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

Comparing IO-AIO/README (file contents):
Revision 1.8 by root, Sun Jul 31 17:24:05 2005 UTC vs.
Revision 1.11 by root, Sat Aug 20 00:32:42 2005 UTC

… …
62 argument when the given syscall has been executed asynchronously. 62 argument when the given syscall has been executed asynchronously.
63 63
64 All functions expecting a filehandle keep a copy of the filehandle 64 All functions expecting a filehandle keep a copy of the filehandle
65 internally until the request has finished. 65 internally until the request has finished.
66 66
67 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
68 for this is that at the time the request is being executed, the current 68 in byte form. The reason for the former is that at the time the request
69 working directory could have changed. Alternatively, you can make sure 69 is being executed, the current working directory could have changed.
70 that you 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.
71 79
72 aio_open $pathname, $flags, $mode, $callback 80 aio_open $pathname, $flags, $mode, $callback
73 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
74 newly created filehandle for the file. 82 newly created filehandle for the file.
75 83
… …
110 Reads or writes "length" bytes from the specified "fh" and "offset" 118 Reads or writes "length" bytes from the specified "fh" and "offset"
111 into the scalar given by "data" and offset "dataoffset" and calls 119 into the scalar given by "data" and offset "dataoffset" and calls
112 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
113 error, just like the syscall). 121 error, just like the syscall).
114 122
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
115 Example: Read 15 bytes at offset 7 into scalar $buffer, starting at 127 Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
116 offset 0 within the scalar: 128 offset 0 within the scalar:
117 129
118 aio_read $fh, 7, 15, $buffer, 0, sub { 130 aio_read $fh, 7, 15, $buffer, 0, sub {
119 $_[0] > 0 or die "read error: $!"; 131 $_[0] > 0 or die "read error: $!";
120 print "read $_[0] bytes: <$buffer>\n"; 132 print "read $_[0] bytes: <$buffer>\n";
121 }; 133 };
122 134
123 aio_readahead $fh,$offset,$length, $callback 135 aio_readahead $fh,$offset,$length, $callback
124 Asynchronously reads the specified byte range into the page cache,
125 using the "readahead" syscall. If that syscall doesn't exist (likely
126 if your OS isn't Linux) the status will be -1 and $! is set to
127 "ENOSYS".
128
129 "aio_readahead" populates the page cache with data from a file so 136 "aio_readahead" populates the page cache with data from a file so
130 that 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
131 $offset argument specifies the starting point from which data is to 138 $offset argument specifies the starting point from which data is to
132 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
133 performed in whole pages, so that offset is effectively rounded down 140 performed in whole pages, so that offset is effectively rounded down
134 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
135 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
136 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
137 is left unchanged. 144 is left unchanged.
138 145
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.
149
139 aio_stat $fh_or_path, $callback 150 aio_stat $fh_or_path, $callback
140 aio_lstat $fh, $callback 151 aio_lstat $fh, $callback
141 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
142 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
143 using "stat _" or "-s _" etc... 154 using "stat _" or "-s _" etc...
… …
159 170
160 aio_unlink $pathname, $callback 171 aio_unlink $pathname, $callback
161 Asynchronously unlink (delete) a file and call the callback with the 172 Asynchronously unlink (delete) a file and call the callback with the
162 result code. 173 result code.
163 174
175 aio_rmdir $pathname, $callback
176 Asynchronously rmdir (delete) a directory and call the callback with
177 the result code.
178
164 aio_fsync $fh, $callback 179 aio_fsync $fh, $callback
165 Asynchronously call fsync on the given filehandle and call the 180 Asynchronously call fsync on the given filehandle and call the
166 callback with the fsync result code. 181 callback with the fsync result code.
167 182
168 aio_fdatasync $fh, $callback 183 aio_fdatasync $fh, $callback
169 Asynchronously call fdatasync on the given filehandle and call the 184 Asynchronously call fdatasync on the given filehandle and call the
170 callback with the fdatasync result code. Might set $! to "ENOSYS" if 185 callback with the fdatasync result code.
171 "fdatasync" is not available. 186
187 If this call isn't available because your OS lacks it or it couldn't
188 be detected, it will be emulated by calling "fsync" instead.
172 189
173 SUPPORT FUNCTIONS 190 SUPPORT FUNCTIONS
174 $fileno = IO::AIO::poll_fileno 191 $fileno = IO::AIO::poll_fileno
175 Return the *request result pipe file descriptor*. This filehandle 192 Return the *request result pipe file descriptor*. This filehandle
176 must be polled for reading by some mechanism outside this module 193 must be polled for reading by some mechanism outside this module
… …
222 239
223 IO::AIO::poll_wait, IO::AIO::poll_cb 240 IO::AIO::poll_wait, IO::AIO::poll_cb
224 if IO::AIO::nreqs; 241 if IO::AIO::nreqs;
225 242
226 IO::AIO::min_parallel $nthreads 243 IO::AIO::min_parallel $nthreads
227 Set the minimum number of AIO threads to $nthreads. The default is 244 Set the minimum number of AIO threads to $nthreads. The current
228 1, which means a single asynchronous operation can be done at one 245 default is 4, which means four asynchronous operations can be done
229 time (the number of outstanding operations, however, is unlimited). 246 at one time (the number of outstanding operations, however, is
247 unlimited).
248
249 IO::AIO starts threads only on demand, when an AIO request is queued
250 and no free thread exists.
230 251
231 It is recommended to keep the number of threads low, as some Linux 252 It is recommended to keep the number of threads low, as some Linux
232 kernel versions will scale negatively with the number of threads 253 kernel versions will scale negatively with the number of threads
233 (higher parallelity => MUCH higher latency). With current Linux 2.6 254 (higher parallelity => MUCH higher latency). With current Linux 2.6
234 versions, 4-32 threads should be fine. 255 versions, 4-32 threads should be fine.
235 256
236 Under normal circumstances you don't need to call this function, as 257 Under most circumstances you don't need to call this function, as
237 this module automatically starts some threads (the exact number 258 the module selects a default that is suitable for low to moderate
238 might change, and is currently 4). 259 load.
239 260
240 IO::AIO::max_parallel $nthreads 261 IO::AIO::max_parallel $nthreads
241 Sets the maximum number of AIO threads to $nthreads. If more than 262 Sets the maximum number of AIO threads to $nthreads. If more than
242 the specified number of threads are currently running, kill them. 263 the specified number of threads are currently running, this function
243 This function blocks until the limit is reached. 264 kills them. This function blocks until the limit is reached.
265
266 While $nthreads are zero, aio requests get queued but not executed
267 until the number of threads has been increased again.
244 268
245 This module automatically runs "max_parallel 0" at program end, to 269 This module automatically runs "max_parallel 0" at program end, to
246 ensure that all threads are killed and that there are no outstanding 270 ensure that all threads are killed and that there are no outstanding
247 requests. 271 requests.
248 272
… …
252 Sets the maximum number of outstanding requests to $nreqs. If you 276 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 277 try to queue up more than this number of requests, the caller will
254 block until some requests have been handled. 278 block until some requests have been handled.
255 279
256 The default is very large, so normally there is no practical limit. 280 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 281 If you queue up many requests in a loop it often improves speed if
258 if you set this to a relatively low number, such as 100. 282 you set this to a relatively low number, such as 100.
259 283
260 Under normal circumstances you don't need to call this function. 284 Under normal circumstances you don't need to call this function.
285
286 FORK BEHAVIOUR
287 Before the fork, IO::AIO enters a quiescent state where no requests can
288 be added in other threads and no results will be processed. After the
289 fork the parent simply leaves the quiescent state and continues
290 request/result processing, while the child clears the request/result
291 queue (so the requests started before the fork will only be handled in
292 the parent). Threats will be started on demand until the limit ste in
293 the parent process has been reached again.
261 294
262SEE ALSO 295SEE ALSO
263 Coro, Linux::AIO. 296 Coro, Linux::AIO.
264 297
265AUTHOR 298AUTHOR

Diff Legend

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