1466 croak "missing argument to ->new" unless defined $max; 1467 my $self = []; 1468 bless $self => $pack; 1469 @$self = (Tie::File::Heap->new($self), {}, $max, 0); 1470 $self; 1471 } 1472 1473 sub adj_limit { 1474 my ($self, $n) = @_; 1475 $self->[MAX] += $n; 1476 } 1477 1478 sub set_limit { 1479 my ($self, $n) = @_; 1480 $self->[MAX] = $n; 1481 } 1482 1483 # For internal use only 1484 # Will be called by the heap structure to notify us that a certain 1485 # piece of data has moved from one heap element to another. 1486 # $k is the hash key of the item 1487 # $n is the new index into the heap at which it is stored 1488 # If $n is undefined, the item has been removed from the heap. 1489 sub _heap_move { 1490 my ($self, $k, $n) = @_; 1491 if (defined $n) { 1492 $self->[HASH]{$k} = $n; 1493 } else { 1494 delete $self->[HASH]{$k}; 1495 } 1496 } 1497 1498 sub insert { 1499 my ($self, $key, $val) = @_; 1500 local *_; 1501 croak "missing argument to ->insert" unless defined $key; 1502 unless (defined $self->[MAX]) { 1503 confess "undefined max" ; 1504 } 1505 confess "undefined val" unless defined $val; 1506 return if length($val) > $self->[MAX]; 1507 1508 # if ($self->[STAT]) { 1509 # $self->[STAT][$key] = 1; 1510 # return; 1511 # } 1512 1513 my $oldnode = $self->[HASH]{$key}; 1514 if (defined $oldnode) { 1515 my $oldval = $self->[HEAP]->set_val($oldnode, $val); 1516 $self->[BYTES] -= length($oldval); 1517 } else { 1518 $self->[HEAP]->insert($key, $val); 1519 } 1520 $self->[BYTES] += length($val); 1521 $self->flush if $self->[BYTES] > $self->[MAX]; 1522 } 1523 1524 sub expire { 1525 my $self = shift; 1526 my $old_data = $self->[HEAP]->popheap; 1527 return unless defined $old_data; 1528 $self->[BYTES] -= length $old_data; 1529 $old_data; 1530 } 1531 1532 sub remove { 1533 my ($self, @keys) = @_; 1534 my @result; 1535 1536 # if ($self->[STAT]) { 1537 # for my $key (@keys) { 1538 # $self->[STAT][$key] = 0; 1539 # } 1540 # return; 1541 # } 1542 1543 for my $key (@keys) { 1544 next unless exists $self->[HASH]{$key}; 1545 my $old_data = $self->[HEAP]->remove($self->[HASH]{$key}); 1546 $self->[BYTES] -= length $old_data; 1547 push @result, $old_data; 1548 } 1549 @result; 1550 } 1551 1552 sub lookup { 1553 my ($self, $key) = @_; 1554 local *_; 1555 croak "missing argument to ->lookup" unless defined $key; 1556 1557 # if ($self->[STAT]) { 1558 # $self->[MISS]++ if $self->[STAT][$key]++ == 0; 1559 # $self->[REQ]++; 1560 # my $hit_rate = 1 - $self->[MISS] / $self->[REQ]; 1561 # # Do some testing to determine this threshhold 1562 # $#$self = STAT - 1 if $hit_rate > 0.20; 1563 # } 1564 1565 if (exists $self->[HASH]{$key}) { 1566 $self->[HEAP]->lookup($self->[HASH]{$key}); 1567 } else { 1568 return; 1569 } 1570 } 1571 1572 # For internal use only 1573 sub _produce { 1574 my ($self, $key) = @_; 1575 my $loc = $self->[HASH]{$key}; 1576 return unless defined $loc; 1577 $self->[HEAP][$loc][2]; 1578 } 1579 1580 # For internal use only 1581 sub _promote { 1582 my ($self, $key) = @_; 1583 $self->[HEAP]->promote($self->[HASH]{$key}); 1584 } 1585 1586 sub empty { 1587 my ($self) = @_; 1588 %{$self->[HASH]} = (); 1589 $self->[BYTES] = 0; 1590 $self->[HEAP]->empty; 1591 # @{$self->[STAT]} = (); 1592 # $self->[MISS] = 0; 1593 # $self->[REQ] = 0; 1594 } 1595 1596 sub is_empty { 1597 my ($self) = @_; 1598 keys %{$self->[HASH]} == 0; 1599 } 1600 1601 sub update { 1602 my ($self, $key, $val) = @_; 1603 local *_; 1604 croak "missing argument to ->update" unless defined $key; 1605 if (length($val) > $self->[MAX]) { 1606 my ($oldval) = $self->remove($key); 1607 $self->[BYTES] -= length($oldval) if defined $oldval; 1608 } elsif (exists $self->[HASH]{$key}) { 1609 my $oldval = $self->[HEAP]->set_val($self->[HASH]{$key}, $val); 1610 $self->[BYTES] += length($val); 1611 $self->[BYTES] -= length($oldval) if defined $oldval; 1612 } else { 1613 $self->[HEAP]->insert($key, $val); 1614 $self->[BYTES] += length($val); 1615 } 1616 $self->flush; 1617 } 1618 1619 sub rekey { 1620 my ($self, $okeys, $nkeys) = @_; 1621 local *_; 1622 my %map; 1623 @map{@$okeys} = @$nkeys; 1624 croak "missing argument to ->rekey" unless defined $nkeys; 1625 croak "length mismatch in ->rekey arguments" unless @$nkeys == @$okeys; 1626 my %adjusted; # map new keys to heap indices 1627 # You should be able to cut this to one loop TODO XXX 1628 for (0 .. $#$okeys) { 1629 $adjusted{$nkeys->[$_]} = delete $self->[HASH]{$okeys->[$_]}; 1630 } 1631 while (my ($nk, $ix) = each %adjusted) { 1632 # @{$self->[HASH]}{keys %adjusted} = values %adjusted; 1633 $self->[HEAP]->rekey($ix, $nk); 1634 $self->[HASH]{$nk} = $ix; 1635 } 1636 } 1637 1638 sub ckeys { 1639 my $self = shift; 1640 my @a = keys %{$self->[HASH]}; 1641 @a; 1642 } 1643 1644 # Return total amount of cached data 1645 sub bytes { 1646 my $self = shift; 1647 $self->[BYTES]; 1648 } 1649 1650 # Expire oldest item from cache until cache size is smaller than $max 1651 sub reduce_size_to { 1652 my ($self, $max) = @_; 1653 until ($self->[BYTES] <= $max) { 1654 # Note that Tie::File::Cache::expire has been inlined here 1655 my $old_data = $self->[HEAP]->popheap; 1656 return unless defined $old_data; 1657 $self->[BYTES] -= length $old_data; 1658 } 1659 } 1660 1661 # Why not just $self->reduce_size_to($self->[MAX])? 1662 # Try this when things stabilize TODO XXX 1663 # If the cache is too full, expire the oldest records 1664 sub flush { 1665 my $self = shift; 1666 $self->reduce_size_to($self->[MAX]) if $self->[BYTES] > $self->[MAX]; 1667 } 1668 1669 # For internal use only 1670 sub _produce_lru { 1671 my $self = shift; 1672 $self->[HEAP]->expire_order; 1673 } 1674 1675 BEGIN { *_ci_warn = \&Tie::File::_ci_warn } 1676 1677 sub _check_integrity { # For CACHE 1678 my $self = shift; 1679 my $good = 1; 1680 1681 # Test HEAP 1682 $self->[HEAP]->_check_integrity or $good = 0; 1683 1684 # Test HASH 1685 my $bytes = 0; 1686 for my $k (keys %{$self->[HASH]}) { 1687 if ($k ne '0' && $k !~ /^[1-9][0-9]*$/) { 1688 $good = 0; 1689 _ci_warn "Cache hash key <$k> is non-numeric"; 1690 } 1691 1692 my $h = $self->[HASH]{$k}; 1693 if (! defined $h) { 1694 $good = 0; 1695 _ci_warn "Heap index number for key $k is undefined"; 1696 } elsif ($h == 0) { 1697 $good = 0; 1698 _ci_warn "Heap index number for key $k is zero"; 1699 } else { 1700 my $j = $self->[HEAP][$h]; 1701 if (! defined $j) { 1702 $good = 0; 1703 _ci_warn "Heap contents key $k (=> $h) are undefined"; 1704 } else { 1705 $bytes += length($j->[2]); 1706 if ($k ne $j->[1]) { 1707 $good = 0; 1708 _ci_warn "Heap contents key $k (=> $h) is $j->[1], should be $k"; 1709 } 1710 } 1711 } 1712 } 1713 1714 # Test BYTES 1715 if ($bytes != $self->[BYTES]) { 1716 $good = 0; 1717 _ci_warn "Total data in cache is $bytes, expected $self->[BYTES]"; 1718 } 1719 1720 # Test MAX 1721 if ($bytes > $self->[MAX]) { 1722 $good = 0; 1723 _ci_warn "Total data in cache is $bytes, exceeds maximum $self->[MAX]"; 1724 } 1725 1726 return $good; 1727 } 1728 1729 sub delink { 1730 my $self = shift; 1731 $self->[HEAP] = undef; # Bye bye heap 1732 } 1733 1734 ################################################################ 1735 # 1736 # Tie::File::Heap 1737 # 1738 # Heap data structure for use by cache LRU routines 1739 1740 package Tie::File::Heap; 1741 use Carp ':DEFAULT', 'confess'; 1742 $Tie::File::Heap::VERSION = $Tie::File::Cache::VERSION; 1743 sub SEQ () { 0 }; 1744 sub KEY () { 1 }; 1745 sub DAT () { 2 }; 1746 1747 sub new { 1748 my ($pack, $cache) = @_; 1749 die "$pack: Parent cache object $cache does not support _heap_move method" 1750 unless eval { $cache->can('_heap_move') }; 1751 my $self = [[0,$cache,0]]; 1752 bless $self => $pack; 1753 } 1754 1755 # Allocate a new sequence number, larger than all previously allocated numbers 1756 sub _nseq { 1757 my $self = shift; 1758 $self->[0][0]++; 1759 } 1760 1761 sub _cache { 1762 my $self = shift; 1763 $self->[0][1]; 1764 } 1765 1766 sub _nelts { 1767 my $self = shift; 1768 $self->[0][2]; 1769 } 1770 1771 sub _nelts_inc { 1772 my $self = shift; 1773 ++$self->[0][2]; 1774 } 1775 1776 sub _nelts_dec { 1777 my $self = shift; 1778 --$self->[0][2]; 1779 } 1780 1781 sub is_empty { 1782 my $self = shift; 1783 $self->_nelts == 0; 1784 } 1785 1786 sub empty { 1787 my $self = shift; 1788 $#$self = 0; 1789 $self->[0][2] = 0; 1790 $self->[0][0] = 0; # might as well reset the sequence numbers 1791 } 1792 1793 # notify the parent cache object that we moved something 1794 sub _heap_move { 1795 my $self = shift; 1796 $self->_cache->_heap_move(@_); 1797 } 1798 1799 # Insert a piece of data into the heap with the indicated sequence number. 1800 # The item with the smallest sequence number is always at the top. 1801 # If no sequence number is specified, allocate a new one and insert the 1802 # item at the bottom. 1803 sub insert { 1804 my ($self, $key, $data, $seq) = @_; 1805 $seq = $self->_nseq unless defined $seq; 1806 $self->_insert_new([$seq, $key, $data]); 1807 } 1808 1809 # Insert a new, fresh item at the bottom of the heap 1810 sub _insert_new { 1811 my ($self, $item) = @_; 1812 my $i = @$self; 1813 $i = int($i/2) until defined $self->[$i/2]; 1814 $self->[$i] = $item; 1815 $self->[0][1]->_heap_move($self->[$i][KEY], $i); 1816 $self->_nelts_inc; 1817 } 1818 1819 # Insert [$data, $seq] pair at or below item $i in the heap. 1820 # If $i is omitted, default to 1 (the top element.) 1821 sub _insert { 1822 my ($self, $item, $i) = @_; 1823 # $self->_check_loc($i) if defined $i; 1824 $i = 1 unless defined $i; 1825 until (! defined $self->[$i]) { 1826 if ($self->[$i][SEQ] > $item->[SEQ]) { # inserted item is older 1827 ($self->[$i], $item) = ($item, $self->[$i]); 1828 $self->[0][1]->_heap_move($self->[$i][KEY], $i); 1829 } 1830 # If either is undefined, go that way. Otherwise, choose at random 1831 my $dir; 1832 $dir = 0 if !defined $self->[2*$i]; 1833 $dir = 1 if !defined $self->[2*$i+1]; 1834 $dir = int(rand(2)) unless defined $dir; 1835 $i = 2*$i + $dir; 1836 } 1837 $self->[$i] = $item; 1838 $self->[0][1]->_heap_move($self->[$i][KEY], $i); 1839 $self->_nelts_inc; 1840 } 1841 1842 # Remove the item at node $i from the heap, moving child items upwards. 1843 # The item with the smallest sequence number is always at the top. 1844 # Moving items upwards maintains this condition. 1845 # Return the removed item. Return undef if there was no item at node $i. 1846 sub remove { 1847 my ($self, $i) = @_; 1848 $i = 1 unless defined $i; 1849 my $top = $self->[$i]; 1850 return unless defined $top; 1851 while (1) { 1852 my $ii; 1853 my ($L, $R) = (2*$i, 2*$i+1); 1854 1855 # If either is undefined, go the other way. 1856 # Otherwise, go towards the smallest. 1857 last unless defined $self->[$L] || defined $self->[$R]; 1858 $ii = $R if not defined $self->[$L]; 1859 $ii = $L if not defined $self->[$R]; 1860 unless (defined $ii) { 1861 $ii = $self->[$L][SEQ] < $self->[$R][SEQ] ? $L : $R; 1862 } 1863 1864 $self->[$i] = $self->[$ii]; # Promote child to fill vacated spot 1865 $self->[0][1]->_heap_move($self->[$i][KEY], $i); 1866 $i = $ii; # Fill new vacated spot 1867 } 1868 $self->[0][1]->_heap_move($top->[KEY], undef); 1869 undef $self->[$i]; 1870 $self->_nelts_dec; 1871 return $top->[DAT]; 1872 } 1873 1874 sub popheap { 1875 my $self = shift; 1876 $self->remove(1); 1877 } 1878 1879 # set the sequence number of the indicated item to a higher number 1880 # than any other item in the heap, and bubble the item down to the 1881 # bottom. 1882 sub promote { 1883 my ($self, $n) = @_; 1884 # $self->_check_loc($n); 1885 $self->[$n][SEQ] = $self->_nseq; 1886 my $i = $n; 1887 while (1) { 1888 my ($L, $R) = (2*$i, 2*$i+1); 1889 my $dir; 1890 last unless defined $self->[$L] || defined $self->[$R]; 1891 $dir = $R unless defined $self->[$L]; 1892 $dir = $L unless defined $self->[$R]; 1893 unless (defined $dir) { 1894 $dir = $self->[$L][SEQ] < $self->[$R][SEQ] ? $L : $R; 1895 } 1896 @{$self}[$i, $dir] = @{$self}[$dir, $i]; 1897 for ($i, $dir) { 1898 $self->[0][1]->_heap_move($self->[$_][KEY], $_) if defined $self->[$_]; 1899 } 1900 $i = $dir; 1901 } 1902 } 1903 1904 # Return item $n from the heap, promoting its LRU status 1905 sub lookup { 1906 my ($self, $n) = @_; 1907 # $self->_check_loc($n); 1908 my $val = $self->[$n]; 1909 $self->promote($n); 1910 $val->[DAT]; 1911 } 1912 1913 1914 # Assign a new value for node $n, promoting it to the bottom of the heap 1915 sub set_val { 1916 my ($self, $n, $val) = @_; 1917 # $self->_check_loc($n); 1918 my $oval = $self->[$n][DAT]; 1919 $self->[$n][DAT] = $val; 1920 $self->promote($n); 1921 return $oval; 1922 } 1923 1924 # The hask key has changed for an item; 1925 # alter the heap's record of the hash key 1926 sub rekey { 1927 my ($self, $n, $new_key) = @_; 1928 # $self->_check_loc($n); 1929 $self->[$n][KEY] = $new_key; 1930 } 1931 1932 sub _check_loc { 1933 my ($self, $n) = @_; 1934 unless (1 || defined $self->[$n]) { 1935 confess "_check_loc($n) failed"; 1936 } 1937 } 1938 1939 BEGIN { *_ci_warn = \&Tie::File::_ci_warn } 1940 1941 sub _check_integrity { 1942 my $self = shift; 1943 my $good = 1; 1944 my %seq; 1945 1946 unless (eval {$self->[0][1]->isa("Tie::File::Cache")}) { 1947 _ci_warn "Element 0 of heap corrupt"; 1948 $good = 0; 1949 } 1950 $good = 0 unless $self->_satisfies_heap_condition(1); 1951 for my $i (2 .. $#{$self}) { 1952 my $p = int($i/2); # index of parent node 1953 if (defined $self->[$i] && ! defined $self->[$p]) { 1954 _ci_warn "Element $i of heap defined, but parent $p isn't"; 1955 $good = 0; 1956 } 1957 1958 if (defined $self->[$i]) { 1959 if ($seq{$self->[$i][SEQ]}) { 1960 my $seq = $self->[$i][SEQ]; 1961 _ci_warn "Nodes $i and $seq{$seq} both have SEQ=$seq"; 1962 $good = 0; 1963 } else { 1964 $seq{$self->[$i][SEQ]} = $i; 1965 } 1966 } 1967 } 1968 1969 return $good; 1970 } 1971 1972 sub _satisfies_heap_condition { 1973 my $self = shift; 1974 my $n = shift || 1; 1975 my $good = 1; 1976 for (0, 1) { 1977 my $c = $n*2 + $_; 1978 next unless defined $self->[$c]; 1979 if ($self->[$n][SEQ] >= $self->[$c]) { 1980 _ci_warn "Node $n of heap does not predate node $c"; 1981 $good = 0 ; 1982 } 1983 $good = 0 unless $self->_satisfies_heap_condition($c); 1984 } 1985 return $good; 1986 } 1987 1988 # Return a list of all the values, sorted by expiration order 1989 sub expire_order { 1990 my $self = shift; 1991 my @nodes = sort {$a->[SEQ] <=> $b->[SEQ]} $self->_nodes; 1992 map { $_->[KEY] } @nodes; 1993 } 1994 1995 sub _nodes { 1996 my $self = shift; 1997 my $i = shift || 1; 1998 return unless defined $self->[$i]; 1999 ($self->[$i], $self->_nodes($i*2), $self->_nodes($i*2+1)); 2000 } 2001 2002 "Cogito, ergo sum."; # don't forget to return a true value from the file 2003 2004 __END__ 2005 2006 =head1 NAME 2007 2008 Tie::File - Access the lines of a disk file via a Perl array 2009 2010 =head1 SYNOPSIS 2011 2012 # This file documents Tie::File version 0.97 2013 use Tie::File; 2014 2015 tie @array, 'Tie::File', filename or die ...; 2016 2017 $array[13] = 'blah'; # line 13 of the file is now 'blah' 2018 print $array[42]; # display line 42 of the file 2019 2020 $n_recs = @array; # how many records are in the file? 2021 $#array -= 2; # chop two records off the end 2022 2023 2024 for (@array) { 2025 s/PERL/Perl/g; # Replace PERL with Perl everywhere in the file 2026 } 2027 2028 # These are just like regular push, pop, unshift, shift, and splice 2029 # Except that they modify the file in the way you would expect 2030 2031 push @array, new recs...; 2032 my $r1 = pop @array; 2033 unshift @array, new recs...; 2034 my $r2 = shift @array; 2035 @old_recs = splice @array, 3, 7, new recs...; 2036 2037 untie @array; # all finished 2038 2039 2040 =head1 DESCRIPTION 2041 2042 C<Tie::File> represents a regular text file as a Perl array. Each 2043 element in the array corresponds to a record in the file. The first 2044 line of the file is element 0 of the array; the second line is element 2045 1, and so on. 2046 2047 The file is I<not> loaded into memory, so this will work even for 2048 gigantic files. 2049 2050 Changes to the array are reflected in the file immediately. 2051 2052 Lazy people and beginners may now stop reading the manual. 2053 2054 =head2 C<recsep> 2055 2056 What is a 'record'? By default, the meaning is the same as for the 2057 C<E<lt>...E<gt>> operator: It's a string terminated by C<$/>, which is 2058 probably C<"\n">. (Minor exception: on DOS and Win32 systems, a 2059 'record' is a string terminated by C<"\r\n">.) You may change the 2060 definition of "record" by supplying the C<recsep> option in the C<tie> 2061 call: 2062 2063 tie @array, 'Tie::File', $file, recsep => 'es'; 2064 2065 This says that records are delimited by the string C<es>. If the file 2066 contained the following data: 2067 2068 Curse these pesky flies!\n 2069 2070 then the C<@array> would appear to have four elements: 2071 2072 "Curse th" 2073 "e p" 2074 "ky fli" 2075 "!\n" 2076 2077 An undefined value is not permitted as a record separator. Perl's 2078 special "paragraph mode" semantics (E<agrave> la C<$/ = "">) are not 2079 emulated. 2080 2081 Records read from the tied array do not have the record separator 2082 string on the end; this is to allow 2083 2084 $array[17] .= "extra"; 2085 2086 to work as expected. 2087 2088 (See L<"autochomp">, below.) Records stored into the array will have 2089 the record separator string appended before they are written to the 2090 file, if they don't have one already. For example, if the record 2091 separator string is C<"\n">, then the following two lines do exactly 2092 the same thing: 2093 2094 $array[17] = "Cherry pie"; 2095 $array[17] = "Cherry pie\n"; 2096 2097 The result is that the contents of line 17 of the file will be 2098 replaced with "Cherry pie"; a newline character will separate line 17 2099 from line 18. This means that this code will do nothing: 2100 2101 chomp $array[17]; 2102 2103 Because the C<chomp>ed value will have the separator reattached when 2104 it is written back to the file. There is no way to create a file 2105 whose trailing record separator string is missing. 2106 2107 Inserting records that I<contain> the record separator string is not 2108 supported by this module. It will probably produce a reasonable 2109 result, but what this result will be may change in a future version. 2110 Use 'splice' to insert records or to replace one record with several. 2111 2112 =head2 C<autochomp> 2113 2114 Normally, array elements have the record separator removed, so that if 2115 the file contains the text 2116 2117 Gold 2118 Frankincense 2119 Myrrh 2120 2121 the tied array will appear to contain C<("Gold", "Frankincense", 2122 "Myrrh")>. If you set C<autochomp> to a false value, the record 2123 separator will not be removed. If the file above was tied with 2124 2125 tie @gifts, "Tie::File", $gifts, autochomp => 0; 2126 2127 then the array C<@gifts> would appear to contain C<("Gold\n", 2128 "Frankincense\n", "Myrrh\n")>, or (on Win32 systems) C<("Gold\r\n", 2129 "Frankincense\r\n", "Myrrh\r\n")>. 2130 2131 =head2 C<mode> 2132 2133 Normally, the specified file will be opened for read and write access, 2134 and will be created if it does not exist. (That is, the flags 2135 C<O_RDWR | O_CREAT> are supplied in the C<open> call.) If you want to 2136 change this, you may supply alternative flags in the C<mode> option. 2137 See L<Fcntl> for a listing of available flags. 2138 For example: 2139 2140 # open the file if it exists, but fail if it does not exist 2141 use Fcntl 'O_RDWR'; 2142 tie @array, 'Tie::File', $file, mode => O_RDWR; 2143 2144 # create the file if it does not exist 2145 use Fcntl 'O_RDWR', 'O_CREAT'; 2146 tie @array, 'Tie::File', $file, mode => O_RDWR | O_CREAT; 2147 2148 # open an existing file in read-only mode 2149 use Fcntl 'O_RDONLY'; 2150 tie @array, 'Tie::File', $file, mode => O_RDONLY; 2151 2152 Opening the data file in write-only or append mode is not supported. 2153 2154 =head2 C<memory> 2155 2156 This is an upper limit on the amount of memory that C<Tie::File> will 2157 consume at any time while managing the file. This is used for two 2158 things: managing the I<read cache> and managing the I<deferred write 2159 buffer>. 2160 2161 Records read in from the file are cached, to avoid having to re-read 2162 them repeatedly. If you read the same record twice, the first time it 2163 will be stored in memory, and the second time it will be fetched from 2164 the I<read cache>. The amount of data in the read cache will not 2165 exceed the value you specified for C<memory>. If C<Tie::File> wants 2166 to cache a new record, but the read cache is full, it will make room 2167 by expiring the least-recently visited records from the read cache. 2168 2169 The default memory limit is 2Mib. You can adjust the maximum read 2170 cache size by supplying the C<memory> option. The argument is the 2171 desired cache size, in bytes. 2172 2173 # I have a lot of memory, so use a large cache to speed up access 2174 tie @array, 'Tie::File', $file, memory => 20_000_000; 2175 2176 Setting the memory limit to 0 will inhibit caching; records will be 2177 fetched from disk every time you examine them. 2178 2179 The C<memory> value is not an absolute or exact limit on the memory 2180 used. C<Tie::File> objects contains some structures besides the read 2181 cache and the deferred write buffer, whose sizes are not charged 2182 against C<memory>. 2183 2184 The cache itself consumes about 310 bytes per cached record, so if 2185 your file has many short records, you may want to decrease the cache 2186 memory limit, or else the cache overhead may exceed the size of the 2187 cached data. 2188 2189 2190 =head2 C<dw_size> 2191 2192 (This is an advanced feature. Skip this section on first reading.) 2193 2194 If you use deferred writing (See L<"Deferred Writing">, below) then 2195 data you write into the array will not be written directly to the 2196 file; instead, it will be saved in the I<deferred write buffer> to be 2197 written out later. Data in the deferred write buffer is also charged 2198 against the memory limit you set with the C<memory> option. 2199 2200 You may set the C<dw_size> option to limit the amount of data that can 2201 be saved in the deferred write buffer. This limit may not exceed the 2202 total memory limit. For example, if you set C<dw_size> to 1000 and 2203 C<memory> to 2500, that means that no more than 1000 bytes of deferred 2204 writes will be saved up. The space available for the read cache will 2205 vary, but it will always be at least 1500 bytes (if the deferred write 2206 buffer is full) and it could grow as large as 2500 bytes (if the 2207 deferred write buffer is empty.) 2208 2209 If you don't specify a C<dw_size>, it defaults to the entire memory 2210 limit. 2211 2212 =head2 Option Format 2213 2214 C<-mode> is a synonym for C<mode>. C<-recsep> is a synonym for 2215 C<recsep>. C<-memory> is a synonym for C<memory>. You get the 2216 idea. 2217 2218 =head1 Public Methods 2219 2220 The C<tie> call returns an object, say C<$o>. You may call 2221 2222 $rec = $o->FETCH($n); 2223 $o->STORE($n, $rec); 2224 2225 to fetch or store the record at line C<$n>, respectively; similarly 2226 the other tied array methods. (See L<perltie> for details.) You may 2227 also call the following methods on this object: 2228 2229 =head2 C<flock> 2230 2231 $o->flock(MODE) 2232 2233 will lock the tied file. C<MODE> has the same meaning as the second 2234 argument to the Perl built-in C<flock> function; for example 2235 C<LOCK_SH> or C<LOCK_EX | LOCK_NB>. (These constants are provided by 2236 the C<use Fcntl ':flock'> declaration.) 2237 2238 C<MODE> is optional; the default is C<LOCK_EX>. 2239 2240 C<Tie::File> maintains an internal table of the byte offset of each 2241 record it has seen in the file. 2242 2243 When you use C<flock> to lock the file, C<Tie::File> assumes that the 2244 read cache is no longer trustworthy, because another process might 2245 have modified the file since the last time it was read. Therefore, a 2246 successful call to C<flock> discards the contents of the read cache 2247 and the internal record offset table. 2248 2249 C<Tie::File> promises that the following sequence of operations will 2250 be safe: 2251 2252 my $o = tie @array, "Tie::File", $filename; 2253 $o->flock; 2254 2255 In particular, C<Tie::File> will I<not> read or write the file during 2256 the C<tie> call. (Exception: Using C<mode =E<gt> O_TRUNC> will, of 2257 course, erase the file during the C<tie> call. If you want to do this 2258 safely, then open the file without C<O_TRUNC>, lock the file, and use 2259 C<@array = ()>.) 2260 2261 The best way to unlock a file is to discard the object and untie the 2262 array. It is probably unsafe to unlock the file without also untying 2263 it, because if you do, changes may remain unwritten inside the object. 2264 That is why there is no shortcut for unlocking. If you really want to 2265 unlock the file prematurely, you know what to do; if you don't know 2266 what to do, then don't do it. 2267 2268 All the usual warnings about file locking apply here. In particular, 2269 note that file locking in Perl is B<advisory>, which means that 2270 holding a lock will not prevent anyone else from reading, writing, or 2271 erasing the file; it only prevents them from getting another lock at 2272 the same time. Locks are analogous to green traffic lights: If you 2273 have a green light, that does not prevent the idiot coming the other 2274 way from plowing into you sideways; it merely guarantees to you that 2275 the idiot does not also have a green light at the same time. 2276 2277 =head2 C<autochomp> 2278 2279 my $old_value = $o->autochomp(0); # disable autochomp option 2280 my $old_value = $o->autochomp(1); # enable autochomp option 2281 2282 my $ac = $o->autochomp(); # recover current value 2283 2284 See L<"autochomp">, above. 2285 2286 =head2 C<defer>, C<flush>, C<discard>, and C<autodefer> 2287 2288 See L<"Deferred Writing">, below. 2289 2290 =head2 C<offset> 2291 2292 $off = $o->offset($n); 2293 2294 This method returns the byte offset of the start of the C<$n>th record 2295 in the file. If there is no such record, it returns an undefined 2296 value. 2297 2298 =head1 Tying to an already-opened filehandle 2299 2300 If C<$fh> is a filehandle, such as is returned by C<IO::File> or one 2301 of the other C<IO> modules, you may use: 2302 2303 tie @array, 'Tie::File', $fh, ...; 2304 2305 Similarly if you opened that handle C<FH> with regular C<open> or 2306 C<sysopen>, you may use: 2307 2308 tie @array, 'Tie::File', \*FH, ...; 2309 2310 Handles that were opened write-only won't work. Handles that were 2311 opened read-only will work as long as you don't try to modify the 2312 array. Handles must be attached to seekable sources of data---that 2313 means no pipes or sockets. If C<Tie::File> can detect that you 2314 supplied a non-seekable handle, the C<tie> call will throw an 2315 exception. (On Unix systems, it can detect this.) 2316 2317 Note that Tie::File will only close any filehandles that it opened 2318 internally. If you passed it a filehandle as above, you "own" the 2319 filehandle, and are responsible for closing it after you have untied 2320 the @array. 2321 2322 =head1 Deferred Writing 2323 2324 (This is an advanced feature. Skip this section on first reading.) 2325 2326 Normally, modifying a C<Tie::File> array writes to the underlying file 2327 immediately. Every assignment like C<$a[3] = ...> rewrites as much of 2328 the file as is necessary; typically, everything from line 3 through 2329 the end will need to be rewritten. This is the simplest and most 2330 transparent behavior. Performance even for large files is reasonably 2331 good. 2332 2333 However, under some circumstances, this behavior may be excessively 2334 slow. For example, suppose you have a million-record file, and you 2335 want to do: 2336 2337 for (@FILE) { 2338 $_ = "> $_"; 2339 } 2340 2341 The first time through the loop, you will rewrite the entire file, 2342 from line 0 through the end. The second time through the loop, you 2343 will rewrite the entire file from line 1 through the end. The third 2344 time through the loop, you will rewrite the entire file from line 2 to 2345 the end. And so on. 2346 2347 If the performance in such cases is unacceptable, you may defer the 2348 actual writing, and then have it done all at once. The following loop 2349 will perform much better for large files: 2350 2351 (tied @a)->defer; 2352 for (@a) { 2353 $_ = "> $_"; 2354 } 2355 (tied @a)->flush; 2356 2357 If C<Tie::File>'s memory limit is large enough, all the writing will 2358 done in memory. Then, when you call C<-E<gt>flush>, the entire file 2359 will be rewritten in a single pass. 2360 2361 (Actually, the preceding discussion is something of a fib. You don't 2362 need to enable deferred writing to get good performance for this 2363 common case, because C<Tie::File> will do it for you automatically 2364 unless you specifically tell it not to. See L<"autodeferring">, 2365 below.) 2366 2367 Calling C<-E<gt>flush> returns the array to immediate-write mode. If 2368 you wish to discard the deferred writes, you may call C<-E<gt>discard> 2369 instead of C<-E<gt>flush>. Note that in some cases, some of the data 2370 will have been written already, and it will be too late for 2371 C<-E<gt>discard> to discard all the changes. Support for 2372 C<-E<gt>discard> may be withdrawn in a future version of C<Tie::File>. 2373 2374 Deferred writes are cached in memory up to the limit specified by the 2375 C<dw_size> option (see above). If the deferred-write buffer is full 2376 and you try to write still more deferred data, the buffer will be 2377 flushed. All buffered data will be written immediately, the buffer 2378 will be emptied, and the now-empty space will be used for future 2379 deferred writes. 2380 2381 If the deferred-write buffer isn't yet full, but the total size of the 2382 buffer and the read cache would exceed the C<memory> limit, the oldest 2383 records will be expired from the read cache until the total size is 2384 under the limit. 2385 2386 C<push>, C<pop>, C<shift>, C<unshift>, and C<splice> cannot be 2387 deferred. When you perform one of these operations, any deferred data 2388 is written to the file and the operation is performed immediately. 2389 This may change in a future version. 2390 2391 If you resize the array with deferred writing enabled, the file will 2392 be resized immediately, but deferred records will not be written. 2393 This has a surprising consequence: C<@a = (...)> erases the file 2394 immediately, but the writing of the actual data is deferred. This 2395 might be a bug. If it is a bug, it will be fixed in a future version. 2396 2397 =head2 Autodeferring 2398 2399 C<Tie::File> tries to guess when deferred writing might be helpful, 2400 and to turn it on and off automatically. 2401 2402 for (@a) { 2403 $_ = "> $_"; 2404 } 2405 2406 In this example, only the first two assignments will be done 2407 immediately; after this, all the changes to the file will be deferred 2408 up to the user-specified memory limit. 2409 2410 You should usually be able to ignore this and just use the module 2411 without thinking about deferring. However, special applications may 2412 require fine control over which writes are deferred, or may require 2413 that all writes be immediate. To disable the autodeferment feature, 2414 use 2415 2416 (tied @o)->autodefer(0); 2417 2418 or 2419 2420 tie @array, 'Tie::File', $file, autodefer => 0; 2421 2422 2423 Similarly, C<-E<gt>autodefer(1)> re-enables autodeferment, and 2424 C<-E<gt>autodefer()> recovers the current value of the autodefer setting. 2425 2426 2427 =head1 CONCURRENT ACCESS TO FILES 2428 2429 Caching and deferred writing are inappropriate if you want the same 2430 file to be accessed simultaneously from more than one process. Other 2431 optimizations performed internally by this module are also 2432 incompatible with concurrent access. A future version of this module will 2433 support a C<concurrent =E<gt> 1> option that enables safe concurrent access. 2434 2435 Previous versions of this documentation suggested using C<memory 2436 =E<gt> 0> for safe concurrent access. This was mistaken. Tie::File 2437 will not support safe concurrent access before version 0.98. 2438 2439 =head1 CAVEATS 2440 2441 (That's Latin for 'warnings'.) 2442 2443 =over 4 2444 2445 =item * 2446 2447 Reasonable effort was made to make this module efficient. Nevertheless, 2448 changing the size of a record in the middle of a large file will 2449 always be fairly slow, because everything after the new record must be 2450 moved. 2451 2452 =item * 2453 2454 The behavior of tied arrays is not precisely the same as for regular 2455 arrays. For example: 2456 2457 # This DOES print "How unusual!" 2458 undef $a[10]; print "How unusual!\n" if defined $a[10]; 2459 2460 C<undef>-ing a C<Tie::File> array element just blanks out the 2461 corresponding record in the file. When you read it back again, you'll 2462 get the empty string, so the supposedly-C<undef>'ed value will be 2463 defined. Similarly, if you have C<autochomp> disabled, then 2464 2465 # This DOES print "How unusual!" if 'autochomp' is disabled 2466 undef $a[10]; 2467 print "How unusual!\n" if $a[10]; 2468 2469 Because when C<autochomp> is disabled, C<$a[10]> will read back as 2470 C<"\n"> (or whatever the record separator string is.) 2471 2472 There are other minor differences, particularly regarding C<exists> 2473 and C<delete>, but in general, the correspondence is extremely close. 2474 2475 =item * 2476 2477 I have supposed that since this module is concerned with file I/O, 2478 almost all normal use of it will be heavily I/O bound. This means 2479 that the time to maintain complicated data structures inside the 2480 module will be dominated by the time to actually perform the I/O. 2481 When there was an opportunity to spend CPU time to avoid doing I/O, I 2482 usually tried to take it. 2483 2484 =item * 2485 2486 You might be tempted to think that deferred writing is like 2487 transactions, with C<flush> as C<commit> and C<discard> as 2488 C<rollback>, but it isn't, so don't. 2489 2490 =item * 2491 2492 There is a large memory overhead for each record offset and for each 2493 cache entry: about 310 bytes per cached data record, and about 21 bytes per offset table entry. 2494 2495 The per-record overhead will limit the maximum number of records you 2496 can access per file. Note that I<accessing> the length of the array 2497 via C<$x = scalar @tied_file> accesses B<all> records and stores their 2498 offsets. The same for C<foreach (@tied_file)>, even if you exit the 2499 loop early. 2500 2501 =back 2502 2503 =head1 SUBCLASSING 2504 2505 This version promises absolutely nothing about the internals, which 2506 may change without notice. A future version of the module will have a 2507 well-defined and stable subclassing API. 2508 2509 =head1 WHAT ABOUT C<DB_File>? 2510 2511 People sometimes point out that L<DB_File> will do something similar, 2512 and ask why C<Tie::File> module is necessary. 2513 2514 There are a number of reasons that you might prefer C<Tie::File>. 2515 A list is available at C<http://perl.plover.com/TieFile/why-not-DB_File>. 2516 2517 =head1 AUTHOR 2518 2519 Mark Jason Dominus 2520 2521 To contact the author, send email to: C<mjd-perl-tiefile+@plover.com> 2522 2523 To receive an announcement whenever a new version of this module is 2524 released, send a blank email message to 2525 C<mjd-perl-tiefile-subscribe@plover.com>. 2526 2527 The most recent version of this module, including documentation and 2528 any news of importance, will be available at 2529 2530 http://perl.plover.com/TieFile/ 2531 2532 2533 =head1 LICENSE 2534 2535 C<Tie::File> version 0.97 is copyright (C) 2003 Mark Jason Dominus. 2536 2537 This library is free software; you may redistribute it and/or modify 2538 it under the same terms as Perl itself. 2539 2540 These terms are your choice of any of (1) the Perl Artistic Licence, 2541 or (2) version 2 of the GNU General Public License as published by the 2542 Free Software Foundation, or (3) any later version of the GNU General 2543 Public License. 2544 2545 This library is distributed in the hope that it will be useful, 2546 but WITHOUT ANY WARRANTY; without even the implied warranty of 2547 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 2548 GNU General Public License for more details. 2549 2550 You should have received a copy of the GNU General Public License 2551 along with this library program; it should be in the file C<COPYING>. 2552 If not, write to the Free Software Foundation, Inc., 51 Franklin Street, 2553 Fifth Floor, Boston, MA 02110-1301, USA 2554 2555 For licensing inquiries, contact the author at: 2556 2557 Mark Jason Dominus 2558 255 S. Warnock St. 2559 Philadelphia, PA 19107 2560 2561 =head1 WARRANTY 2562 2563 C<Tie::File> version 0.97 comes with ABSOLUTELY NO WARRANTY. 2564 For details, see the license. 2565 2566 =head1 THANKS 2567 2568 Gigantic thanks to Jarkko Hietaniemi, for agreeing to put this in the 2569 core when I hadn't written it yet, and for generally being helpful, 2570 supportive, and competent. (Usually the rule is "choose any one.") 2571 Also big thanks to Abhijit Menon-Sen for all of the same things. 2572 2573 Special thanks to Craig Berry and Peter Prymmer (for VMS portability 2574 help), Randy Kobes (for Win32 portability help), Clinton Pierce and 2575 Autrijus Tang (for heroic eleventh-hour Win32 testing above and beyond 2576 the call of duty), Michael G Schwern (for testing advice), and the 2577 rest of the CPAN testers (for testing generally). 2578 2579 Special thanks to Tels for suggesting several speed and memory 2580 optimizations. 2581 2582 Additional thanks to: 2583 Edward Avis / 2584 Mattia Barbon / 2585 Tom Christiansen / 2586 Gerrit Haase / 2587 Gurusamy Sarathy / 2588 Jarkko Hietaniemi (again) / 2589 Nikola Knezevic / 2590 John Kominetz / 2591 Nick Ing-Simmons / 2592 Tassilo von Parseval / 2593 H. Dieter Pearcey / 2594 Slaven Rezic / 2595 Eric Roode / 2596 Peter Scott / 2597 Peter Somu / 2598 Autrijus Tang (again) / 2599 Tels (again) / 2600 Juerd Waalboer 2601 2602 =head1 TODO 2603 2604 More tests. (Stuff I didn't think of yet.) 2605 2606 Paragraph mode? 2607 2608 Fixed-length mode. Leave-blanks mode. 2609 2610 Maybe an autolocking mode? 2611 2612 For many common uses of the module, the read cache is a liability. 2613 For example, a program that inserts a single record, or that scans the 2614 file once, will have a cache hit rate of zero. This suggests a major 2615 optimization: The cache should be initially disabled. Here's a hybrid 2616 approach: Initially, the cache is disabled, but the cache code 2617 maintains statistics about how high the hit rate would be *if* it were 2618 enabled. When it sees the hit rate get high enough, it enables 2619 itself. The STAT comments in this code are the beginning of an 2620 implementation of this. 2621 2622 Record locking with fcntl()? Then the module might support an undo 2623 log and get real transactions. What a tour de force that would be. 2624 2625 Keeping track of the highest cached record. This would allow reads-in-a-row 2626 to skip the cache lookup faster (if reading from 1..N with empty cache at 2627 start, the last cached value will be always N-1). 2628 2629 More tests. 2630 2631 =cut 2632
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