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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 \&IO::AIO::poll_cb;
26
27 # Tk
28 Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
29 readable => \&IO::AIO::poll_cb);
30
7DESCRIPTION 31DESCRIPTION
8 This module implements asynchronous I/O using whatever means your 32 This module implements asynchronous I/O using whatever means your
9 operating system supports. Currently, it falls back to Linux::AIO if 33 operating system supports.
10 that module is available, or uses pthreads to emulato aio functionality.
11 34
12 Currently, in this module a number of threads are started that execute 35 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 36 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 37 or perl, and the threads created by this module will not be visible to
15 will not be visible to the pthreads library. 38 the pthreads library. In the future, this module might make use of the
39 native aio functions available on many operating systems. However, they
40 are often not well-supported (Linux doesn't allow them on normal files
41 currently, for example), and they would only support aio_read and
42 aio_write, so the remaining functionality would have to be implemented
43 using threads anyway.
16 44
17 Although the module will work with in the presence of other threads, it 45 Although the module will work with in the presence of other threads, it
18 is not reentrant, so use appropriate locking yourself. 46 is currently not reentrant, so use appropriate locking yourself.
19 47
20 API NOTES 48FUNCTIONS
49 AIO FUNCTIONS
21 All the "aio_*" calls are more or less thin wrappers around the syscall 50 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 51 with the same name (sans "aio_"). The arguments are similar or
23 identical, and they all accept an additional $callback argument which 52 identical, and they all accept an additional $callback argument which
24 must be a code reference. This code reference will get called with the 53 must be a code reference. This code reference will get called with the
25 syscall return code (e.g. most syscalls return -1 on error, unlike perl, 54 syscall return code (e.g. most syscalls return -1 on error, unlike perl,
… …
32 The filenames you pass to these routines *must* be absolute. The reason 61 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 62 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 63 directory could have changed. Alternatively, you can make sure that you
35 never change the current working directory. 64 never change the current working directory.
36 65
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 66 aio_open $pathname, $flags, $mode, $callback
95 Asynchronously open or create a file and call the callback with the 67 Asynchronously open or create a file and call the callback with a
96 filedescriptor (NOT a perl filehandle, sorry for that, but watch 68 newly created filehandle for the file.
97 out, this might change in the future). 69
70 The pathname passed to "aio_open" must be absolute. See API NOTES,
71 above, for an explanation.
98 72
99 The $mode argument is a bitmask. See the "Fcntl" module for a list. 73 The $mode argument is a bitmask. See the "Fcntl" module for a list.
100 They are the same as used in "sysopen". 74 They are the same as used in "sysopen".
101 75
102 Example: 76 Example:
103 77
104 aio_open "/etc/passwd", O_RDONLY, 0, sub { 78 aio_open "/etc/passwd", O_RDONLY, 0, sub {
105 if ($_[0] >= 0) { 79 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"; 80 print "open successful, fh is $_[0]\n";
109 ... 81 ...
110 } else { 82 } else {
111 die "open failed: $!\n"; 83 die "open failed: $!\n";
112 } 84 }
113 }; 85 };
114 86
115 aio_close $fh, $callback 87 aio_close $fh, $callback
116 Asynchronously close a file and call the callback with the result 88 Asynchronously close a file and call the callback with the result
117 code. 89 code. *WARNING:* although accepted, you should not pass in a perl
90 filehandle here, as perl will likely close the file descriptor
91 itself when the filehandle is destroyed. Normally, you can safely
92 call perls "close" or just let filehandles go out of scope.
118 93
119 aio_read $fh,$offset,$length, $data,$dataoffset,$callback 94 aio_read $fh,$offset,$length, $data,$dataoffset,$callback
120 aio_write $fh,$offset,$length, $data,$dataoffset,$callback 95 aio_write $fh,$offset,$length, $data,$dataoffset,$callback
121 Reads or writes "length" bytes from the specified "fh" and "offset" 96 Reads or writes "length" bytes from the specified "fh" and "offset"
122 into the scalar given by "data" and offset "dataoffset" and calls 97 into the scalar given by "data" and offset "dataoffset" and calls
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125 100
126 Example: Read 15 bytes at offset 7 into scalar $buffer, strating at 101 Example: Read 15 bytes at offset 7 into scalar $buffer, strating at
127 offset 0 within the scalar: 102 offset 0 within the scalar:
128 103
129 aio_read $fh, 7, 15, $buffer, 0, sub { 104 aio_read $fh, 7, 15, $buffer, 0, sub {
130 $_[0] >= 0 or die "read error: $!"; 105 $_[0] > 0 or die "read error: $!";
131 print "read <$buffer>\n"; 106 print "read $_[0] bytes: <$buffer>\n";
132 }; 107 };
133 108
134 aio_readahead $fh,$offset,$length, $callback 109 aio_readahead $fh,$offset,$length, $callback
135 Asynchronously reads the specified byte range into the page cache, 110 Asynchronously reads the specified byte range into the page cache,
136 using the "readahead" syscall. 111 using the "readahead" syscall. If that syscall doesn't exist the
112 status will be -1 and $! is set to ENOSYS.
137 113
138 readahead() populates the page cache with data from a file so that 114 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 115 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 116 $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 117 be read and $length specifies the number of bytes to be read. I/O is
… …
176 152
177 aio_fdatasync $fh, $callback 153 aio_fdatasync $fh, $callback
178 Asynchronously call fdatasync on the given filehandle and call the 154 Asynchronously call fdatasync on the given filehandle and call the
179 callback with the fdatasync result code. 155 callback with the fdatasync result code.
180 156
181BUGS 157 SUPPORT FUNCTIONS
182 This module has been extensively tested in a large and very busy 158 $fileno = IO::AIO::poll_fileno
183 webserver for many years now. 159 Return the *request result pipe filehandle*. This filehandle must be
160 polled for reading by some mechanism outside this module (e.g. Event
161 or select, see below). If the pipe becomes readable you have to call
162 "poll_cb" to check the results.
184 163
185 - aio_open gives a fd, but all other functions expect a perl filehandle. 164 See "poll_cb" for an example.
165
166 IO::AIO::poll_cb
167 Process all outstanding events on the result pipe. You have to call
168 this regularly. Returns the number of events processed. Returns
169 immediately when no events are outstanding.
170
171 You can use Event to multiplex, e.g.:
172
173 Event->io (fd => IO::AIO::poll_fileno,
174 poll => 'r', async => 1,
175 cb => \&IO::AIO::poll_cb);
176
177 IO::AIO::poll_wait
178 Wait till the result filehandle becomes ready for reading (simply
179 does a select on the filehandle. This is useful if you want to
180 synchronously wait for some requests to finish).
181
182 See "nreqs" for an example.
183
184 IO::AIO::nreqs
185 Returns the number of requests currently outstanding.
186
187 Example: wait till there are no outstanding requests anymore:
188
189 IO::AIO::poll_wait, IO::AIO::poll_cb
190 while IO::AIO::nreqs;
191
192 IO::AIO::min_parallel $nthreads
193 Set the minimum number of AIO threads to $nthreads. The default is
194 1, which means a single asynchronous operation can be done at one
195 time (the number of outstanding operations, however, is unlimited).
196
197 It is recommended to keep the number of threads low, as some Linux
198 kernel versions will scale negatively with the number of threads
199 (higher parallelity => MUCH higher latency). With current Linux 2.6
200 versions, 4-32 threads should be fine.
201
202 Under normal circumstances you don't need to call this function, as
203 this module automatically starts some threads (the exact number
204 might change, and is currently 4).
205
206 IO::AIO::max_parallel $nthreads
207 Sets the maximum number of AIO threads to $nthreads. If more than
208 the specified number of threads are currently running, kill them.
209 This function blocks until the limit is reached.
210
211 This module automatically runs "max_parallel 0" at program end, to
212 ensure that all threads are killed and that there are no outstanding
213 requests.
214
215 Under normal circumstances you don't need to call this function.
216
217 $oldnreqs = IO::AIO::max_outstanding $nreqs
218 Sets the maximum number of outstanding requests to $nreqs. If you
219 try to queue up more than this number of requests, the caller will
220 block until some requests have been handled.
221
222 The default is very large, so normally there is no practical limit.
223 If you queue up many requests in a loop it it often improves speed
224 if you set this to a relatively low number, such as 100.
225
226 Under normal circumstances you don't need to call this function.
186 227
187SEE ALSO 228SEE ALSO
188 Coro. 229 Coro, Linux::AIO.
189 230
190AUTHOR 231AUTHOR
191 Marc Lehmann <schmorp@schmorp.de> 232 Marc Lehmann <schmorp@schmorp.de>
192 http://home.schmorp.de/ 233 http://home.schmorp.de/
193 234

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