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 1.12 by root, Tue Aug 23 00:05:00 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
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
123 aio_readahead $fh,$offset,$length, $callback 157 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 158 "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 159 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 160 $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 161 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 162 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 163 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 164 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 165 read beyond the end of the file. The current file offset of the file
137 is left unchanged. 166 is left unchanged.
138 167
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.
171
139 aio_stat $fh_or_path, $callback 172 aio_stat $fh_or_path, $callback
140 aio_lstat $fh, $callback 173 aio_lstat $fh, $callback
141 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
142 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
143 using "stat _" or "-s _" etc... 176 using "stat _" or "-s _" etc...
… …
159 192
160 aio_unlink $pathname, $callback 193 aio_unlink $pathname, $callback
161 Asynchronously unlink (delete) a file and call the callback with the 194 Asynchronously unlink (delete) a file and call the callback with the
162 result code. 195 result code.
163 196
197 aio_rmdir $pathname, $callback
198 Asynchronously rmdir (delete) a directory and call the callback with
199 the result code.
200
164 aio_fsync $fh, $callback 201 aio_fsync $fh, $callback
165 Asynchronously call fsync on the given filehandle and call the 202 Asynchronously call fsync on the given filehandle and call the
166 callback with the fsync result code. 203 callback with the fsync result code.
167 204
168 aio_fdatasync $fh, $callback 205 aio_fdatasync $fh, $callback
169 Asynchronously call fdatasync on the given filehandle and call the 206 Asynchronously call fdatasync on the given filehandle and call the
170 callback with the fdatasync result code. Might set $! to "ENOSYS" if 207 callback with the fdatasync result code.
171 "fdatasync" is not available. 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.
172 211
173 SUPPORT FUNCTIONS 212 SUPPORT FUNCTIONS
174 $fileno = IO::AIO::poll_fileno 213 $fileno = IO::AIO::poll_fileno
175 Return the *request result pipe file descriptor*. This filehandle 214 Return the *request result pipe file descriptor*. This filehandle
176 must be polled for reading by some mechanism outside this module 215 must be polled for reading by some mechanism outside this module
… …
222 261
223 IO::AIO::poll_wait, IO::AIO::poll_cb 262 IO::AIO::poll_wait, IO::AIO::poll_cb
224 if IO::AIO::nreqs; 263 if IO::AIO::nreqs;
225 264
226 IO::AIO::min_parallel $nthreads 265 IO::AIO::min_parallel $nthreads
227 Set the minimum number of AIO threads to $nthreads. The default is 266 Set the minimum number of AIO threads to $nthreads. The current
228 1, which means a single asynchronous operation can be done at one 267 default is 4, which means four asynchronous operations can be done
229 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.
230 273
231 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
232 kernel versions will scale negatively with the number of threads 275 kernel versions will scale negatively with the number of threads
233 (higher parallelity => MUCH higher latency). With current Linux 2.6 276 (higher parallelity => MUCH higher latency). With current Linux 2.6
234 versions, 4-32 threads should be fine. 277 versions, 4-32 threads should be fine.
235 278
236 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
237 this module automatically starts some threads (the exact number 280 the module selects a default that is suitable for low to moderate
238 might change, and is currently 4). 281 load.
239 282
240 IO::AIO::max_parallel $nthreads 283 IO::AIO::max_parallel $nthreads
241 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
242 the specified number of threads are currently running, kill them. 285 the specified number of threads are currently running, this function
243 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.
244 290
245 This module automatically runs "max_parallel 0" at program end, to 291 This module automatically runs "max_parallel 0" at program end, to
246 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
247 requests. 293 requests.
248 294
… …
252 Sets the maximum number of outstanding requests to $nreqs. If you 298 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 299 try to queue up more than this number of requests, the caller will
254 block until some requests have been handled. 300 block until some requests have been handled.
255 301
256 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.
257 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
258 if you set this to a relatively low number, such as 100. 304 you set this to a relatively low number, such as 100.
259 305
260 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.
261 316
262SEE ALSO 317SEE ALSO
263 Coro, Linux::AIO. 318 Coro, Linux::AIO.
264 319
265AUTHOR 320AUTHOR

Diff Legend

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