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Revision 1.17 by root, Mon Jun 26 14:53:55 2006 UTC

1NAME 1NAME
2 IO::AIO - Asynchronous Input/Output 2 IO::AIO - Asynchronous Input/Output
3 3
4SYNOPSIS 4SYNOPSIS
5 use IO::AIO; 5 use IO::AIO;
6
7 aio_open "/etc/passwd", O_RDONLY, 0, sub {
8 my ($fh) = @_;
9 ...
10 };
11
12 aio_unlink "/tmp/file", sub { };
13
14 aio_read $fh, 30000, 1024, $buffer, 0, sub {
15 $_[0] > 0 or die "read error: $!";
16 };
17
18 # AnyEvent
19 open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
20 my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
21
22 # Event
23 Event->io (fd => IO::AIO::poll_fileno,
24 poll => 'r',
25 cb => \&IO::AIO::poll_cb);
26
27 # Glib/Gtk2
28 add_watch Glib::IO IO::AIO::poll_fileno,
29 in => sub { IO::AIO::poll_cb; 1 };
30
31 # Tk
32 Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
33 readable => \&IO::AIO::poll_cb);
34
35 # Danga::Socket
36 Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
37 \&IO::AIO::poll_cb);
6 38
7DESCRIPTION 39DESCRIPTION
8 This module implements asynchronous I/O using whatever means your 40 This module implements asynchronous I/O using whatever means your
9 operating system supports. 41 operating system supports.
10 42
… …
17 currently, for example), and they would only support aio_read and 49 currently, for example), and they would only support aio_read and
18 aio_write, so the remaining functionality would have to be implemented 50 aio_write, so the remaining functionality would have to be implemented
19 using threads anyway. 51 using threads anyway.
20 52
21 Although the module will work with in the presence of other threads, it 53 Although the module will work with in the presence of other threads, it
22 is currently not reentrant, so use appropriate locking yourself. 54 is currently not reentrant, so use appropriate locking yourself, always
55 call "poll_cb" from within the same thread, or never call "poll_cb" (or
56 other "aio_" functions) recursively.
23 57
24FUNCTIONS 58FUNCTIONS
25 AIO FUNCTIONS 59 AIO FUNCTIONS
26 All the "aio_*" calls are more or less thin wrappers around the syscall 60 All the "aio_*" calls are more or less thin wrappers around the syscall
27 with the same name (sans "aio_"). The arguments are similar or 61 with the same name (sans "aio_"). The arguments are similar or
28 identical, and they all accept an additional $callback argument which 62 identical, and they all accept an additional (and optional) $callback
29 must be a code reference. This code reference will get called with the 63 argument which must be a code reference. This code reference will get
30 syscall return code (e.g. most syscalls return -1 on error, unlike perl, 64 called with the syscall return code (e.g. most syscalls return -1 on
31 which usually delivers "false") as it's sole argument when the given 65 error, unlike perl, which usually delivers "false") as it's sole
32 syscall has been executed asynchronously. 66 argument when the given syscall has been executed asynchronously.
33 67
34 All functions that expect a filehandle will also accept a file 68 All functions expecting a filehandle keep a copy of the filehandle
35 descriptor. 69 internally until the request has finished.
36 70
37 The filenames you pass to these routines *must* be absolute. The reason 71 The pathnames you pass to these routines *must* be absolute and encoded
38 is that at the time the request is being executed, the current working 72 in byte form. The reason for the former is that at the time the request
39 directory could have changed. Alternatively, you can make sure that you 73 is being executed, the current working directory could have changed.
40 never change the current working directory. 74 Alternatively, you can make sure that you never change the current
75 working directory.
41 76
77 To encode pathnames to byte form, either make sure you either: a) always
78 pass in filenames you got from outside (command line, readdir etc.), b)
79 are ASCII or ISO 8859-1, c) use the Encode module and encode your
80 pathnames to the locale (or other) encoding in effect in the user
81 environment, d) use Glib::filename_from_unicode on unicode filenames or
82 e) use something else.
83
42 aio_open $pathname, $flags, $mode, $callback 84 aio_open $pathname, $flags, $mode, $callback->($fh)
43 Asynchronously open or create a file and call the callback with a 85 Asynchronously open or create a file and call the callback with a
44 newly created filehandle for the file. 86 newly created filehandle for the file.
45 87
46 The pathname passed to "aio_open" must be absolute. See API NOTES, 88 The pathname passed to "aio_open" must be absolute. See API NOTES,
47 above, for an explanation. 89 above, for an explanation.
48 90
49 The $mode argument is a bitmask. See the "Fcntl" module for a list. 91 The $flags argument is a bitmask. See the "Fcntl" module for a list.
50 They are the same as used in "sysopen". 92 They are the same as used by "sysopen".
93
94 Likewise, $mode specifies the mode of the newly created file, if it
95 didn't exist and "O_CREAT" has been given, just like perl's
96 "sysopen", except that it is mandatory (i.e. use 0 if you don't
97 create new files, and 0666 or 0777 if you do).
51 98
52 Example: 99 Example:
53 100
54 aio_open "/etc/passwd", O_RDONLY, 0, sub { 101 aio_open "/etc/passwd", O_RDONLY, 0, sub {
55 if ($_[0]) { 102 if ($_[0]) {
… …
58 } else { 105 } else {
59 die "open failed: $!\n"; 106 die "open failed: $!\n";
60 } 107 }
61 }; 108 };
62 109
63 aio_close $fh, $callback 110 aio_close $fh, $callback->($status)
64 Asynchronously close a file and call the callback with the result 111 Asynchronously close a file and call the callback with the result
65 code. *WARNING:* although accepted, you should not pass in a perl 112 code. *WARNING:* although accepted, you should not pass in a perl
66 filehandle here, as perl will likely close the file descriptor 113 filehandle here, as perl will likely close the file descriptor
67 itself when the filehandle is destroyed. Normally, you can safely 114 another time when the filehandle is destroyed. Normally, you can
68 call perls "close" or just let filehandles go out of scope. 115 safely call perls "close" or just let filehandles go out of scope.
69 116
117 This is supposed to be a bug in the API, so that might change. It's
118 therefore best to avoid this function.
119
70 aio_read $fh,$offset,$length, $data,$dataoffset,$callback 120 aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
71 aio_write $fh,$offset,$length, $data,$dataoffset,$callback 121 aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
72 Reads or writes "length" bytes from the specified "fh" and "offset" 122 Reads or writes "length" bytes from the specified "fh" and "offset"
73 into the scalar given by "data" and offset "dataoffset" and calls 123 into the scalar given by "data" and offset "dataoffset" and calls
74 the callback without the actual number of bytes read (or -1 on 124 the callback without the actual number of bytes read (or -1 on
75 error, just like the syscall). 125 error, just like the syscall).
76 126
127 The $data scalar *MUST NOT* be modified in any way while the request
128 is outstanding. Modifying it can result in segfaults or WW3 (if the
129 necessary/optional hardware is installed).
130
77 Example: Read 15 bytes at offset 7 into scalar $buffer, strating at 131 Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
78 offset 0 within the scalar: 132 offset 0 within the scalar:
79 133
80 aio_read $fh, 7, 15, $buffer, 0, sub { 134 aio_read $fh, 7, 15, $buffer, 0, sub {
81 $_[0] >= 0 or die "read error: $!"; 135 $_[0] > 0 or die "read error: $!";
82 print "read <$buffer>\n"; 136 print "read $_[0] bytes: <$buffer>\n";
83 }; 137 };
84 138
139 aio_move $srcpath, $dstpath, $callback->($status)
140 [EXPERIMENTAL]
141
142 Try to move the *file* (directories not supported as either source
143 or destination) from $srcpath to $dstpath and call the callback with
144 the 0 (error) or -1 ok.
145
146 This is a composite request that tries to rename(2) the file first.
147 If rename files with "EXDEV", it creates the destination file with
148 mode 0200 and copies the contents of the source file into it using
149 "aio_sendfile", followed by restoring atime, mtime, access mode and
150 uid/gid, in that order, and unlinking the $srcpath.
151
152 If an error occurs, the partial destination file will be unlinked,
153 if possible, except when setting atime, mtime, access mode and
154 uid/gid, where errors are being ignored.
155
156 aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
157 Tries to copy $length bytes from $in_fh to $out_fh. It starts
158 reading at byte offset $in_offset, and starts writing at the current
159 file offset of $out_fh. Because of that, it is not safe to issue
160 more than one "aio_sendfile" per $out_fh, as they will interfere
161 with each other.
162
163 This call tries to make use of a native "sendfile" syscall to
164 provide zero-copy operation. For this to work, $out_fh should refer
165 to a socket, and $in_fh should refer to mmap'able file.
166
167 If the native sendfile call fails or is not implemented, it will be
168 emulated, so you can call "aio_sendfile" on any type of filehandle
169 regardless of the limitations of the operating system.
170
171 Please note, however, that "aio_sendfile" can read more bytes from
172 $in_fh than are written, and there is no way to find out how many
173 bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
174 only provides the number of bytes written to $out_fh. Only if the
175 result value equals $length one can assume that $length bytes have
176 been read.
177
85 aio_readahead $fh,$offset,$length, $callback 178 aio_readahead $fh,$offset,$length, $callback->($retval)
86 Asynchronously reads the specified byte range into the page cache,
87 using the "readahead" syscall. If that syscall doesn't exist the
88 status will be -1 and $! is set to ENOSYS.
89
90 readahead() populates the page cache with data from a file so that 179 "aio_readahead" populates the page cache with data from a file so
91 subsequent reads from that file will not block on disk I/O. The 180 that subsequent reads from that file will not block on disk I/O. The
92 $offset argument specifies the starting point from which data is to 181 $offset argument specifies the starting point from which data is to
93 be read and $length specifies the number of bytes to be read. I/O is 182 be read and $length specifies the number of bytes to be read. I/O is
94 performed in whole pages, so that offset is effectively rounded down 183 performed in whole pages, so that offset is effectively rounded down
95 to a page boundary and bytes are read up to the next page boundary 184 to a page boundary and bytes are read up to the next page boundary
96 greater than or equal to (off-set+length). aio_readahead() does not 185 greater than or equal to (off-set+length). "aio_readahead" does not
97 read beyond the end of the file. The current file offset of the file 186 read beyond the end of the file. The current file offset of the file
98 is left unchanged. 187 is left unchanged.
99 188
189 If that syscall doesn't exist (likely if your OS isn't Linux) it
190 will be emulated by simply reading the data, which would have a
191 similar effect.
192
100 aio_stat $fh_or_path, $callback 193 aio_stat $fh_or_path, $callback->($status)
101 aio_lstat $fh, $callback 194 aio_lstat $fh, $callback->($status)
102 Works like perl's "stat" or "lstat" in void context. The callback 195 Works like perl's "stat" or "lstat" in void context. The callback
103 will be called after the stat and the results will be available 196 will be called after the stat and the results will be available
104 using "stat _" or "-s _" etc... 197 using "stat _" or "-s _" etc...
105 198
106 The pathname passed to "aio_stat" must be absolute. See API NOTES, 199 The pathname passed to "aio_stat" must be absolute. See API NOTES,
… …
116 aio_stat "/etc/passwd", sub { 209 aio_stat "/etc/passwd", sub {
117 $_[0] and die "stat failed: $!"; 210 $_[0] and die "stat failed: $!";
118 print "size is ", -s _, "\n"; 211 print "size is ", -s _, "\n";
119 }; 212 };
120 213
121 aio_unlink $pathname, $callback 214 aio_unlink $pathname, $callback->($status)
122 Asynchronously unlink (delete) a file and call the callback with the 215 Asynchronously unlink (delete) a file and call the callback with the
123 result code. 216 result code.
124 217
218 aio_link $srcpath, $dstpath, $callback->($status)
219 Asynchronously create a new link to the existing object at $srcpath
220 at the path $dstpath and call the callback with the result code.
221
222 aio_symlink $srcpath, $dstpath, $callback->($status)
223 Asynchronously create a new symbolic link to the existing object at
224 $srcpath at the path $dstpath and call the callback with the result
225 code.
226
227 aio_rename $srcpath, $dstpath, $callback->($status)
228 Asynchronously rename the object at $srcpath to $dstpath, just as
229 rename(2) and call the callback with the result code.
230
231 aio_rmdir $pathname, $callback->($status)
232 Asynchronously rmdir (delete) a directory and call the callback with
233 the result code.
234
235 aio_readdir $pathname, $callback->($entries)
236 Unlike the POSIX call of the same name, "aio_readdir" reads an
237 entire directory (i.e. opendir + readdir + closedir). The entries
238 will not be sorted, and will NOT include the "." and ".." entries.
239
240 The callback a single argument which is either "undef" or an
241 array-ref with the filenames.
242
243 aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
244 Scans a directory (similar to "aio_readdir") and tries to separate
245 the entries of directory $path into two sets of names, ones you can
246 recurse into (directories), and ones you cannot recurse into
247 (everything else).
248
249 "aio_scandir" is a composite request that consists of many
250 aio-primitives. $maxreq specifies the maximum number of outstanding
251 aio requests that this function generates. If it is "<= 0", then a
252 suitable default will be chosen (currently 8).
253
254 On error, the callback is called without arguments, otherwise it
255 receives two array-refs with path-relative entry names.
256
257 Example:
258
259 aio_scandir $dir, 0, sub {
260 my ($dirs, $nondirs) = @_;
261 print "real directories: @$dirs\n";
262 print "everything else: @$nondirs\n";
263 };
264
265 Implementation notes.
266
267 The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
268 can.
269
270 After reading the directory, the modification time, size etc. of the
271 directory before and after the readdir is checked, and if they
272 match, the link count will be used to decide how many entries are
273 directories (if >= 2). Otherwise, no knowledge of the number of
274 subdirectories will be assumed.
275
276 Then entires will be sorted into likely directories (everything
277 without a non-initial dot) and likely non-directories (everything
278 else). Then every entry + "/." will be "stat"'ed, likely directories
279 first. This is often faster because filesystems might detect the
280 type of the entry without reading the inode data (e.g. ext2fs
281 filetype feature). If that succeeds, it assumes that the entry is a
282 directory or a symlink to directory (which will be checked
283 seperately).
284
285 If the known number of directories has been reached, the rest of the
286 entries is assumed to be non-directories.
287
125 aio_fsync $fh, $callback 288 aio_fsync $fh, $callback->($status)
126 Asynchronously call fsync on the given filehandle and call the 289 Asynchronously call fsync on the given filehandle and call the
127 callback with the fsync result code. 290 callback with the fsync result code.
128 291
129 aio_fdatasync $fh, $callback 292 aio_fdatasync $fh, $callback->($status)
130 Asynchronously call fdatasync on the given filehandle and call the 293 Asynchronously call fdatasync on the given filehandle and call the
131 callback with the fdatasync result code. 294 callback with the fdatasync result code.
132 295
296 If this call isn't available because your OS lacks it or it couldn't
297 be detected, it will be emulated by calling "fsync" instead.
298
133 SUPPORT FUNCTIONS 299 SUPPORT FUNCTIONS
134 $fileno = IO::AIO::poll_fileno 300 $fileno = IO::AIO::poll_fileno
135 Return the *request result pipe filehandle*. This filehandle must be 301 Return the *request result pipe file descriptor*. This filehandle
136 polled for reading by some mechanism outside this module (e.g. Event 302 must be polled for reading by some mechanism outside this module
137 or select, see below). If the pipe becomes readable you have to call 303 (e.g. Event or select, see below or the SYNOPSIS). If the pipe
138 "poll_cb" to check the results. 304 becomes readable you have to call "poll_cb" to check the results.
139 305
140 See "poll_cb" for an example. 306 See "poll_cb" for an example.
141 307
142 IO::AIO::poll_cb 308 IO::AIO::poll_cb
143 Process all outstanding events on the result pipe. You have to call 309 Process all outstanding events on the result pipe. You have to call
144 this regularly. Returns the number of events processed. Returns 310 this regularly. Returns the number of events processed. Returns
145 immediately when no events are outstanding. 311 immediately when no events are outstanding.
146 312
147 You can use Event to multiplex, e.g.: 313 Example: Install an Event watcher that automatically calls
314 IO::AIO::poll_cb with high priority:
148 315
149 Event->io (fd => IO::AIO::poll_fileno, 316 Event->io (fd => IO::AIO::poll_fileno,
150 poll => 'r', async => 1, 317 poll => 'r', async => 1,
151 cb => \&IO::AIO::poll_cb); 318 cb => \&IO::AIO::poll_cb);
152 319
153 IO::AIO::poll_wait 320 IO::AIO::poll_wait
154 Wait till the result filehandle becomes ready for reading (simply 321 Wait till the result filehandle becomes ready for reading (simply
155 does a select on the filehandle. This is useful if you want to 322 does a "select" on the filehandle. This is useful if you want to
156 synchronously wait for some requests to finish). 323 synchronously wait for some requests to finish).
157 324
158 See "nreqs" for an example. 325 See "nreqs" for an example.
159 326
160 IO::AIO::nreqs 327 IO::AIO::nreqs
161 Returns the number of requests currently outstanding. 328 Returns the number of requests currently outstanding (i.e. for which
329 their callback has not been invoked yet).
162 330
163 Example: wait till there are no outstanding requests anymore: 331 Example: wait till there are no outstanding requests anymore:
164 332
165 IO::AIO::poll_wait, IO::AIO::poll_cb 333 IO::AIO::poll_wait, IO::AIO::poll_cb
166 while IO::AIO::nreqs; 334 while IO::AIO::nreqs;
167 335
336 IO::AIO::flush
337 Wait till all outstanding AIO requests have been handled.
338
339 Strictly equivalent to:
340
341 IO::AIO::poll_wait, IO::AIO::poll_cb
342 while IO::AIO::nreqs;
343
344 IO::AIO::poll
345 Waits until some requests have been handled.
346
347 Strictly equivalent to:
348
349 IO::AIO::poll_wait, IO::AIO::poll_cb
350 if IO::AIO::nreqs;
351
168 IO::AIO::min_parallel $nthreads 352 IO::AIO::min_parallel $nthreads
169 Set the minimum number of AIO threads to $nthreads. The default is 353 Set the minimum number of AIO threads to $nthreads. The current
170 1, which means a single asynchronous operation can be done at one 354 default is 4, which means four asynchronous operations can be done
171 time (the number of outstanding operations, however, is unlimited). 355 at one time (the number of outstanding operations, however, is
356 unlimited).
357
358 IO::AIO starts threads only on demand, when an AIO request is queued
359 and no free thread exists.
172 360
173 It is recommended to keep the number of threads low, as some Linux 361 It is recommended to keep the number of threads low, as some Linux
174 kernel versions will scale negatively with the number of threads 362 kernel versions will scale negatively with the number of threads
175 (higher parallelity => MUCH higher latency). With current Linux 2.6 363 (higher parallelity => MUCH higher latency). With current Linux 2.6
176 versions, 4-32 threads should be fine. 364 versions, 4-32 threads should be fine.
177 365
178 Under normal circumstances you don't need to call this function, as 366 Under most circumstances you don't need to call this function, as
179 this module automatically starts some threads (the exact number 367 the module selects a default that is suitable for low to moderate
180 might change, and is currently 4). 368 load.
181 369
182 IO::AIO::max_parallel $nthreads 370 IO::AIO::max_parallel $nthreads
183 Sets the maximum number of AIO threads to $nthreads. If more than 371 Sets the maximum number of AIO threads to $nthreads. If more than
184 the specified number of threads are currently running, kill them. 372 the specified number of threads are currently running, this function
185 This function blocks until the limit is reached. 373 kills them. This function blocks until the limit is reached.
374
375 While $nthreads are zero, aio requests get queued but not executed
376 until the number of threads has been increased again.
186 377
187 This module automatically runs "max_parallel 0" at program end, to 378 This module automatically runs "max_parallel 0" at program end, to
188 ensure that all threads are killed and that there are no outstanding 379 ensure that all threads are killed and that there are no outstanding
189 requests. 380 requests.
190 381
… …
194 Sets the maximum number of outstanding requests to $nreqs. If you 385 Sets the maximum number of outstanding requests to $nreqs. If you
195 try to queue up more than this number of requests, the caller will 386 try to queue up more than this number of requests, the caller will
196 block until some requests have been handled. 387 block until some requests have been handled.
197 388
198 The default is very large, so normally there is no practical limit. 389 The default is very large, so normally there is no practical limit.
199 If you queue up many requests in a loop it it often improves speed 390 If you queue up many requests in a loop it often improves speed if
200 if you set this to a relatively low number, such as 100. 391 you set this to a relatively low number, such as 100.
201 392
202 Under normal circumstances you don't need to call this function. 393 Under normal circumstances you don't need to call this function.
394
395 FORK BEHAVIOUR
396 Before the fork, IO::AIO enters a quiescent state where no requests can
397 be added in other threads and no results will be processed. After the
398 fork the parent simply leaves the quiescent state and continues
399 request/result processing, while the child clears the request/result
400 queue (so the requests started before the fork will only be handled in
401 the parent). Threats will be started on demand until the limit ste in
402 the parent process has been reached again.
203 403
204SEE ALSO 404SEE ALSO
205 Coro, Linux::AIO. 405 Coro, Linux::AIO.
206 406
207AUTHOR 407AUTHOR

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