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Revision 1.10 by root, Wed Aug 17 05:26:20 2005 UTC vs.
Revision 1.12 by root, Tue Aug 23 00:05:00 2005 UTC

… …
129 129
130 aio_read $fh, 7, 15, $buffer, 0, sub { 130 aio_read $fh, 7, 15, $buffer, 0, sub {
131 $_[0] > 0 or die "read error: $!"; 131 $_[0] > 0 or die "read error: $!";
132 print "read $_[0] bytes: <$buffer>\n"; 132 print "read $_[0] bytes: <$buffer>\n";
133 }; 133 };
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.
134 156
135 aio_readahead $fh,$offset,$length, $callback 157 aio_readahead $fh,$offset,$length, $callback
136 "aio_readahead" populates the page cache with data from a file so 158 "aio_readahead" populates the page cache with data from a file so
137 that 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
138 $offset argument specifies the starting point from which data is to 160 $offset argument specifies the starting point from which data is to
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239 261
240 IO::AIO::poll_wait, IO::AIO::poll_cb 262 IO::AIO::poll_wait, IO::AIO::poll_cb
241 if IO::AIO::nreqs; 263 if IO::AIO::nreqs;
242 264
243 IO::AIO::min_parallel $nthreads 265 IO::AIO::min_parallel $nthreads
244 Set the minimum number of AIO threads to $nthreads. The default is 266 Set the minimum number of AIO threads to $nthreads. The current
245 1, which means a single asynchronous operation can be done at one 267 default is 4, which means four asynchronous operations can be done
246 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.
247 273
248 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
249 kernel versions will scale negatively with the number of threads 275 kernel versions will scale negatively with the number of threads
250 (higher parallelity => MUCH higher latency). With current Linux 2.6 276 (higher parallelity => MUCH higher latency). With current Linux 2.6
251 versions, 4-32 threads should be fine. 277 versions, 4-32 threads should be fine.
252 278
253 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
254 this module automatically starts some threads (the exact number 280 the module selects a default that is suitable for low to moderate
255 might change, and is currently 4). 281 load.
256 282
257 IO::AIO::max_parallel $nthreads 283 IO::AIO::max_parallel $nthreads
258 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
259 the specified number of threads are currently running, kill them. 285 the specified number of threads are currently running, this function
260 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.
261 290
262 This module automatically runs "max_parallel 0" at program end, to 291 This module automatically runs "max_parallel 0" at program end, to
263 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
264 requests. 293 requests.
265 294
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269 Sets the maximum number of outstanding requests to $nreqs. If you 298 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 299 try to queue up more than this number of requests, the caller will
271 block until some requests have been handled. 300 block until some requests have been handled.
272 301
273 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.
274 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
275 if you set this to a relatively low number, such as 100. 304 you set this to a relatively low number, such as 100.
276 305
277 Under normal circumstances you don't need to call this function. 306 Under normal circumstances you don't need to call this function.
278 307
279 FORK BEHAVIOUR 308 FORK BEHAVIOUR
280 Before the fork IO::AIO enters a quiescent state where no requests can 309 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 310 be added in other threads and no results will be processed. After the
282 fork the parent simply leaves the quiescent state and continues 311 fork the parent simply leaves the quiescent state and continues
283 request/result processing, while the child clears the request/result 312 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 313 queue (so the requests started before the fork will only be handled in
285 parent. 314 the parent). Threats will be started on demand until the limit ste in
315 the parent process has been reached again.
286 316
287SEE ALSO 317SEE ALSO
288 Coro, Linux::AIO. 318 Coro, Linux::AIO.
289 319
290AUTHOR 320AUTHOR

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