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Revision 1.8 by root, Sun Jul 31 17:24:05 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
24 API NOTES 54FUNCTIONS
55 AIO FUNCTIONS
25 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
26 with the same name (sans "aio_"). The arguments are similar or 57 with the same name (sans "aio_"). The arguments are similar or
27 identical, and they all accept an additional $callback argument which 58 identical, and they all accept an additional (and optional) $callback
28 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
29 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
30 which usually delivers "false") as it's sole argument when the given 61 error, unlike perl, which usually delivers "false") as it's sole
31 syscall has been executed asynchronously. 62 argument when the given syscall has been executed asynchronously.
32 63
33 All functions that expect a filehandle will also accept a file 64 All functions expecting a filehandle keep a copy of the filehandle
34 descriptor. 65 internally until the request has finished.
35 66
36 The filenames you pass to these routines *must* be absolute. The reason 67 The filenames you pass to these routines *must* be absolute. The reason
37 is that at the time the request is being executed, the current working 68 for this is that at the time the request is being executed, the current
38 directory could have changed. Alternatively, you can make sure that you 69 working directory could have changed. Alternatively, you can make sure
39 never change the current working directory. 70 that you never change the current working directory.
40
41 IO::AIO::min_parallel $nthreads
42 Set the minimum number of AIO threads to $nthreads. The default is
43 1, which means a single asynchronous operation can be done at one
44 time (the number of outstanding operations, however, is unlimited).
45
46 It is recommended to keep the number of threads low, as some Linux
47 kernel versions will scale negatively with the number of threads
48 (higher parallelity => MUCH higher latency). With current Linux 2.6
49 versions, 4-32 threads should be fine.
50
51 Under normal circumstances you don't need to call this function, as
52 this module automatically starts some threads (the exact number
53 might change, and is currently 4).
54
55 IO::AIO::max_parallel $nthreads
56 Sets the maximum number of AIO threads to $nthreads. If more than
57 the specified number of threads are currently running, kill them.
58 This function blocks until the limit is reached.
59
60 This module automatically runs "max_parallel 0" at program end, to
61 ensure that all threads are killed and that there are no outstanding
62 requests.
63
64 Under normal circumstances you don't need to call this function.
65
66 $oldnreqs = IO::AIO::max_outstanding $nreqs
67 Sets the maximum number of outstanding requests to $nreqs. If you
68 try to queue up more than this number of requests, the caller will
69 block until some requests have been handled.
70
71 The default is very large, so normally there is no practical limit.
72 If you queue up many requests in a loop it it often improves speed
73 if you set this to a relatively low number, such as 100.
74
75 Under normal circumstances you don't need to call this function.
76
77 $fileno = IO::AIO::poll_fileno
78 Return the *request result pipe filehandle*. This filehandle must be
79 polled for reading by some mechanism outside this module (e.g. Event
80 or select, see below). If the pipe becomes readable you have to call
81 "poll_cb" to check the results.
82
83 See "poll_cb" for an example.
84
85 IO::AIO::poll_cb
86 Process all outstanding events on the result pipe. You have to call
87 this regularly. Returns the number of events processed. Returns
88 immediately when no events are outstanding.
89
90 You can use Event to multiplex, e.g.:
91
92 Event->io (fd => IO::AIO::poll_fileno,
93 poll => 'r', async => 1,
94 cb => \&IO::AIO::poll_cb);
95
96 IO::AIO::poll_wait
97 Wait till the result filehandle becomes ready for reading (simply
98 does a select on the filehandle. This is useful if you want to
99 synchronously wait for some requests to finish).
100
101 See "nreqs" for an example.
102
103 IO::AIO::nreqs
104 Returns the number of requests currently outstanding.
105
106 Example: wait till there are no outstanding requests anymore:
107
108 IO::AIO::poll_wait, IO::AIO::poll_cb
109 while IO::AIO::nreqs;
110 71
111 aio_open $pathname, $flags, $mode, $callback 72 aio_open $pathname, $flags, $mode, $callback
112 Asynchronously open or create a file and call the callback with a 73 Asynchronously open or create a file and call the callback with a
113 newly created filehandle for the file. 74 newly created filehandle for the file.
114 75
115 The pathname passed to "aio_open" must be absolute. See API NOTES, 76 The pathname passed to "aio_open" must be absolute. See API NOTES,
116 above, for an explanation. 77 above, for an explanation.
117 78
118 The $mode argument is a bitmask. See the "Fcntl" module for a list. 79 The $flags argument is a bitmask. See the "Fcntl" module for a list.
119 They are the same as used in "sysopen". 80 They are the same as used by "sysopen".
81
82 Likewise, $mode specifies the mode of the newly created file, if it
83 didn't exist and "O_CREAT" has been given, just like perl's
84 "sysopen", except that it is mandatory (i.e. use 0 if you don't
85 create new files, and 0666 or 0777 if you do).
120 86
121 Example: 87 Example:
122 88
123 aio_open "/etc/passwd", O_RDONLY, 0, sub { 89 aio_open "/etc/passwd", O_RDONLY, 0, sub {
124 if ($_[0]) { 90 if ($_[0]) {
… …
131 97
132 aio_close $fh, $callback 98 aio_close $fh, $callback
133 Asynchronously close a file and call the callback with the result 99 Asynchronously close a file and call the callback with the result
134 code. *WARNING:* although accepted, you should not pass in a perl 100 code. *WARNING:* although accepted, you should not pass in a perl
135 filehandle here, as perl will likely close the file descriptor 101 filehandle here, as perl will likely close the file descriptor
136 itself when the filehandle is destroyed. Normally, you can safely 102 another time when the filehandle is destroyed. Normally, you can
137 call perls "close" or just let filehandles go out of scope. 103 safely call perls "close" or just let filehandles go out of scope.
104
105 This is supposed to be a bug in the API, so that might change. It's
106 therefore best to avoid this function.
138 107
139 aio_read $fh,$offset,$length, $data,$dataoffset,$callback 108 aio_read $fh,$offset,$length, $data,$dataoffset,$callback
140 aio_write $fh,$offset,$length, $data,$dataoffset,$callback 109 aio_write $fh,$offset,$length, $data,$dataoffset,$callback
141 Reads or writes "length" bytes from the specified "fh" and "offset" 110 Reads or writes "length" bytes from the specified "fh" and "offset"
142 into the scalar given by "data" and offset "dataoffset" and calls 111 into the scalar given by "data" and offset "dataoffset" and calls
143 the callback without the actual number of bytes read (or -1 on 112 the callback without the actual number of bytes read (or -1 on
144 error, just like the syscall). 113 error, just like the syscall).
145 114
146 Example: Read 15 bytes at offset 7 into scalar $buffer, strating at 115 Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
147 offset 0 within the scalar: 116 offset 0 within the scalar:
148 117
149 aio_read $fh, 7, 15, $buffer, 0, sub { 118 aio_read $fh, 7, 15, $buffer, 0, sub {
150 $_[0] >= 0 or die "read error: $!"; 119 $_[0] > 0 or die "read error: $!";
151 print "read <$buffer>\n"; 120 print "read $_[0] bytes: <$buffer>\n";
152 }; 121 };
153 122
154 aio_readahead $fh,$offset,$length, $callback 123 aio_readahead $fh,$offset,$length, $callback
155 Asynchronously reads the specified byte range into the page cache, 124 Asynchronously reads the specified byte range into the page cache,
156 using the "readahead" syscall. If that syscall doesn't exist the 125 using the "readahead" syscall. If that syscall doesn't exist (likely
157 status will be -1 and $! is set to ENOSYS. 126 if your OS isn't Linux) the status will be -1 and $! is set to
127 "ENOSYS".
158 128
159 readahead() populates the page cache with data from a file so that 129 "aio_readahead" populates the page cache with data from a file so
160 subsequent reads from that file will not block on disk I/O. The 130 that subsequent reads from that file will not block on disk I/O. The
161 $offset argument specifies the starting point from which data is to 131 $offset argument specifies the starting point from which data is to
162 be read and $length specifies the number of bytes to be read. I/O is 132 be read and $length specifies the number of bytes to be read. I/O is
163 performed in whole pages, so that offset is effectively rounded down 133 performed in whole pages, so that offset is effectively rounded down
164 to a page boundary and bytes are read up to the next page boundary 134 to a page boundary and bytes are read up to the next page boundary
165 greater than or equal to (off-set+length). aio_readahead() does not 135 greater than or equal to (off-set+length). "aio_readahead" does not
166 read beyond the end of the file. The current file offset of the file 136 read beyond the end of the file. The current file offset of the file
167 is left unchanged. 137 is left unchanged.
168 138
169 aio_stat $fh_or_path, $callback 139 aio_stat $fh_or_path, $callback
170 aio_lstat $fh, $callback 140 aio_lstat $fh, $callback
… …
195 Asynchronously call fsync on the given filehandle and call the 165 Asynchronously call fsync on the given filehandle and call the
196 callback with the fsync result code. 166 callback with the fsync result code.
197 167
198 aio_fdatasync $fh, $callback 168 aio_fdatasync $fh, $callback
199 Asynchronously call fdatasync on the given filehandle and call the 169 Asynchronously call fdatasync on the given filehandle and call the
200 callback with the fdatasync result code. 170 callback with the fdatasync result code. Might set $! to "ENOSYS" if
171 "fdatasync" is not available.
201 172
202BUGS 173 SUPPORT FUNCTIONS
203 - could be optimized to use more semaphores instead of filehandles. 174 $fileno = IO::AIO::poll_fileno
175 Return the *request result pipe file descriptor*. This filehandle
176 must be polled for reading by some mechanism outside this module
177 (e.g. Event or select, see below or the SYNOPSIS). If the pipe
178 becomes readable you have to call "poll_cb" to check the results.
179
180 See "poll_cb" for an example.
181
182 IO::AIO::poll_cb
183 Process all outstanding events on the result pipe. You have to call
184 this regularly. Returns the number of events processed. Returns
185 immediately when no events are outstanding.
186
187 Example: Install an Event watcher that automatically calls
188 IO::AIO::poll_cb with high priority:
189
190 Event->io (fd => IO::AIO::poll_fileno,
191 poll => 'r', async => 1,
192 cb => \&IO::AIO::poll_cb);
193
194 IO::AIO::poll_wait
195 Wait till the result filehandle becomes ready for reading (simply
196 does a "select" on the filehandle. This is useful if you want to
197 synchronously wait for some requests to finish).
198
199 See "nreqs" for an example.
200
201 IO::AIO::nreqs
202 Returns the number of requests currently outstanding (i.e. for which
203 their callback has not been invoked yet).
204
205 Example: wait till there are no outstanding requests anymore:
206
207 IO::AIO::poll_wait, IO::AIO::poll_cb
208 while IO::AIO::nreqs;
209
210 IO::AIO::flush
211 Wait till all outstanding AIO requests have been handled.
212
213 Strictly equivalent to:
214
215 IO::AIO::poll_wait, IO::AIO::poll_cb
216 while IO::AIO::nreqs;
217
218 IO::AIO::poll
219 Waits until some requests have been handled.
220
221 Strictly equivalent to:
222
223 IO::AIO::poll_wait, IO::AIO::poll_cb
224 if IO::AIO::nreqs;
225
226 IO::AIO::min_parallel $nthreads
227 Set the minimum number of AIO threads to $nthreads. The default is
228 1, which means a single asynchronous operation can be done at one
229 time (the number of outstanding operations, however, is unlimited).
230
231 It is recommended to keep the number of threads low, as some Linux
232 kernel versions will scale negatively with the number of threads
233 (higher parallelity => MUCH higher latency). With current Linux 2.6
234 versions, 4-32 threads should be fine.
235
236 Under normal circumstances you don't need to call this function, as
237 this module automatically starts some threads (the exact number
238 might change, and is currently 4).
239
240 IO::AIO::max_parallel $nthreads
241 Sets the maximum number of AIO threads to $nthreads. If more than
242 the specified number of threads are currently running, kill them.
243 This function blocks until the limit is reached.
244
245 This module automatically runs "max_parallel 0" at program end, to
246 ensure that all threads are killed and that there are no outstanding
247 requests.
248
249 Under normal circumstances you don't need to call this function.
250
251 $oldnreqs = IO::AIO::max_outstanding $nreqs
252 Sets the maximum number of outstanding requests to $nreqs. If you
253 try to queue up more than this number of requests, the caller will
254 block until some requests have been handled.
255
256 The default is very large, so normally there is no practical limit.
257 If you queue up many requests in a loop it it often improves speed
258 if you set this to a relatively low number, such as 100.
259
260 Under normal circumstances you don't need to call this function.
204 261
205SEE ALSO 262SEE ALSO
206 Coro, Linux::AIO. 263 Coro, Linux::AIO.
207 264
208AUTHOR 265AUTHOR

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