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… …
3 3
4SYNOPSIS 4SYNOPSIS
5 use IO::AIO; 5 use IO::AIO;
6 6
7 aio_open "/etc/passwd", O_RDONLY, 0, sub { 7 aio_open "/etc/passwd", O_RDONLY, 0, sub {
8 my ($fh) = @_; 8 my $fh = shift
9 or die "/etc/passwd: $!";
9 ... 10 ...
10 }; 11 };
11 12
12 aio_unlink "/tmp/file", sub { }; 13 aio_unlink "/tmp/file", sub { };
13 14
… …
23 $req->cancel; # cancel request if still in queue 24 $req->cancel; # cancel request if still in queue
24 25
25 my $grp = aio_group sub { print "all stats done\n" }; 26 my $grp = aio_group sub { print "all stats done\n" };
26 add $grp aio_stat "..." for ...; 27 add $grp aio_stat "..." for ...;
27 28
29 # AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
30 use AnyEvent::AIO;
31
28 # AnyEvent integration 32 # EV integration
29 open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!"; 33 my $w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
30 my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
31 34
32 # Event integration 35 # Event integration
33 Event->io (fd => IO::AIO::poll_fileno, 36 Event->io (fd => IO::AIO::poll_fileno,
34 poll => 'r', 37 poll => 'r',
35 cb => \&IO::AIO::poll_cb); 38 cb => \&IO::AIO::poll_cb);
… …
58 but can also be used to easily do operations in parallel that are 61 but can also be used to easily do operations in parallel that are
59 normally done sequentially, e.g. stat'ing many files, which is much 62 normally done sequentially, e.g. stat'ing many files, which is much
60 faster on a RAID volume or over NFS when you do a number of stat 63 faster on a RAID volume or over NFS when you do a number of stat
61 operations concurrently. 64 operations concurrently.
62 65
63 While this works on all types of file descriptors (for example sockets), 66 While most of this works on all types of file descriptors (for example
64 using these functions on file descriptors that support nonblocking 67 sockets), using these functions on file descriptors that support
65 operation (again, sockets, pipes etc.) is very inefficient. Use an event 68 nonblocking operation (again, sockets, pipes etc.) is very inefficient.
66 loop for that (such as the Event module): IO::AIO will naturally fit 69 Use an event loop for that (such as the Event module): IO::AIO will
67 into such an event loop itself. 70 naturally fit into such an event loop itself.
68 71
69 In this version, a number of threads are started that execute your 72 In this version, a number of threads are started that execute your
70 requests and signal their completion. You don't need thread support in 73 requests and signal their completion. You don't need thread support in
71 perl, and the threads created by this module will not be visible to 74 perl, and the threads created by this module will not be visible to
72 perl. In the future, this module might make use of the native aio 75 perl. In the future, this module might make use of the native aio
… …
74 not well-supported or restricted (GNU/Linux doesn't allow them on normal 77 not well-supported or restricted (GNU/Linux doesn't allow them on normal
75 files currently, for example), and they would only support aio_read and 78 files currently, for example), and they would only support aio_read and
76 aio_write, so the remaining functionality would have to be implemented 79 aio_write, so the remaining functionality would have to be implemented
77 using threads anyway. 80 using threads anyway.
78 81
79 Although the module will work with in the presence of other (Perl-) 82 Although the module will work in the presence of other (Perl-) threads,
80 threads, it is currently not reentrant in any way, so use appropriate 83 it is currently not reentrant in any way, so use appropriate locking
81 locking yourself, always call "poll_cb" from within the same thread, or 84 yourself, always call "poll_cb" from within the same thread, or never
82 never call "poll_cb" (or other "aio_" functions) recursively. 85 call "poll_cb" (or other "aio_" functions) recursively.
83 86
84 EXAMPLE 87 EXAMPLE
85 This is a simple example that uses the Event module and loads 88 This is a simple example that uses the Event module and loads
86 /etc/passwd asynchronously: 89 /etc/passwd asynchronously:
87 90
… …
94 poll => 'r', 97 poll => 'r',
95 cb => \&IO::AIO::poll_cb); 98 cb => \&IO::AIO::poll_cb);
96 99
97 # queue the request to open /etc/passwd 100 # queue the request to open /etc/passwd
98 aio_open "/etc/passwd", O_RDONLY, 0, sub { 101 aio_open "/etc/passwd", O_RDONLY, 0, sub {
99 my $fh = $_[0] 102 my $fh = shift
100 or die "error while opening: $!"; 103 or die "error while opening: $!";
101 104
102 # stat'ing filehandles is generally non-blocking 105 # stat'ing filehandles is generally non-blocking
103 my $size = -s $fh; 106 my $size = -s $fh;
104 107
… …
167 the actual aio request is severed and calling its methods will 170 the actual aio request is severed and calling its methods will
168 either do nothing or result in a runtime error). 171 either do nothing or result in a runtime error).
169 172
170FUNCTIONS 173FUNCTIONS
171 AIO REQUEST FUNCTIONS 174 AIO REQUEST FUNCTIONS
172 All the "aio_*" calls are more or less thin wrappers around the 175 All the "aio_*" calls are more or less thin wrappers around the syscall
173 syscall with the same name (sans "aio_"). The arguments are similar 176 with the same name (sans "aio_"). The arguments are similar or
174 or identical, and they all accept an additional (and optional) 177 identical, and they all accept an additional (and optional) $callback
175 $callback argument which must be a code reference. This code 178 argument which must be a code reference. This code reference will get
176 reference will get called with the syscall return code (e.g. most 179 called with the syscall return code (e.g. most syscalls return -1 on
177 syscalls return -1 on error, unlike perl, which usually delivers 180 error, unlike perl, which usually delivers "false") as its sole argument
178 "false") as it's sole argument when the given syscall has been 181 after the given syscall has been executed asynchronously.
179 executed asynchronously.
180 182
181 All functions expecting a filehandle keep a copy of the filehandle 183 All functions expecting a filehandle keep a copy of the filehandle
182 internally until the request has finished. 184 internally until the request has finished.
183 185
184 All functions return request objects of type IO::AIO::REQ that allow 186 All functions return request objects of type IO::AIO::REQ that allow
185 further manipulation of those requests while they are in-flight. 187 further manipulation of those requests while they are in-flight.
186 188
187 The pathnames you pass to these routines *must* be absolute and 189 The pathnames you pass to these routines *must* be absolute and encoded
188 encoded as octets. The reason for the former is that at the time the 190 as octets. The reason for the former is that at the time the request is
189 request is being executed, the current working directory could have 191 being executed, the current working directory could have changed.
190 changed. Alternatively, you can make sure that you never change the 192 Alternatively, you can make sure that you never change the current
191 current working directory anywhere in the program and then use 193 working directory anywhere in the program and then use relative paths.
192 relative paths.
193 194
194 To encode pathnames as octets, either make sure you either: a) 195 To encode pathnames as octets, either make sure you either: a) always
195 always pass in filenames you got from outside (command line, readdir 196 pass in filenames you got from outside (command line, readdir etc.)
196 etc.) without tinkering, b) are ASCII or ISO 8859-1, c) use the 197 without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
197 Encode module and encode your pathnames to the locale (or other) 198 and encode your pathnames to the locale (or other) encoding in effect in
198 encoding in effect in the user environment, d) use 199 the user environment, d) use Glib::filename_from_unicode on unicode
199 Glib::filename_from_unicode on unicode filenames or e) use something 200 filenames or e) use something else to ensure your scalar has the correct
200 else to ensure your scalar has the correct contents. 201 contents.
201 202
202 This works, btw. independent of the internal UTF-8 bit, which 203 This works, btw. independent of the internal UTF-8 bit, which IO::AIO
203 IO::AIO handles correctly wether it is set or not. 204 handles correctly whether it is set or not.
204 205
205 $prev_pri = aioreq_pri [$pri] 206 $prev_pri = aioreq_pri [$pri]
206 Returns the priority value that would be used for the next 207 Returns the priority value that would be used for the next request
207 request and, if $pri is given, sets the priority for the next 208 and, if $pri is given, sets the priority for the next aio request.
208 aio request.
209 209
210 The default priority is 0, the minimum and maximum priorities 210 The default priority is 0, the minimum and maximum priorities are -4
211 are -4 and 4, respectively. Requests with higher priority will 211 and 4, respectively. Requests with higher priority will be serviced
212 be serviced first. 212 first.
213 213
214 The priority will be reset to 0 after each call to one of the 214 The priority will be reset to 0 after each call to one of the
215 "aio_*" functions. 215 "aio_*" functions.
216 216
217 Example: open a file with low priority, then read something from 217 Example: open a file with low priority, then read something from it
218 it with higher priority so the read request is serviced before 218 with higher priority so the read request is serviced before other
219 other low priority open requests (potentially spamming the 219 low priority open requests (potentially spamming the cache):
220 cache):
221 220
221 aioreq_pri -3;
222 aio_open ..., sub {
223 return unless $_[0];
224
222 aioreq_pri -3; 225 aioreq_pri -2;
223 aio_open ..., sub {
224 return unless $_[0];
225
226 aioreq_pri -2;
227 aio_read $_[0], ..., sub { 226 aio_read $_[0], ..., sub {
228 ...
229 };
230 };
231
232 aioreq_nice $pri_adjust
233 Similar to "aioreq_pri", but subtracts the given value from the
234 current priority, so the effect is cumulative.
235
236 aio_open $pathname, $flags, $mode, $callback->($fh)
237 Asynchronously open or create a file and call the callback with
238 a newly created filehandle for the file.
239
240 The pathname passed to "aio_open" must be absolute. See API
241 NOTES, above, for an explanation.
242
243 The $flags argument is a bitmask. See the "Fcntl" module for a
244 list. They are the same as used by "sysopen".
245
246 Likewise, $mode specifies the mode of the newly created file, if
247 it didn't exist and "O_CREAT" has been given, just like perl's
248 "sysopen", except that it is mandatory (i.e. use 0 if you don't
249 create new files, and 0666 or 0777 if you do).
250
251 Example:
252
253 aio_open "/etc/passwd", O_RDONLY, 0, sub {
254 if ($_[0]) {
255 print "open successful, fh is $_[0]\n";
256 ...
257 } else {
258 die "open failed: $!\n";
259 }
260 };
261
262 aio_close $fh, $callback->($status)
263 Asynchronously close a file and call the callback with the
264 result code. *WARNING:* although accepted, you should not pass
265 in a perl filehandle here, as perl will likely close the file
266 descriptor another time when the filehandle is destroyed.
267 Normally, you can safely call perls "close" or just let
268 filehandles go out of scope.
269
270 This is supposed to be a bug in the API, so that might change.
271 It's therefore best to avoid this function.
272
273 aio_read $fh,$offset,$length, $data,$dataoffset,
274 $callback->($retval)
275 aio_write $fh,$offset,$length, $data,$dataoffset,
276 $callback->($retval)
277 Reads or writes "length" bytes from the specified "fh" and
278 "offset" into the scalar given by "data" and offset "dataoffset"
279 and calls the callback without the actual number of bytes read
280 (or -1 on error, just like the syscall).
281
282 The $data scalar *MUST NOT* be modified in any way while the
283 request is outstanding. Modifying it can result in segfaults or
284 WW3 (if the necessary/optional hardware is installed).
285
286 Example: Read 15 bytes at offset 7 into scalar $buffer, starting
287 at offset 0 within the scalar:
288
289 aio_read $fh, 7, 15, $buffer, 0, sub {
290 $_[0] > 0 or die "read error: $!";
291 print "read $_[0] bytes: <$buffer>\n";
292 };
293
294 aio_sendfile $out_fh, $in_fh, $in_offset, $length,
295 $callback->($retval)
296 Tries to copy $length bytes from $in_fh to $out_fh. It starts
297 reading at byte offset $in_offset, and starts writing at the
298 current file offset of $out_fh. Because of that, it is not safe
299 to issue more than one "aio_sendfile" per $out_fh, as they will
300 interfere with each other.
301
302 This call tries to make use of a native "sendfile" syscall to
303 provide zero-copy operation. For this to work, $out_fh should
304 refer to a socket, and $in_fh should refer to mmap'able file.
305
306 If the native sendfile call fails or is not implemented, it will
307 be emulated, so you can call "aio_sendfile" on any type of
308 filehandle regardless of the limitations of the operating
309 system.
310
311 Please note, however, that "aio_sendfile" can read more bytes
312 from $in_fh than are written, and there is no way to find out
313 how many bytes have been read from "aio_sendfile" alone, as
314 "aio_sendfile" only provides the number of bytes written to
315 $out_fh. Only if the result value equals $length one can assume
316 that $length bytes have been read.
317
318 aio_readahead $fh,$offset,$length, $callback->($retval)
319 "aio_readahead" populates the page cache with data from a file
320 so that subsequent reads from that file will not block on disk
321 I/O. The $offset argument specifies the starting point from
322 which data is to be read and $length specifies the number of
323 bytes to be read. I/O is performed in whole pages, so that
324 offset is effectively rounded down to a page boundary and bytes
325 are read up to the next page boundary greater than or equal to
326 (off-set+length). "aio_readahead" does not read beyond the end
327 of the file. The current file offset of the file is left
328 unchanged.
329
330 If that syscall doesn't exist (likely if your OS isn't Linux) it
331 will be emulated by simply reading the data, which would have a
332 similar effect.
333
334 aio_stat $fh_or_path, $callback->($status)
335 aio_lstat $fh, $callback->($status)
336 Works like perl's "stat" or "lstat" in void context. The
337 callback will be called after the stat and the results will be
338 available using "stat _" or "-s _" etc...
339
340 The pathname passed to "aio_stat" must be absolute. See API
341 NOTES, above, for an explanation.
342
343 Currently, the stats are always 64-bit-stats, i.e. instead of
344 returning an error when stat'ing a large file, the results will
345 be silently truncated unless perl itself is compiled with large
346 file support.
347
348 Example: Print the length of /etc/passwd:
349
350 aio_stat "/etc/passwd", sub {
351 $_[0] and die "stat failed: $!";
352 print "size is ", -s _, "\n";
353 };
354
355 aio_unlink $pathname, $callback->($status)
356 Asynchronously unlink (delete) a file and call the callback with
357 the result code.
358
359 aio_mknod $path, $mode, $dev, $callback->($status)
360 [EXPERIMENTAL]
361
362 Asynchronously create a device node (or fifo). See mknod(2).
363
364 The only (POSIX-) portable way of calling this function is:
365
366 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
367
368 aio_link $srcpath, $dstpath, $callback->($status)
369 Asynchronously create a new link to the existing object at
370 $srcpath at the path $dstpath and call the callback with the
371 result code.
372
373 aio_symlink $srcpath, $dstpath, $callback->($status)
374 Asynchronously create a new symbolic link to the existing object
375 at $srcpath at the path $dstpath and call the callback with the
376 result code.
377
378 aio_rename $srcpath, $dstpath, $callback->($status)
379 Asynchronously rename the object at $srcpath to $dstpath, just
380 as rename(2) and call the callback with the result code.
381
382 aio_rmdir $pathname, $callback->($status)
383 Asynchronously rmdir (delete) a directory and call the callback
384 with the result code.
385
386 aio_readdir $pathname, $callback->($entries)
387 Unlike the POSIX call of the same name, "aio_readdir" reads an
388 entire directory (i.e. opendir + readdir + closedir). The
389 entries will not be sorted, and will NOT include the "." and
390 ".." entries.
391
392 The callback a single argument which is either "undef" or an
393 array-ref with the filenames.
394
395 aio_copy $srcpath, $dstpath, $callback->($status)
396 Try to copy the *file* (directories not supported as either
397 source or destination) from $srcpath to $dstpath and call the
398 callback with the 0 (error) or -1 ok.
399
400 This is a composite request that it creates the destination file
401 with mode 0200 and copies the contents of the source file into
402 it using "aio_sendfile", followed by restoring atime, mtime,
403 access mode and uid/gid, in that order.
404
405 If an error occurs, the partial destination file will be
406 unlinked, if possible, except when setting atime, mtime, access
407 mode and uid/gid, where errors are being ignored.
408
409 aio_move $srcpath, $dstpath, $callback->($status)
410 Try to move the *file* (directories not supported as either
411 source or destination) from $srcpath to $dstpath and call the
412 callback with the 0 (error) or -1 ok.
413
414 This is a composite request that tries to rename(2) the file
415 first. If rename files with "EXDEV", it copies the file with
416 "aio_copy" and, if that is successful, unlinking the $srcpath.
417
418 aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
419 Scans a directory (similar to "aio_readdir") but additionally
420 tries to efficiently separate the entries of directory $path
421 into two sets of names, directories you can recurse into
422 (directories), and ones you cannot recurse into (everything
423 else, including symlinks to directories).
424
425 "aio_scandir" is a composite request that creates of many sub
426 requests_ $maxreq specifies the maximum number of outstanding
427 aio requests that this function generates. If it is "<= 0", then
428 a suitable default will be chosen (currently 4).
429
430 On error, the callback is called without arguments, otherwise it
431 receives two array-refs with path-relative entry names.
432
433 Example:
434
435 aio_scandir $dir, 0, sub {
436 my ($dirs, $nondirs) = @_;
437 print "real directories: @$dirs\n";
438 print "everything else: @$nondirs\n";
439 };
440
441 Implementation notes.
442
443 The "aio_readdir" cannot be avoided, but "stat()"'ing every
444 entry can.
445
446 After reading the directory, the modification time, size etc. of
447 the directory before and after the readdir is checked, and if
448 they match (and isn't the current time), the link count will be
449 used to decide how many entries are directories (if >= 2).
450 Otherwise, no knowledge of the number of subdirectories will be
451 assumed.
452
453 Then entries will be sorted into likely directories (everything
454 without a non-initial dot currently) and likely non-directories
455 (everything else). Then every entry plus an appended "/." will
456 be "stat"'ed, likely directories first. If that succeeds, it
457 assumes that the entry is a directory or a symlink to directory
458 (which will be checked seperately). This is often faster than
459 stat'ing the entry itself because filesystems might detect the
460 type of the entry without reading the inode data (e.g. ext2fs
461 filetype feature).
462
463 If the known number of directories (link count - 2) has been
464 reached, the rest of the entries is assumed to be
465 non-directories.
466
467 This only works with certainty on POSIX (= UNIX) filesystems,
468 which fortunately are the vast majority of filesystems around.
469
470 It will also likely work on non-POSIX filesystems with reduced
471 efficiency as those tend to return 0 or 1 as link counts, which
472 disables the directory counting heuristic.
473
474 aio_fsync $fh, $callback->($status)
475 Asynchronously call fsync on the given filehandle and call the
476 callback with the fsync result code.
477
478 aio_fdatasync $fh, $callback->($status)
479 Asynchronously call fdatasync on the given filehandle and call
480 the callback with the fdatasync result code.
481
482 If this call isn't available because your OS lacks it or it
483 couldn't be detected, it will be emulated by calling "fsync"
484 instead.
485
486 aio_group $callback->(...)
487 This is a very special aio request: Instead of doing something,
488 it is a container for other aio requests, which is useful if you
489 want to bundle many requests into a single, composite, request
490 with a definite callback and the ability to cancel the whole
491 request with its subrequests.
492
493 Returns an object of class IO::AIO::GRP. See its documentation
494 below for more info.
495
496 Example:
497
498 my $grp = aio_group sub {
499 print "all stats done\n";
500 };
501
502 add $grp
503 (aio_stat ...),
504 (aio_stat ...),
505 ...; 227 ...
506
507 aio_nop $callback->()
508 This is a special request - it does nothing in itself and is
509 only used for side effects, such as when you want to add a dummy
510 request to a group so that finishing the requests in the group
511 depends on executing the given code.
512
513 While this request does nothing, it still goes through the
514 execution phase and still requires a worker thread. Thus, the
515 callback will not be executed immediately but only after other
516 requests in the queue have entered their execution phase. This
517 can be used to measure request latency.
518
519 IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
520 Mainly used for debugging and benchmarking, this aio request
521 puts one of the request workers to sleep for the given time.
522
523 While it is theoretically handy to have simple I/O scheduling
524 requests like sleep and file handle readable/writable, the
525 overhead this creates is immense (it blocks a thread for a long
526 time) so do not use this function except to put your application
527 under artificial I/O pressure.
528
529 IO::AIO::REQ CLASS
530 All non-aggregate "aio_*" functions return an object of this class
531 when called in non-void context.
532
533 cancel $req
534 Cancels the request, if possible. Has the effect of skipping
535 execution when entering the execute state and skipping calling
536 the callback when entering the the result state, but will leave
537 the request otherwise untouched. That means that requests that
538 currently execute will not be stopped and resources held by the
539 request will not be freed prematurely.
540
541 cb $req $callback->(...)
542 Replace (or simply set) the callback registered to the request.
543
544 IO::AIO::GRP CLASS
545 This class is a subclass of IO::AIO::REQ, so all its methods apply
546 to objects of this class, too.
547
548 A IO::AIO::GRP object is a special request that can contain multiple
549 other aio requests.
550
551 You create one by calling the "aio_group" constructing function with
552 a callback that will be called when all contained requests have
553 entered the "done" state:
554
555 my $grp = aio_group sub {
556 print "all requests are done\n";
557 };
558
559 You add requests by calling the "add" method with one or more
560 "IO::AIO::REQ" objects:
561
562 $grp->add (aio_unlink "...");
563
564 add $grp aio_stat "...", sub {
565 $_[0] or return $grp->result ("error");
566
567 # add another request dynamically, if first succeeded
568 add $grp aio_open "...", sub {
569 $grp->result ("ok");
570 }; 228 };
571 }; 229 };
572 230
231 aioreq_nice $pri_adjust
232 Similar to "aioreq_pri", but subtracts the given value from the
233 current priority, so the effect is cumulative.
234
235 aio_open $pathname, $flags, $mode, $callback->($fh)
236 Asynchronously open or create a file and call the callback with a
237 newly created filehandle for the file.
238
239 The pathname passed to "aio_open" must be absolute. See API NOTES,
240 above, for an explanation.
241
242 The $flags argument is a bitmask. See the "Fcntl" module for a list.
243 They are the same as used by "sysopen".
244
245 Likewise, $mode specifies the mode of the newly created file, if it
246 didn't exist and "O_CREAT" has been given, just like perl's
247 "sysopen", except that it is mandatory (i.e. use 0 if you don't
248 create new files, and 0666 or 0777 if you do). Note that the $mode
249 will be modified by the umask in effect then the request is being
250 executed, so better never change the umask.
251
252 Example:
253
254 aio_open "/etc/passwd", O_RDONLY, 0, sub {
255 if ($_[0]) {
256 print "open successful, fh is $_[0]\n";
257 ...
258 } else {
259 die "open failed: $!\n";
260 }
261 };
262
263 aio_close $fh, $callback->($status)
264 Asynchronously close a file and call the callback with the result
265 code.
266
267 Unfortunately, you can't do this to perl. Perl *insists* very
268 strongly on closing the file descriptor associated with the
269 filehandle itself.
270
271 Therefore, "aio_close" will not close the filehandle - instead it
272 will use dup2 to overwrite the file descriptor with the write-end of
273 a pipe (the pipe fd will be created on demand and will be cached).
274
275 Or in other words: the file descriptor will be closed, but it will
276 not be free for reuse until the perl filehandle is closed.
277
278 aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
279 aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
280 Reads or writes $length bytes from or to the specified $fh and
281 $offset into the scalar given by $data and offset $dataoffset and
282 calls the callback without the actual number of bytes read (or -1 on
283 error, just like the syscall).
284
285 "aio_read" will, like "sysread", shrink or grow the $data scalar to
286 offset plus the actual number of bytes read.
287
288 If $offset is undefined, then the current file descriptor offset
289 will be used (and updated), otherwise the file descriptor offset
290 will not be changed by these calls.
291
292 If $length is undefined in "aio_write", use the remaining length of
293 $data.
294
295 If $dataoffset is less than zero, it will be counted from the end of
296 $data.
297
298 The $data scalar *MUST NOT* be modified in any way while the request
299 is outstanding. Modifying it can result in segfaults or World War
300 III (if the necessary/optional hardware is installed).
301
302 Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
303 offset 0 within the scalar:
304
305 aio_read $fh, 7, 15, $buffer, 0, sub {
306 $_[0] > 0 or die "read error: $!";
307 print "read $_[0] bytes: <$buffer>\n";
308 };
309
310 aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
311 Tries to copy $length bytes from $in_fh to $out_fh. It starts
312 reading at byte offset $in_offset, and starts writing at the current
313 file offset of $out_fh. Because of that, it is not safe to issue
314 more than one "aio_sendfile" per $out_fh, as they will interfere
315 with each other.
316
317 This call tries to make use of a native "sendfile" syscall to
318 provide zero-copy operation. For this to work, $out_fh should refer
319 to a socket, and $in_fh should refer to mmap'able file.
320
321 If the native sendfile call fails or is not implemented, it will be
322 emulated, so you can call "aio_sendfile" on any type of filehandle
323 regardless of the limitations of the operating system.
324
325 Please note, however, that "aio_sendfile" can read more bytes from
326 $in_fh than are written, and there is no way to find out how many
327 bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
328 only provides the number of bytes written to $out_fh. Only if the
329 result value equals $length one can assume that $length bytes have
330 been read.
331
332 aio_readahead $fh,$offset,$length, $callback->($retval)
333 "aio_readahead" populates the page cache with data from a file so
334 that subsequent reads from that file will not block on disk I/O. The
335 $offset argument specifies the starting point from which data is to
336 be read and $length specifies the number of bytes to be read. I/O is
337 performed in whole pages, so that offset is effectively rounded down
338 to a page boundary and bytes are read up to the next page boundary
339 greater than or equal to (off-set+length). "aio_readahead" does not
340 read beyond the end of the file. The current file offset of the file
341 is left unchanged.
342
343 If that syscall doesn't exist (likely if your OS isn't Linux) it
344 will be emulated by simply reading the data, which would have a
345 similar effect.
346
347 aio_stat $fh_or_path, $callback->($status)
348 aio_lstat $fh, $callback->($status)
349 Works like perl's "stat" or "lstat" in void context. The callback
350 will be called after the stat and the results will be available
351 using "stat _" or "-s _" etc...
352
353 The pathname passed to "aio_stat" must be absolute. See API NOTES,
354 above, for an explanation.
355
356 Currently, the stats are always 64-bit-stats, i.e. instead of
357 returning an error when stat'ing a large file, the results will be
358 silently truncated unless perl itself is compiled with large file
359 support.
360
361 Example: Print the length of /etc/passwd:
362
363 aio_stat "/etc/passwd", sub {
364 $_[0] and die "stat failed: $!";
365 print "size is ", -s _, "\n";
366 };
367
368 aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
369 Works like perl's "utime" function (including the special case of
370 $atime and $mtime being undef). Fractional times are supported if
371 the underlying syscalls support them.
372
373 When called with a pathname, uses utimes(2) if available, otherwise
374 utime(2). If called on a file descriptor, uses futimes(2) if
375 available, otherwise returns ENOSYS, so this is not portable.
376
377 Examples:
378
379 # set atime and mtime to current time (basically touch(1)):
380 aio_utime "path", undef, undef;
381 # set atime to current time and mtime to beginning of the epoch:
382 aio_utime "path", time, undef; # undef==0
383
384 aio_chown $fh_or_path, $uid, $gid, $callback->($status)
385 Works like perl's "chown" function, except that "undef" for either
386 $uid or $gid is being interpreted as "do not change" (but -1 can
387 also be used).
388
389 Examples:
390
391 # same as "chown root path" in the shell:
392 aio_chown "path", 0, -1;
393 # same as above:
394 aio_chown "path", 0, undef;
395
396 aio_truncate $fh_or_path, $offset, $callback->($status)
397 Works like truncate(2) or ftruncate(2).
398
399 aio_chmod $fh_or_path, $mode, $callback->($status)
400 Works like perl's "chmod" function.
401
402 aio_unlink $pathname, $callback->($status)
403 Asynchronously unlink (delete) a file and call the callback with the
404 result code.
405
406 aio_mknod $path, $mode, $dev, $callback->($status)
407 [EXPERIMENTAL]
408
409 Asynchronously create a device node (or fifo). See mknod(2).
410
411 The only (POSIX-) portable way of calling this function is:
412
413 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
414
415 aio_link $srcpath, $dstpath, $callback->($status)
416 Asynchronously create a new link to the existing object at $srcpath
417 at the path $dstpath and call the callback with the result code.
418
419 aio_symlink $srcpath, $dstpath, $callback->($status)
420 Asynchronously create a new symbolic link to the existing object at
421 $srcpath at the path $dstpath and call the callback with the result
422 code.
423
424 aio_readlink $path, $callback->($link)
425 Asynchronously read the symlink specified by $path and pass it to
426 the callback. If an error occurs, nothing or undef gets passed to
427 the callback.
428
429 aio_rename $srcpath, $dstpath, $callback->($status)
430 Asynchronously rename the object at $srcpath to $dstpath, just as
431 rename(2) and call the callback with the result code.
432
433 aio_mkdir $pathname, $mode, $callback->($status)
434 Asynchronously mkdir (create) a directory and call the callback with
435 the result code. $mode will be modified by the umask at the time the
436 request is executed, so do not change your umask.
437
438 aio_rmdir $pathname, $callback->($status)
439 Asynchronously rmdir (delete) a directory and call the callback with
440 the result code.
441
442 aio_readdir $pathname, $callback->($entries)
443 Unlike the POSIX call of the same name, "aio_readdir" reads an
444 entire directory (i.e. opendir + readdir + closedir). The entries
445 will not be sorted, and will NOT include the "." and ".." entries.
446
447 The callback a single argument which is either "undef" or an
448 array-ref with the filenames.
449
450 aio_load $path, $data, $callback->($status)
451 This is a composite request that tries to fully load the given file
452 into memory. Status is the same as with aio_read.
453
454 aio_copy $srcpath, $dstpath, $callback->($status)
455 Try to copy the *file* (directories not supported as either source
456 or destination) from $srcpath to $dstpath and call the callback with
457 the 0 (error) or -1 ok.
458
459 This is a composite request that creates the destination file with
460 mode 0200 and copies the contents of the source file into it using
461 "aio_sendfile", followed by restoring atime, mtime, access mode and
462 uid/gid, in that order.
463
464 If an error occurs, the partial destination file will be unlinked,
465 if possible, except when setting atime, mtime, access mode and
466 uid/gid, where errors are being ignored.
467
468 aio_move $srcpath, $dstpath, $callback->($status)
469 Try to move the *file* (directories not supported as either source
470 or destination) from $srcpath to $dstpath and call the callback with
471 the 0 (error) or -1 ok.
472
473 This is a composite request that tries to rename(2) the file first;
474 if rename fails with "EXDEV", it copies the file with "aio_copy"
475 and, if that is successful, unlinks the $srcpath.
476
477 aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
478 Scans a directory (similar to "aio_readdir") but additionally tries
479 to efficiently separate the entries of directory $path into two sets
480 of names, directories you can recurse into (directories), and ones
481 you cannot recurse into (everything else, including symlinks to
482 directories).
483
484 "aio_scandir" is a composite request that creates of many sub
485 requests_ $maxreq specifies the maximum number of outstanding aio
486 requests that this function generates. If it is "<= 0", then a
487 suitable default will be chosen (currently 4).
488
489 On error, the callback is called without arguments, otherwise it
490 receives two array-refs with path-relative entry names.
491
492 Example:
493
494 aio_scandir $dir, 0, sub {
495 my ($dirs, $nondirs) = @_;
496 print "real directories: @$dirs\n";
497 print "everything else: @$nondirs\n";
498 };
499
500 Implementation notes.
501
502 The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
503 can.
504
505 After reading the directory, the modification time, size etc. of the
506 directory before and after the readdir is checked, and if they match
507 (and isn't the current time), the link count will be used to decide
508 how many entries are directories (if >= 2). Otherwise, no knowledge
509 of the number of subdirectories will be assumed.
510
511 Then entries will be sorted into likely directories (everything
512 without a non-initial dot currently) and likely non-directories
513 (everything else). Then every entry plus an appended "/." will be
514 "stat"'ed, likely directories first. If that succeeds, it assumes
515 that the entry is a directory or a symlink to directory (which will
516 be checked seperately). This is often faster than stat'ing the entry
517 itself because filesystems might detect the type of the entry
518 without reading the inode data (e.g. ext2fs filetype feature).
519
520 If the known number of directories (link count - 2) has been
521 reached, the rest of the entries is assumed to be non-directories.
522
523 This only works with certainty on POSIX (= UNIX) filesystems, which
524 fortunately are the vast majority of filesystems around.
525
526 It will also likely work on non-POSIX filesystems with reduced
527 efficiency as those tend to return 0 or 1 as link counts, which
528 disables the directory counting heuristic.
529
530 aio_rmtree $path, $callback->($status)
531 Delete a directory tree starting (and including) $path, return the
532 status of the final "rmdir" only. This is a composite request that
533 uses "aio_scandir" to recurse into and rmdir directories, and unlink
534 everything else.
535
536 aio_sync $callback->($status)
537 Asynchronously call sync and call the callback when finished.
538
539 aio_fsync $fh, $callback->($status)
540 Asynchronously call fsync on the given filehandle and call the
541 callback with the fsync result code.
542
543 aio_fdatasync $fh, $callback->($status)
544 Asynchronously call fdatasync on the given filehandle and call the
545 callback with the fdatasync result code.
546
547 If this call isn't available because your OS lacks it or it couldn't
548 be detected, it will be emulated by calling "fsync" instead.
549
550 aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
551 Sync the data portion of the file specified by $offset and $length
552 to disk (but NOT the metadata), by calling the Linux-specific
553 sync_file_range call. If sync_file_range is not available or it
554 returns ENOSYS, then fdatasync or fsync is being substituted.
555
556 $flags can be a combination of
557 "IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE",
558 "IO::AIO::SYNC_FILE_RANGE_WRITE" and
559 "IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the sync_file_range
560 manpage for details.
561
562 aio_pathsync $path, $callback->($status)
563 This request tries to open, fsync and close the given path. This is
564 a composite request intended to sync directories after directory
565 operations (E.g. rename). This might not work on all operating
566 systems or have any specific effect, but usually it makes sure that
567 directory changes get written to disc. It works for anything that
568 can be opened for read-only, not just directories.
569
570 Passes 0 when everything went ok, and -1 on error.
571
572 aio_group $callback->(...)
573 This is a very special aio request: Instead of doing something, it
574 is a container for other aio requests, which is useful if you want
575 to bundle many requests into a single, composite, request with a
576 definite callback and the ability to cancel the whole request with
577 its subrequests.
578
579 Returns an object of class IO::AIO::GRP. See its documentation below
580 for more info.
581
582 Example:
583
584 my $grp = aio_group sub {
585 print "all stats done\n";
586 };
587
588 add $grp
589 (aio_stat ...),
590 (aio_stat ...),
591 ...;
592
593 aio_nop $callback->()
594 This is a special request - it does nothing in itself and is only
595 used for side effects, such as when you want to add a dummy request
596 to a group so that finishing the requests in the group depends on
597 executing the given code.
598
599 While this request does nothing, it still goes through the execution
600 phase and still requires a worker thread. Thus, the callback will
601 not be executed immediately but only after other requests in the
602 queue have entered their execution phase. This can be used to
603 measure request latency.
604
605 IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
606 Mainly used for debugging and benchmarking, this aio request puts
607 one of the request workers to sleep for the given time.
608
609 While it is theoretically handy to have simple I/O scheduling
610 requests like sleep and file handle readable/writable, the overhead
611 this creates is immense (it blocks a thread for a long time) so do
612 not use this function except to put your application under
613 artificial I/O pressure.
614
615 IO::AIO::REQ CLASS
616 All non-aggregate "aio_*" functions return an object of this class when
617 called in non-void context.
618
619 cancel $req
620 Cancels the request, if possible. Has the effect of skipping
621 execution when entering the execute state and skipping calling the
622 callback when entering the the result state, but will leave the
623 request otherwise untouched. That means that requests that currently
624 execute will not be stopped and resources held by the request will
625 not be freed prematurely.
626
627 cb $req $callback->(...)
628 Replace (or simply set) the callback registered to the request.
629
630 IO::AIO::GRP CLASS
631 This class is a subclass of IO::AIO::REQ, so all its methods apply to
632 objects of this class, too.
633
634 A IO::AIO::GRP object is a special request that can contain multiple
635 other aio requests.
636
637 You create one by calling the "aio_group" constructing function with a
638 callback that will be called when all contained requests have entered
639 the "done" state:
640
641 my $grp = aio_group sub {
642 print "all requests are done\n";
643 };
644
645 You add requests by calling the "add" method with one or more
646 "IO::AIO::REQ" objects:
647
648 $grp->add (aio_unlink "...");
649
650 add $grp aio_stat "...", sub {
651 $_[0] or return $grp->result ("error");
652
653 # add another request dynamically, if first succeeded
654 add $grp aio_open "...", sub {
655 $grp->result ("ok");
656 };
657 };
658
573 This makes it very easy to create composite requests (see the source 659 This makes it very easy to create composite requests (see the source of
574 of "aio_move" for an application) that work and feel like simple 660 "aio_move" for an application) that work and feel like simple requests.
575 requests.
576 661
577 * The IO::AIO::GRP objects will be cleaned up during calls to 662 * The IO::AIO::GRP objects will be cleaned up during calls to
578 "IO::AIO::poll_cb", just like any other request. 663 "IO::AIO::poll_cb", just like any other request.
664
579 * They can be canceled like any other request. Canceling will cancel 665 * They can be canceled like any other request. Canceling will cancel
580 not only the request itself, but also all requests it contains. 666 not only the request itself, but also all requests it contains.
667
581 * They can also can also be added to other IO::AIO::GRP objects. 668 * They can also can also be added to other IO::AIO::GRP objects.
669
582 * You must not add requests to a group from within the group 670 * You must not add requests to a group from within the group callback
583 callback (or any later time). 671 (or any later time).
584 672
585 Their lifetime, simplified, looks like this: when they are empty, 673 Their lifetime, simplified, looks like this: when they are empty, they
586 they will finish very quickly. If they contain only requests that 674 will finish very quickly. If they contain only requests that are in the
587 are in the "done" state, they will also finish. Otherwise they will 675 "done" state, they will also finish. Otherwise they will continue to
588 continue to exist. 676 exist.
589 677
590 That means after creating a group you have some time to add 678 That means after creating a group you have some time to add requests
679 (precisely before the callback has been invoked, which is only done
591 requests. And in the callbacks of those requests, you can add 680 within the "poll_cb"). And in the callbacks of those requests, you can
592 further requests to the group. And only when all those requests have 681 add further requests to the group. And only when all those requests have
593 finished will the the group itself finish. 682 finished will the the group itself finish.
594 683
595 add $grp ... 684 add $grp ...
596 $grp->add (...) 685 $grp->add (...)
597 Add one or more requests to the group. Any type of IO::AIO::REQ 686 Add one or more requests to the group. Any type of IO::AIO::REQ can
598 can be added, including other groups, as long as you do not 687 be added, including other groups, as long as you do not create
599 create circular dependencies. 688 circular dependencies.
600 689
601 Returns all its arguments. 690 Returns all its arguments.
602 691
603 $grp->cancel_subs 692 $grp->cancel_subs
604 Cancel all subrequests and clears any feeder, but not the group 693 Cancel all subrequests and clears any feeder, but not the group
605 request itself. Useful when you queued a lot of events but got a 694 request itself. Useful when you queued a lot of events but got a
606 result early. 695 result early.
607 696
608 $grp->result (...) 697 $grp->result (...)
609 Set the result value(s) that will be passed to the group 698 Set the result value(s) that will be passed to the group callback
610 callback when all subrequests have finished and set thre groups 699 when all subrequests have finished and set the groups errno to the
611 errno to the current value of errno (just like calling "errno" 700 current value of errno (just like calling "errno" without an error
612 without an error number). By default, no argument will be passed 701 number). By default, no argument will be passed and errno is zero.
613 and errno is zero.
614 702
615 $grp->errno ([$errno]) 703 $grp->errno ([$errno])
616 Sets the group errno value to $errno, or the current value of 704 Sets the group errno value to $errno, or the current value of errno
617 errno when the argument is missing. 705 when the argument is missing.
618 706
619 Every aio request has an associated errno value that is restored 707 Every aio request has an associated errno value that is restored
620 when the callback is invoked. This method lets you change this 708 when the callback is invoked. This method lets you change this value
621 value from its default (0). 709 from its default (0).
622 710
623 Calling "result" will also set errno, so make sure you either 711 Calling "result" will also set errno, so make sure you either set $!
624 set $! before the call to "result", or call c<errno> after it. 712 before the call to "result", or call c<errno> after it.
625 713
626 feed $grp $callback->($grp) 714 feed $grp $callback->($grp)
627 Sets a feeder/generator on this group: every group can have an 715 Sets a feeder/generator on this group: every group can have an
628 attached generator that generates requests if idle. The idea 716 attached generator that generates requests if idle. The idea behind
629 behind this is that, although you could just queue as many 717 this is that, although you could just queue as many requests as you
630 requests as you want in a group, this might starve other 718 want in a group, this might starve other requests for a potentially
631 requests for a potentially long time. For example, "aio_scandir" 719 long time. For example, "aio_scandir" might generate hundreds of
632 might generate hundreds of thousands "aio_stat" requests, 720 thousands "aio_stat" requests, delaying any later requests for a
633 delaying any later requests for a long time. 721 long time.
634 722
635 To avoid this, and allow incremental generation of requests, you 723 To avoid this, and allow incremental generation of requests, you can
636 can instead a group and set a feeder on it that generates those 724 instead a group and set a feeder on it that generates those
637 requests. The feed callback will be called whenever there are 725 requests. The feed callback will be called whenever there are few
638 few enough (see "limit", below) requests active in the group 726 enough (see "limit", below) requests active in the group itself and
639 itself and is expected to queue more requests. 727 is expected to queue more requests.
640 728
641 The feed callback can queue as many requests as it likes (i.e. 729 The feed callback can queue as many requests as it likes (i.e. "add"
642 "add" does not impose any limits). 730 does not impose any limits).
643 731
644 If the feed does not queue more requests when called, it will be 732 If the feed does not queue more requests when called, it will be
645 automatically removed from the group. 733 automatically removed from the group.
646 734
647 If the feed limit is 0, it will be set to 2 automatically. 735 If the feed limit is 0 when this method is called, it will be set to
736 2 automatically.
648 737
649 Example: 738 Example:
650 739
651 # stat all files in @files, but only ever use four aio requests concurrently: 740 # stat all files in @files, but only ever use four aio requests concurrently:
652 741
653 my $grp = aio_group sub { print "finished\n" }; 742 my $grp = aio_group sub { print "finished\n" };
654 limit $grp 4; 743 limit $grp 4;
655 feed $grp sub { 744 feed $grp sub {
656 my $file = pop @files 745 my $file = pop @files
657 or return; 746 or return;
658 747
659 add $grp aio_stat $file, sub { ... }; 748 add $grp aio_stat $file, sub { ... };
660 }; 749 };
661 750
662 limit $grp $num 751 limit $grp $num
663 Sets the feeder limit for the group: The feeder will be called 752 Sets the feeder limit for the group: The feeder will be called
664 whenever the group contains less than this many requests. 753 whenever the group contains less than this many requests.
665 754
666 Setting the limit to 0 will pause the feeding process. 755 Setting the limit to 0 will pause the feeding process.
756
757 The default value for the limit is 0, but note that setting a feeder
758 automatically bumps it up to 2.
667 759
668 SUPPORT FUNCTIONS 760 SUPPORT FUNCTIONS
669 EVENT PROCESSING AND EVENT LOOP INTEGRATION 761 EVENT PROCESSING AND EVENT LOOP INTEGRATION
670 $fileno = IO::AIO::poll_fileno 762 $fileno = IO::AIO::poll_fileno
671 Return the *request result pipe file descriptor*. This 763 Return the *request result pipe file descriptor*. This filehandle
672 filehandle must be polled for reading by some mechanism outside 764 must be polled for reading by some mechanism outside this module
673 this module (e.g. Event or select, see below or the SYNOPSIS). 765 (e.g. Event or select, see below or the SYNOPSIS). If the pipe
674 If the pipe becomes readable you have to call "poll_cb" to check 766 becomes readable you have to call "poll_cb" to check the results.
675 the results.
676 767
677 See "poll_cb" for an example. 768 See "poll_cb" for an example.
678 769
679 IO::AIO::poll_cb 770 IO::AIO::poll_cb
680 Process some outstanding events on the result pipe. You have to 771 Process some outstanding events on the result pipe. You have to call
681 call this regularly. Returns the number of events processed. 772 this regularly. Returns 0 if all events could be processed, or -1 if
682 Returns immediately when no events are outstanding. The amount 773 it returned earlier for whatever reason. Returns immediately when no
683 of events processed depends on the settings of 774 events are outstanding. The amount of events processed depends on
684 "IO::AIO::max_poll_req" and "IO::AIO::max_poll_time". 775 the settings of "IO::AIO::max_poll_req" and
776 "IO::AIO::max_poll_time".
685 777
686 If not all requests were processed for whatever reason, the 778 If not all requests were processed for whatever reason, the
687 filehandle will still be ready when "poll_cb" returns. 779 filehandle will still be ready when "poll_cb" returns, so normally
780 you don't have to do anything special to have it called later.
688 781
689 Example: Install an Event watcher that automatically calls 782 Example: Install an Event watcher that automatically calls
690 IO::AIO::poll_cb with high priority: 783 IO::AIO::poll_cb with high priority:
691 784
692 Event->io (fd => IO::AIO::poll_fileno, 785 Event->io (fd => IO::AIO::poll_fileno,
693 poll => 'r', async => 1, 786 poll => 'r', async => 1,
694 cb => \&IO::AIO::poll_cb); 787 cb => \&IO::AIO::poll_cb);
695 788
696 IO::AIO::max_poll_reqs $nreqs 789 IO::AIO::max_poll_reqs $nreqs
697 IO::AIO::max_poll_time $seconds 790 IO::AIO::max_poll_time $seconds
698 These set the maximum number of requests (default 0, meaning 791 These set the maximum number of requests (default 0, meaning
699 infinity) that are being processed by "IO::AIO::poll_cb" in one 792 infinity) that are being processed by "IO::AIO::poll_cb" in one
700 call, respectively the maximum amount of time (default 0, 793 call, respectively the maximum amount of time (default 0, meaning
701 meaning infinity) spent in "IO::AIO::poll_cb" to process 794 infinity) spent in "IO::AIO::poll_cb" to process requests (more
702 requests (more correctly the mininum amount of time "poll_cb" is 795 correctly the mininum amount of time "poll_cb" is allowed to use).
703 allowed to use).
704 796
797 Setting "max_poll_time" to a non-zero value creates an overhead of
798 one syscall per request processed, which is not normally a problem
799 unless your callbacks are really really fast or your OS is really
800 really slow (I am not mentioning Solaris here). Using
801 "max_poll_reqs" incurs no overhead.
802
705 Setting these is useful if you want to ensure some level of 803 Setting these is useful if you want to ensure some level of
706 interactiveness when perl is not fast enough to process all 804 interactiveness when perl is not fast enough to process all requests
707 requests in time. 805 in time.
708 806
709 For interactive programs, values such as 0.01 to 0.1 should be 807 For interactive programs, values such as 0.01 to 0.1 should be fine.
710 fine.
711 808
712 Example: Install an Event watcher that automatically calls 809 Example: Install an Event watcher that automatically calls
713 IO::AIO::poll_some with low priority, to ensure that other parts 810 IO::AIO::poll_cb with low priority, to ensure that other parts of
714 of the program get the CPU sometimes even under high AIO load. 811 the program get the CPU sometimes even under high AIO load.
715 812
716 # try not to spend much more than 0.1s in poll_cb 813 # try not to spend much more than 0.1s in poll_cb
717 IO::AIO::max_poll_time 0.1; 814 IO::AIO::max_poll_time 0.1;
718 815
719 # use a low priority so other tasks have priority 816 # use a low priority so other tasks have priority
720 Event->io (fd => IO::AIO::poll_fileno, 817 Event->io (fd => IO::AIO::poll_fileno,
721 poll => 'r', nice => 1, 818 poll => 'r', nice => 1,
722 cb => &IO::AIO::poll_cb); 819 cb => &IO::AIO::poll_cb);
723 820
724 IO::AIO::poll_wait 821 IO::AIO::poll_wait
822 If there are any outstanding requests and none of them in the result
725 Wait till the result filehandle becomes ready for reading 823 phase, wait till the result filehandle becomes ready for reading
726 (simply does a "select" on the filehandle. This is useful if you 824 (simply does a "select" on the filehandle. This is useful if you
727 want to synchronously wait for some requests to finish). 825 want to synchronously wait for some requests to finish).
728 826
729 See "nreqs" for an example. 827 See "nreqs" for an example.
730 828
731 IO::AIO::poll 829 IO::AIO::poll
732 Waits until some requests have been handled. 830 Waits until some requests have been handled.
733 831
832 Returns the number of requests processed, but is otherwise strictly
734 Strictly equivalent to: 833 equivalent to:
735 834
736 IO::AIO::poll_wait, IO::AIO::poll_cb 835 IO::AIO::poll_wait, IO::AIO::poll_cb
737 if IO::AIO::nreqs;
738 836
739 IO::AIO::flush 837 IO::AIO::flush
740 Wait till all outstanding AIO requests have been handled. 838 Wait till all outstanding AIO requests have been handled.
741 839
742 Strictly equivalent to: 840 Strictly equivalent to:
743 841
744 IO::AIO::poll_wait, IO::AIO::poll_cb 842 IO::AIO::poll_wait, IO::AIO::poll_cb
745 while IO::AIO::nreqs; 843 while IO::AIO::nreqs;
746 844
747 CONTROLLING THE NUMBER OF THREADS 845 CONTROLLING THE NUMBER OF THREADS
748 IO::AIO::min_parallel $nthreads 846 IO::AIO::min_parallel $nthreads
749 Set the minimum number of AIO threads to $nthreads. The current 847 Set the minimum number of AIO threads to $nthreads. The current
750 default is 8, which means eight asynchronous operations can 848 default is 8, which means eight asynchronous operations can execute
751 execute concurrently at any one time (the number of outstanding 849 concurrently at any one time (the number of outstanding requests,
752 requests, however, is unlimited). 850 however, is unlimited).
753 851
754 IO::AIO starts threads only on demand, when an AIO request is 852 IO::AIO starts threads only on demand, when an AIO request is queued
755 queued and no free thread exists. Please note that queueing up a 853 and no free thread exists. Please note that queueing up a hundred
756 hundred requests can create demand for a hundred threads, even 854 requests can create demand for a hundred threads, even if it turns
757 if it turns out that everything is in the cache and could have 855 out that everything is in the cache and could have been processed
758 been processed faster by a single thread. 856 faster by a single thread.
759 857
760 It is recommended to keep the number of threads relatively low, 858 It is recommended to keep the number of threads relatively low, as
761 as some Linux kernel versions will scale negatively with the 859 some Linux kernel versions will scale negatively with the number of
762 number of threads (higher parallelity => MUCH higher latency). 860 threads (higher parallelity => MUCH higher latency). With current
763 With current Linux 2.6 versions, 4-32 threads should be fine. 861 Linux 2.6 versions, 4-32 threads should be fine.
764 862
765 Under most circumstances you don't need to call this function, 863 Under most circumstances you don't need to call this function, as
766 as the module selects a default that is suitable for low to 864 the module selects a default that is suitable for low to moderate
767 moderate load. 865 load.
768 866
769 IO::AIO::max_parallel $nthreads 867 IO::AIO::max_parallel $nthreads
770 Sets the maximum number of AIO threads to $nthreads. If more 868 Sets the maximum number of AIO threads to $nthreads. If more than
771 than the specified number of threads are currently running, this 869 the specified number of threads are currently running, this function
772 function kills them. This function blocks until the limit is 870 kills them. This function blocks until the limit is reached.
773 reached.
774 871
775 While $nthreads are zero, aio requests get queued but not 872 While $nthreads are zero, aio requests get queued but not executed
776 executed until the number of threads has been increased again. 873 until the number of threads has been increased again.
777 874
778 This module automatically runs "max_parallel 0" at program end, 875 This module automatically runs "max_parallel 0" at program end, to
779 to ensure that all threads are killed and that there are no 876 ensure that all threads are killed and that there are no outstanding
780 outstanding requests. 877 requests.
781 878
782 Under normal circumstances you don't need to call this function. 879 Under normal circumstances you don't need to call this function.
783 880
784 IO::AIO::max_idle $nthreads 881 IO::AIO::max_idle $nthreads
785 Limit the number of threads (default: 4) that are allowed to 882 Limit the number of threads (default: 4) that are allowed to idle
786 idle (i.e., threads that did not get a request to process within 883 (i.e., threads that did not get a request to process within 10
787 10 seconds). That means if a thread becomes idle while $nthreads 884 seconds). That means if a thread becomes idle while $nthreads other
788 other threads are also idle, it will free its resources and 885 threads are also idle, it will free its resources and exit.
789 exit.
790 886
791 This is useful when you allow a large number of threads (e.g. 887 This is useful when you allow a large number of threads (e.g. 100 or
792 100 or 1000) to allow for extremely high load situations, but 888 1000) to allow for extremely high load situations, but want to free
793 want to free resources under normal circumstances (1000 threads 889 resources under normal circumstances (1000 threads can easily
794 can easily consume 30MB of RAM). 890 consume 30MB of RAM).
795 891
796 The default is probably ok in most situations, especially if 892 The default is probably ok in most situations, especially if thread
797 thread creation is fast. If thread creation is very slow on your 893 creation is fast. If thread creation is very slow on your system you
798 system you might want to use larger values. 894 might want to use larger values.
799 895
800 $oldmaxreqs = IO::AIO::max_outstanding $maxreqs 896 IO::AIO::max_outstanding $maxreqs
801 This is a very bad function to use in interactive programs 897 This is a very bad function to use in interactive programs because
802 because it blocks, and a bad way to reduce concurrency because 898 it blocks, and a bad way to reduce concurrency because it is
803 it is inexact: Better use an "aio_group" together with a feed 899 inexact: Better use an "aio_group" together with a feed callback.
804 callback.
805 900
806 Sets the maximum number of outstanding requests to $nreqs. If 901 Sets the maximum number of outstanding requests to $nreqs. If you do
807 you to queue up more than this number of requests, the next call 902 queue up more than this number of requests, the next call to the
808 to the "poll_cb" (and "poll_some" and other functions calling 903 "poll_cb" (and "poll_some" and other functions calling "poll_cb")
809 "poll_cb") function will block until the limit is no longer 904 function will block until the limit is no longer exceeded.
810 exceeded.
811 905
812 The default value is very large, so there is no practical limit 906 The default value is very large, so there is no practical limit on
813 on the number of outstanding requests. 907 the number of outstanding requests.
814 908
815 You can still queue as many requests as you want. Therefore, 909 You can still queue as many requests as you want. Therefore,
816 "max_oustsanding" is mainly useful in simple scripts (with low 910 "max_outstanding" is mainly useful in simple scripts (with low
817 values) or as a stop gap to shield against fatal memory overflow 911 values) or as a stop gap to shield against fatal memory overflow
818 (with large values). 912 (with large values).
819 913
820 STATISTICAL INFORMATION 914 STATISTICAL INFORMATION
821 IO::AIO::nreqs 915 IO::AIO::nreqs
822 Returns the number of requests currently in the ready, execute 916 Returns the number of requests currently in the ready, execute or
823 or pending states (i.e. for which their callback has not been 917 pending states (i.e. for which their callback has not been invoked
824 invoked yet). 918 yet).
825 919
826 Example: wait till there are no outstanding requests anymore: 920 Example: wait till there are no outstanding requests anymore:
827 921
828 IO::AIO::poll_wait, IO::AIO::poll_cb 922 IO::AIO::poll_wait, IO::AIO::poll_cb
829 while IO::AIO::nreqs; 923 while IO::AIO::nreqs;
830 924
831 IO::AIO::nready 925 IO::AIO::nready
832 Returns the number of requests currently in the ready state (not 926 Returns the number of requests currently in the ready state (not yet
833 yet executed). 927 executed).
834 928
835 IO::AIO::npending 929 IO::AIO::npending
836 Returns the number of requests currently in the pending state 930 Returns the number of requests currently in the pending state
837 (executed, but not yet processed by poll_cb). 931 (executed, but not yet processed by poll_cb).
838 932
839 FORK BEHAVIOUR 933 FORK BEHAVIOUR
840 This module should do "the right thing" when the process using it 934 This module should do "the right thing" when the process using it forks:
841 forks:
842 935
843 Before the fork, IO::AIO enters a quiescent state where no requests 936 Before the fork, IO::AIO enters a quiescent state where no requests can
844 can be added in other threads and no results will be processed. 937 be added in other threads and no results will be processed. After the
845 After the fork the parent simply leaves the quiescent state and 938 fork the parent simply leaves the quiescent state and continues
846 continues request/result processing, while the child frees the 939 request/result processing, while the child frees the request/result
847 request/result queue (so that the requests started before the fork 940 queue (so that the requests started before the fork will only be handled
848 will only be handled in the parent). Threads will be started on 941 in the parent). Threads will be started on demand until the limit set in
849 demand until the limit set in the parent process has been reached 942 the parent process has been reached again.
850 again.
851 943
852 In short: the parent will, after a short pause, continue as if fork 944 In short: the parent will, after a short pause, continue as if fork had
853 had not been called, while the child will act as if IO::AIO has not 945 not been called, while the child will act as if IO::AIO has not been
854 been used yet. 946 used yet.
855 947
856 MEMORY USAGE 948 MEMORY USAGE
857 Per-request usage: 949 Per-request usage:
858 950
859 Each aio request uses - depending on your architecture - around 951 Each aio request uses - depending on your architecture - around 100-200
860 100-200 bytes of memory. In addition, stat requests need a stat 952 bytes of memory. In addition, stat requests need a stat buffer (possibly
861 buffer (possibly a few hundred bytes), readdir requires a result 953 a few hundred bytes), readdir requires a result buffer and so on. Perl
862 buffer and so on. Perl scalars and other data passed into aio 954 scalars and other data passed into aio requests will also be locked and
863 requests will also be locked and will consume memory till the 955 will consume memory till the request has entered the done state.
864 request has entered the done state.
865 956
866 This is now awfully much, so queuing lots of requests is not usually 957 This is not awfully much, so queuing lots of requests is not usually a
867 a problem. 958 problem.
868 959
869 Per-thread usage: 960 Per-thread usage:
870 961
871 In the execution phase, some aio requests require more memory for 962 In the execution phase, some aio requests require more memory for
872 temporary buffers, and each thread requires a stack and other data 963 temporary buffers, and each thread requires a stack and other data
873 structures (usually around 16k-128k, depending on the OS). 964 structures (usually around 16k-128k, depending on the OS).
874 965
875KNOWN BUGS 966KNOWN BUGS
876 Known bugs will be fixed in the next release. 967 Known bugs will be fixed in the next release.
877 968
878SEE ALSO 969SEE ALSO
879 Coro::AIO. 970 AnyEvent::AIO for easy integration into event loops, Coro::AIO for a
971 more natural syntax.
880 972
881AUTHOR 973AUTHOR
882 Marc Lehmann <schmorp@schmorp.de> 974 Marc Lehmann <schmorp@schmorp.de>
883 http://home.schmorp.de/ 975 http://home.schmorp.de/
884 976

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