ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/IO-AIO/AIO.pm
Revision: 1.34
Committed: Thu Aug 18 16:32:10 2005 UTC (19 years, 3 months ago) by root
Branch: MAIN
CVS Tags: rel-1_5
Changes since 1.33: +22 -15 lines
Log Message:
*** empty log message ***

File Contents

# Content
1 =head1 NAME
2
3 IO::AIO - Asynchronous Input/Output
4
5 =head1 SYNOPSIS
6
7 use IO::AIO;
8
9 aio_open "/etc/passwd", O_RDONLY, 0, sub {
10 my ($fh) = @_;
11 ...
12 };
13
14 aio_unlink "/tmp/file", sub { };
15
16 aio_read $fh, 30000, 1024, $buffer, 0, sub {
17 $_[0] > 0 or die "read error: $!";
18 };
19
20 # Event
21 Event->io (fd => IO::AIO::poll_fileno,
22 poll => 'r',
23 cb => \&IO::AIO::poll_cb);
24
25 # Glib/Gtk2
26 add_watch Glib::IO IO::AIO::poll_fileno,
27 in => sub { IO::AIO::poll_cb; 1 };
28
29 # Tk
30 Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31 readable => \&IO::AIO::poll_cb);
32
33 # Danga::Socket
34 Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35 \&IO::AIO::poll_cb);
36
37
38 =head1 DESCRIPTION
39
40 This module implements asynchronous I/O using whatever means your
41 operating system supports.
42
43 Currently, a number of threads are started that execute your read/writes
44 and signal their completion. You don't need thread support in your libc or
45 perl, and the threads created by this module will not be visible to the
46 pthreads library. In the future, this module might make use of the native
47 aio functions available on many operating systems. However, they are often
48 not well-supported (Linux doesn't allow them on normal files currently,
49 for example), and they would only support aio_read and aio_write, so the
50 remaining functionality would have to be implemented using threads anyway.
51
52 Although the module will work with in the presence of other threads, it is
53 currently not reentrant, so use appropriate locking yourself, always call
54 C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
55 C<aio_> functions) recursively.
56
57 =cut
58
59 package IO::AIO;
60
61 no warnings;
62
63 use base 'Exporter';
64
65 use Fcntl ();
66
67 BEGIN {
68 $VERSION = 1.5;
69
70 @EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
71 aio_rmdir aio_symlink aio_fsync aio_fdatasync aio_readahead);
72 @EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
73
74 require XSLoader;
75 XSLoader::load IO::AIO, $VERSION;
76 }
77
78 =head1 FUNCTIONS
79
80 =head2 AIO FUNCTIONS
81
82 All the C<aio_*> calls are more or less thin wrappers around the syscall
83 with the same name (sans C<aio_>). The arguments are similar or identical,
84 and they all accept an additional (and optional) C<$callback> argument
85 which must be a code reference. This code reference will get called with
86 the syscall return code (e.g. most syscalls return C<-1> on error, unlike
87 perl, which usually delivers "false") as it's sole argument when the given
88 syscall has been executed asynchronously.
89
90 All functions expecting a filehandle keep a copy of the filehandle
91 internally until the request has finished.
92
93 The pathnames you pass to these routines I<must> be absolute and
94 encoded in byte form. The reason for the former is that at the time the
95 request is being executed, the current working directory could have
96 changed. Alternatively, you can make sure that you never change the
97 current working directory.
98
99 To encode pathnames to byte form, either make sure you either: a)
100 always pass in filenames you got from outside (command line, readdir
101 etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode
102 your pathnames to the locale (or other) encoding in effect in the user
103 environment, d) use Glib::filename_from_unicode on unicode filenames or e)
104 use something else.
105
106 =over 4
107
108 =item aio_open $pathname, $flags, $mode, $callback
109
110 Asynchronously open or create a file and call the callback with a newly
111 created filehandle for the file.
112
113 The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
114 for an explanation.
115
116 The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
117 list. They are the same as used by C<sysopen>.
118
119 Likewise, C<$mode> specifies the mode of the newly created file, if it
120 didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
121 except that it is mandatory (i.e. use C<0> if you don't create new files,
122 and C<0666> or C<0777> if you do).
123
124 Example:
125
126 aio_open "/etc/passwd", O_RDONLY, 0, sub {
127 if ($_[0]) {
128 print "open successful, fh is $_[0]\n";
129 ...
130 } else {
131 die "open failed: $!\n";
132 }
133 };
134
135 =item aio_close $fh, $callback
136
137 Asynchronously close a file and call the callback with the result
138 code. I<WARNING:> although accepted, you should not pass in a perl
139 filehandle here, as perl will likely close the file descriptor another
140 time when the filehandle is destroyed. Normally, you can safely call perls
141 C<close> or just let filehandles go out of scope.
142
143 This is supposed to be a bug in the API, so that might change. It's
144 therefore best to avoid this function.
145
146 =item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
147
148 =item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
149
150 Reads or writes C<length> bytes from the specified C<fh> and C<offset>
151 into the scalar given by C<data> and offset C<dataoffset> and calls the
152 callback without the actual number of bytes read (or -1 on error, just
153 like the syscall).
154
155 The C<$data> scalar I<MUST NOT> be modified in any way while the request
156 is outstanding. Modifying it can result in segfaults or WW3 (if the
157 necessary/optional hardware is installed).
158
159 Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
160 offset C<0> within the scalar:
161
162 aio_read $fh, 7, 15, $buffer, 0, sub {
163 $_[0] > 0 or die "read error: $!";
164 print "read $_[0] bytes: <$buffer>\n";
165 };
166
167 =item aio_readahead $fh,$offset,$length, $callback
168
169 C<aio_readahead> populates the page cache with data from a file so that
170 subsequent reads from that file will not block on disk I/O. The C<$offset>
171 argument specifies the starting point from which data is to be read and
172 C<$length> specifies the number of bytes to be read. I/O is performed in
173 whole pages, so that offset is effectively rounded down to a page boundary
174 and bytes are read up to the next page boundary greater than or equal to
175 (off-set+length). C<aio_readahead> does not read beyond the end of the
176 file. The current file offset of the file is left unchanged.
177
178 If that syscall doesn't exist (likely if your OS isn't Linux) it will be
179 emulated by simply reading the data, which would have a similar effect.
180
181 =item aio_stat $fh_or_path, $callback
182
183 =item aio_lstat $fh, $callback
184
185 Works like perl's C<stat> or C<lstat> in void context. The callback will
186 be called after the stat and the results will be available using C<stat _>
187 or C<-s _> etc...
188
189 The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
190 for an explanation.
191
192 Currently, the stats are always 64-bit-stats, i.e. instead of returning an
193 error when stat'ing a large file, the results will be silently truncated
194 unless perl itself is compiled with large file support.
195
196 Example: Print the length of F</etc/passwd>:
197
198 aio_stat "/etc/passwd", sub {
199 $_[0] and die "stat failed: $!";
200 print "size is ", -s _, "\n";
201 };
202
203 =item aio_unlink $pathname, $callback
204
205 Asynchronously unlink (delete) a file and call the callback with the
206 result code.
207
208 =item aio_rmdir $pathname, $callback
209
210 Asynchronously rmdir (delete) a directory and call the callback with the
211 result code.
212
213 =item aio_fsync $fh, $callback
214
215 Asynchronously call fsync on the given filehandle and call the callback
216 with the fsync result code.
217
218 =item aio_fdatasync $fh, $callback
219
220 Asynchronously call fdatasync on the given filehandle and call the
221 callback with the fdatasync result code.
222
223 If this call isn't available because your OS lacks it or it couldn't be
224 detected, it will be emulated by calling C<fsync> instead.
225
226 =back
227
228 =head2 SUPPORT FUNCTIONS
229
230 =over 4
231
232 =item $fileno = IO::AIO::poll_fileno
233
234 Return the I<request result pipe file descriptor>. This filehandle must be
235 polled for reading by some mechanism outside this module (e.g. Event or
236 select, see below or the SYNOPSIS). If the pipe becomes readable you have
237 to call C<poll_cb> to check the results.
238
239 See C<poll_cb> for an example.
240
241 =item IO::AIO::poll_cb
242
243 Process all outstanding events on the result pipe. You have to call this
244 regularly. Returns the number of events processed. Returns immediately
245 when no events are outstanding.
246
247 Example: Install an Event watcher that automatically calls
248 IO::AIO::poll_cb with high priority:
249
250 Event->io (fd => IO::AIO::poll_fileno,
251 poll => 'r', async => 1,
252 cb => \&IO::AIO::poll_cb);
253
254 =item IO::AIO::poll_wait
255
256 Wait till the result filehandle becomes ready for reading (simply does a
257 C<select> on the filehandle. This is useful if you want to synchronously wait
258 for some requests to finish).
259
260 See C<nreqs> for an example.
261
262 =item IO::AIO::nreqs
263
264 Returns the number of requests currently outstanding (i.e. for which their
265 callback has not been invoked yet).
266
267 Example: wait till there are no outstanding requests anymore:
268
269 IO::AIO::poll_wait, IO::AIO::poll_cb
270 while IO::AIO::nreqs;
271
272 =item IO::AIO::flush
273
274 Wait till all outstanding AIO requests have been handled.
275
276 Strictly equivalent to:
277
278 IO::AIO::poll_wait, IO::AIO::poll_cb
279 while IO::AIO::nreqs;
280
281 =item IO::AIO::poll
282
283 Waits until some requests have been handled.
284
285 Strictly equivalent to:
286
287 IO::AIO::poll_wait, IO::AIO::poll_cb
288 if IO::AIO::nreqs;
289
290 =item IO::AIO::min_parallel $nthreads
291
292 Set the minimum number of AIO threads to C<$nthreads>. The current default
293 is C<4>, which means four asynchronous operations can be done at one time
294 (the number of outstanding operations, however, is unlimited).
295
296 IO::AIO starts threads only on demand, when an AIO request is queued and
297 no free thread exists.
298
299 It is recommended to keep the number of threads low, as some Linux
300 kernel versions will scale negatively with the number of threads (higher
301 parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
302 threads should be fine.
303
304 Under most circumstances you don't need to call this function, as the
305 module selects a default that is suitable for low to moderate load.
306
307 =item IO::AIO::max_parallel $nthreads
308
309 Sets the maximum number of AIO threads to C<$nthreads>. If more than the
310 specified number of threads are currently running, this function kills
311 them. This function blocks until the limit is reached.
312
313 While C<$nthreads> are zero, aio requests get queued but not executed
314 until the number of threads has been increased again.
315
316 This module automatically runs C<max_parallel 0> at program end, to ensure
317 that all threads are killed and that there are no outstanding requests.
318
319 Under normal circumstances you don't need to call this function.
320
321 =item $oldnreqs = IO::AIO::max_outstanding $nreqs
322
323 Sets the maximum number of outstanding requests to C<$nreqs>. If you
324 try to queue up more than this number of requests, the caller will block until
325 some requests have been handled.
326
327 The default is very large, so normally there is no practical limit. If you
328 queue up many requests in a loop it often improves speed if you set
329 this to a relatively low number, such as C<100>.
330
331 Under normal circumstances you don't need to call this function.
332
333 =back
334
335 =cut
336
337 # support function to convert a fd into a perl filehandle
338 sub _fd2fh {
339 return undef if $_[0] < 0;
340
341 # try to generate nice filehandles
342 my $sym = "IO::AIO::fd#$_[0]";
343 local *$sym;
344
345 open *$sym, "+<&=$_[0]" # usually works under any unix
346 or open *$sym, "<&=$_[0]" # cygwin needs this
347 or open *$sym, ">&=$_[0]" # or this
348 or return undef;
349
350 *$sym
351 }
352
353 min_parallel 4;
354
355 END {
356 max_parallel 0;
357 }
358
359 1;
360
361 =head2 FORK BEHAVIOUR
362
363 Before the fork, IO::AIO enters a quiescent state where no requests
364 can be added in other threads and no results will be processed. After
365 the fork the parent simply leaves the quiescent state and continues
366 request/result processing, while the child clears the request/result
367 queue (so the requests started before the fork will only be handled in
368 the parent). Threats will be started on demand until the limit ste in the
369 parent process has been reached again.
370
371 =head1 SEE ALSO
372
373 L<Coro>, L<Linux::AIO>.
374
375 =head1 AUTHOR
376
377 Marc Lehmann <schmorp@schmorp.de>
378 http://home.schmorp.de/
379
380 =cut
381