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Revision 1.13 by root, Tue Aug 30 15:45:10 2005 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 # Event
19 Event->io (fd => IO::AIO::poll_fileno,
20 poll => 'r',
21 cb => \&IO::AIO::poll_cb);
22
23 # Glib/Gtk2
24 add_watch Glib::IO IO::AIO::poll_fileno,
25 in => sub { IO::AIO::poll_cb; 1 };
26
27 # Tk
28 Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
29 readable => \&IO::AIO::poll_cb);
30
31 # Danga::Socket
32 Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
33 \&IO::AIO::poll_cb);
6 34
7DESCRIPTION 35DESCRIPTION
8 This module implements asynchronous I/O using whatever means your 36 This module implements asynchronous I/O using whatever means your
9 operating system supports. 37 operating system supports.
10 38
… …
17 currently, for example), and they would only support aio_read and 45 currently, for example), and they would only support aio_read and
18 aio_write, so the remaining functionality would have to be implemented 46 aio_write, so the remaining functionality would have to be implemented
19 using threads anyway. 47 using threads anyway.
20 48
21 Although the module will work with in the presence of other threads, it 49 Although the module will work with in the presence of other threads, it
22 is currently not reentrant, so use appropriate locking yourself. 50 is currently not reentrant, so use appropriate locking yourself, always
51 call "poll_cb" from within the same thread, or never call "poll_cb" (or
52 other "aio_" functions) recursively.
23 53
24FUNCTIONS 54FUNCTIONS
25 AIO FUNCTIONS 55 AIO FUNCTIONS
26 All the "aio_*" calls are more or less thin wrappers around the syscall 56 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 57 with the same name (sans "aio_"). The arguments are similar or
28 identical, and they all accept an additional $callback argument which 58 identical, and they all accept an additional (and optional) $callback
29 must be a code reference. This code reference will get called with the 59 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, 60 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 61 error, unlike perl, which usually delivers "false") as it's sole
32 syscall has been executed asynchronously. 62 argument when the given syscall has been executed asynchronously.
33 63
34 All functions that expect a filehandle will also accept a file 64 All functions expecting a filehandle keep a copy of the filehandle
35 descriptor. 65 internally until the request has finished.
36 66
37 The filenames you pass to these routines *must* be absolute. The reason 67 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 68 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 69 is being executed, the current working directory could have changed.
40 never change the current working directory. 70 Alternatively, you can make sure that you never change the current
71 working directory.
41 72
73 To encode pathnames to byte form, either make sure you either: a) always
74 pass in filenames you got from outside (command line, readdir etc.), b)
75 are ASCII or ISO 8859-1, c) use the Encode module and encode your
76 pathnames to the locale (or other) encoding in effect in the user
77 environment, d) use Glib::filename_from_unicode on unicode filenames or
78 e) use something else.
79
42 aio_open $pathname, $flags, $mode, $callback 80 aio_open $pathname, $flags, $mode, $callback->($fh)
43 Asynchronously open or create a file and call the callback with a 81 Asynchronously open or create a file and call the callback with a
44 newly created filehandle for the file. 82 newly created filehandle for the file.
45 83
46 The pathname passed to "aio_open" must be absolute. See API NOTES, 84 The pathname passed to "aio_open" must be absolute. See API NOTES,
47 above, for an explanation. 85 above, for an explanation.
48 86
49 The $mode argument is a bitmask. See the "Fcntl" module for a list. 87 The $flags argument is a bitmask. See the "Fcntl" module for a list.
50 They are the same as used in "sysopen". 88 They are the same as used by "sysopen".
89
90 Likewise, $mode specifies the mode of the newly created file, if it
91 didn't exist and "O_CREAT" has been given, just like perl's
92 "sysopen", except that it is mandatory (i.e. use 0 if you don't
93 create new files, and 0666 or 0777 if you do).
51 94
52 Example: 95 Example:
53 96
54 aio_open "/etc/passwd", O_RDONLY, 0, sub { 97 aio_open "/etc/passwd", O_RDONLY, 0, sub {
55 if ($_[0]) { 98 if ($_[0]) {
… …
58 } else { 101 } else {
59 die "open failed: $!\n"; 102 die "open failed: $!\n";
60 } 103 }
61 }; 104 };
62 105
63 aio_close $fh, $callback 106 aio_close $fh, $callback->($status)
64 Asynchronously close a file and call the callback with the result 107 Asynchronously close a file and call the callback with the result
65 code. *WARNING:* although accepted, you should not pass in a perl 108 code. *WARNING:* although accepted, you should not pass in a perl
66 filehandle here, as perl will likely close the file descriptor 109 filehandle here, as perl will likely close the file descriptor
67 itself when the filehandle is destroyed. Normally, you can safely 110 another time when the filehandle is destroyed. Normally, you can
68 call perls "close" or just let filehandles go out of scope. 111 safely call perls "close" or just let filehandles go out of scope.
69 112
113 This is supposed to be a bug in the API, so that might change. It's
114 therefore best to avoid this function.
115
70 aio_read $fh,$offset,$length, $data,$dataoffset,$callback 116 aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
71 aio_write $fh,$offset,$length, $data,$dataoffset,$callback 117 aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
72 Reads or writes "length" bytes from the specified "fh" and "offset" 118 Reads or writes "length" bytes from the specified "fh" and "offset"
73 into the scalar given by "data" and offset "dataoffset" and calls 119 into the scalar given by "data" and offset "dataoffset" and calls
74 the callback without the actual number of bytes read (or -1 on 120 the callback without the actual number of bytes read (or -1 on
75 error, just like the syscall). 121 error, just like the syscall).
76 122
123 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
125 necessary/optional hardware is installed).
126
77 Example: Read 15 bytes at offset 7 into scalar $buffer, strating at 127 Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
78 offset 0 within the scalar: 128 offset 0 within the scalar:
79 129
80 aio_read $fh, 7, 15, $buffer, 0, sub { 130 aio_read $fh, 7, 15, $buffer, 0, sub {
81 $_[0] >= 0 or die "read error: $!"; 131 $_[0] > 0 or die "read error: $!";
82 print "read <$buffer>\n"; 132 print "read $_[0] bytes: <$buffer>\n";
83 }; 133 };
84 134
135 aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
136 Tries to copy $length bytes from $in_fh to $out_fh. It starts
137 reading at byte offset $in_offset, and starts writing at the current
138 file offset of $out_fh. Because of that, it is not safe to issue
139 more than one "aio_sendfile" per $out_fh, as they will interfere
140 with each other.
141
142 This call tries to make use of a native "sendfile" syscall to
143 provide zero-copy operation. For this to work, $out_fh should refer
144 to a socket, and $in_fh should refer to mmap'able file.
145
146 If the native sendfile call fails or is not implemented, it will be
147 emulated, so you can call "aio_sendfile" on any type of filehandle
148 regardless of the limitations of the operating system.
149
150 Please note, however, that "aio_sendfile" can read more bytes from
151 $in_fh than are written, and there is no way to find out how many
152 bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
153 only provides the number of bytes written to $out_fh. Only if the
154 result value equals $length one can assume that $length bytes have
155 been read.
156
85 aio_readahead $fh,$offset,$length, $callback 157 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 158 "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 159 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 160 $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 161 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 162 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 163 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 164 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 165 read beyond the end of the file. The current file offset of the file
98 is left unchanged. 166 is left unchanged.
99 167
168 If that syscall doesn't exist (likely if your OS isn't Linux) it
169 will be emulated by simply reading the data, which would have a
170 similar effect.
171
100 aio_stat $fh_or_path, $callback 172 aio_stat $fh_or_path, $callback->($status)
101 aio_lstat $fh, $callback 173 aio_lstat $fh, $callback->($status)
102 Works like perl's "stat" or "lstat" in void context. The callback 174 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 175 will be called after the stat and the results will be available
104 using "stat _" or "-s _" etc... 176 using "stat _" or "-s _" etc...
105 177
106 The pathname passed to "aio_stat" must be absolute. See API NOTES, 178 The pathname passed to "aio_stat" must be absolute. See API NOTES,
… …
116 aio_stat "/etc/passwd", sub { 188 aio_stat "/etc/passwd", sub {
117 $_[0] and die "stat failed: $!"; 189 $_[0] and die "stat failed: $!";
118 print "size is ", -s _, "\n"; 190 print "size is ", -s _, "\n";
119 }; 191 };
120 192
121 aio_unlink $pathname, $callback 193 aio_unlink $pathname, $callback->($status)
122 Asynchronously unlink (delete) a file and call the callback with the 194 Asynchronously unlink (delete) a file and call the callback with the
123 result code. 195 result code.
124 196
197 aio_rmdir $pathname, $callback->($status)
198 Asynchronously rmdir (delete) a directory and call the callback with
199 the result code.
200
201 aio_readdir $pathname $callback->($entries)
202 Unlike the POSIX call of the same name, "aio_readdir" reads an
203 entire directory (i.e. opendir + readdir + closedir). The entries
204 will not be sorted, and will NOT include the "." and ".." entries.
205
206 The callback a single argument which is either "undef" or an
207 array-ref with the filenames.
208
209 aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
210 Scans a directory (similar to "aio_readdir") and tries to separate
211 the entries of directory $path into two sets of names, ones you can
212 recurse into (directories), and ones you cannot recurse into
213 (everything else).
214
215 "aio_scandir" is a composite request that consists of many
216 aio-primitives. $maxreq specifies the maximum number of outstanding
217 aio requests that this function generates. If it is "<= 0", then a
218 suitable default will be chosen (currently 8).
219
220 On error, the callback is called without arguments, otherwise it
221 receives two array-refs with path-relative entry names.
222
223 Example:
224
225 aio_scandir $dir, 0, sub {
226 my ($dirs, $nondirs) = @_;
227 print "real directories: @$dirs\n";
228 print "everything else: @$nondirs\n";
229 };
230
231 Implementation notes.
232
233 The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
234 can.
235
236 After reading the directory, the modification time, size etc. of the
237 directory before and after the readdir is checked, and if they
238 match, the link count will be used to decide how many entries are
239 directories (if >= 2). Otherwise, no knowledge of the number of
240 subdirectories will be assumed.
241
242 Then entires will be sorted into likely directories (everything
243 without a non-initial dot) and likely non-directories (everything
244 else). Then every entry + "/." will be "stat"'ed, likely directories
245 first. This is often faster because filesystems might detect the
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
249 seperately).
250
251 If the known number of directories has been reached, the rest of the
252 entries is assumed to be non-directories.
253
125 aio_fsync $fh, $callback 254 aio_fsync $fh, $callback->($status)
126 Asynchronously call fsync on the given filehandle and call the 255 Asynchronously call fsync on the given filehandle and call the
127 callback with the fsync result code. 256 callback with the fsync result code.
128 257
129 aio_fdatasync $fh, $callback 258 aio_fdatasync $fh, $callback->($status)
130 Asynchronously call fdatasync on the given filehandle and call the 259 Asynchronously call fdatasync on the given filehandle and call the
131 callback with the fdatasync result code. 260 callback with the fdatasync result code.
132 261
262 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.
264
133 SUPPORT FUNCTIONS 265 SUPPORT FUNCTIONS
134 $fileno = IO::AIO::poll_fileno 266 $fileno = IO::AIO::poll_fileno
135 Return the *request result pipe filehandle*. This filehandle must be 267 Return the *request result pipe file descriptor*. This filehandle
136 polled for reading by some mechanism outside this module (e.g. Event 268 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 269 (e.g. Event or select, see below or the SYNOPSIS). If the pipe
138 "poll_cb" to check the results. 270 becomes readable you have to call "poll_cb" to check the results.
139 271
140 See "poll_cb" for an example. 272 See "poll_cb" for an example.
141 273
142 IO::AIO::poll_cb 274 IO::AIO::poll_cb
143 Process all outstanding events on the result pipe. You have to call 275 Process all outstanding events on the result pipe. You have to call
144 this regularly. Returns the number of events processed. Returns 276 this regularly. Returns the number of events processed. Returns
145 immediately when no events are outstanding. 277 immediately when no events are outstanding.
146 278
147 You can use Event to multiplex, e.g.: 279 Example: Install an Event watcher that automatically calls
280 IO::AIO::poll_cb with high priority:
148 281
149 Event->io (fd => IO::AIO::poll_fileno, 282 Event->io (fd => IO::AIO::poll_fileno,
150 poll => 'r', async => 1, 283 poll => 'r', async => 1,
151 cb => \&IO::AIO::poll_cb); 284 cb => \&IO::AIO::poll_cb);
152 285
153 IO::AIO::poll_wait 286 IO::AIO::poll_wait
154 Wait till the result filehandle becomes ready for reading (simply 287 Wait till the result filehandle becomes ready for reading (simply
155 does a select on the filehandle. This is useful if you want to 288 does a "select" on the filehandle. This is useful if you want to
156 synchronously wait for some requests to finish). 289 synchronously wait for some requests to finish).
157 290
158 See "nreqs" for an example. 291 See "nreqs" for an example.
159 292
160 IO::AIO::nreqs 293 IO::AIO::nreqs
161 Returns the number of requests currently outstanding. 294 Returns the number of requests currently outstanding (i.e. for which
295 their callback has not been invoked yet).
162 296
163 Example: wait till there are no outstanding requests anymore: 297 Example: wait till there are no outstanding requests anymore:
164 298
165 IO::AIO::poll_wait, IO::AIO::poll_cb 299 IO::AIO::poll_wait, IO::AIO::poll_cb
166 while IO::AIO::nreqs; 300 while IO::AIO::nreqs;
167 301
302 IO::AIO::flush
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
168 IO::AIO::min_parallel $nthreads 318 IO::AIO::min_parallel $nthreads
169 Set the minimum number of AIO threads to $nthreads. The default is 319 Set the minimum number of AIO threads to $nthreads. The current
170 1, which means a single asynchronous operation can be done at one 320 default is 4, which means four asynchronous operations can be done
171 time (the number of outstanding operations, however, is unlimited). 321 at one time (the number of outstanding operations, however, is
322 unlimited).
323
324 IO::AIO starts threads only on demand, when an AIO request is queued
325 and no free thread exists.
172 326
173 It is recommended to keep the number of threads low, as some Linux 327 It is recommended to keep the number of threads low, as some Linux
174 kernel versions will scale negatively with the number of threads 328 kernel versions will scale negatively with the number of threads
175 (higher parallelity => MUCH higher latency). With current Linux 2.6 329 (higher parallelity => MUCH higher latency). With current Linux 2.6
176 versions, 4-32 threads should be fine. 330 versions, 4-32 threads should be fine.
177 331
178 Under normal circumstances you don't need to call this function, as 332 Under most circumstances you don't need to call this function, as
179 this module automatically starts some threads (the exact number 333 the module selects a default that is suitable for low to moderate
180 might change, and is currently 4). 334 load.
181 335
182 IO::AIO::max_parallel $nthreads 336 IO::AIO::max_parallel $nthreads
183 Sets the maximum number of AIO threads to $nthreads. If more than 337 Sets the maximum number of AIO threads to $nthreads. If more than
184 the specified number of threads are currently running, kill them. 338 the specified number of threads are currently running, this function
185 This function blocks until the limit is reached. 339 kills them. This function blocks until the limit is reached.
340
341 While $nthreads are zero, aio requests get queued but not executed
342 until the number of threads has been increased again.
186 343
187 This module automatically runs "max_parallel 0" at program end, to 344 This module automatically runs "max_parallel 0" at program end, to
188 ensure that all threads are killed and that there are no outstanding 345 ensure that all threads are killed and that there are no outstanding
189 requests. 346 requests.
190 347
… …
194 Sets the maximum number of outstanding requests to $nreqs. If you 351 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 352 try to queue up more than this number of requests, the caller will
196 block until some requests have been handled. 353 block until some requests have been handled.
197 354
198 The default is very large, so normally there is no practical limit. 355 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 356 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. 357 you set this to a relatively low number, such as 100.
201 358
202 Under normal circumstances you don't need to call this function. 359 Under normal circumstances you don't need to call this function.
360
361 FORK BEHAVIOUR
362 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
364 fork the parent simply leaves the quiescent state and continues
365 request/result processing, while the child clears the request/result
366 queue (so the requests started before the fork will only be handled in
367 the parent). Threats will be started on demand until the limit ste in
368 the parent process has been reached again.
203 369
204SEE ALSO 370SEE ALSO
205 Coro, Linux::AIO. 371 Coro, Linux::AIO.
206 372
207AUTHOR 373AUTHOR

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