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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
… …
58 but can also be used to easily do operations in parallel that are 59 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 60 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 61 faster on a RAID volume or over NFS when you do a number of stat
61 operations concurrently. 62 operations concurrently.
62 63
63 While this works on all types of file descriptors (for example sockets), 64 While most of this works on all types of file descriptors (for example
64 using these functions on file descriptors that support nonblocking 65 sockets), using these functions on file descriptors that support
65 operation (again, sockets, pipes etc.) is very inefficient. Use an event 66 nonblocking operation (again, sockets, pipes etc.) is very inefficient.
66 loop for that (such as the Event module): IO::AIO will naturally fit 67 Use an event loop for that (such as the Event module): IO::AIO will
67 into such an event loop itself. 68 naturally fit into such an event loop itself.
68 69
69 In this version, a number of threads are started that execute your 70 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 71 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 72 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 73 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 75 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 76 files currently, for example), and they would only support aio_read and
76 aio_write, so the remaining functionality would have to be implemented 77 aio_write, so the remaining functionality would have to be implemented
77 using threads anyway. 78 using threads anyway.
78 79
79 Although the module will work with in the presence of other (Perl-) 80 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 81 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 82 yourself, always call "poll_cb" from within the same thread, or never
82 never call "poll_cb" (or other "aio_" functions) recursively. 83 call "poll_cb" (or other "aio_" functions) recursively.
83 84
84 EXAMPLE 85 EXAMPLE
85 This is a simple example that uses the Event module and loads 86 This is a simple example that uses the Event module and loads
86 /etc/passwd asynchronously: 87 /etc/passwd asynchronously:
87 88
… …
94 poll => 'r', 95 poll => 'r',
95 cb => \&IO::AIO::poll_cb); 96 cb => \&IO::AIO::poll_cb);
96 97
97 # queue the request to open /etc/passwd 98 # queue the request to open /etc/passwd
98 aio_open "/etc/passwd", O_RDONLY, 0, sub { 99 aio_open "/etc/passwd", O_RDONLY, 0, sub {
99 my $fh = $_[0] 100 my $fh = shift
100 or die "error while opening: $!"; 101 or die "error while opening: $!";
101 102
102 # stat'ing filehandles is generally non-blocking 103 # stat'ing filehandles is generally non-blocking
103 my $size = -s $fh; 104 my $size = -s $fh;
104 105
… …
167 the actual aio request is severed and calling its methods will 168 the actual aio request is severed and calling its methods will
168 either do nothing or result in a runtime error). 169 either do nothing or result in a runtime error).
169 170
170FUNCTIONS 171FUNCTIONS
171 AIO REQUEST FUNCTIONS 172 AIO REQUEST FUNCTIONS
172 All the "aio_*" calls are more or less thin wrappers around the 173 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 174 with the same name (sans "aio_"). The arguments are similar or
174 or identical, and they all accept an additional (and optional) 175 identical, and they all accept an additional (and optional) $callback
175 $callback argument which must be a code reference. This code 176 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 177 called with the syscall return code (e.g. most syscalls return -1 on
177 syscalls return -1 on error, unlike perl, which usually delivers 178 error, unlike perl, which usually delivers "false") as it's sole
178 "false") as it's sole argument when the given syscall has been 179 argument when the given syscall has been executed asynchronously.
179 executed asynchronously.
180 180
181 All functions expecting a filehandle keep a copy of the filehandle 181 All functions expecting a filehandle keep a copy of the filehandle
182 internally until the request has finished. 182 internally until the request has finished.
183 183
184 All functions return request objects of type IO::AIO::REQ that allow 184 All functions return request objects of type IO::AIO::REQ that allow
185 further manipulation of those requests while they are in-flight. 185 further manipulation of those requests while they are in-flight.
186 186
187 The pathnames you pass to these routines *must* be absolute and 187 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 188 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 189 being executed, the current working directory could have changed.
190 changed. Alternatively, you can make sure that you never change the 190 Alternatively, you can make sure that you never change the current
191 current working directory anywhere in the program and then use 191 working directory anywhere in the program and then use relative paths.
192 relative paths.
193 192
194 To encode pathnames as octets, either make sure you either: a) 193 To encode pathnames as octets, either make sure you either: a) always
195 always pass in filenames you got from outside (command line, readdir 194 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 195 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) 196 and encode your pathnames to the locale (or other) encoding in effect in
198 encoding in effect in the user environment, d) use 197 the user environment, d) use Glib::filename_from_unicode on unicode
199 Glib::filename_from_unicode on unicode filenames or e) use something 198 filenames or e) use something else to ensure your scalar has the correct
200 else to ensure your scalar has the correct contents. 199 contents.
201 200
202 This works, btw. independent of the internal UTF-8 bit, which 201 This works, btw. independent of the internal UTF-8 bit, which IO::AIO
203 IO::AIO handles correctly wether it is set or not. 202 handles correctly wether it is set or not.
204 203
205 $prev_pri = aioreq_pri [$pri] 204 $prev_pri = aioreq_pri [$pri]
206 Returns the priority value that would be used for the next 205 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 206 and, if $pri is given, sets the priority for the next aio request.
208 aio request.
209 207
210 The default priority is 0, the minimum and maximum priorities 208 The default priority is 0, the minimum and maximum priorities are -4
211 are -4 and 4, respectively. Requests with higher priority will 209 and 4, respectively. Requests with higher priority will be serviced
212 be serviced first. 210 first.
213 211
214 The priority will be reset to 0 after each call to one of the 212 The priority will be reset to 0 after each call to one of the
215 "aio_*" functions. 213 "aio_*" functions.
216 214
217 Example: open a file with low priority, then read something from 215 Example: open a file with low priority, then read something from it
218 it with higher priority so the read request is serviced before 216 with higher priority so the read request is serviced before other
219 other low priority open requests (potentially spamming the 217 low priority open requests (potentially spamming the cache):
220 cache):
221 218
219 aioreq_pri -3;
220 aio_open ..., sub {
221 return unless $_[0];
222
222 aioreq_pri -3; 223 aioreq_pri -2;
223 aio_open ..., sub {
224 return unless $_[0];
225
226 aioreq_pri -2;
227 aio_read $_[0], ..., sub { 224 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 ...; 225 ...
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 }; 226 };
571 }; 227 };
572 228
229 aioreq_nice $pri_adjust
230 Similar to "aioreq_pri", but subtracts the given value from the
231 current priority, so the effect is cumulative.
232
233 aio_open $pathname, $flags, $mode, $callback->($fh)
234 Asynchronously open or create a file and call the callback with a
235 newly created filehandle for the file.
236
237 The pathname passed to "aio_open" must be absolute. See API NOTES,
238 above, for an explanation.
239
240 The $flags argument is a bitmask. See the "Fcntl" module for a list.
241 They are the same as used by "sysopen".
242
243 Likewise, $mode specifies the mode of the newly created file, if it
244 didn't exist and "O_CREAT" has been given, just like perl's
245 "sysopen", except that it is mandatory (i.e. use 0 if you don't
246 create new files, and 0666 or 0777 if you do). Note that the $mode
247 will be modified by the umask in effect then the request is being
248 executed, so better never change the umask.
249
250 Example:
251
252 aio_open "/etc/passwd", O_RDONLY, 0, sub {
253 if ($_[0]) {
254 print "open successful, fh is $_[0]\n";
255 ...
256 } else {
257 die "open failed: $!\n";
258 }
259 };
260
261 aio_close $fh, $callback->($status)
262 Asynchronously close a file and call the callback with the result
263 code.
264
265 Unfortunately, you can't do this to perl. Perl *insists* very
266 strongly on closing the file descriptor associated with the
267 filehandle itself. Here is what aio_close will try:
268
269 1. dup()licate the fd
270 2. asynchronously close() the duplicated fd
271 3. dup()licate the fd once more
272 4. let perl close() the filehandle
273 5. asynchronously close the duplicated fd
274
275 The idea is that the first close() flushes stuff to disk that
276 closing an fd will flush, so when perl closes the fd, nothing much
277 will need to be flushed. The second async. close() will then flush
278 stuff to disk that closing the last fd to the file will flush.
279
280 Just FYI, SuSv3 has this to say on close:
281
282 All outstanding record locks owned by the process on the file
283 associated with the file descriptor shall be removed.
284
285 If fildes refers to a socket, close() shall cause the socket to be
286 destroyed. ... close() shall block for up to the current linger
287 interval until all data is transmitted.
288 [this actually sounds like a specification bug, but who knows]
289
290 And at least Linux additionally actually flushes stuff on every
291 close, even when the file itself is still open.
292
293 Sounds enourmously inefficient and complicated? Yes... please show
294 me how to nuke perl's fd out of existence...
295
296 aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
297 aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
298 Reads or writes $length bytes from the specified $fh and $offset
299 into the scalar given by $data and offset $dataoffset and calls the
300 callback without the actual number of bytes read (or -1 on error,
301 just like the syscall).
302
303 If $offset is undefined, then the current file descriptor offset
304 will be used (and updated), otherwise the file descriptor offset
305 will not be changed by these calls.
306
307 If $length is undefined in "aio_write", use the remaining length of
308 $data.
309
310 If $dataoffset is less than zero, it will be counted from the end of
311 $data.
312
313 The $data scalar *MUST NOT* be modified in any way while the request
314 is outstanding. Modifying it can result in segfaults or World War
315 III (if the necessary/optional hardware is installed).
316
317 Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
318 offset 0 within the scalar:
319
320 aio_read $fh, 7, 15, $buffer, 0, sub {
321 $_[0] > 0 or die "read error: $!";
322 print "read $_[0] bytes: <$buffer>\n";
323 };
324
325 aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
326 Tries to copy $length bytes from $in_fh to $out_fh. It starts
327 reading at byte offset $in_offset, and starts writing at the current
328 file offset of $out_fh. Because of that, it is not safe to issue
329 more than one "aio_sendfile" per $out_fh, as they will interfere
330 with each other.
331
332 This call tries to make use of a native "sendfile" syscall to
333 provide zero-copy operation. For this to work, $out_fh should refer
334 to a socket, and $in_fh should refer to mmap'able file.
335
336 If the native sendfile call fails or is not implemented, it will be
337 emulated, so you can call "aio_sendfile" on any type of filehandle
338 regardless of the limitations of the operating system.
339
340 Please note, however, that "aio_sendfile" can read more bytes from
341 $in_fh than are written, and there is no way to find out how many
342 bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
343 only provides the number of bytes written to $out_fh. Only if the
344 result value equals $length one can assume that $length bytes have
345 been read.
346
347 aio_readahead $fh,$offset,$length, $callback->($retval)
348 "aio_readahead" populates the page cache with data from a file so
349 that subsequent reads from that file will not block on disk I/O. The
350 $offset argument specifies the starting point from which data is to
351 be read and $length specifies the number of bytes to be read. I/O is
352 performed in whole pages, so that offset is effectively rounded down
353 to a page boundary and bytes are read up to the next page boundary
354 greater than or equal to (off-set+length). "aio_readahead" does not
355 read beyond the end of the file. The current file offset of the file
356 is left unchanged.
357
358 If that syscall doesn't exist (likely if your OS isn't Linux) it
359 will be emulated by simply reading the data, which would have a
360 similar effect.
361
362 aio_stat $fh_or_path, $callback->($status)
363 aio_lstat $fh, $callback->($status)
364 Works like perl's "stat" or "lstat" in void context. The callback
365 will be called after the stat and the results will be available
366 using "stat _" or "-s _" etc...
367
368 The pathname passed to "aio_stat" must be absolute. See API NOTES,
369 above, for an explanation.
370
371 Currently, the stats are always 64-bit-stats, i.e. instead of
372 returning an error when stat'ing a large file, the results will be
373 silently truncated unless perl itself is compiled with large file
374 support.
375
376 Example: Print the length of /etc/passwd:
377
378 aio_stat "/etc/passwd", sub {
379 $_[0] and die "stat failed: $!";
380 print "size is ", -s _, "\n";
381 };
382
383 aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
384 Works like perl's "utime" function (including the special case of
385 $atime and $mtime being undef). Fractional times are supported if
386 the underlying syscalls support them.
387
388 When called with a pathname, uses utimes(2) if available, otherwise
389 utime(2). If called on a file descriptor, uses futimes(2) if
390 available, otherwise returns ENOSYS, so this is not portable.
391
392 Examples:
393
394 # set atime and mtime to current time (basically touch(1)):
395 aio_utime "path", undef, undef;
396 # set atime to current time and mtime to beginning of the epoch:
397 aio_utime "path", time, undef; # undef==0
398
399 aio_chown $fh_or_path, $uid, $gid, $callback->($status)
400 Works like perl's "chown" function, except that "undef" for either
401 $uid or $gid is being interpreted as "do not change" (but -1 can
402 also be used).
403
404 Examples:
405
406 # same as "chown root path" in the shell:
407 aio_chown "path", 0, -1;
408 # same as above:
409 aio_chown "path", 0, undef;
410
411 aio_truncate $fh_or_path, $offset, $callback->($status)
412 Works like truncate(2) or ftruncate(2).
413
414 aio_chmod $fh_or_path, $mode, $callback->($status)
415 Works like perl's "chmod" function.
416
417 aio_unlink $pathname, $callback->($status)
418 Asynchronously unlink (delete) a file and call the callback with the
419 result code.
420
421 aio_mknod $path, $mode, $dev, $callback->($status)
422 [EXPERIMENTAL]
423
424 Asynchronously create a device node (or fifo). See mknod(2).
425
426 The only (POSIX-) portable way of calling this function is:
427
428 aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
429
430 aio_link $srcpath, $dstpath, $callback->($status)
431 Asynchronously create a new link to the existing object at $srcpath
432 at the path $dstpath and call the callback with the result code.
433
434 aio_symlink $srcpath, $dstpath, $callback->($status)
435 Asynchronously create a new symbolic link to the existing object at
436 $srcpath at the path $dstpath and call the callback with the result
437 code.
438
439 aio_readlink $path, $callback->($link)
440 Asynchronously read the symlink specified by $path and pass it to
441 the callback. If an error occurs, nothing or undef gets passed to
442 the callback.
443
444 aio_rename $srcpath, $dstpath, $callback->($status)
445 Asynchronously rename the object at $srcpath to $dstpath, just as
446 rename(2) and call the callback with the result code.
447
448 aio_mkdir $pathname, $mode, $callback->($status)
449 Asynchronously mkdir (create) a directory and call the callback with
450 the result code. $mode will be modified by the umask at the time the
451 request is executed, so do not change your umask.
452
453 aio_rmdir $pathname, $callback->($status)
454 Asynchronously rmdir (delete) a directory and call the callback with
455 the result code.
456
457 aio_readdir $pathname, $callback->($entries)
458 Unlike the POSIX call of the same name, "aio_readdir" reads an
459 entire directory (i.e. opendir + readdir + closedir). The entries
460 will not be sorted, and will NOT include the "." and ".." entries.
461
462 The callback a single argument which is either "undef" or an
463 array-ref with the filenames.
464
465 aio_load $path, $data, $callback->($status)
466 This is a composite request that tries to fully load the given file
467 into memory. Status is the same as with aio_read.
468
469 aio_copy $srcpath, $dstpath, $callback->($status)
470 Try to copy the *file* (directories not supported as either source
471 or destination) from $srcpath to $dstpath and call the callback with
472 the 0 (error) or -1 ok.
473
474 This is a composite request that it creates the destination file
475 with mode 0200 and copies the contents of the source file into it
476 using "aio_sendfile", followed by restoring atime, mtime, access
477 mode and uid/gid, in that order.
478
479 If an error occurs, the partial destination file will be unlinked,
480 if possible, except when setting atime, mtime, access mode and
481 uid/gid, where errors are being ignored.
482
483 aio_move $srcpath, $dstpath, $callback->($status)
484 Try to move the *file* (directories not supported as either source
485 or destination) from $srcpath to $dstpath and call the callback with
486 the 0 (error) or -1 ok.
487
488 This is a composite request that tries to rename(2) the file first.
489 If rename files with "EXDEV", it copies the file with "aio_copy"
490 and, if that is successful, unlinking the $srcpath.
491
492 aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
493 Scans a directory (similar to "aio_readdir") but additionally tries
494 to efficiently separate the entries of directory $path into two sets
495 of names, directories you can recurse into (directories), and ones
496 you cannot recurse into (everything else, including symlinks to
497 directories).
498
499 "aio_scandir" is a composite request that creates of many sub
500 requests_ $maxreq specifies the maximum number of outstanding aio
501 requests that this function generates. If it is "<= 0", then a
502 suitable default will be chosen (currently 4).
503
504 On error, the callback is called without arguments, otherwise it
505 receives two array-refs with path-relative entry names.
506
507 Example:
508
509 aio_scandir $dir, 0, sub {
510 my ($dirs, $nondirs) = @_;
511 print "real directories: @$dirs\n";
512 print "everything else: @$nondirs\n";
513 };
514
515 Implementation notes.
516
517 The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
518 can.
519
520 After reading the directory, the modification time, size etc. of the
521 directory before and after the readdir is checked, and if they match
522 (and isn't the current time), the link count will be used to decide
523 how many entries are directories (if >= 2). Otherwise, no knowledge
524 of the number of subdirectories will be assumed.
525
526 Then entries will be sorted into likely directories (everything
527 without a non-initial dot currently) and likely non-directories
528 (everything else). Then every entry plus an appended "/." will be
529 "stat"'ed, likely directories first. If that succeeds, it assumes
530 that the entry is a directory or a symlink to directory (which will
531 be checked seperately). This is often faster than stat'ing the entry
532 itself because filesystems might detect the type of the entry
533 without reading the inode data (e.g. ext2fs filetype feature).
534
535 If the known number of directories (link count - 2) has been
536 reached, the rest of the entries is assumed to be non-directories.
537
538 This only works with certainty on POSIX (= UNIX) filesystems, which
539 fortunately are the vast majority of filesystems around.
540
541 It will also likely work on non-POSIX filesystems with reduced
542 efficiency as those tend to return 0 or 1 as link counts, which
543 disables the directory counting heuristic.
544
545 aio_rmtree $path, $callback->($status)
546 Delete a directory tree starting (and including) $path, return the
547 status of the final "rmdir" only. This is a composite request that
548 uses "aio_scandir" to recurse into and rmdir directories, and unlink
549 everything else.
550
551 aio_fsync $fh, $callback->($status)
552 Asynchronously call fsync on the given filehandle and call the
553 callback with the fsync result code.
554
555 aio_fdatasync $fh, $callback->($status)
556 Asynchronously call fdatasync on the given filehandle and call the
557 callback with the fdatasync result code.
558
559 If this call isn't available because your OS lacks it or it couldn't
560 be detected, it will be emulated by calling "fsync" instead.
561
562 aio_group $callback->(...)
563 This is a very special aio request: Instead of doing something, it
564 is a container for other aio requests, which is useful if you want
565 to bundle many requests into a single, composite, request with a
566 definite callback and the ability to cancel the whole request with
567 its subrequests.
568
569 Returns an object of class IO::AIO::GRP. See its documentation below
570 for more info.
571
572 Example:
573
574 my $grp = aio_group sub {
575 print "all stats done\n";
576 };
577
578 add $grp
579 (aio_stat ...),
580 (aio_stat ...),
581 ...;
582
583 aio_nop $callback->()
584 This is a special request - it does nothing in itself and is only
585 used for side effects, such as when you want to add a dummy request
586 to a group so that finishing the requests in the group depends on
587 executing the given code.
588
589 While this request does nothing, it still goes through the execution
590 phase and still requires a worker thread. Thus, the callback will
591 not be executed immediately but only after other requests in the
592 queue have entered their execution phase. This can be used to
593 measure request latency.
594
595 IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
596 Mainly used for debugging and benchmarking, this aio request puts
597 one of the request workers to sleep for the given time.
598
599 While it is theoretically handy to have simple I/O scheduling
600 requests like sleep and file handle readable/writable, the overhead
601 this creates is immense (it blocks a thread for a long time) so do
602 not use this function except to put your application under
603 artificial I/O pressure.
604
605 IO::AIO::REQ CLASS
606 All non-aggregate "aio_*" functions return an object of this class when
607 called in non-void context.
608
609 cancel $req
610 Cancels the request, if possible. Has the effect of skipping
611 execution when entering the execute state and skipping calling the
612 callback when entering the the result state, but will leave the
613 request otherwise untouched. That means that requests that currently
614 execute will not be stopped and resources held by the request will
615 not be freed prematurely.
616
617 cb $req $callback->(...)
618 Replace (or simply set) the callback registered to the request.
619
620 IO::AIO::GRP CLASS
621 This class is a subclass of IO::AIO::REQ, so all its methods apply to
622 objects of this class, too.
623
624 A IO::AIO::GRP object is a special request that can contain multiple
625 other aio requests.
626
627 You create one by calling the "aio_group" constructing function with a
628 callback that will be called when all contained requests have entered
629 the "done" state:
630
631 my $grp = aio_group sub {
632 print "all requests are done\n";
633 };
634
635 You add requests by calling the "add" method with one or more
636 "IO::AIO::REQ" objects:
637
638 $grp->add (aio_unlink "...");
639
640 add $grp aio_stat "...", sub {
641 $_[0] or return $grp->result ("error");
642
643 # add another request dynamically, if first succeeded
644 add $grp aio_open "...", sub {
645 $grp->result ("ok");
646 };
647 };
648
573 This makes it very easy to create composite requests (see the source 649 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 650 "aio_move" for an application) that work and feel like simple requests.
575 requests.
576 651
577 * The IO::AIO::GRP objects will be cleaned up during calls to 652 * The IO::AIO::GRP objects will be cleaned up during calls to
578 "IO::AIO::poll_cb", just like any other request. 653 "IO::AIO::poll_cb", just like any other request.
579 * They can be canceled like any other request. Canceling will cancel 654 * They can be canceled like any other request. Canceling will cancel not
580 not only the request itself, but also all requests it contains. 655 only the request itself, but also all requests it contains.
581 * They can also can also be added to other IO::AIO::GRP objects. 656 * They can also can also be added to other IO::AIO::GRP objects.
582 * You must not add requests to a group from within the group 657 * You must not add requests to a group from within the group callback
583 callback (or any later time). 658 (or any later time).
584 659
585 Their lifetime, simplified, looks like this: when they are empty, 660 Their lifetime, simplified, looks like this: when they are empty, they
586 they will finish very quickly. If they contain only requests that 661 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 662 "done" state, they will also finish. Otherwise they will continue to
588 continue to exist. 663 exist.
589 664
590 That means after creating a group you have some time to add 665 That means after creating a group you have some time to add requests.
591 requests. And in the callbacks of those requests, you can add 666 And in the callbacks of those requests, you can add further requests to
592 further requests to the group. And only when all those requests have 667 the group. And only when all those requests have finished will the the
593 finished will the the group itself finish. 668 group itself finish.
594 669
595 add $grp ... 670 add $grp ...
596 $grp->add (...) 671 $grp->add (...)
597 Add one or more requests to the group. Any type of IO::AIO::REQ 672 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 673 be added, including other groups, as long as you do not create
599 create circular dependencies. 674 circular dependencies.
600 675
601 Returns all its arguments. 676 Returns all its arguments.
602 677
603 $grp->cancel_subs 678 $grp->cancel_subs
604 Cancel all subrequests and clears any feeder, but not the group 679 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 680 request itself. Useful when you queued a lot of events but got a
606 result early. 681 result early.
607 682
608 $grp->result (...) 683 $grp->result (...)
609 Set the result value(s) that will be passed to the group 684 Set the result value(s) that will be passed to the group callback
610 callback when all subrequests have finished and set thre groups 685 when all subrequests have finished and set thre groups errno to the
611 errno to the current value of errno (just like calling "errno" 686 current value of errno (just like calling "errno" without an error
612 without an error number). By default, no argument will be passed 687 number). By default, no argument will be passed and errno is zero.
613 and errno is zero.
614 688
615 $grp->errno ([$errno]) 689 $grp->errno ([$errno])
616 Sets the group errno value to $errno, or the current value of 690 Sets the group errno value to $errno, or the current value of errno
617 errno when the argument is missing. 691 when the argument is missing.
618 692
619 Every aio request has an associated errno value that is restored 693 Every aio request has an associated errno value that is restored
620 when the callback is invoked. This method lets you change this 694 when the callback is invoked. This method lets you change this value
621 value from its default (0). 695 from its default (0).
622 696
623 Calling "result" will also set errno, so make sure you either 697 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. 698 before the call to "result", or call c<errno> after it.
625 699
626 feed $grp $callback->($grp) 700 feed $grp $callback->($grp)
627 Sets a feeder/generator on this group: every group can have an 701 Sets a feeder/generator on this group: every group can have an
628 attached generator that generates requests if idle. The idea 702 attached generator that generates requests if idle. The idea behind
629 behind this is that, although you could just queue as many 703 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 704 want in a group, this might starve other requests for a potentially
631 requests for a potentially long time. For example, "aio_scandir" 705 long time. For example, "aio_scandir" might generate hundreds of
632 might generate hundreds of thousands "aio_stat" requests, 706 thousands "aio_stat" requests, delaying any later requests for a
633 delaying any later requests for a long time. 707 long time.
634 708
635 To avoid this, and allow incremental generation of requests, you 709 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 710 instead a group and set a feeder on it that generates those
637 requests. The feed callback will be called whenever there are 711 requests. The feed callback will be called whenever there are few
638 few enough (see "limit", below) requests active in the group 712 enough (see "limit", below) requests active in the group itself and
639 itself and is expected to queue more requests. 713 is expected to queue more requests.
640 714
641 The feed callback can queue as many requests as it likes (i.e. 715 The feed callback can queue as many requests as it likes (i.e. "add"
642 "add" does not impose any limits). 716 does not impose any limits).
643 717
644 If the feed does not queue more requests when called, it will be 718 If the feed does not queue more requests when called, it will be
645 automatically removed from the group. 719 automatically removed from the group.
646 720
647 If the feed limit is 0, it will be set to 2 automatically. 721 If the feed limit is 0, it will be set to 2 automatically.
648 722
649 Example: 723 Example:
650 724
651 # stat all files in @files, but only ever use four aio requests concurrently: 725 # stat all files in @files, but only ever use four aio requests concurrently:
652 726
653 my $grp = aio_group sub { print "finished\n" }; 727 my $grp = aio_group sub { print "finished\n" };
654 limit $grp 4; 728 limit $grp 4;
655 feed $grp sub { 729 feed $grp sub {
656 my $file = pop @files 730 my $file = pop @files
657 or return; 731 or return;
658 732
659 add $grp aio_stat $file, sub { ... }; 733 add $grp aio_stat $file, sub { ... };
660 }; 734 };
661 735
662 limit $grp $num 736 limit $grp $num
663 Sets the feeder limit for the group: The feeder will be called 737 Sets the feeder limit for the group: The feeder will be called
664 whenever the group contains less than this many requests. 738 whenever the group contains less than this many requests.
665 739
666 Setting the limit to 0 will pause the feeding process. 740 Setting the limit to 0 will pause the feeding process.
667 741
668 SUPPORT FUNCTIONS 742 SUPPORT FUNCTIONS
669 EVENT PROCESSING AND EVENT LOOP INTEGRATION 743 EVENT PROCESSING AND EVENT LOOP INTEGRATION
670 $fileno = IO::AIO::poll_fileno 744 $fileno = IO::AIO::poll_fileno
671 Return the *request result pipe file descriptor*. This 745 Return the *request result pipe file descriptor*. This filehandle
672 filehandle must be polled for reading by some mechanism outside 746 must be polled for reading by some mechanism outside this module
673 this module (e.g. Event or select, see below or the SYNOPSIS). 747 (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 748 becomes readable you have to call "poll_cb" to check the results.
675 the results.
676 749
677 See "poll_cb" for an example. 750 See "poll_cb" for an example.
678 751
679 IO::AIO::poll_cb 752 IO::AIO::poll_cb
680 Process some outstanding events on the result pipe. You have to 753 Process some outstanding events on the result pipe. You have to call
681 call this regularly. Returns the number of events processed. 754 this regularly. Returns the number of events processed. Returns
682 Returns immediately when no events are outstanding. The amount 755 immediately when no events are outstanding. The amount of events
683 of events processed depends on the settings of 756 processed depends on the settings of "IO::AIO::max_poll_req" and
684 "IO::AIO::max_poll_req" and "IO::AIO::max_poll_time". 757 "IO::AIO::max_poll_time".
685 758
686 If not all requests were processed for whatever reason, the 759 If not all requests were processed for whatever reason, the
687 filehandle will still be ready when "poll_cb" returns. 760 filehandle will still be ready when "poll_cb" returns.
688 761
689 Example: Install an Event watcher that automatically calls 762 Example: Install an Event watcher that automatically calls
690 IO::AIO::poll_cb with high priority: 763 IO::AIO::poll_cb with high priority:
691 764
692 Event->io (fd => IO::AIO::poll_fileno, 765 Event->io (fd => IO::AIO::poll_fileno,
693 poll => 'r', async => 1, 766 poll => 'r', async => 1,
694 cb => \&IO::AIO::poll_cb); 767 cb => \&IO::AIO::poll_cb);
695 768
696 IO::AIO::max_poll_reqs $nreqs 769 IO::AIO::max_poll_reqs $nreqs
697 IO::AIO::max_poll_time $seconds 770 IO::AIO::max_poll_time $seconds
698 These set the maximum number of requests (default 0, meaning 771 These set the maximum number of requests (default 0, meaning
699 infinity) that are being processed by "IO::AIO::poll_cb" in one 772 infinity) that are being processed by "IO::AIO::poll_cb" in one
700 call, respectively the maximum amount of time (default 0, 773 call, respectively the maximum amount of time (default 0, meaning
701 meaning infinity) spent in "IO::AIO::poll_cb" to process 774 infinity) spent in "IO::AIO::poll_cb" to process requests (more
702 requests (more correctly the mininum amount of time "poll_cb" is 775 correctly the mininum amount of time "poll_cb" is allowed to use).
703 allowed to use).
704 776
777 Setting "max_poll_time" to a non-zero value creates an overhead of
778 one syscall per request processed, which is not normally a problem
779 unless your callbacks are really really fast or your OS is really
780 really slow (I am not mentioning Solaris here). Using
781 "max_poll_reqs" incurs no overhead.
782
705 Setting these is useful if you want to ensure some level of 783 Setting these is useful if you want to ensure some level of
706 interactiveness when perl is not fast enough to process all 784 interactiveness when perl is not fast enough to process all requests
707 requests in time. 785 in time.
708 786
709 For interactive programs, values such as 0.01 to 0.1 should be 787 For interactive programs, values such as 0.01 to 0.1 should be fine.
710 fine.
711 788
712 Example: Install an Event watcher that automatically calls 789 Example: Install an Event watcher that automatically calls
713 IO::AIO::poll_some with low priority, to ensure that other parts 790 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. 791 the program get the CPU sometimes even under high AIO load.
715 792
716 # try not to spend much more than 0.1s in poll_cb 793 # try not to spend much more than 0.1s in poll_cb
717 IO::AIO::max_poll_time 0.1; 794 IO::AIO::max_poll_time 0.1;
718 795
719 # use a low priority so other tasks have priority 796 # use a low priority so other tasks have priority
720 Event->io (fd => IO::AIO::poll_fileno, 797 Event->io (fd => IO::AIO::poll_fileno,
721 poll => 'r', nice => 1, 798 poll => 'r', nice => 1,
722 cb => &IO::AIO::poll_cb); 799 cb => &IO::AIO::poll_cb);
723 800
724 IO::AIO::poll_wait 801 IO::AIO::poll_wait
802 If there are any outstanding requests and none of them in the result
725 Wait till the result filehandle becomes ready for reading 803 phase, wait till the result filehandle becomes ready for reading
726 (simply does a "select" on the filehandle. This is useful if you 804 (simply does a "select" on the filehandle. This is useful if you
727 want to synchronously wait for some requests to finish). 805 want to synchronously wait for some requests to finish).
728 806
729 See "nreqs" for an example. 807 See "nreqs" for an example.
730 808
731 IO::AIO::poll 809 IO::AIO::poll
732 Waits until some requests have been handled. 810 Waits until some requests have been handled.
733 811
812 Returns the number of requests processed, but is otherwise strictly
734 Strictly equivalent to: 813 equivalent to:
735 814
736 IO::AIO::poll_wait, IO::AIO::poll_cb 815 IO::AIO::poll_wait, IO::AIO::poll_cb
737 if IO::AIO::nreqs;
738 816
739 IO::AIO::flush 817 IO::AIO::flush
740 Wait till all outstanding AIO requests have been handled. 818 Wait till all outstanding AIO requests have been handled.
741 819
742 Strictly equivalent to: 820 Strictly equivalent to:
743 821
744 IO::AIO::poll_wait, IO::AIO::poll_cb 822 IO::AIO::poll_wait, IO::AIO::poll_cb
745 while IO::AIO::nreqs; 823 while IO::AIO::nreqs;
746 824
747 CONTROLLING THE NUMBER OF THREADS 825 CONTROLLING THE NUMBER OF THREADS
748 IO::AIO::min_parallel $nthreads 826 IO::AIO::min_parallel $nthreads
749 Set the minimum number of AIO threads to $nthreads. The current 827 Set the minimum number of AIO threads to $nthreads. The current
750 default is 8, which means eight asynchronous operations can 828 default is 8, which means eight asynchronous operations can execute
751 execute concurrently at any one time (the number of outstanding 829 concurrently at any one time (the number of outstanding requests,
752 requests, however, is unlimited). 830 however, is unlimited).
753 831
754 IO::AIO starts threads only on demand, when an AIO request is 832 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 833 and no free thread exists. Please note that queueing up a hundred
756 hundred requests can create demand for a hundred threads, even 834 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 835 out that everything is in the cache and could have been processed
758 been processed faster by a single thread. 836 faster by a single thread.
759 837
760 It is recommended to keep the number of threads relatively low, 838 It is recommended to keep the number of threads relatively low, as
761 as some Linux kernel versions will scale negatively with the 839 some Linux kernel versions will scale negatively with the number of
762 number of threads (higher parallelity => MUCH higher latency). 840 threads (higher parallelity => MUCH higher latency). With current
763 With current Linux 2.6 versions, 4-32 threads should be fine. 841 Linux 2.6 versions, 4-32 threads should be fine.
764 842
765 Under most circumstances you don't need to call this function, 843 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 844 the module selects a default that is suitable for low to moderate
767 moderate load. 845 load.
768 846
769 IO::AIO::max_parallel $nthreads 847 IO::AIO::max_parallel $nthreads
770 Sets the maximum number of AIO threads to $nthreads. If more 848 Sets the maximum number of AIO threads to $nthreads. If more than
771 than the specified number of threads are currently running, this 849 the specified number of threads are currently running, this function
772 function kills them. This function blocks until the limit is 850 kills them. This function blocks until the limit is reached.
773 reached.
774 851
775 While $nthreads are zero, aio requests get queued but not 852 While $nthreads are zero, aio requests get queued but not executed
776 executed until the number of threads has been increased again. 853 until the number of threads has been increased again.
777 854
778 This module automatically runs "max_parallel 0" at program end, 855 This module automatically runs "max_parallel 0" at program end, to
779 to ensure that all threads are killed and that there are no 856 ensure that all threads are killed and that there are no outstanding
780 outstanding requests. 857 requests.
781 858
782 Under normal circumstances you don't need to call this function. 859 Under normal circumstances you don't need to call this function.
783 860
784 IO::AIO::max_idle $nthreads 861 IO::AIO::max_idle $nthreads
785 Limit the number of threads (default: 4) that are allowed to 862 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 863 (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 864 seconds). That means if a thread becomes idle while $nthreads other
788 other threads are also idle, it will free its resources and 865 threads are also idle, it will free its resources and exit.
789 exit.
790 866
791 This is useful when you allow a large number of threads (e.g. 867 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 868 1000) to allow for extremely high load situations, but want to free
793 want to free resources under normal circumstances (1000 threads 869 resources under normal circumstances (1000 threads can easily
794 can easily consume 30MB of RAM). 870 consume 30MB of RAM).
795 871
796 The default is probably ok in most situations, especially if 872 The default is probably ok in most situations, especially if thread
797 thread creation is fast. If thread creation is very slow on your 873 creation is fast. If thread creation is very slow on your system you
798 system you might want to use larger values. 874 might want to use larger values.
799 875
800 $oldmaxreqs = IO::AIO::max_outstanding $maxreqs 876 $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
801 This is a very bad function to use in interactive programs 877 This is a very bad function to use in interactive programs because
802 because it blocks, and a bad way to reduce concurrency because 878 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 879 inexact: Better use an "aio_group" together with a feed callback.
804 callback.
805 880
806 Sets the maximum number of outstanding requests to $nreqs. If 881 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 882 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 883 "poll_cb" (and "poll_some" and other functions calling "poll_cb")
809 "poll_cb") function will block until the limit is no longer 884 function will block until the limit is no longer exceeded.
810 exceeded.
811 885
812 The default value is very large, so there is no practical limit 886 The default value is very large, so there is no practical limit on
813 on the number of outstanding requests. 887 the number of outstanding requests.
814 888
815 You can still queue as many requests as you want. Therefore, 889 You can still queue as many requests as you want. Therefore,
816 "max_oustsanding" is mainly useful in simple scripts (with low 890 "max_oustsanding" is mainly useful in simple scripts (with low
817 values) or as a stop gap to shield against fatal memory overflow 891 values) or as a stop gap to shield against fatal memory overflow
818 (with large values). 892 (with large values).
819 893
820 STATISTICAL INFORMATION 894 STATISTICAL INFORMATION
821 IO::AIO::nreqs 895 IO::AIO::nreqs
822 Returns the number of requests currently in the ready, execute 896 Returns the number of requests currently in the ready, execute or
823 or pending states (i.e. for which their callback has not been 897 pending states (i.e. for which their callback has not been invoked
824 invoked yet). 898 yet).
825 899
826 Example: wait till there are no outstanding requests anymore: 900 Example: wait till there are no outstanding requests anymore:
827 901
828 IO::AIO::poll_wait, IO::AIO::poll_cb 902 IO::AIO::poll_wait, IO::AIO::poll_cb
829 while IO::AIO::nreqs; 903 while IO::AIO::nreqs;
830 904
831 IO::AIO::nready 905 IO::AIO::nready
832 Returns the number of requests currently in the ready state (not 906 Returns the number of requests currently in the ready state (not yet
833 yet executed). 907 executed).
834 908
835 IO::AIO::npending 909 IO::AIO::npending
836 Returns the number of requests currently in the pending state 910 Returns the number of requests currently in the pending state
837 (executed, but not yet processed by poll_cb). 911 (executed, but not yet processed by poll_cb).
838 912
839 FORK BEHAVIOUR 913 FORK BEHAVIOUR
840 This module should do "the right thing" when the process using it 914 This module should do "the right thing" when the process using it forks:
841 forks:
842 915
843 Before the fork, IO::AIO enters a quiescent state where no requests 916 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. 917 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 918 fork the parent simply leaves the quiescent state and continues
846 continues request/result processing, while the child frees the 919 request/result processing, while the child frees the request/result
847 request/result queue (so that the requests started before the fork 920 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 921 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 922 the parent process has been reached again.
850 again.
851 923
852 In short: the parent will, after a short pause, continue as if fork 924 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 925 not been called, while the child will act as if IO::AIO has not been
854 been used yet. 926 used yet.
855 927
856 MEMORY USAGE 928 MEMORY USAGE
857 Per-request usage: 929 Per-request usage:
858 930
859 Each aio request uses - depending on your architecture - around 931 Each aio request uses - depending on your architecture - around 100-200
860 100-200 bytes of memory. In addition, stat requests need a stat 932 bytes of memory. In addition, stat requests need a stat buffer (possibly
861 buffer (possibly a few hundred bytes), readdir requires a result 933 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 934 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 935 will consume memory till the request has entered the done state.
864 request has entered the done state.
865 936
866 This is now awfully much, so queuing lots of requests is not usually 937 This is not awfully much, so queuing lots of requests is not usually a
867 a problem. 938 problem.
868 939
869 Per-thread usage: 940 Per-thread usage:
870 941
871 In the execution phase, some aio requests require more memory for 942 In the execution phase, some aio requests require more memory for
872 temporary buffers, and each thread requires a stack and other data 943 temporary buffers, and each thread requires a stack and other data
873 structures (usually around 16k-128k, depending on the OS). 944 structures (usually around 16k-128k, depending on the OS).
874 945
875KNOWN BUGS 946KNOWN BUGS
876 Known bugs will be fixed in the next release. 947 Known bugs will be fixed in the next release.
877 948
878SEE ALSO 949SEE ALSO
879 Coro::AIO. 950 Coro::AIO.
880 951
881AUTHOR 952AUTHOR
882 Marc Lehmann <schmorp@schmorp.de> 953 Marc Lehmann <schmorp@schmorp.de>
883 http://home.schmorp.de/ 954 http://home.schmorp.de/
884 955

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