ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/IO-AIO/README
(Generate patch)

Comparing IO-AIO/README (file contents):
Revision 1.4 by root, Sun Jul 10 21:04:46 2005 UTC vs.
Revision 1.12 by root, Tue Aug 23 00:05:00 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.
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.
41 79
42 aio_open $pathname, $flags, $mode, $callback 80 aio_open $pathname, $flags, $mode, $callback
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]) {
… …
62 105
63 aio_close $fh, $callback 106 aio_close $fh, $callback
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.
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.
69 115
70 aio_read $fh,$offset,$length, $data,$dataoffset,$callback 116 aio_read $fh,$offset,$length, $data,$dataoffset,$callback
71 aio_write $fh,$offset,$length, $data,$dataoffset,$callback 117 aio_write $fh,$offset,$length, $data,$dataoffset,$callback
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
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
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.
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.
99 171
100 aio_stat $fh_or_path, $callback 172 aio_stat $fh_or_path, $callback
101 aio_lstat $fh, $callback 173 aio_lstat $fh, $callback
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
… …
120 192
121 aio_unlink $pathname, $callback 193 aio_unlink $pathname, $callback
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
198 Asynchronously rmdir (delete) a directory and call the callback with
199 the result code.
200
125 aio_fsync $fh, $callback 201 aio_fsync $fh, $callback
126 Asynchronously call fsync on the given filehandle and call the 202 Asynchronously call fsync on the given filehandle and call the
127 callback with the fsync result code. 203 callback with the fsync result code.
128 204
129 aio_fdatasync $fh, $callback 205 aio_fdatasync $fh, $callback
130 Asynchronously call fdatasync on the given filehandle and call the 206 Asynchronously call fdatasync on the given filehandle and call the
131 callback with the fdatasync result code. 207 callback with the fdatasync result code.
132 208
209 If this call isn't available because your OS lacks it or it couldn't
210 be detected, it will be emulated by calling "fsync" instead.
211
133 SUPPORT FUNCTIONS 212 SUPPORT FUNCTIONS
134 $fileno = IO::AIO::poll_fileno 213 $fileno = IO::AIO::poll_fileno
135 Return the *request result pipe filehandle*. This filehandle must be 214 Return the *request result pipe file descriptor*. This filehandle
136 polled for reading by some mechanism outside this module (e.g. Event 215 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 216 (e.g. Event or select, see below or the SYNOPSIS). If the pipe
138 "poll_cb" to check the results. 217 becomes readable you have to call "poll_cb" to check the results.
139 218
140 See "poll_cb" for an example. 219 See "poll_cb" for an example.
141 220
142 IO::AIO::poll_cb 221 IO::AIO::poll_cb
143 Process all outstanding events on the result pipe. You have to call 222 Process all outstanding events on the result pipe. You have to call
144 this regularly. Returns the number of events processed. Returns 223 this regularly. Returns the number of events processed. Returns
145 immediately when no events are outstanding. 224 immediately when no events are outstanding.
146 225
147 You can use Event to multiplex, e.g.: 226 Example: Install an Event watcher that automatically calls
227 IO::AIO::poll_cb with high priority:
148 228
149 Event->io (fd => IO::AIO::poll_fileno, 229 Event->io (fd => IO::AIO::poll_fileno,
150 poll => 'r', async => 1, 230 poll => 'r', async => 1,
151 cb => \&IO::AIO::poll_cb); 231 cb => \&IO::AIO::poll_cb);
152 232
153 IO::AIO::poll_wait 233 IO::AIO::poll_wait
154 Wait till the result filehandle becomes ready for reading (simply 234 Wait till the result filehandle becomes ready for reading (simply
155 does a select on the filehandle. This is useful if you want to 235 does a "select" on the filehandle. This is useful if you want to
156 synchronously wait for some requests to finish). 236 synchronously wait for some requests to finish).
157 237
158 See "nreqs" for an example. 238 See "nreqs" for an example.
159 239
160 IO::AIO::nreqs 240 IO::AIO::nreqs
161 Returns the number of requests currently outstanding. 241 Returns the number of requests currently outstanding (i.e. for which
242 their callback has not been invoked yet).
162 243
163 Example: wait till there are no outstanding requests anymore: 244 Example: wait till there are no outstanding requests anymore:
164 245
165 IO::AIO::poll_wait, IO::AIO::poll_cb 246 IO::AIO::poll_wait, IO::AIO::poll_cb
166 while IO::AIO::nreqs; 247 while IO::AIO::nreqs;
167 248
249 IO::AIO::flush
250 Wait till all outstanding AIO requests have been handled.
251
252 Strictly equivalent to:
253
254 IO::AIO::poll_wait, IO::AIO::poll_cb
255 while IO::AIO::nreqs;
256
257 IO::AIO::poll
258 Waits until some requests have been handled.
259
260 Strictly equivalent to:
261
262 IO::AIO::poll_wait, IO::AIO::poll_cb
263 if IO::AIO::nreqs;
264
168 IO::AIO::min_parallel $nthreads 265 IO::AIO::min_parallel $nthreads
169 Set the minimum number of AIO threads to $nthreads. The default is 266 Set the minimum number of AIO threads to $nthreads. The current
170 1, which means a single asynchronous operation can be done at one 267 default is 4, which means four asynchronous operations can be done
171 time (the number of outstanding operations, however, is unlimited). 268 at one time (the number of outstanding operations, however, is
269 unlimited).
270
271 IO::AIO starts threads only on demand, when an AIO request is queued
272 and no free thread exists.
172 273
173 It is recommended to keep the number of threads low, as some Linux 274 It is recommended to keep the number of threads low, as some Linux
174 kernel versions will scale negatively with the number of threads 275 kernel versions will scale negatively with the number of threads
175 (higher parallelity => MUCH higher latency). With current Linux 2.6 276 (higher parallelity => MUCH higher latency). With current Linux 2.6
176 versions, 4-32 threads should be fine. 277 versions, 4-32 threads should be fine.
177 278
178 Under normal circumstances you don't need to call this function, as 279 Under most circumstances you don't need to call this function, as
179 this module automatically starts some threads (the exact number 280 the module selects a default that is suitable for low to moderate
180 might change, and is currently 4). 281 load.
181 282
182 IO::AIO::max_parallel $nthreads 283 IO::AIO::max_parallel $nthreads
183 Sets the maximum number of AIO threads to $nthreads. If more than 284 Sets the maximum number of AIO threads to $nthreads. If more than
184 the specified number of threads are currently running, kill them. 285 the specified number of threads are currently running, this function
185 This function blocks until the limit is reached. 286 kills them. This function blocks until the limit is reached.
287
288 While $nthreads are zero, aio requests get queued but not executed
289 until the number of threads has been increased again.
186 290
187 This module automatically runs "max_parallel 0" at program end, to 291 This module automatically runs "max_parallel 0" at program end, to
188 ensure that all threads are killed and that there are no outstanding 292 ensure that all threads are killed and that there are no outstanding
189 requests. 293 requests.
190 294
… …
194 Sets the maximum number of outstanding requests to $nreqs. If you 298 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 299 try to queue up more than this number of requests, the caller will
196 block until some requests have been handled. 300 block until some requests have been handled.
197 301
198 The default is very large, so normally there is no practical limit. 302 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 303 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. 304 you set this to a relatively low number, such as 100.
201 305
202 Under normal circumstances you don't need to call this function. 306 Under normal circumstances you don't need to call this function.
307
308 FORK BEHAVIOUR
309 Before the fork, IO::AIO enters a quiescent state where no requests can
310 be added in other threads and no results will be processed. After the
311 fork the parent simply leaves the quiescent state and continues
312 request/result processing, while the child clears the request/result
313 queue (so the requests started before the fork will only be handled in
314 the parent). Threats will be started on demand until the limit ste in
315 the parent process has been reached again.
203 316
204SEE ALSO 317SEE ALSO
205 Coro, Linux::AIO. 318 Coro, Linux::AIO.
206 319
207AUTHOR 320AUTHOR

Diff Legend

– Removed lines
+ Added lines
< Changed lines
> Changed lines