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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
14 aio_read $fh, 30000, 1024, $buffer, 0, sub { 15 aio_read $fh, 30000, 1024, $buffer, 0, sub {
15 $_[0] > 0 or die "read error: $!"; 16 $_[0] > 0 or die "read error: $!";
16 }; 17 };
17 18
18 # Event 19 # version 2+ has request and group objects
20 use IO::AIO 2;
21
22 aioreq_pri 4; # give next request a very high priority
23 my $req = aio_unlink "/tmp/file", sub { };
24 $req->cancel; # cancel request if still in queue
25
26 my $grp = aio_group sub { print "all stats done\n" };
27 add $grp aio_stat "..." for ...;
28
29 # AnyEvent integration
30 open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
31 my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
32
33 # Event integration
19 Event->io (fd => IO::AIO::poll_fileno, 34 Event->io (fd => IO::AIO::poll_fileno,
20 poll => 'r', 35 poll => 'r',
21 cb => \&IO::AIO::poll_cb); 36 cb => \&IO::AIO::poll_cb);
22 37
23 # Glib/Gtk2 38 # Glib/Gtk2 integration
24 add_watch Glib::IO IO::AIO::poll_fileno, 39 add_watch Glib::IO IO::AIO::poll_fileno,
25 in => sub { IO::AIO::poll_cb; 1 }; 40 in => sub { IO::AIO::poll_cb; 1 };
26 41
27 # Tk 42 # Tk integration
28 Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "", 43 Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
29 readable => \&IO::AIO::poll_cb); 44 readable => \&IO::AIO::poll_cb);
30 45
31 # Danga::Socket 46 # Danga::Socket integration
32 Danga::Socket->AddOtherFds (IO::AIO::poll_fileno => 47 Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
33 \&IO::AIO::poll_cb); 48 \&IO::AIO::poll_cb);
34 49
35DESCRIPTION 50DESCRIPTION
36 This module implements asynchronous I/O using whatever means your 51 This module implements asynchronous I/O using whatever means your
37 operating system supports. 52 operating system supports.
38 53
54 Asynchronous means that operations that can normally block your program
55 (e.g. reading from disk) will be done asynchronously: the operation will
56 still block, but you can do something else in the meantime. This is
57 extremely useful for programs that need to stay interactive even when
58 doing heavy I/O (GUI programs, high performance network servers etc.),
59 but can also be used to easily do operations in parallel that are
60 normally done sequentially, e.g. stat'ing many files, which is much
61 faster on a RAID volume or over NFS when you do a number of stat
62 operations concurrently.
63
64 While most of this works on all types of file descriptors (for example
65 sockets), using these functions on file descriptors that support
66 nonblocking operation (again, sockets, pipes etc.) is very inefficient.
67 Use an event loop for that (such as the Event module): IO::AIO will
68 naturally fit into such an event loop itself.
69
39 Currently, a number of threads are started that execute your read/writes 70 In this version, a number of threads are started that execute your
40 and signal their completion. You don't need thread support in your libc 71 requests and signal their completion. You don't need thread support in
41 or 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
42 the pthreads library. In the future, this module might make use of the 73 perl. In the future, this module might make use of the native aio
43 native aio functions available on many operating systems. However, they 74 functions available on many operating systems. However, they are often
44 are often not well-supported (Linux doesn't allow them on normal files 75 not well-supported or restricted (GNU/Linux doesn't allow them on normal
45 currently, for example), and they would only support aio_read and 76 files currently, for example), and they would only support aio_read and
46 aio_write, so the remaining functionality would have to be implemented 77 aio_write, so the remaining functionality would have to be implemented
47 using threads anyway. 78 using threads anyway.
48 79
49 Although the module will work with in the presence of other threads, it 80 Although the module will work in the presence of other (Perl-) threads,
50 is currently not reentrant, so use appropriate locking yourself, always 81 it is currently not reentrant in any way, so use appropriate locking
51 call "poll_cb" from within the same thread, or never call "poll_cb" (or 82 yourself, always call "poll_cb" from within the same thread, or never
52 other "aio_" functions) recursively. 83 call "poll_cb" (or other "aio_" functions) recursively.
84
85 EXAMPLE
86 This is a simple example that uses the Event module and loads
87 /etc/passwd asynchronously:
88
89 use Fcntl;
90 use Event;
91 use IO::AIO;
92
93 # register the IO::AIO callback with Event
94 Event->io (fd => IO::AIO::poll_fileno,
95 poll => 'r',
96 cb => \&IO::AIO::poll_cb);
97
98 # queue the request to open /etc/passwd
99 aio_open "/etc/passwd", O_RDONLY, 0, sub {
100 my $fh = shift
101 or die "error while opening: $!";
102
103 # stat'ing filehandles is generally non-blocking
104 my $size = -s $fh;
105
106 # queue a request to read the file
107 my $contents;
108 aio_read $fh, 0, $size, $contents, 0, sub {
109 $_[0] == $size
110 or die "short read: $!";
111
112 close $fh;
113
114 # file contents now in $contents
115 print $contents;
116
117 # exit event loop and program
118 Event::unloop;
119 };
120 };
121
122 # possibly queue up other requests, or open GUI windows,
123 # check for sockets etc. etc.
124
125 # process events as long as there are some:
126 Event::loop;
127
128REQUEST ANATOMY AND LIFETIME
129 Every "aio_*" function creates a request. which is a C data structure
130 not directly visible to Perl.
131
132 If called in non-void context, every request function returns a Perl
133 object representing the request. In void context, nothing is returned,
134 which saves a bit of memory.
135
136 The perl object is a fairly standard ref-to-hash object. The hash
137 contents are not used by IO::AIO so you are free to store anything you
138 like in it.
139
140 During their existance, aio requests travel through the following
141 states, in order:
142
143 ready
144 Immediately after a request is created it is put into the ready
145 state, waiting for a thread to execute it.
146
147 execute
148 A thread has accepted the request for processing and is currently
149 executing it (e.g. blocking in read).
150
151 pending
152 The request has been executed and is waiting for result processing.
153
154 While request submission and execution is fully asynchronous, result
155 processing is not and relies on the perl interpreter calling
156 "poll_cb" (or another function with the same effect).
157
158 result
159 The request results are processed synchronously by "poll_cb".
160
161 The "poll_cb" function will process all outstanding aio requests by
162 calling their callbacks, freeing memory associated with them and
163 managing any groups they are contained in.
164
165 done
166 Request has reached the end of its lifetime and holds no resources
167 anymore (except possibly for the Perl object, but its connection to
168 the actual aio request is severed and calling its methods will
169 either do nothing or result in a runtime error).
53 170
54FUNCTIONS 171FUNCTIONS
55 AIO FUNCTIONS 172 AIO REQUEST FUNCTIONS
56 All the "aio_*" calls are more or less thin wrappers around the syscall 173 All the "aio_*" calls are more or less thin wrappers around the syscall
57 with the same name (sans "aio_"). The arguments are similar or 174 with the same name (sans "aio_"). The arguments are similar or
58 identical, and they all accept an additional (and optional) $callback 175 identical, and they all accept an additional (and optional) $callback
59 argument which must be a code reference. This code reference will get 176 argument which must be a code reference. This code reference will get
60 called with the syscall return code (e.g. most syscalls return -1 on 177 called with the syscall return code (e.g. most syscalls return -1 on
… …
62 argument when the given syscall has been executed asynchronously. 179 argument when the given syscall has been executed asynchronously.
63 180
64 All functions expecting a filehandle keep a copy of the filehandle 181 All functions expecting a filehandle keep a copy of the filehandle
65 internally until the request has finished. 182 internally until the request has finished.
66 183
184 All functions return request objects of type IO::AIO::REQ that allow
185 further manipulation of those requests while they are in-flight.
186
67 The pathnames you pass to these routines *must* be absolute and encoded 187 The pathnames you pass to these routines *must* be absolute and encoded
68 in byte form. The reason for the former is that at the time the request 188 as octets. The reason for the former is that at the time the request is
69 is being executed, the current working directory could have changed. 189 being executed, the current working directory could have changed.
70 Alternatively, you can make sure that you never change the current 190 Alternatively, you can make sure that you never change the current
71 working directory. 191 working directory anywhere in the program and then use relative paths.
72 192
73 To encode pathnames to byte form, either make sure you either: a) always 193 To encode pathnames as octets, either make sure you either: a) always
74 pass in filenames you got from outside (command line, readdir etc.), b) 194 pass in filenames you got from outside (command line, readdir etc.)
75 are ASCII or ISO 8859-1, c) use the Encode module and encode your 195 without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
76 pathnames to the locale (or other) encoding in effect in the user 196 and encode your pathnames to the locale (or other) encoding in effect in
77 environment, d) use Glib::filename_from_unicode on unicode filenames or 197 the user environment, d) use Glib::filename_from_unicode on unicode
78 e) use something else. 198 filenames or e) use something else to ensure your scalar has the correct
199 contents.
200
201 This works, btw. independent of the internal UTF-8 bit, which IO::AIO
202 handles correctly wether it is set or not.
203
204 $prev_pri = aioreq_pri [$pri]
205 Returns the priority value that would be used for the next request
206 and, if $pri is given, sets the priority for the next aio request.
207
208 The default priority is 0, the minimum and maximum priorities are -4
209 and 4, respectively. Requests with higher priority will be serviced
210 first.
211
212 The priority will be reset to 0 after each call to one of the
213 "aio_*" functions.
214
215 Example: open a file with low priority, then read something from it
216 with higher priority so the read request is serviced before other
217 low priority open requests (potentially spamming the cache):
218
219 aioreq_pri -3;
220 aio_open ..., sub {
221 return unless $_[0];
222
223 aioreq_pri -2;
224 aio_read $_[0], ..., sub {
225 ...
226 };
227 };
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.
79 232
80 aio_open $pathname, $flags, $mode, $callback->($fh) 233 aio_open $pathname, $flags, $mode, $callback->($fh)
81 Asynchronously open or create a file and call the callback with a 234 Asynchronously open or create a file and call the callback with a
82 newly created filehandle for the file. 235 newly created filehandle for the file.
83 236
… …
88 They are the same as used by "sysopen". 241 They are the same as used by "sysopen".
89 242
90 Likewise, $mode specifies the mode of the newly created file, if it 243 Likewise, $mode specifies the mode of the newly created file, if it
91 didn't exist and "O_CREAT" has been given, just like perl's 244 didn't exist and "O_CREAT" has been given, just like perl's
92 "sysopen", except that it is mandatory (i.e. use 0 if you don't 245 "sysopen", except that it is mandatory (i.e. use 0 if you don't
93 create new files, and 0666 or 0777 if you do). 246 create new files, and 0666 or 0777 if you do). Note that the $mode
247 will be modified by the umask in effect then the request is being
248 executed, so better never change the umask.
94 249
95 Example: 250 Example:
96 251
97 aio_open "/etc/passwd", O_RDONLY, 0, sub { 252 aio_open "/etc/passwd", O_RDONLY, 0, sub {
98 if ($_[0]) { 253 if ($_[0]) {
… …
103 } 258 }
104 }; 259 };
105 260
106 aio_close $fh, $callback->($status) 261 aio_close $fh, $callback->($status)
107 Asynchronously close a file and call the callback with the result 262 Asynchronously close a file and call the callback with the result
108 code. *WARNING:* although accepted, you should not pass in a perl 263 code.
109 filehandle here, as perl will likely close the file descriptor
110 another time when the filehandle is destroyed. Normally, you can
111 safely call perls "close" or just let filehandles go out of scope.
112 264
113 This is supposed to be a bug in the API, so that might change. It's 265 Unfortunately, you can't do this to perl. Perl *insists* very
114 therefore best to avoid this function. 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...
115 295
116 aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval) 296 aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
117 aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval) 297 aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
118 Reads or writes "length" bytes from the specified "fh" and "offset" 298 Reads or writes $length bytes from the specified $fh and $offset
119 into the scalar given by "data" and offset "dataoffset" and calls 299 into the scalar given by $data and offset $dataoffset and calls the
120 the callback without the actual number of bytes read (or -1 on 300 callback without the actual number of bytes read (or -1 on error,
121 error, just like the syscall). 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.
122 312
123 The $data scalar *MUST NOT* be modified in any way while the request 313 The $data scalar *MUST NOT* be modified in any way while the request
124 is outstanding. Modifying it can result in segfaults or WW3 (if the 314 is outstanding. Modifying it can result in segfaults or World War
125 necessary/optional hardware is installed). 315 III (if the necessary/optional hardware is installed).
126 316
127 Example: Read 15 bytes at offset 7 into scalar $buffer, starting at 317 Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
128 offset 0 within the scalar: 318 offset 0 within the scalar:
129 319
130 aio_read $fh, 7, 15, $buffer, 0, sub { 320 aio_read $fh, 7, 15, $buffer, 0, sub {
… …
188 aio_stat "/etc/passwd", sub { 378 aio_stat "/etc/passwd", sub {
189 $_[0] and die "stat failed: $!"; 379 $_[0] and die "stat failed: $!";
190 print "size is ", -s _, "\n"; 380 print "size is ", -s _, "\n";
191 }; 381 };
192 382
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
193 aio_unlink $pathname, $callback->($status) 417 aio_unlink $pathname, $callback->($status)
194 Asynchronously unlink (delete) a file and call the callback with the 418 Asynchronously unlink (delete) a file and call the callback with the
195 result code. 419 result code.
196 420
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
197 aio_rmdir $pathname, $callback->($status) 453 aio_rmdir $pathname, $callback->($status)
198 Asynchronously rmdir (delete) a directory and call the callback with 454 Asynchronously rmdir (delete) a directory and call the callback with
199 the result code. 455 the result code.
200 456
201 aio_readdir $pathname $callback->($entries) 457 aio_readdir $pathname, $callback->($entries)
202 Unlike the POSIX call of the same name, "aio_readdir" reads an 458 Unlike the POSIX call of the same name, "aio_readdir" reads an
203 entire directory (i.e. opendir + readdir + closedir). The entries 459 entire directory (i.e. opendir + readdir + closedir). The entries
204 will not be sorted, and will NOT include the "." and ".." entries. 460 will not be sorted, and will NOT include the "." and ".." entries.
205 461
206 The callback a single argument which is either "undef" or an 462 The callback a single argument which is either "undef" or an
207 array-ref with the filenames. 463 array-ref with the filenames.
208 464
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
209 aio_scandir $path, $maxreq, $callback->($dirs, $nondirs) 492 aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
210 Scans a directory (similar to "aio_readdir") and tries to separate 493 Scans a directory (similar to "aio_readdir") but additionally tries
211 the entries of directory $path into two sets of names, ones you can 494 to efficiently separate the entries of directory $path into two sets
212 recurse into (directories), and ones you cannot recurse into 495 of names, directories you can recurse into (directories), and ones
213 (everything else). 496 you cannot recurse into (everything else, including symlinks to
497 directories).
214 498
215 "aio_scandir" is a composite request that consists of many 499 "aio_scandir" is a composite request that creates of many sub
216 aio-primitives. $maxreq specifies the maximum number of outstanding 500 requests_ $maxreq specifies the maximum number of outstanding aio
217 aio requests that this function generates. If it is "<= 0", then a 501 requests that this function generates. If it is "<= 0", then a
218 suitable default will be chosen (currently 8). 502 suitable default will be chosen (currently 4).
219 503
220 On error, the callback is called without arguments, otherwise it 504 On error, the callback is called without arguments, otherwise it
221 receives two array-refs with path-relative entry names. 505 receives two array-refs with path-relative entry names.
222 506
223 Example: 507 Example:
… …
232 516
233 The "aio_readdir" cannot be avoided, but "stat()"'ing every entry 517 The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
234 can. 518 can.
235 519
236 After reading the directory, the modification time, size etc. of the 520 After reading the directory, the modification time, size etc. of the
237 directory before and after the readdir is checked, and if they 521 directory before and after the readdir is checked, and if they match
238 match, the link count will be used to decide how many entries are 522 (and isn't the current time), the link count will be used to decide
239 directories (if >= 2). Otherwise, no knowledge of the number of 523 how many entries are directories (if >= 2). Otherwise, no knowledge
240 subdirectories will be assumed. 524 of the number of subdirectories will be assumed.
241 525
242 Then entires will be sorted into likely directories (everything 526 Then entries will be sorted into likely directories (everything
243 without a non-initial dot) and likely non-directories (everything 527 without a non-initial dot currently) and likely non-directories
244 else). Then every entry + "/." will be "stat"'ed, likely directories 528 (everything else). Then every entry plus an appended "/." will be
245 first. This is often faster because filesystems might detect the 529 "stat"'ed, likely directories first. If that succeeds, it assumes
246 type of the entry without reading the inode data (e.g. ext2s
247 filetype feature). If that succeeds, it assumes that the entry is a
248 directory or a symlink to directory (which will be checked 530 that the entry is a directory or a symlink to directory (which will
249 seperately). 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).
250 534
251 If the known number of directories has been reached, the rest of the 535 If the known number of directories (link count - 2) has been
252 entries is assumed to be non-directories. 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.
253 550
254 aio_fsync $fh, $callback->($status) 551 aio_fsync $fh, $callback->($status)
255 Asynchronously call fsync on the given filehandle and call the 552 Asynchronously call fsync on the given filehandle and call the
256 callback with the fsync result code. 553 callback with the fsync result code.
257 554
… …
260 callback with the fdatasync result code. 557 callback with the fdatasync result code.
261 558
262 If this call isn't available because your OS lacks it or it couldn't 559 If this call isn't available because your OS lacks it or it couldn't
263 be detected, it will be emulated by calling "fsync" instead. 560 be detected, it will be emulated by calling "fsync" instead.
264 561
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
649 This makes it very easy to create composite requests (see the source of
650 "aio_move" for an application) that work and feel like simple requests.
651
652 * The IO::AIO::GRP objects will be cleaned up during calls to
653 "IO::AIO::poll_cb", just like any other request.
654 * They can be canceled like any other request. Canceling will cancel not
655 only the request itself, but also all requests it contains.
656 * They can also can also be added to other IO::AIO::GRP objects.
657 * You must not add requests to a group from within the group callback
658 (or any later time).
659
660 Their lifetime, simplified, looks like this: when they are empty, they
661 will finish very quickly. If they contain only requests that are in the
662 "done" state, they will also finish. Otherwise they will continue to
663 exist.
664
665 That means after creating a group you have some time to add requests.
666 And in the callbacks of those requests, you can add further requests to
667 the group. And only when all those requests have finished will the the
668 group itself finish.
669
670 add $grp ...
671 $grp->add (...)
672 Add one or more requests to the group. Any type of IO::AIO::REQ can
673 be added, including other groups, as long as you do not create
674 circular dependencies.
675
676 Returns all its arguments.
677
678 $grp->cancel_subs
679 Cancel all subrequests and clears any feeder, but not the group
680 request itself. Useful when you queued a lot of events but got a
681 result early.
682
683 $grp->result (...)
684 Set the result value(s) that will be passed to the group callback
685 when all subrequests have finished and set thre groups errno to the
686 current value of errno (just like calling "errno" without an error
687 number). By default, no argument will be passed and errno is zero.
688
689 $grp->errno ([$errno])
690 Sets the group errno value to $errno, or the current value of errno
691 when the argument is missing.
692
693 Every aio request has an associated errno value that is restored
694 when the callback is invoked. This method lets you change this value
695 from its default (0).
696
697 Calling "result" will also set errno, so make sure you either set $!
698 before the call to "result", or call c<errno> after it.
699
700 feed $grp $callback->($grp)
701 Sets a feeder/generator on this group: every group can have an
702 attached generator that generates requests if idle. The idea behind
703 this is that, although you could just queue as many requests as you
704 want in a group, this might starve other requests for a potentially
705 long time. For example, "aio_scandir" might generate hundreds of
706 thousands "aio_stat" requests, delaying any later requests for a
707 long time.
708
709 To avoid this, and allow incremental generation of requests, you can
710 instead a group and set a feeder on it that generates those
711 requests. The feed callback will be called whenever there are few
712 enough (see "limit", below) requests active in the group itself and
713 is expected to queue more requests.
714
715 The feed callback can queue as many requests as it likes (i.e. "add"
716 does not impose any limits).
717
718 If the feed does not queue more requests when called, it will be
719 automatically removed from the group.
720
721 If the feed limit is 0, it will be set to 2 automatically.
722
723 Example:
724
725 # stat all files in @files, but only ever use four aio requests concurrently:
726
727 my $grp = aio_group sub { print "finished\n" };
728 limit $grp 4;
729 feed $grp sub {
730 my $file = pop @files
731 or return;
732
733 add $grp aio_stat $file, sub { ... };
734 };
735
736 limit $grp $num
737 Sets the feeder limit for the group: The feeder will be called
738 whenever the group contains less than this many requests.
739
740 Setting the limit to 0 will pause the feeding process.
741
265 SUPPORT FUNCTIONS 742 SUPPORT FUNCTIONS
743 EVENT PROCESSING AND EVENT LOOP INTEGRATION
266 $fileno = IO::AIO::poll_fileno 744 $fileno = IO::AIO::poll_fileno
267 Return the *request result pipe file descriptor*. This filehandle 745 Return the *request result pipe file descriptor*. This filehandle
268 must be polled for reading by some mechanism outside this module 746 must be polled for reading by some mechanism outside this module
269 (e.g. Event or select, see below or the SYNOPSIS). If the pipe 747 (e.g. Event or select, see below or the SYNOPSIS). If the pipe
270 becomes readable you have to call "poll_cb" to check the results. 748 becomes readable you have to call "poll_cb" to check the results.
271 749
272 See "poll_cb" for an example. 750 See "poll_cb" for an example.
273 751
274 IO::AIO::poll_cb 752 IO::AIO::poll_cb
275 Process all outstanding events on the result pipe. You have to call 753 Process some outstanding events on the result pipe. You have to call
276 this regularly. Returns the number of events processed. Returns 754 this regularly. Returns the number of events processed. Returns
277 immediately when no events are outstanding. 755 immediately when no events are outstanding. The amount of events
756 processed depends on the settings of "IO::AIO::max_poll_req" and
757 "IO::AIO::max_poll_time".
758
759 If not all requests were processed for whatever reason, the
760 filehandle will still be ready when "poll_cb" returns.
278 761
279 Example: Install an Event watcher that automatically calls 762 Example: Install an Event watcher that automatically calls
280 IO::AIO::poll_cb with high priority: 763 IO::AIO::poll_cb with high priority:
281 764
282 Event->io (fd => IO::AIO::poll_fileno, 765 Event->io (fd => IO::AIO::poll_fileno,
283 poll => 'r', async => 1, 766 poll => 'r', async => 1,
284 cb => \&IO::AIO::poll_cb); 767 cb => \&IO::AIO::poll_cb);
285 768
769 IO::AIO::max_poll_reqs $nreqs
770 IO::AIO::max_poll_time $seconds
771 These set the maximum number of requests (default 0, meaning
772 infinity) that are being processed by "IO::AIO::poll_cb" in one
773 call, respectively the maximum amount of time (default 0, meaning
774 infinity) spent in "IO::AIO::poll_cb" to process requests (more
775 correctly the mininum amount of time "poll_cb" is allowed to use).
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
783 Setting these is useful if you want to ensure some level of
784 interactiveness when perl is not fast enough to process all requests
785 in time.
786
787 For interactive programs, values such as 0.01 to 0.1 should be fine.
788
789 Example: Install an Event watcher that automatically calls
790 IO::AIO::poll_cb with low priority, to ensure that other parts of
791 the program get the CPU sometimes even under high AIO load.
792
793 # try not to spend much more than 0.1s in poll_cb
794 IO::AIO::max_poll_time 0.1;
795
796 # use a low priority so other tasks have priority
797 Event->io (fd => IO::AIO::poll_fileno,
798 poll => 'r', nice => 1,
799 cb => &IO::AIO::poll_cb);
800
286 IO::AIO::poll_wait 801 IO::AIO::poll_wait
802 If there are any outstanding requests and none of them in the result
287 Wait till the result filehandle becomes ready for reading (simply 803 phase, wait till the result filehandle becomes ready for reading
288 does a "select" on the filehandle. This is useful if you want to 804 (simply does a "select" on the filehandle. This is useful if you
289 synchronously wait for some requests to finish). 805 want to synchronously wait for some requests to finish).
290 806
291 See "nreqs" for an example. 807 See "nreqs" for an example.
292 808
809 IO::AIO::poll
810 Waits until some requests have been handled.
811
812 Returns the number of requests processed, but is otherwise strictly
813 equivalent to:
814
815 IO::AIO::poll_wait, IO::AIO::poll_cb
816
293 IO::AIO::nreqs 817 IO::AIO::flush
294 Returns the number of requests currently outstanding (i.e. for which 818 Wait till all outstanding AIO requests have been handled.
295 their callback has not been invoked yet).
296 819
297 Example: wait till there are no outstanding requests anymore: 820 Strictly equivalent to:
298 821
299 IO::AIO::poll_wait, IO::AIO::poll_cb 822 IO::AIO::poll_wait, IO::AIO::poll_cb
300 while IO::AIO::nreqs; 823 while IO::AIO::nreqs;
301 824
302 IO::AIO::flush 825 CONTROLLING THE NUMBER OF THREADS
303 Wait till all outstanding AIO requests have been handled.
304
305 Strictly equivalent to:
306
307 IO::AIO::poll_wait, IO::AIO::poll_cb
308 while IO::AIO::nreqs;
309
310 IO::AIO::poll
311 Waits until some requests have been handled.
312
313 Strictly equivalent to:
314
315 IO::AIO::poll_wait, IO::AIO::poll_cb
316 if IO::AIO::nreqs;
317
318 IO::AIO::min_parallel $nthreads 826 IO::AIO::min_parallel $nthreads
319 Set the minimum number of AIO threads to $nthreads. The current 827 Set the minimum number of AIO threads to $nthreads. The current
320 default is 4, which means four asynchronous operations can be done 828 default is 8, which means eight asynchronous operations can execute
321 at one time (the number of outstanding operations, however, is 829 concurrently at any one time (the number of outstanding requests,
322 unlimited). 830 however, is unlimited).
323 831
324 IO::AIO starts threads only on demand, when an AIO request is queued 832 IO::AIO starts threads only on demand, when an AIO request is queued
325 and no free thread exists. 833 and no free thread exists. Please note that queueing up a hundred
834 requests can create demand for a hundred threads, even if it turns
835 out that everything is in the cache and could have been processed
836 faster by a single thread.
326 837
327 It is recommended to keep the number of threads low, as some Linux 838 It is recommended to keep the number of threads relatively low, as
328 kernel versions will scale negatively with the number of threads 839 some Linux kernel versions will scale negatively with the number of
329 (higher parallelity => MUCH higher latency). With current Linux 2.6 840 threads (higher parallelity => MUCH higher latency). With current
330 versions, 4-32 threads should be fine. 841 Linux 2.6 versions, 4-32 threads should be fine.
331 842
332 Under most circumstances you don't need to call this function, as 843 Under most circumstances you don't need to call this function, as
333 the module selects a default that is suitable for low to moderate 844 the module selects a default that is suitable for low to moderate
334 load. 845 load.
335 846
… …
345 ensure that all threads are killed and that there are no outstanding 856 ensure that all threads are killed and that there are no outstanding
346 requests. 857 requests.
347 858
348 Under normal circumstances you don't need to call this function. 859 Under normal circumstances you don't need to call this function.
349 860
861 IO::AIO::max_idle $nthreads
862 Limit the number of threads (default: 4) that are allowed to idle
863 (i.e., threads that did not get a request to process within 10
864 seconds). That means if a thread becomes idle while $nthreads other
865 threads are also idle, it will free its resources and exit.
866
867 This is useful when you allow a large number of threads (e.g. 100 or
868 1000) to allow for extremely high load situations, but want to free
869 resources under normal circumstances (1000 threads can easily
870 consume 30MB of RAM).
871
872 The default is probably ok in most situations, especially if thread
873 creation is fast. If thread creation is very slow on your system you
874 might want to use larger values.
875
350 $oldnreqs = IO::AIO::max_outstanding $nreqs 876 $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
877 This is a very bad function to use in interactive programs because
878 it blocks, and a bad way to reduce concurrency because it is
879 inexact: Better use an "aio_group" together with a feed callback.
880
351 Sets the maximum number of outstanding requests to $nreqs. If you 881 Sets the maximum number of outstanding requests to $nreqs. If you do
352 try to queue up more than this number of requests, the caller will 882 queue up more than this number of requests, the next call to the
353 block until some requests have been handled. 883 "poll_cb" (and "poll_some" and other functions calling "poll_cb")
884 function will block until the limit is no longer exceeded.
354 885
355 The default is very large, so normally there is no practical limit. 886 The default value is very large, so there is no practical limit on
356 If you queue up many requests in a loop it often improves speed if 887 the number of outstanding requests.
357 you set this to a relatively low number, such as 100.
358 888
359 Under normal circumstances you don't need to call this function. 889 You can still queue as many requests as you want. Therefore,
890 "max_oustsanding" is mainly useful in simple scripts (with low
891 values) or as a stop gap to shield against fatal memory overflow
892 (with large values).
893
894 STATISTICAL INFORMATION
895 IO::AIO::nreqs
896 Returns the number of requests currently in the ready, execute or
897 pending states (i.e. for which their callback has not been invoked
898 yet).
899
900 Example: wait till there are no outstanding requests anymore:
901
902 IO::AIO::poll_wait, IO::AIO::poll_cb
903 while IO::AIO::nreqs;
904
905 IO::AIO::nready
906 Returns the number of requests currently in the ready state (not yet
907 executed).
908
909 IO::AIO::npending
910 Returns the number of requests currently in the pending state
911 (executed, but not yet processed by poll_cb).
360 912
361 FORK BEHAVIOUR 913 FORK BEHAVIOUR
914 This module should do "the right thing" when the process using it forks:
915
362 Before the fork, IO::AIO enters a quiescent state where no requests can 916 Before the fork, IO::AIO enters a quiescent state where no requests can
363 be added in other threads and no results will be processed. After the 917 be added in other threads and no results will be processed. After the
364 fork the parent simply leaves the quiescent state and continues 918 fork the parent simply leaves the quiescent state and continues
365 request/result processing, while the child clears the request/result 919 request/result processing, while the child frees the request/result
366 queue (so the requests started before the fork will only be handled in 920 queue (so that the requests started before the fork will only be handled
367 the parent). Threats will be started on demand until the limit ste in 921 in the parent). Threads will be started on demand until the limit set in
368 the parent process has been reached again. 922 the parent process has been reached again.
369 923
924 In short: the parent will, after a short pause, continue as if fork had
925 not been called, while the child will act as if IO::AIO has not been
926 used yet.
927
928 MEMORY USAGE
929 Per-request usage:
930
931 Each aio request uses - depending on your architecture - around 100-200
932 bytes of memory. In addition, stat requests need a stat buffer (possibly
933 a few hundred bytes), readdir requires a result buffer and so on. Perl
934 scalars and other data passed into aio requests will also be locked and
935 will consume memory till the request has entered the done state.
936
937 This is not awfully much, so queuing lots of requests is not usually a
938 problem.
939
940 Per-thread usage:
941
942 In the execution phase, some aio requests require more memory for
943 temporary buffers, and each thread requires a stack and other data
944 structures (usually around 16k-128k, depending on the OS).
945
946KNOWN BUGS
947 Known bugs will be fixed in the next release.
948
370SEE ALSO 949SEE ALSO
371 Coro, Linux::AIO. 950 Coro::AIO.
372 951
373AUTHOR 952AUTHOR
374 Marc Lehmann <schmorp@schmorp.de> 953 Marc Lehmann <schmorp@schmorp.de>
375 http://home.schmorp.de/ 954 http://home.schmorp.de/
376 955

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