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50 50
51=head1 DESCRIPTION 51=head1 DESCRIPTION
52 52
53This module implements asynchronous I/O using whatever means your 53This module implements asynchronous I/O using whatever means your
54operating system supports. 54operating system supports.
55
56Asynchronous means that operations that can normally block your program
57(e.g. reading from disk) will be done asynchronously: the operation
58will still block, but you can do something else in the meantime. This
59is extremely useful for programs that need to stay interactive even
60when doing heavy I/O (GUI programs, high performance network servers
61etc.), but can also be used to easily do operations in parallel that are
62normally done sequentially, e.g. stat'ing many files, which is much faster
63on a RAID volume or over NFS when you do a number of stat operations
64concurrently.
65
66While most of this works on all types of file descriptors (for example
67sockets), using these functions on file descriptors that support
68nonblocking operation (again, sockets, pipes etc.) is very inefficient or
69might not work (aio_read fails on sockets/pipes/fifos). Use an event loop
70for that (such as the L<Event|Event> module): IO::AIO will naturally fit
71into such an event loop itself.
55 72
56In this version, a number of threads are started that execute your 73In this version, a number of threads are started that execute your
57requests and signal their completion. You don't need thread support 74requests and signal their completion. You don't need thread support
58in perl, and the threads created by this module will not be visible 75in perl, and the threads created by this module will not be visible
59to perl. In the future, this module might make use of the native aio 76to perl. In the future, this module might make use of the native aio
60functions available on many operating systems. However, they are often 77functions available on many operating systems. However, they are often
61not well-supported or restricted (Linux doesn't allow them on normal 78not well-supported or restricted (GNU/Linux doesn't allow them on normal
62files currently, for example), and they would only support aio_read and 79files currently, for example), and they would only support aio_read and
63aio_write, so the remaining functionality would have to be implemented 80aio_write, so the remaining functionality would have to be implemented
64using threads anyway. 81using threads anyway.
65 82
66Although the module will work with in the presence of other (Perl-) 83Although the module will work with in the presence of other (Perl-)
67threads, it is currently not reentrant in any way, so use appropriate 84threads, it is currently not reentrant in any way, so use appropriate
68locking yourself, always call C<poll_cb> from within the same thread, or 85locking yourself, always call C<poll_cb> from within the same thread, or
69never call C<poll_cb> (or other C<aio_> functions) recursively. 86never call C<poll_cb> (or other C<aio_> functions) recursively.
70 87
88=head2 EXAMPLE
89
90This is a simple example that uses the Event module and loads
91F</etc/passwd> asynchronously:
92
93 use Fcntl;
94 use Event;
95 use IO::AIO;
96
97 # register the IO::AIO callback with Event
98 Event->io (fd => IO::AIO::poll_fileno,
99 poll => 'r',
100 cb => \&IO::AIO::poll_cb);
101
102 # queue the request to open /etc/passwd
103 aio_open "/etc/passwd", O_RDONLY, 0, sub {
104 my $fh = $_[0]
105 or die "error while opening: $!";
106
107 # stat'ing filehandles is generally non-blocking
108 my $size = -s $fh;
109
110 # queue a request to read the file
111 my $contents;
112 aio_read $fh, 0, $size, $contents, 0, sub {
113 $_[0] == $size
114 or die "short read: $!";
115
116 close $fh;
117
118 # file contents now in $contents
119 print $contents;
120
121 # exit event loop and program
122 Event::unloop;
123 };
124 };
125
126 # possibly queue up other requests, or open GUI windows,
127 # check for sockets etc. etc.
128
129 # process events as long as there are some:
130 Event::loop;
131
71=head1 REQUEST ANATOMY AND LIFETIME 132=head1 REQUEST ANATOMY AND LIFETIME
72 133
73Every C<aio_*> function creates a request. which is a C data structure not 134Every C<aio_*> function creates a request. which is a C data structure not
74directly visible to Perl. 135directly visible to Perl.
75 136
… …
116Request has reached the end of its lifetime and holds no resources anymore 177Request has reached the end of its lifetime and holds no resources anymore
117(except possibly for the Perl object, but its connection to the actual 178(except possibly for the Perl object, but its connection to the actual
118aio request is severed and calling its methods will either do nothing or 179aio request is severed and calling its methods will either do nothing or
119result in a runtime error). 180result in a runtime error).
120 181
182=back
183
121=cut 184=cut
122 185
123package IO::AIO; 186package IO::AIO;
124 187
125no warnings; 188no warnings;
126use strict 'vars'; 189use strict 'vars';
127 190
128use base 'Exporter'; 191use base 'Exporter';
129 192
130BEGIN { 193BEGIN {
131 our $VERSION = '2.0'; 194 our $VERSION = '2.2';
132 195
133 our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat 196 our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
134 aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink 197 aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
135 aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move 198 aio_readlink aio_fsync aio_fdatasync aio_readahead aio_rename aio_link
136 aio_group aio_nop); 199 aio_move aio_copy aio_group aio_nop aio_mknod);
137 our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice)); 200 our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
138 our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush 201 our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
139 min_parallel max_parallel nreqs nready npending); 202 min_parallel max_parallel max_idle
203 nreqs nready npending nthreads
204 max_poll_time max_poll_reqs);
140 205
141 @IO::AIO::GRP::ISA = 'IO::AIO::REQ'; 206 @IO::AIO::GRP::ISA = 'IO::AIO::REQ';
142 207
143 require XSLoader; 208 require XSLoader;
144 XSLoader::load ("IO::AIO", $VERSION); 209 XSLoader::load ("IO::AIO", $VERSION);
145} 210}
146 211
147=head1 FUNCTIONS 212=head1 FUNCTIONS
148 213
149=head2 AIO FUNCTIONS 214=head2 AIO REQUEST FUNCTIONS
150 215
151All the C<aio_*> calls are more or less thin wrappers around the syscall 216All the C<aio_*> calls are more or less thin wrappers around the syscall
152with the same name (sans C<aio_>). The arguments are similar or identical, 217with the same name (sans C<aio_>). The arguments are similar or identical,
153and they all accept an additional (and optional) C<$callback> argument 218and they all accept an additional (and optional) C<$callback> argument
154which must be a code reference. This code reference will get called with 219which must be a code reference. This code reference will get called with
… …
157syscall has been executed asynchronously. 222syscall has been executed asynchronously.
158 223
159All functions expecting a filehandle keep a copy of the filehandle 224All functions expecting a filehandle keep a copy of the filehandle
160internally until the request has finished. 225internally until the request has finished.
161 226
162All requests return objects of type L<IO::AIO::REQ> that allow further 227All functions return request objects of type L<IO::AIO::REQ> that allow
163manipulation of those requests while they are in-flight. 228further manipulation of those requests while they are in-flight.
164 229
165The pathnames you pass to these routines I<must> be absolute and 230The pathnames you pass to these routines I<must> be absolute and
166encoded in byte form. The reason for the former is that at the time the 231encoded as octets. The reason for the former is that at the time the
167request is being executed, the current working directory could have 232request is being executed, the current working directory could have
168changed. Alternatively, you can make sure that you never change the 233changed. Alternatively, you can make sure that you never change the
169current working directory. 234current working directory anywhere in the program and then use relative
235paths.
170 236
171To encode pathnames to byte form, either make sure you either: a) 237To encode pathnames as octets, either make sure you either: a) always pass
172always pass in filenames you got from outside (command line, readdir 238in filenames you got from outside (command line, readdir etc.) without
173etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode 239tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
174your pathnames to the locale (or other) encoding in effect in the user 240your pathnames to the locale (or other) encoding in effect in the user
175environment, d) use Glib::filename_from_unicode on unicode filenames or e) 241environment, d) use Glib::filename_from_unicode on unicode filenames or e)
176use something else. 242use something else to ensure your scalar has the correct contents.
243
244This works, btw. independent of the internal UTF-8 bit, which IO::AIO
245handles correctly wether it is set or not.
177 246
178=over 4 247=over 4
179 248
180=item $prev_pri = aioreq_pri [$pri] 249=item $prev_pri = aioreq_pri [$pri]
181 250
… …
204 }; 273 };
205 274
206=item aioreq_nice $pri_adjust 275=item aioreq_nice $pri_adjust
207 276
208Similar to C<aioreq_pri>, but subtracts the given value from the current 277Similar to C<aioreq_pri>, but subtracts the given value from the current
209priority, so effects are cumulative. 278priority, so the effect is cumulative.
210 279
211=item aio_open $pathname, $flags, $mode, $callback->($fh) 280=item aio_open $pathname, $flags, $mode, $callback->($fh)
212 281
213Asynchronously open or create a file and call the callback with a newly 282Asynchronously open or create a file and call the callback with a newly
214created filehandle for the file. 283created filehandle for the file.
… …
264 333
265 aio_read $fh, 7, 15, $buffer, 0, sub { 334 aio_read $fh, 7, 15, $buffer, 0, sub {
266 $_[0] > 0 or die "read error: $!"; 335 $_[0] > 0 or die "read error: $!";
267 print "read $_[0] bytes: <$buffer>\n"; 336 print "read $_[0] bytes: <$buffer>\n";
268 }; 337 };
269
270=item aio_move $srcpath, $dstpath, $callback->($status)
271
272Try to move the I<file> (directories not supported as either source or
273destination) from C<$srcpath> to C<$dstpath> and call the callback with
274the C<0> (error) or C<-1> ok.
275
276This is a composite request that tries to rename(2) the file first. If
277rename files with C<EXDEV>, it creates the destination file with mode 0200
278and copies the contents of the source file into it using C<aio_sendfile>,
279followed by restoring atime, mtime, access mode and uid/gid, in that
280order, and unlinking the C<$srcpath>.
281
282If an error occurs, the partial destination file will be unlinked, if
283possible, except when setting atime, mtime, access mode and uid/gid, where
284errors are being ignored.
285
286=cut
287
288sub aio_move($$$) {
289 my ($src, $dst, $cb) = @_;
290
291 my $pri = aioreq_pri;
292 my $grp = aio_group $cb;
293
294 aioreq_pri $pri;
295 add $grp aio_rename $src, $dst, sub {
296 if ($_[0] && $! == EXDEV) {
297 aioreq_pri $pri;
298 add $grp aio_open $src, O_RDONLY, 0, sub {
299 if (my $src_fh = $_[0]) {
300 my @stat = stat $src_fh;
301
302 aioreq_pri $pri;
303 add $grp aio_open $dst, O_WRONLY, 0200, sub {
304 if (my $dst_fh = $_[0]) {
305 aioreq_pri $pri;
306 add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
307 close $src_fh;
308
309 if ($_[0] == $stat[7]) {
310 utime $stat[8], $stat[9], $dst;
311 chmod $stat[2] & 07777, $dst_fh;
312 chown $stat[4], $stat[5], $dst_fh;
313 close $dst_fh;
314
315 aioreq_pri $pri;
316 add $grp aio_unlink $src, sub {
317 $grp->result ($_[0]);
318 };
319 } else {
320 my $errno = $!;
321 aioreq_pri $pri;
322 add $grp aio_unlink $dst, sub {
323 $! = $errno;
324 $grp->result (-1);
325 };
326 }
327 };
328 } else {
329 $grp->result (-1);
330 }
331 },
332
333 } else {
334 $grp->result (-1);
335 }
336 };
337 } else {
338 $grp->result ($_[0]);
339 }
340 };
341
342 $grp
343}
344 338
345=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval) 339=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
346 340
347Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts 341Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
348reading at byte offset C<$in_offset>, and starts writing at the current 342reading at byte offset C<$in_offset>, and starts writing at the current
… …
404=item aio_unlink $pathname, $callback->($status) 398=item aio_unlink $pathname, $callback->($status)
405 399
406Asynchronously unlink (delete) a file and call the callback with the 400Asynchronously unlink (delete) a file and call the callback with the
407result code. 401result code.
408 402
403=item aio_mknod $path, $mode, $dev, $callback->($status)
404
405[EXPERIMENTAL]
406
407Asynchronously create a device node (or fifo). See mknod(2).
408
409The only (POSIX-) portable way of calling this function is:
410
411 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
412
409=item aio_link $srcpath, $dstpath, $callback->($status) 413=item aio_link $srcpath, $dstpath, $callback->($status)
410 414
411Asynchronously create a new link to the existing object at C<$srcpath> at 415Asynchronously create a new link to the existing object at C<$srcpath> at
412the path C<$dstpath> and call the callback with the result code. 416the path C<$dstpath> and call the callback with the result code.
413 417
414=item aio_symlink $srcpath, $dstpath, $callback->($status) 418=item aio_symlink $srcpath, $dstpath, $callback->($status)
415 419
416Asynchronously create a new symbolic link to the existing object at C<$srcpath> at 420Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
417the path C<$dstpath> and call the callback with the result code. 421the path C<$dstpath> and call the callback with the result code.
422
423=item aio_readlink $path, $callback->($link)
424
425Asynchronously read the symlink specified by C<$path> and pass it to
426the callback. If an error occurs, nothing or undef gets passed to the
427callback.
418 428
419=item aio_rename $srcpath, $dstpath, $callback->($status) 429=item aio_rename $srcpath, $dstpath, $callback->($status)
420 430
421Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as 431Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
422rename(2) and call the callback with the result code. 432rename(2) and call the callback with the result code.
… …
432directory (i.e. opendir + readdir + closedir). The entries will not be 442directory (i.e. opendir + readdir + closedir). The entries will not be
433sorted, and will B<NOT> include the C<.> and C<..> entries. 443sorted, and will B<NOT> include the C<.> and C<..> entries.
434 444
435The callback a single argument which is either C<undef> or an array-ref 445The callback a single argument which is either C<undef> or an array-ref
436with the filenames. 446with the filenames.
447
448=item aio_copy $srcpath, $dstpath, $callback->($status)
449
450Try to copy the I<file> (directories not supported as either source or
451destination) from C<$srcpath> to C<$dstpath> and call the callback with
452the C<0> (error) or C<-1> ok.
453
454This is a composite request that it creates the destination file with
455mode 0200 and copies the contents of the source file into it using
456C<aio_sendfile>, followed by restoring atime, mtime, access mode and
457uid/gid, in that order.
458
459If an error occurs, the partial destination file will be unlinked, if
460possible, except when setting atime, mtime, access mode and uid/gid, where
461errors are being ignored.
462
463=cut
464
465sub aio_copy($$;$) {
466 my ($src, $dst, $cb) = @_;
467
468 my $pri = aioreq_pri;
469 my $grp = aio_group $cb;
470
471 aioreq_pri $pri;
472 add $grp aio_open $src, O_RDONLY, 0, sub {
473 if (my $src_fh = $_[0]) {
474 my @stat = stat $src_fh;
475
476 aioreq_pri $pri;
477 add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
478 if (my $dst_fh = $_[0]) {
479 aioreq_pri $pri;
480 add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
481 if ($_[0] == $stat[7]) {
482 $grp->result (0);
483 close $src_fh;
484
485 # those should not normally block. should. should.
486 utime $stat[8], $stat[9], $dst;
487 chmod $stat[2] & 07777, $dst_fh;
488 chown $stat[4], $stat[5], $dst_fh;
489 close $dst_fh;
490 } else {
491 $grp->result (-1);
492 close $src_fh;
493 close $dst_fh;
494
495 aioreq $pri;
496 add $grp aio_unlink $dst;
497 }
498 };
499 } else {
500 $grp->result (-1);
501 }
502 },
503
504 } else {
505 $grp->result (-1);
506 }
507 };
508
509 $grp
510}
511
512=item aio_move $srcpath, $dstpath, $callback->($status)
513
514Try to move the I<file> (directories not supported as either source or
515destination) from C<$srcpath> to C<$dstpath> and call the callback with
516the C<0> (error) or C<-1> ok.
517
518This is a composite request that tries to rename(2) the file first. If
519rename files with C<EXDEV>, it copies the file with C<aio_copy> and, if
520that is successful, unlinking the C<$srcpath>.
521
522=cut
523
524sub aio_move($$;$) {
525 my ($src, $dst, $cb) = @_;
526
527 my $pri = aioreq_pri;
528 my $grp = aio_group $cb;
529
530 aioreq_pri $pri;
531 add $grp aio_rename $src, $dst, sub {
532 if ($_[0] && $! == EXDEV) {
533 aioreq_pri $pri;
534 add $grp aio_copy $src, $dst, sub {
535 $grp->result ($_[0]);
536
537 if (!$_[0]) {
538 aioreq_pri $pri;
539 add $grp aio_unlink $src;
540 }
541 };
542 } else {
543 $grp->result ($_[0]);
544 }
545 };
546
547 $grp
548}
437 549
438=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs) 550=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
439 551
440Scans a directory (similar to C<aio_readdir>) but additionally tries to 552Scans a directory (similar to C<aio_readdir>) but additionally tries to
441efficiently separate the entries of directory C<$path> into two sets of 553efficiently separate the entries of directory C<$path> into two sets of
… …
794 906
795=back 907=back
796 908
797=head2 SUPPORT FUNCTIONS 909=head2 SUPPORT FUNCTIONS
798 910
911=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
912
799=over 4 913=over 4
800 914
801=item $fileno = IO::AIO::poll_fileno 915=item $fileno = IO::AIO::poll_fileno
802 916
803Return the I<request result pipe file descriptor>. This filehandle must be 917Return the I<request result pipe file descriptor>. This filehandle must be
… …
807 921
808See C<poll_cb> for an example. 922See C<poll_cb> for an example.
809 923
810=item IO::AIO::poll_cb 924=item IO::AIO::poll_cb
811 925
812Process all outstanding events on the result pipe. You have to call this 926Process some outstanding events on the result pipe. You have to call this
813regularly. Returns the number of events processed. Returns immediately 927regularly. Returns the number of events processed. Returns immediately
814when no events are outstanding. 928when no events are outstanding. The amount of events processed depends on
929the settings of C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
815 930
816If not all requests were processed for whatever reason, the filehandle 931If not all requests were processed for whatever reason, the filehandle
817will still be ready when C<poll_cb> returns. 932will still be ready when C<poll_cb> returns.
818 933
819Example: Install an Event watcher that automatically calls 934Example: Install an Event watcher that automatically calls
… …
821 936
822 Event->io (fd => IO::AIO::poll_fileno, 937 Event->io (fd => IO::AIO::poll_fileno,
823 poll => 'r', async => 1, 938 poll => 'r', async => 1,
824 cb => \&IO::AIO::poll_cb); 939 cb => \&IO::AIO::poll_cb);
825 940
826=item IO::AIO::poll_some $max_requests 941=item IO::AIO::max_poll_reqs $nreqs
827 942
828Similar to C<poll_cb>, but only processes up to C<$max_requests> requests 943=item IO::AIO::max_poll_time $seconds
829at a time.
830 944
831Useful if you want to ensure some level of interactiveness when perl is 945These set the maximum number of requests (default C<0>, meaning infinity)
832not fast enough to process all requests in time. 946that are being processed by C<IO::AIO::poll_cb> in one call, respectively
947the maximum amount of time (default C<0>, meaning infinity) spent in
948C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
949of time C<poll_cb> is allowed to use).
950
951Setting C<max_poll_time> to a non-zero value creates an overhead of one
952syscall per request processed, which is not normally a problem unless your
953callbacks are really really fast or your OS is really really slow (I am
954not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
955
956Setting these is useful if you want to ensure some level of
957interactiveness when perl is not fast enough to process all requests in
958time.
959
960For interactive programs, values such as C<0.01> to C<0.1> should be fine.
833 961
834Example: Install an Event watcher that automatically calls 962Example: Install an Event watcher that automatically calls
835IO::AIO::poll_some with low priority, to ensure that other parts of the 963IO::AIO::poll_cb with low priority, to ensure that other parts of the
836program get the CPU sometimes even under high AIO load. 964program get the CPU sometimes even under high AIO load.
837 965
966 # try not to spend much more than 0.1s in poll_cb
967 IO::AIO::max_poll_time 0.1;
968
969 # use a low priority so other tasks have priority
838 Event->io (fd => IO::AIO::poll_fileno, 970 Event->io (fd => IO::AIO::poll_fileno,
839 poll => 'r', nice => 1, 971 poll => 'r', nice => 1,
840 cb => sub { IO::AIO::poll_some 256 }); 972 cb => &IO::AIO::poll_cb);
841 973
842=item IO::AIO::poll_wait 974=item IO::AIO::poll_wait
843 975
976If there are any outstanding requests and none of them in the result
844Wait till the result filehandle becomes ready for reading (simply does a 977phase, wait till the result filehandle becomes ready for reading (simply
845C<select> on the filehandle. This is useful if you want to synchronously wait 978does a C<select> on the filehandle. This is useful if you want to
846for some requests to finish). 979synchronously wait for some requests to finish).
847 980
848See C<nreqs> for an example. 981See C<nreqs> for an example.
849 982
983=item IO::AIO::poll
984
985Waits until some requests have been handled.
986
987Returns the number of requests processed, but is otherwise strictly
988equivalent to:
989
990 IO::AIO::poll_wait, IO::AIO::poll_cb
991
850=item IO::AIO::nreqs 992=item IO::AIO::flush
851 993
852Returns the number of requests currently in the ready, execute or pending 994Wait till all outstanding AIO requests have been handled.
853states (i.e. for which their callback has not been invoked yet).
854 995
855Example: wait till there are no outstanding requests anymore: 996Strictly equivalent to:
856 997
857 IO::AIO::poll_wait, IO::AIO::poll_cb 998 IO::AIO::poll_wait, IO::AIO::poll_cb
858 while IO::AIO::nreqs; 999 while IO::AIO::nreqs;
859 1000
860=item IO::AIO::nready 1001=head3 CONTROLLING THE NUMBER OF THREADS
861
862Returns the number of requests currently in the ready state (not yet
863executed).
864
865=item IO::AIO::npending
866
867Returns the number of requests currently in the pending state (executed,
868but not yet processed by poll_cb).
869
870=item IO::AIO::flush
871
872Wait till all outstanding AIO requests have been handled.
873
874Strictly equivalent to:
875
876 IO::AIO::poll_wait, IO::AIO::poll_cb
877 while IO::AIO::nreqs;
878
879=item IO::AIO::poll
880
881Waits until some requests have been handled.
882
883Strictly equivalent to:
884
885 IO::AIO::poll_wait, IO::AIO::poll_cb
886 if IO::AIO::nreqs;
887 1002
888=item IO::AIO::min_parallel $nthreads 1003=item IO::AIO::min_parallel $nthreads
889 1004
890Set the minimum number of AIO threads to C<$nthreads>. The current 1005Set the minimum number of AIO threads to C<$nthreads>. The current
891default is C<8>, which means eight asynchronous operations can execute 1006default is C<8>, which means eight asynchronous operations can execute
892concurrently at any one time (the number of outstanding requests, 1007concurrently at any one time (the number of outstanding requests,
893however, is unlimited). 1008however, is unlimited).
894 1009
895IO::AIO starts threads only on demand, when an AIO request is queued and 1010IO::AIO starts threads only on demand, when an AIO request is queued and
896no free thread exists. 1011no free thread exists. Please note that queueing up a hundred requests can
1012create demand for a hundred threads, even if it turns out that everything
1013is in the cache and could have been processed faster by a single thread.
897 1014
898It is recommended to keep the number of threads relatively low, as some 1015It is recommended to keep the number of threads relatively low, as some
899Linux kernel versions will scale negatively with the number of threads 1016Linux kernel versions will scale negatively with the number of threads
900(higher parallelity => MUCH higher latency). With current Linux 2.6 1017(higher parallelity => MUCH higher latency). With current Linux 2.6
901versions, 4-32 threads should be fine. 1018versions, 4-32 threads should be fine.
… …
915This module automatically runs C<max_parallel 0> at program end, to ensure 1032This module automatically runs C<max_parallel 0> at program end, to ensure
916that all threads are killed and that there are no outstanding requests. 1033that all threads are killed and that there are no outstanding requests.
917 1034
918Under normal circumstances you don't need to call this function. 1035Under normal circumstances you don't need to call this function.
919 1036
1037=item IO::AIO::max_idle $nthreads
1038
1039Limit the number of threads (default: 4) that are allowed to idle (i.e.,
1040threads that did not get a request to process within 10 seconds). That
1041means if a thread becomes idle while C<$nthreads> other threads are also
1042idle, it will free its resources and exit.
1043
1044This is useful when you allow a large number of threads (e.g. 100 or 1000)
1045to allow for extremely high load situations, but want to free resources
1046under normal circumstances (1000 threads can easily consume 30MB of RAM).
1047
1048The default is probably ok in most situations, especially if thread
1049creation is fast. If thread creation is very slow on your system you might
1050want to use larger values.
1051
920=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs 1052=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
921 1053
922This is a very bad function to use in interactive programs because it 1054This is a very bad function to use in interactive programs because it
923blocks, and a bad way to reduce concurrency because it is inexact: Better 1055blocks, and a bad way to reduce concurrency because it is inexact: Better
924use an C<aio_group> together with a feed callback. 1056use an C<aio_group> together with a feed callback.
… …
933 1065
934You can still queue as many requests as you want. Therefore, 1066You can still queue as many requests as you want. Therefore,
935C<max_oustsanding> is mainly useful in simple scripts (with low values) or 1067C<max_oustsanding> is mainly useful in simple scripts (with low values) or
936as a stop gap to shield against fatal memory overflow (with large values). 1068as a stop gap to shield against fatal memory overflow (with large values).
937 1069
1070=head3 STATISTICAL INFORMATION
1071
1072=item IO::AIO::nreqs
1073
1074Returns the number of requests currently in the ready, execute or pending
1075states (i.e. for which their callback has not been invoked yet).
1076
1077Example: wait till there are no outstanding requests anymore:
1078
1079 IO::AIO::poll_wait, IO::AIO::poll_cb
1080 while IO::AIO::nreqs;
1081
1082=item IO::AIO::nready
1083
1084Returns the number of requests currently in the ready state (not yet
1085executed).
1086
1087=item IO::AIO::npending
1088
1089Returns the number of requests currently in the pending state (executed,
1090but not yet processed by poll_cb).
1091
938=back 1092=back
939 1093
940=cut 1094=cut
941 1095
942# support function to convert a fd into a perl filehandle 1096# support function to convert a fd into a perl filehandle
… …
954 1108
955 *$sym 1109 *$sym
956} 1110}
957 1111
958min_parallel 8; 1112min_parallel 8;
1113
1114END {
1115 min_parallel 1;
1116 flush;
1117};
959 1118
9601; 11191;
961 1120
962=head2 FORK BEHAVIOUR 1121=head2 FORK BEHAVIOUR
963 1122

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