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Revision 1.207 by root, Mon Jul 25 16:50:33 2011 UTC vs.
Revision 1.219 by root, Tue Mar 27 18:54:45 2012 UTC

… …
168use common::sense; 168use common::sense;
169 169
170use base 'Exporter'; 170use base 'Exporter';
171 171
172BEGIN { 172BEGIN {
173 our $VERSION = '4.0'; 173 our $VERSION = '4.12';
174 174
175 our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close 175 our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close
176 aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx 176 aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx
177 aio_scandir aio_symlink aio_readlink aio_realpath aio_sync 177 aio_scandir aio_symlink aio_readlink aio_realpath aio_sync
178 aio_fsync aio_syncfs aio_fdatasync aio_sync_file_range aio_fallocate 178 aio_fsync aio_syncfs aio_fdatasync aio_sync_file_range aio_fallocate
179 aio_pathsync aio_readahead 179 aio_pathsync aio_readahead
180 aio_rename aio_link aio_move aio_copy aio_group 180 aio_rename aio_link aio_move aio_copy aio_group
181 aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown 181 aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown
182 aio_chmod aio_utime aio_truncate 182 aio_chmod aio_utime aio_truncate
183 aio_msync aio_mtouch aio_mlock aio_mlockall 183 aio_msync aio_mtouch aio_mlock aio_mlockall
184 aio_statvfs); 184 aio_statvfs
185 aio_wd);
185 186
186 our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice)); 187 our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
187 our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush 188 our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
188 min_parallel max_parallel max_idle idle_timeout 189 min_parallel max_parallel max_idle idle_timeout
189 nreqs nready npending nthreads 190 nreqs nready npending nthreads
… …
205 206
206This section simply lists the prototypes of the most important functions 207This section simply lists the prototypes of the most important functions
207for quick reference. See the following sections for function-by-function 208for quick reference. See the following sections for function-by-function
208documentation. 209documentation.
209 210
211 aio_wd $pathname, $callback->($wd)
210 aio_open $pathname, $flags, $mode, $callback->($fh) 212 aio_open $pathname, $flags, $mode, $callback->($fh)
211 aio_close $fh, $callback->($status) 213 aio_close $fh, $callback->($status)
212 aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval) 214 aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
213 aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval) 215 aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
214 aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval) 216 aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
… …
219 aio_utime $fh_or_path, $atime, $mtime, $callback->($status) 221 aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
220 aio_chown $fh_or_path, $uid, $gid, $callback->($status) 222 aio_chown $fh_or_path, $uid, $gid, $callback->($status)
221 aio_truncate $fh_or_path, $offset, $callback->($status) 223 aio_truncate $fh_or_path, $offset, $callback->($status)
222 aio_chmod $fh_or_path, $mode, $callback->($status) 224 aio_chmod $fh_or_path, $mode, $callback->($status)
223 aio_unlink $pathname, $callback->($status) 225 aio_unlink $pathname, $callback->($status)
224 aio_mknod $path, $mode, $dev, $callback->($status) 226 aio_mknod $pathname, $mode, $dev, $callback->($status)
225 aio_link $srcpath, $dstpath, $callback->($status) 227 aio_link $srcpath, $dstpath, $callback->($status)
226 aio_symlink $srcpath, $dstpath, $callback->($status) 228 aio_symlink $srcpath, $dstpath, $callback->($status)
227 aio_readlink $path, $callback->($link) 229 aio_readlink $pathname, $callback->($link)
228 aio_realpath $path, $callback->($link) 230 aio_realpath $pathname, $callback->($link)
229 aio_rename $srcpath, $dstpath, $callback->($status) 231 aio_rename $srcpath, $dstpath, $callback->($status)
230 aio_mkdir $pathname, $mode, $callback->($status) 232 aio_mkdir $pathname, $mode, $callback->($status)
231 aio_rmdir $pathname, $callback->($status) 233 aio_rmdir $pathname, $callback->($status)
232 aio_readdir $pathname, $callback->($entries) 234 aio_readdir $pathname, $callback->($entries)
233 aio_readdirx $pathname, $flags, $callback->($entries, $flags) 235 aio_readdirx $pathname, $flags, $callback->($entries, $flags)
234 IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST 236 IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
235 IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN 237 IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
238 aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
236 aio_load $path, $data, $callback->($status) 239 aio_load $pathname, $data, $callback->($status)
237 aio_copy $srcpath, $dstpath, $callback->($status) 240 aio_copy $srcpath, $dstpath, $callback->($status)
238 aio_move $srcpath, $dstpath, $callback->($status) 241 aio_move $srcpath, $dstpath, $callback->($status)
239 aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
240 aio_rmtree $path, $callback->($status) 242 aio_rmtree $pathname, $callback->($status)
241 aio_sync $callback->($status) 243 aio_sync $callback->($status)
242 aio_syncfs $fh, $callback->($status) 244 aio_syncfs $fh, $callback->($status)
243 aio_fsync $fh, $callback->($status) 245 aio_fsync $fh, $callback->($status)
244 aio_fdatasync $fh, $callback->($status) 246 aio_fdatasync $fh, $callback->($status)
245 aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status) 247 aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
246 aio_pathsync $path, $callback->($status) 248 aio_pathsync $pathname, $callback->($status)
247 aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status) 249 aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
248 aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status) 250 aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
249 aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status) 251 aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
250 aio_mlockall $flags, $callback->($status) 252 aio_mlockall $flags, $callback->($status)
251 aio_group $callback->(...) 253 aio_group $callback->(...)
… …
274 IO::AIO::madvise $scalar, $offset, $length, $advice 276 IO::AIO::madvise $scalar, $offset, $length, $advice
275 IO::AIO::mprotect $scalar, $offset, $length, $protect 277 IO::AIO::mprotect $scalar, $offset, $length, $protect
276 IO::AIO::munlock $scalar, $offset = 0, $length = undef 278 IO::AIO::munlock $scalar, $offset = 0, $length = undef
277 IO::AIO::munlockall 279 IO::AIO::munlockall
278 280
279=head2 AIO REQUEST FUNCTIONS 281=head2 API NOTES
280 282
281All the C<aio_*> calls are more or less thin wrappers around the syscall 283All the C<aio_*> calls are more or less thin wrappers around the syscall
282with the same name (sans C<aio_>). The arguments are similar or identical, 284with the same name (sans C<aio_>). The arguments are similar or identical,
283and they all accept an additional (and optional) C<$callback> argument 285and they all accept an additional (and optional) C<$callback> argument
284which must be a code reference. This code reference will get called with 286which must be a code reference. This code reference will be called after
285the syscall return code (e.g. most syscalls return C<-1> on error, unlike 287the syscall has been executed in an asynchronous fashion. The results
286perl, which usually delivers "false") as its sole argument after the given 288of the request will be passed as arguments to the callback (and, if an
287syscall has been executed asynchronously. 289error occured, in C<$!>) - for most requests the syscall return code (e.g.
290most syscalls return C<-1> on error, unlike perl, which usually delivers
291"false").
292
293Some requests (such as C<aio_readdir>) pass the actual results and
294communicate failures by passing C<undef>.
288 295
289All functions expecting a filehandle keep a copy of the filehandle 296All functions expecting a filehandle keep a copy of the filehandle
290internally until the request has finished. 297internally until the request has finished.
291 298
292All functions return request objects of type L<IO::AIO::REQ> that allow 299All functions return request objects of type L<IO::AIO::REQ> that allow
293further manipulation of those requests while they are in-flight. 300further manipulation of those requests while they are in-flight.
294 301
295The pathnames you pass to these routines I<must> be absolute and 302The pathnames you pass to these routines I<should> be absolute. The
296encoded as octets. The reason for the former is that at the time the 303reason for this is that at the time the request is being executed, the
297request is being executed, the current working directory could have 304current working directory could have changed. Alternatively, you can
298changed. Alternatively, you can make sure that you never change the 305make sure that you never change the current working directory anywhere
299current working directory anywhere in the program and then use relative 306in the program and then use relative paths. You can also take advantage
300paths. 307of IO::AIOs working directory abstraction, that lets you specify paths
308relative to some previously-opened "working directory object" - see the
309description of the C<IO::AIO::WD> class later in this document.
301 310
302To encode pathnames as octets, either make sure you either: a) always pass 311To encode pathnames as octets, either make sure you either: a) always pass
303in filenames you got from outside (command line, readdir etc.) without 312in filenames you got from outside (command line, readdir etc.) without
304tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode 313tinkering, b) are in your native filesystem encoding, c) use the Encode
305your pathnames to the locale (or other) encoding in effect in the user 314module and encode your pathnames to the locale (or other) encoding in
306environment, d) use Glib::filename_from_unicode on unicode filenames or e) 315effect in the user environment, d) use Glib::filename_from_unicode on
307use something else to ensure your scalar has the correct contents. 316unicode filenames or e) use something else to ensure your scalar has the
317correct contents.
308 318
309This works, btw. independent of the internal UTF-8 bit, which IO::AIO 319This works, btw. independent of the internal UTF-8 bit, which IO::AIO
310handles correctly whether it is set or not. 320handles correctly whether it is set or not.
321
322=head2 AIO REQUEST FUNCTIONS
311 323
312=over 4 324=over 4
313 325
314=item $prev_pri = aioreq_pri [$pri] 326=item $prev_pri = aioreq_pri [$pri]
315 327
… …
614 626
615Asynchronously unlink (delete) a file and call the callback with the 627Asynchronously unlink (delete) a file and call the callback with the
616result code. 628result code.
617 629
618 630
619=item aio_mknod $path, $mode, $dev, $callback->($status) 631=item aio_mknod $pathname, $mode, $dev, $callback->($status)
620 632
621[EXPERIMENTAL] 633[EXPERIMENTAL]
622 634
623Asynchronously create a device node (or fifo). See mknod(2). 635Asynchronously create a device node (or fifo). See mknod(2).
624 636
625The only (POSIX-) portable way of calling this function is: 637The only (POSIX-) portable way of calling this function is:
626 638
627 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ... 639 aio_mknod $pathname, IO::AIO::S_IFIFO | $mode, 0, sub { ...
628 640
629See C<aio_stat> for info about some potentially helpful extra constants 641See C<aio_stat> for info about some potentially helpful extra constants
630and functions. 642and functions.
631 643
632=item aio_link $srcpath, $dstpath, $callback->($status) 644=item aio_link $srcpath, $dstpath, $callback->($status)
… …
639 651
640Asynchronously create a new symbolic link to the existing object at C<$srcpath> at 652Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
641the path C<$dstpath> and call the callback with the result code. 653the path C<$dstpath> and call the callback with the result code.
642 654
643 655
644=item aio_readlink $path, $callback->($link) 656=item aio_readlink $pathname, $callback->($link)
645 657
646Asynchronously read the symlink specified by C<$path> and pass it to 658Asynchronously read the symlink specified by C<$path> and pass it to
647the callback. If an error occurs, nothing or undef gets passed to the 659the callback. If an error occurs, nothing or undef gets passed to the
648callback. 660callback.
649 661
650 662
651=item aio_realpath $path, $callback->($path) 663=item aio_realpath $pathname, $callback->($path)
652 664
653Asynchronously make the path absolute and resolve any symlinks in 665Asynchronously make the path absolute and resolve any symlinks in
654C<$path>. The resulting path only consists of directories (Same as 666C<$path>. The resulting path only consists of directories (Same as
655L<Cwd::realpath>). 667L<Cwd::realpath>).
656 668
… …
751C<$type>'s are known, which can be used to speed up some algorithms. 763C<$type>'s are known, which can be used to speed up some algorithms.
752 764
753=back 765=back
754 766
755 767
756=item aio_load $path, $data, $callback->($status) 768=item aio_load $pathname, $data, $callback->($status)
757 769
758This is a composite request that tries to fully load the given file into 770This is a composite request that tries to fully load the given file into
759memory. Status is the same as with aio_read. 771memory. Status is the same as with aio_read.
760 772
761=cut 773=cut
… …
896 }; 908 };
897 909
898 $grp 910 $grp
899} 911}
900 912
901=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs) 913=item aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
902 914
903Scans a directory (similar to C<aio_readdir>) but additionally tries to 915Scans a directory (similar to C<aio_readdir>) but additionally tries to
904efficiently separate the entries of directory C<$path> into two sets of 916efficiently separate the entries of directory C<$path> into two sets of
905names, directories you can recurse into (directories), and ones you cannot 917names, directories you can recurse into (directories), and ones you cannot
906recurse into (everything else, including symlinks to directories). 918recurse into (everything else, including symlinks to directories).
… …
963 975
964 my $grp = aio_group $cb; 976 my $grp = aio_group $cb;
965 977
966 $maxreq = 4 if $maxreq <= 0; 978 $maxreq = 4 if $maxreq <= 0;
967 979
968 # stat once 980 # get a wd object
969 aioreq_pri $pri; 981 aioreq_pri $pri;
970 add $grp aio_stat $path, sub { 982 add $grp aio_wd $path, sub {
983 $_[0]
971 return $grp->result () if $_[0]; 984 or return $grp->result ();
972 my $now = time;
973 my $hash1 = join ":", (stat _)[0,1,3,7,9];
974 985
975 # read the directory entries 986 my $wd = [shift, "."];
987
988 # stat once
976 aioreq_pri $pri; 989 aioreq_pri $pri;
977 add $grp aio_readdirx $path, READDIR_DIRS_FIRST, sub { 990 add $grp aio_stat $wd, sub {
978 my $entries = shift
979 or return $grp->result (); 991 return $grp->result () if $_[0];
992 my $now = time;
993 my $hash1 = join ":", (stat _)[0,1,3,7,9];
980 994
981 # stat the dir another time 995 # read the directory entries
982 aioreq_pri $pri; 996 aioreq_pri $pri;
997 add $grp aio_readdirx $wd, READDIR_DIRS_FIRST, sub {
998 my $entries = shift
999 or return $grp->result ();
1000
1001 # stat the dir another time
1002 aioreq_pri $pri;
983 add $grp aio_stat $path, sub { 1003 add $grp aio_stat $wd, sub {
984 my $hash2 = join ":", (stat _)[0,1,3,7,9]; 1004 my $hash2 = join ":", (stat _)[0,1,3,7,9];
985 1005
986 my $ndirs; 1006 my $ndirs;
987 1007
988 # take the slow route if anything looks fishy 1008 # take the slow route if anything looks fishy
989 if ($hash1 ne $hash2 or (stat _)[9] == $now) { 1009 if ($hash1 ne $hash2 or (stat _)[9] == $now) {
990 $ndirs = -1; 1010 $ndirs = -1;
991 } else { 1011 } else {
992 # if nlink == 2, we are finished 1012 # if nlink == 2, we are finished
993 # for non-posix-fs's, we rely on nlink < 2 1013 # for non-posix-fs's, we rely on nlink < 2
994 $ndirs = (stat _)[3] - 2 1014 $ndirs = (stat _)[3] - 2
995 or return $grp->result ([], $entries); 1015 or return $grp->result ([], $entries);
996 } 1016 }
997 1017
998 my (@dirs, @nondirs); 1018 my (@dirs, @nondirs);
999 1019
1000 my $statgrp = add $grp aio_group sub { 1020 my $statgrp = add $grp aio_group sub {
1001 $grp->result (\@dirs, \@nondirs); 1021 $grp->result (\@dirs, \@nondirs);
1002 }; 1022 };
1003 1023
1004 limit $statgrp $maxreq; 1024 limit $statgrp $maxreq;
1005 feed $statgrp sub { 1025 feed $statgrp sub {
1006 return unless @$entries; 1026 return unless @$entries;
1007 my $entry = shift @$entries; 1027 my $entry = shift @$entries;
1008 1028
1009 aioreq_pri $pri; 1029 aioreq_pri $pri;
1030 $wd->[1] = "$entry/.";
1010 add $statgrp aio_stat "$path/$entry/.", sub { 1031 add $statgrp aio_stat $wd, sub {
1011 if ($_[0] < 0) { 1032 if ($_[0] < 0) {
1012 push @nondirs, $entry; 1033 push @nondirs, $entry;
1013 } else { 1034 } else {
1014 # need to check for real directory 1035 # need to check for real directory
1015 aioreq_pri $pri; 1036 aioreq_pri $pri;
1037 $wd->[1] = $entry;
1016 add $statgrp aio_lstat "$path/$entry", sub { 1038 add $statgrp aio_lstat $wd, sub {
1017 if (-d _) { 1039 if (-d _) {
1018 push @dirs, $entry; 1040 push @dirs, $entry;
1019 1041
1020 unless (--$ndirs) { 1042 unless (--$ndirs) {
1021 push @nondirs, @$entries; 1043 push @nondirs, @$entries;
1022 feed $statgrp; 1044 feed $statgrp;
1045 }
1046 } else {
1047 push @nondirs, $entry;
1023 } 1048 }
1024 } else {
1025 push @nondirs, $entry;
1026 } 1049 }
1027 } 1050 }
1028 } 1051 };
1029 }; 1052 };
1030 }; 1053 };
1031 }; 1054 };
1032 }; 1055 };
1033 }; 1056 };
1034 1057
1035 $grp 1058 $grp
1036} 1059}
1037 1060
1038=item aio_rmtree $path, $callback->($status) 1061=item aio_rmtree $pathname, $callback->($status)
1039 1062
1040Delete a directory tree starting (and including) C<$path>, return the 1063Delete a directory tree starting (and including) C<$path>, return the
1041status of the final C<rmdir> only. This is a composite request that 1064status of the final C<rmdir> only. This is a composite request that
1042uses C<aio_scandir> to recurse into and rmdir directories, and unlink 1065uses C<aio_scandir> to recurse into and rmdir directories, and unlink
1043everything else. 1066everything else.
… …
1104C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>, 1127C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
1105C<IO::AIO::SYNC_FILE_RANGE_WRITE> and 1128C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
1106C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range 1129C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
1107manpage for details. 1130manpage for details.
1108 1131
1109=item aio_pathsync $path, $callback->($status) 1132=item aio_pathsync $pathname, $callback->($status)
1110 1133
1111This request tries to open, fsync and close the given path. This is a 1134This request tries to open, fsync and close the given path. This is a
1112composite request intended to sync directories after directory operations 1135composite request intended to sync directories after directory operations
1113(E.g. rename). This might not work on all operating systems or have any 1136(E.g. rename). This might not work on all operating systems or have any
1114specific effect, but usually it makes sure that directory changes get 1137specific effect, but usually it makes sure that directory changes get
… …
1257immense (it blocks a thread for a long time) so do not use this function 1280immense (it blocks a thread for a long time) so do not use this function
1258except to put your application under artificial I/O pressure. 1281except to put your application under artificial I/O pressure.
1259 1282
1260=back 1283=back
1261 1284
1285
1286=head2 IO::AIO::WD - multiple working directories
1287
1288Your process only has one current working directory, which is used by all
1289threads. This makes it hard to use relative paths (some other component
1290could call C<chdir> at any time, and it is hard to control when the path
1291will be used by IO::AIO).
1292
1293One solution for this is to always use absolute paths. This usually works,
1294but can be quite slow (the kernel has to walk the whole path on every
1295access), and can also be a hassle to implement.
1296
1297Newer POSIX systems have a number of functions (openat, fdopendir,
1298futimensat and so on) that make it possible to specify working directories
1299per operation.
1300
1301For portability, and because the clowns who "designed", or shall I write,
1302perpetrated this new interface were obviously half-drunk, this abstraction
1303cannot be perfect, though.
1304
1305IO::AIO allows you to convert directory paths into a so-called IO::AIO::WD
1306object. This object stores the canonicalised, absolute version of the
1307path, and on systems that allow it, also a directory file descriptor.
1308
1309Everywhere where a pathname is accepted by IO::AIO (e.g. in C<aio_stat>
1310or C<aio_unlink>), one can specify an array reference with an IO::AIO::WD
1311object and a pathname instead (or the IO::AIO::WD object alone, which
1312gets interpreted as C<[$wd, "."]>). If the pathname is absolute, the
1313IO::AIO::WD object is ignored, otherwise the pathname is resolved relative
1314to that IO::AIO::WD object.
1315
1316For example, to get a wd object for F</etc> and then stat F<passwd>
1317inside, you would write:
1318
1319 aio_wd "/etc", sub {
1320 my $etcdir = shift;
1321
1322 # although $etcdir can be undef on error, there is generally no reason
1323 # to check for errors here, as aio_stat will fail with ENOENT
1324 # when $etcdir is undef.
1325
1326 aio_stat [$etcdir, "passwd"], sub {
1327 # yay
1328 };
1329 };
1330
1331That C<aio_wd> is a request and not a normal function shows that creating
1332an IO::AIO::WD object is itself a potentially blocking operation, which is
1333why it is done asynchronously.
1334
1335To stat the directory obtained with C<aio_wd> above, one could write
1336either of the following three request calls:
1337
1338 aio_lstat "/etc" , sub { ... # pathname as normal string
1339 aio_lstat [$wd, "."], sub { ... # "." relative to $wd (i.e. $wd itself)
1340 aio_lstat $wd , sub { ... # shorthand for the previous
1341
1342As with normal pathnames, IO::AIO keeps a copy of the working directory
1343object and the pathname string, so you could write the following without
1344causing any issues due to C<$path> getting reused:
1345
1346 my $path = [$wd, undef];
1347
1348 for my $name (qw(abc def ghi)) {
1349 $path->[1] = $name;
1350 aio_stat $path, sub {
1351 # ...
1352 };
1353 }
1354
1355There are some caveats: when directories get renamed (or deleted), the
1356pathname string doesn't change, so will point to the new directory (or
1357nowhere at all), while the directory fd, if available on the system,
1358will still point to the original directory. Most functions accepting a
1359pathname will use the directory fd on newer systems, and the string on
1360older systems. Some functions (such as realpath) will always rely on the
1361string form of the pathname.
1362
1363So this fucntionality is mainly useful to get some protection against
1364C<chdir>, to easily get an absolute path out of a relative path for future
1365reference, and to speed up doing many operations in the same directory
1366(e.g. when stat'ing all files in a directory).
1367
1368The following functions implement this working directory abstraction:
1369
1370=over 4
1371
1372=item aio_wd $pathname, $callback->($wd)
1373
1374Asynchonously canonicalise the given pathname and convert it to an
1375IO::AIO::WD object representing it. If possible and supported on the
1376system, also open a directory fd to speed up pathname resolution relative
1377to this working directory.
1378
1379If something goes wrong, then C<undef> is passwd to the callback instead
1380of a working directory object and C<$!> is set appropriately. Since
1381passing C<undef> as working directory component of a pathname fails the
1382request with C<ENOENT>, there is often no need for error checking in the
1383C<aio_wd> callback, as future requests using the value will fail in the
1384expected way.
1385
1386If this call isn't available because your OS lacks it or it couldn't be
1387detected, it will be emulated by calling C<fsync> instead.
1388
1389=item IO::AIO::CWD
1390
1391This is a compiletime constant (object) that represents the process
1392current working directory.
1393
1394Specifying this object as working directory object for a pathname is as
1395if the pathname would be specified directly, without a directory object,
1396e.g., these calls are functionally identical:
1397
1398 aio_stat "somefile", sub { ... };
1399 aio_stat [IO::AIO::CWD, "somefile"], sub { ... };
1400
1401=back
1402
1403
1262=head2 IO::AIO::REQ CLASS 1404=head2 IO::AIO::REQ CLASS
1263 1405
1264All non-aggregate C<aio_*> functions return an object of this class when 1406All non-aggregate C<aio_*> functions return an object of this class when
1265called in non-void context. 1407called in non-void context.
1266 1408
… …
1383 1525
1384Sets a feeder/generator on this group: every group can have an attached 1526Sets a feeder/generator on this group: every group can have an attached
1385generator that generates requests if idle. The idea behind this is that, 1527generator that generates requests if idle. The idea behind this is that,
1386although you could just queue as many requests as you want in a group, 1528although you could just queue as many requests as you want in a group,
1387this might starve other requests for a potentially long time. For example, 1529this might starve other requests for a potentially long time. For example,
1388C<aio_scandir> might generate hundreds of thousands C<aio_stat> requests, 1530C<aio_scandir> might generate hundreds of thousands of C<aio_stat>
1389delaying any later requests for a long time. 1531requests, delaying any later requests for a long time.
1390 1532
1391To avoid this, and allow incremental generation of requests, you can 1533To avoid this, and allow incremental generation of requests, you can
1392instead a group and set a feeder on it that generates those requests. The 1534instead a group and set a feeder on it that generates those requests. The
1393feed callback will be called whenever there are few enough (see C<limit>, 1535feed callback will be called whenever there are few enough (see C<limit>,
1394below) requests active in the group itself and is expected to queue more 1536below) requests active in the group itself and is expected to queue more

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