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Revision 1.10 by root, Wed Aug 17 05:26:20 2005 UTC

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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 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);
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. Currently, it falls back to Linux::AIO if 37 operating system supports.
10 that module is available, or uses pthreads to emulato aio functionality.
11 38
12 Currently, in this module a number of threads are started that execute 39 Currently, a number of threads are started that execute your read/writes
13 your read/writes and signal their completion. You don't need thread 40 and signal their completion. You don't need thread support in your libc
14 support in your libc or perl, and the threads created by this module 41 or perl, and the threads created by this module will not be visible to
15 will not be visible to the pthreads library. 42 the pthreads library. In the future, this module might make use of the
43 native aio functions available on many operating systems. However, they
44 are often not well-supported (Linux doesn't allow them on normal files
45 currently, for example), and they would only support aio_read and
46 aio_write, so the remaining functionality would have to be implemented
47 using threads anyway.
16 48
17 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
18 is 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.
19 53
20 API NOTES 54FUNCTIONS
55 AIO FUNCTIONS
21 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
22 with the same name (sans "aio_"). The arguments are similar or 57 with the same name (sans "aio_"). The arguments are similar or
23 identical, and they all accept an additional $callback argument which 58 identical, and they all accept an additional (and optional) $callback
24 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
25 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
26 which usually delivers "false") as it's sole argument when the given 61 error, unlike perl, which usually delivers "false") as it's sole
27 syscall has been executed asynchronously. 62 argument when the given syscall has been executed asynchronously.
28 63
29 All functions that expect a filehandle will also accept a file 64 All functions expecting a filehandle keep a copy of the filehandle
30 descriptor. 65 internally until the request has finished.
31 66
32 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
33 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
34 directory could have changed. Alternatively, you can make sure that you 69 is being executed, the current working directory could have changed.
35 never change the current working directory. 70 Alternatively, you can make sure that you never change the current
71 working directory.
36 72
37 IO::AIO::min_parallel $nthreads 73 To encode pathnames to byte form, either make sure you either: a) always
38 Set the minimum number of AIO threads to $nthreads. The default is 74 pass in filenames you got from outside (command line, readdir etc.), b)
39 1, which means a single asynchronous operation can be done at one 75 are ASCII or ISO 8859-1, c) use the Encode module and encode your
40 time (the number of outstanding operations, however, is unlimited). 76 pathnames to the locale (or other) encoding in effect in the user
41 77 environment, d) use Glib::filename_from_unicode on unicode filenames or
42 It is recommended to keep the number of threads low, as some linux 78 e) use something else.
43 kernel versions will scale negatively with the number of threads
44 (higher parallelity => MUCH higher latency).
45
46 Under normal circumstances you don't need to call this function, as
47 this module automatically starts a single async thread.
48
49 IO::AIO::max_parallel $nthreads
50 Sets the maximum number of AIO threads to $nthreads. If more than
51 the specified number of threads are currently running, kill them.
52 This function blocks until the limit is reached.
53
54 This module automatically runs "max_parallel 0" at program end, to
55 ensure that all threads are killed and that there are no outstanding
56 requests.
57
58 Under normal circumstances you don't need to call this function.
59
60 $fileno = IO::AIO::poll_fileno
61 Return the *request result pipe filehandle*. This filehandle must be
62 polled for reading by some mechanism outside this module (e.g. Event
63 or select, see below). If the pipe becomes readable you have to call
64 "poll_cb" to check the results.
65
66 See "poll_cb" for an example.
67
68 IO::AIO::poll_cb
69 Process all outstanding events on the result pipe. You have to call
70 this regularly. Returns the number of events processed. Returns
71 immediately when no events are outstanding.
72
73 You can use Event to multiplex, e.g.:
74
75 Event->io (fd => IO::AIO::poll_fileno,
76 poll => 'r', async => 1,
77 cb => \&IO::AIO::poll_cb);
78
79 IO::AIO::poll_wait
80 Wait till the result filehandle becomes ready for reading (simply
81 does a select on the filehandle. This is useful if you want to
82 synchronously wait for some requests to finish).
83
84 See "nreqs" for an example.
85
86 IO::AIO::nreqs
87 Returns the number of requests currently outstanding.
88
89 Example: wait till there are no outstanding requests anymore:
90
91 IO::AIO::poll_wait, IO::AIO::poll_cb
92 while IO::AIO::nreqs;
93 79
94 aio_open $pathname, $flags, $mode, $callback 80 aio_open $pathname, $flags, $mode, $callback
95 Asynchronously open or create a file and call the callback with the 81 Asynchronously open or create a file and call the callback with a
96 filedescriptor (NOT a perl filehandle, sorry for that, but watch 82 newly created filehandle for the file.
97 out, this might change in the future).
98 83
84 The pathname passed to "aio_open" must be absolute. See API NOTES,
85 above, for an explanation.
86
99 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.
100 They are the same as used in "sysopen". 88 They are the same as used by "sysopen".
89
90 Likewise, $mode specifies the mode of the newly created file, if it
91 didn't exist and "O_CREAT" has been given, just like perl's
92 "sysopen", except that it is mandatory (i.e. use 0 if you don't
93 create new files, and 0666 or 0777 if you do).
101 94
102 Example: 95 Example:
103 96
104 aio_open "/etc/passwd", O_RDONLY, 0, sub { 97 aio_open "/etc/passwd", O_RDONLY, 0, sub {
105 if ($_[0] >= 0) { 98 if ($_[0]) {
106 open my $fh, "<&$_[0]"; # create a copy for perl
107 aio_close $_[0], sub { }; # close the aio handle
108 print "open successful, fh is $fh\n"; 99 print "open successful, fh is $_[0]\n";
109 ... 100 ...
110 } else { 101 } else {
111 die "open failed: $!\n"; 102 die "open failed: $!\n";
112 } 103 }
113 }; 104 };
114 105
115 aio_close $fh, $callback 106 aio_close $fh, $callback
116 Asynchronously close a file and call the callback with the result 107 Asynchronously close a file and call the callback with the result
117 code. 108 code. *WARNING:* although accepted, you should not pass in a perl
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
113 This is supposed to be a bug in the API, so that might change. It's
114 therefore best to avoid this function.
118 115
119 aio_read $fh,$offset,$length, $data,$dataoffset,$callback 116 aio_read $fh,$offset,$length, $data,$dataoffset,$callback
120 aio_write $fh,$offset,$length, $data,$dataoffset,$callback 117 aio_write $fh,$offset,$length, $data,$dataoffset,$callback
121 Reads or writes "length" bytes from the specified "fh" and "offset" 118 Reads or writes "length" bytes from the specified "fh" and "offset"
122 into the scalar given by "data" and offset "dataoffset" and calls 119 into the scalar given by "data" and offset "dataoffset" and calls
123 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
124 error, just like the syscall). 121 error, just like the syscall).
125 122
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
126 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
127 offset 0 within the scalar: 128 offset 0 within the scalar:
128 129
129 aio_read $fh, 7, 15, $buffer, 0, sub { 130 aio_read $fh, 7, 15, $buffer, 0, sub {
130 $_[0] >= 0 or die "read error: $!"; 131 $_[0] > 0 or die "read error: $!";
131 print "read <$buffer>\n"; 132 print "read $_[0] bytes: <$buffer>\n";
132 }; 133 };
133 134
134 aio_readahead $fh,$offset,$length, $callback 135 aio_readahead $fh,$offset,$length, $callback
135 Asynchronously reads the specified byte range into the page cache,
136 using the "readahead" syscall.
137
138 readahead() populates the page cache with data from a file so that 136 "aio_readahead" populates the page cache with data from a file so
139 subsequent reads from that file will not block on disk I/O. The 137 that subsequent reads from that file will not block on disk I/O. The
140 $offset argument specifies the starting point from which data is to 138 $offset argument specifies the starting point from which data is to
141 be read and $length specifies the number of bytes to be read. I/O is 139 be read and $length specifies the number of bytes to be read. I/O is
142 performed in whole pages, so that offset is effectively rounded down 140 performed in whole pages, so that offset is effectively rounded down
143 to a page boundary and bytes are read up to the next page boundary 141 to a page boundary and bytes are read up to the next page boundary
144 greater than or equal to (off-set+length). aio_readahead() does not 142 greater than or equal to (off-set+length). "aio_readahead" does not
145 read beyond the end of the file. The current file offset of the file 143 read beyond the end of the file. The current file offset of the file
146 is left unchanged. 144 is left unchanged.
145
146 If that syscall doesn't exist (likely if your OS isn't Linux) it
147 will be emulated by simply reading the data, which would have a
148 similar effect.
147 149
148 aio_stat $fh_or_path, $callback 150 aio_stat $fh_or_path, $callback
149 aio_lstat $fh, $callback 151 aio_lstat $fh, $callback
150 Works like perl's "stat" or "lstat" in void context. The callback 152 Works like perl's "stat" or "lstat" in void context. The callback
151 will be called after the stat and the results will be available 153 will be called after the stat and the results will be available
… …
168 170
169 aio_unlink $pathname, $callback 171 aio_unlink $pathname, $callback
170 Asynchronously unlink (delete) a file and call the callback with the 172 Asynchronously unlink (delete) a file and call the callback with the
171 result code. 173 result code.
172 174
175 aio_rmdir $pathname, $callback
176 Asynchronously rmdir (delete) a directory and call the callback with
177 the result code.
178
173 aio_fsync $fh, $callback 179 aio_fsync $fh, $callback
174 Asynchronously call fsync on the given filehandle and call the 180 Asynchronously call fsync on the given filehandle and call the
175 callback with the fsync result code. 181 callback with the fsync result code.
176 182
177 aio_fdatasync $fh, $callback 183 aio_fdatasync $fh, $callback
178 Asynchronously call fdatasync on the given filehandle and call the 184 Asynchronously call fdatasync on the given filehandle and call the
179 callback with the fdatasync result code. 185 callback with the fdatasync result code.
180 186
181BUGS 187 If this call isn't available because your OS lacks it or it couldn't
182 This module has been extensively tested in a large and very busy 188 be detected, it will be emulated by calling "fsync" instead.
183 webserver for many years now.
184 189
185 - aio_open gives a fd, but all other functions expect a perl filehandle. 190 SUPPORT FUNCTIONS
191 $fileno = IO::AIO::poll_fileno
192 Return the *request result pipe file descriptor*. This filehandle
193 must be polled for reading by some mechanism outside this module
194 (e.g. Event or select, see below or the SYNOPSIS). If the pipe
195 becomes readable you have to call "poll_cb" to check the results.
196
197 See "poll_cb" for an example.
198
199 IO::AIO::poll_cb
200 Process all outstanding events on the result pipe. You have to call
201 this regularly. Returns the number of events processed. Returns
202 immediately when no events are outstanding.
203
204 Example: Install an Event watcher that automatically calls
205 IO::AIO::poll_cb with high priority:
206
207 Event->io (fd => IO::AIO::poll_fileno,
208 poll => 'r', async => 1,
209 cb => \&IO::AIO::poll_cb);
210
211 IO::AIO::poll_wait
212 Wait till the result filehandle becomes ready for reading (simply
213 does a "select" on the filehandle. This is useful if you want to
214 synchronously wait for some requests to finish).
215
216 See "nreqs" for an example.
217
218 IO::AIO::nreqs
219 Returns the number of requests currently outstanding (i.e. for which
220 their callback has not been invoked yet).
221
222 Example: wait till there are no outstanding requests anymore:
223
224 IO::AIO::poll_wait, IO::AIO::poll_cb
225 while IO::AIO::nreqs;
226
227 IO::AIO::flush
228 Wait till all outstanding AIO requests have been handled.
229
230 Strictly equivalent to:
231
232 IO::AIO::poll_wait, IO::AIO::poll_cb
233 while IO::AIO::nreqs;
234
235 IO::AIO::poll
236 Waits until some requests have been handled.
237
238 Strictly equivalent to:
239
240 IO::AIO::poll_wait, IO::AIO::poll_cb
241 if IO::AIO::nreqs;
242
243 IO::AIO::min_parallel $nthreads
244 Set the minimum number of AIO threads to $nthreads. The default is
245 1, which means a single asynchronous operation can be done at one
246 time (the number of outstanding operations, however, is unlimited).
247
248 It is recommended to keep the number of threads low, as some Linux
249 kernel versions will scale negatively with the number of threads
250 (higher parallelity => MUCH higher latency). With current Linux 2.6
251 versions, 4-32 threads should be fine.
252
253 Under normal circumstances you don't need to call this function, as
254 this module automatically starts some threads (the exact number
255 might change, and is currently 4).
256
257 IO::AIO::max_parallel $nthreads
258 Sets the maximum number of AIO threads to $nthreads. If more than
259 the specified number of threads are currently running, kill them.
260 This function blocks until the limit is reached.
261
262 This module automatically runs "max_parallel 0" at program end, to
263 ensure that all threads are killed and that there are no outstanding
264 requests.
265
266 Under normal circumstances you don't need to call this function.
267
268 $oldnreqs = IO::AIO::max_outstanding $nreqs
269 Sets the maximum number of outstanding requests to $nreqs. If you
270 try to queue up more than this number of requests, the caller will
271 block until some requests have been handled.
272
273 The default is very large, so normally there is no practical limit.
274 If you queue up many requests in a loop it it often improves speed
275 if you set this to a relatively low number, such as 100.
276
277 Under normal circumstances you don't need to call this function.
278
279 FORK BEHAVIOUR
280 Before the fork IO::AIO enters a quiescent state where no requests can
281 be added in other threads and no results will be processed. After the
282 fork the parent simply leaves the quiescent state and continues
283 request/result processing, while the child clears the request/result
284 queue and starts the same number of threads as were in use by the
285 parent.
186 286
187SEE ALSO 287SEE ALSO
188 Coro. 288 Coro, Linux::AIO.
189 289
190AUTHOR 290AUTHOR
191 Marc Lehmann <schmorp@schmorp.de> 291 Marc Lehmann <schmorp@schmorp.de>
192 http://home.schmorp.de/ 292 http://home.schmorp.de/
193 293

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