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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 filenames you pass to these routines *must* be absolute. The reason
33 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
34 directory could have changed. Alternatively, you can make sure that you 69 working directory could have changed. Alternatively, you can make sure
35 never change the current working directory. 70 that you never change the current working directory.
36
37 IO::AIO::min_parallel $nthreads
38 Set the minimum number of AIO threads to $nthreads. The default is
39 1, which means a single asynchronous operation can be done at one
40 time (the number of outstanding operations, however, is unlimited).
41
42 It is recommended to keep the number of threads low, as some linux
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 71
94 aio_open $pathname, $flags, $mode, $callback 72 aio_open $pathname, $flags, $mode, $callback
95 Asynchronously open or create a file and call the callback with the 73 Asynchronously open or create a file and call the callback with a
96 filedescriptor (NOT a perl filehandle, sorry for that, but watch 74 newly created filehandle for the file.
97 out, this might change in the future).
98 75
76 The pathname passed to "aio_open" must be absolute. See API NOTES,
77 above, for an explanation.
78
99 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.
100 They are the same as used in "sysopen". 80 They are the same as used by "sysopen".
81
82 Likewise, $mode specifies the mode of the newly created file, if it
83 didn't exist and "O_CREAT" has been given, just like perl's
84 "sysopen", except that it is mandatory (i.e. use 0 if you don't
85 create new files, and 0666 or 0777 if you do).
101 86
102 Example: 87 Example:
103 88
104 aio_open "/etc/passwd", O_RDONLY, 0, sub { 89 aio_open "/etc/passwd", O_RDONLY, 0, sub {
105 if ($_[0] >= 0) { 90 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"; 91 print "open successful, fh is $_[0]\n";
109 ... 92 ...
110 } else { 93 } else {
111 die "open failed: $!\n"; 94 die "open failed: $!\n";
112 } 95 }
113 }; 96 };
114 97
115 aio_close $fh, $callback 98 aio_close $fh, $callback
116 Asynchronously close a file and call the callback with the result 99 Asynchronously close a file and call the callback with the result
117 code. 100 code. *WARNING:* although accepted, you should not pass in a perl
101 filehandle here, as perl will likely close the file descriptor
102 another time when the filehandle is destroyed. Normally, you can
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.
118 107
119 aio_read $fh,$offset,$length, $data,$dataoffset,$callback 108 aio_read $fh,$offset,$length, $data,$dataoffset,$callback
120 aio_write $fh,$offset,$length, $data,$dataoffset,$callback 109 aio_write $fh,$offset,$length, $data,$dataoffset,$callback
121 Reads or writes "length" bytes from the specified "fh" and "offset" 110 Reads or writes "length" bytes from the specified "fh" and "offset"
122 into the scalar given by "data" and offset "dataoffset" and calls 111 into the scalar given by "data" and offset "dataoffset" and calls
123 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
124 error, just like the syscall). 113 error, just like the syscall).
125 114
126 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
127 offset 0 within the scalar: 116 offset 0 within the scalar:
128 117
129 aio_read $fh, 7, 15, $buffer, 0, sub { 118 aio_read $fh, 7, 15, $buffer, 0, sub {
130 $_[0] >= 0 or die "read error: $!"; 119 $_[0] > 0 or die "read error: $!";
131 print "read <$buffer>\n"; 120 print "read $_[0] bytes: <$buffer>\n";
132 }; 121 };
133 122
134 aio_readahead $fh,$offset,$length, $callback 123 aio_readahead $fh,$offset,$length, $callback
135 Asynchronously reads the specified byte range into the page cache, 124 Asynchronously reads the specified byte range into the page cache,
136 using the "readahead" syscall. 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".
137 128
138 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
139 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
140 $offset argument specifies the starting point from which data is to 131 $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 132 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 133 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 134 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 135 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 136 read beyond the end of the file. The current file offset of the file
146 is left unchanged. 137 is left unchanged.
147 138
148 aio_stat $fh_or_path, $callback 139 aio_stat $fh_or_path, $callback
149 aio_lstat $fh, $callback 140 aio_lstat $fh, $callback
… …
174 Asynchronously call fsync on the given filehandle and call the 165 Asynchronously call fsync on the given filehandle and call the
175 callback with the fsync result code. 166 callback with the fsync result code.
176 167
177 aio_fdatasync $fh, $callback 168 aio_fdatasync $fh, $callback
178 Asynchronously call fdatasync on the given filehandle and call the 169 Asynchronously call fdatasync on the given filehandle and call the
179 callback with the fdatasync result code. 170 callback with the fdatasync result code. Might set $! to "ENOSYS" if
171 "fdatasync" is not available.
180 172
181BUGS 173 SUPPORT FUNCTIONS
182 This module has been extensively tested in a large and very busy 174 $fileno = IO::AIO::poll_fileno
183 webserver for many years now. 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.
184 179
185 - aio_open gives a fd, but all other functions expect a perl filehandle. 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.
186 261
187SEE ALSO 262SEE ALSO
188 Coro. 263 Coro, Linux::AIO.
189 264
190AUTHOR 265AUTHOR
191 Marc Lehmann <schmorp@schmorp.de> 266 Marc Lehmann <schmorp@schmorp.de>
192 http://home.schmorp.de/ 267 http://home.schmorp.de/
193 268

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