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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.
19 51
20 API NOTES 52FUNCTIONS
53 AIO FUNCTIONS
21 All the "aio_*" calls are more or less thin wrappers around the syscall 54 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 55 with the same name (sans "aio_"). The arguments are similar or
23 identical, and they all accept an additional $callback argument which 56 identical, and they all accept an additional (and optional) $callback
24 must be a code reference. This code reference will get called with the 57 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, 58 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 59 error, unlike perl, which usually delivers "false") as it's sole
27 syscall has been executed asynchronously. 60 argument when the given syscall has been executed asynchronously.
28 61
29 All functions that expect a filehandle will also accept a file 62 All functions that expect a filehandle will also accept a file
30 descriptor. 63 descriptor.
31 64
32 The filenames you pass to these routines *must* be absolute. The reason 65 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 66 is that at the time the request is being executed, the current working
34 directory could have changed. Alternatively, you can make sure that you 67 directory could have changed. Alternatively, you can make sure that you
35 never change the current working directory. 68 never change the current working directory.
36 69
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
94 aio_open $pathname, $flags, $mode, $callback 70 aio_open $pathname, $flags, $mode, $callback
95 Asynchronously open or create a file and call the callback with the 71 Asynchronously open or create a file and call the callback with a
96 filedescriptor (NOT a perl filehandle, sorry for that, but watch 72 newly created filehandle for the file.
97 out, this might change in the future). 73
74 The pathname passed to "aio_open" must be absolute. See API NOTES,
75 above, for an explanation.
98 76
99 The $mode argument is a bitmask. See the "Fcntl" module for a list. 77 The $mode argument is a bitmask. See the "Fcntl" module for a list.
100 They are the same as used in "sysopen". 78 They are the same as used in "sysopen".
101 79
102 Example: 80 Example:
103 81
104 aio_open "/etc/passwd", O_RDONLY, 0, sub { 82 aio_open "/etc/passwd", O_RDONLY, 0, sub {
105 if ($_[0] >= 0) { 83 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"; 84 print "open successful, fh is $_[0]\n";
109 ... 85 ...
110 } else { 86 } else {
111 die "open failed: $!\n"; 87 die "open failed: $!\n";
112 } 88 }
113 }; 89 };
114 90
115 aio_close $fh, $callback 91 aio_close $fh, $callback
116 Asynchronously close a file and call the callback with the result 92 Asynchronously close a file and call the callback with the result
117 code. 93 code. *WARNING:* although accepted, you should not pass in a perl
94 filehandle here, as perl will likely close the file descriptor
95 itself when the filehandle is destroyed. Normally, you can safely
96 call perls "close" or just let filehandles go out of scope.
118 97
119 aio_read $fh,$offset,$length, $data,$dataoffset,$callback 98 aio_read $fh,$offset,$length, $data,$dataoffset,$callback
120 aio_write $fh,$offset,$length, $data,$dataoffset,$callback 99 aio_write $fh,$offset,$length, $data,$dataoffset,$callback
121 Reads or writes "length" bytes from the specified "fh" and "offset" 100 Reads or writes "length" bytes from the specified "fh" and "offset"
122 into the scalar given by "data" and offset "dataoffset" and calls 101 into the scalar given by "data" and offset "dataoffset" and calls
123 the callback without the actual number of bytes read (or -1 on 102 the callback without the actual number of bytes read (or -1 on
124 error, just like the syscall). 103 error, just like the syscall).
125 104
126 Example: Read 15 bytes at offset 7 into scalar $buffer, strating at 105 Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
127 offset 0 within the scalar: 106 offset 0 within the scalar:
128 107
129 aio_read $fh, 7, 15, $buffer, 0, sub { 108 aio_read $fh, 7, 15, $buffer, 0, sub {
130 $_[0] >= 0 or die "read error: $!"; 109 $_[0] > 0 or die "read error: $!";
131 print "read <$buffer>\n"; 110 print "read $_[0] bytes: <$buffer>\n";
132 }; 111 };
133 112
134 aio_readahead $fh,$offset,$length, $callback 113 aio_readahead $fh,$offset,$length, $callback
135 Asynchronously reads the specified byte range into the page cache, 114 Asynchronously reads the specified byte range into the page cache,
136 using the "readahead" syscall. 115 using the "readahead" syscall. If that syscall doesn't exist (likely
116 if your OS isn't Linux) the status will be -1 and $! is set to
117 ENOSYS.
137 118
138 readahead() populates the page cache with data from a file so that 119 readahead() populates the page cache with data from a file so that
139 subsequent reads from that file will not block on disk I/O. The 120 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 121 $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 122 be read and $length specifies the number of bytes to be read. I/O is
… …
176 157
177 aio_fdatasync $fh, $callback 158 aio_fdatasync $fh, $callback
178 Asynchronously call fdatasync on the given filehandle and call the 159 Asynchronously call fdatasync on the given filehandle and call the
179 callback with the fdatasync result code. 160 callback with the fdatasync result code.
180 161
181BUGS 162 SUPPORT FUNCTIONS
182 This module has been extensively tested in a large and very busy 163 $fileno = IO::AIO::poll_fileno
183 webserver for many years now. 164 Return the *request result pipe filehandle*. This filehandle must be
165 polled for reading by some mechanism outside this module (e.g. Event
166 or select, see below). If the pipe becomes readable you have to call
167 "poll_cb" to check the results.
184 168
185 - aio_open gives a fd, but all other functions expect a perl filehandle. 169 See "poll_cb" for an example.
170
171 IO::AIO::poll_cb
172 Process all outstanding events on the result pipe. You have to call
173 this regularly. Returns the number of events processed. Returns
174 immediately when no events are outstanding.
175
176 You can use Event to multiplex, e.g.:
177
178 Event->io (fd => IO::AIO::poll_fileno,
179 poll => 'r', async => 1,
180 cb => \&IO::AIO::poll_cb);
181
182 IO::AIO::poll_wait
183 Wait till the result filehandle becomes ready for reading (simply
184 does a select on the filehandle. This is useful if you want to
185 synchronously wait for some requests to finish).
186
187 See "nreqs" for an example.
188
189 IO::AIO::nreqs
190 Returns the number of requests currently outstanding.
191
192 Example: wait till there are no outstanding requests anymore:
193
194 IO::AIO::poll_wait, IO::AIO::poll_cb
195 while IO::AIO::nreqs;
196
197 IO::AIO::flush
198 Wait till all outstanding AIO requests have been handled.
199
200 Strictly equivalent to:
201
202 IO::AIO::poll_wait, IO::AIO::poll_cb
203 while IO::AIO::nreqs;
204
205 IO::AIO::poll
206 Waits until some requests have been handled.
207
208 Strictly equivalent to:
209
210 IO::AIO::poll_wait, IO::AIO::poll_cb
211 if IO::AIO::nreqs;
212
213 IO::AIO::min_parallel $nthreads
214 Set the minimum number of AIO threads to $nthreads. The default is
215 1, which means a single asynchronous operation can be done at one
216 time (the number of outstanding operations, however, is unlimited).
217
218 It is recommended to keep the number of threads low, as some Linux
219 kernel versions will scale negatively with the number of threads
220 (higher parallelity => MUCH higher latency). With current Linux 2.6
221 versions, 4-32 threads should be fine.
222
223 Under normal circumstances you don't need to call this function, as
224 this module automatically starts some threads (the exact number
225 might change, and is currently 4).
226
227 IO::AIO::max_parallel $nthreads
228 Sets the maximum number of AIO threads to $nthreads. If more than
229 the specified number of threads are currently running, kill them.
230 This function blocks until the limit is reached.
231
232 This module automatically runs "max_parallel 0" at program end, to
233 ensure that all threads are killed and that there are no outstanding
234 requests.
235
236 Under normal circumstances you don't need to call this function.
237
238 $oldnreqs = IO::AIO::max_outstanding $nreqs
239 Sets the maximum number of outstanding requests to $nreqs. If you
240 try to queue up more than this number of requests, the caller will
241 block until some requests have been handled.
242
243 The default is very large, so normally there is no practical limit.
244 If you queue up many requests in a loop it it often improves speed
245 if you set this to a relatively low number, such as 100.
246
247 Under normal circumstances you don't need to call this function.
186 248
187SEE ALSO 249SEE ALSO
188 Coro. 250 Coro, Linux::AIO.
189 251
190AUTHOR 252AUTHOR
191 Marc Lehmann <schmorp@schmorp.de> 253 Marc Lehmann <schmorp@schmorp.de>
192 http://home.schmorp.de/ 254 http://home.schmorp.de/
193 255

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