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… …
4SYNOPSIS 4SYNOPSIS
5 use IO::AIO; 5 use IO::AIO;
6 6
7DESCRIPTION 7DESCRIPTION
8 This module implements asynchronous I/O using whatever means your 8 This module implements asynchronous I/O using whatever means your
9 operating system supports. Currently, it falls back to Linux::AIO if 9 operating system supports.
10 that module is available, or uses pthreads to emulato aio functionality.
11 10
12 Currently, in this module a number of threads are started that execute 11 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 12 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 13 or perl, and the threads created by this module will not be visible to
15 will not be visible to the pthreads library. 14 the pthreads library. In the future, this module might make use of the
15 native aio functions available on many operating systems. However, they
16 are often not well-supported (Linux doesn't allow them on normal files
17 currently, for example), and they would only support aio_read and
18 aio_write, so the remaining functionality would have to be implemented
19 using threads anyway.
16 20
17 Although the module will work with in the presence of other threads, it 21 Although the module will work with in the presence of other threads, it
18 is not reentrant, so use appropriate locking yourself. 22 is currently not reentrant, so use appropriate locking yourself.
19 23
20 API NOTES 24 API NOTES
21 All the "aio_*" calls are more or less thin wrappers around the syscall 25 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 26 with the same name (sans "aio_"). The arguments are similar or
23 identical, and they all accept an additional $callback argument which 27 identical, and they all accept an additional $callback argument which
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37 IO::AIO::min_parallel $nthreads 41 IO::AIO::min_parallel $nthreads
38 Set the minimum number of AIO threads to $nthreads. The default is 42 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 43 1, which means a single asynchronous operation can be done at one
40 time (the number of outstanding operations, however, is unlimited). 44 time (the number of outstanding operations, however, is unlimited).
41 45
42 It is recommended to keep the number of threads low, as some linux 46 It is recommended to keep the number of threads low, as some Linux
43 kernel versions will scale negatively with the number of threads 47 kernel versions will scale negatively with the number of threads
44 (higher parallelity => MUCH higher latency). 48 (higher parallelity => MUCH higher latency). With current Linux 2.6
49 versions, 4-32 threads should be fine.
45 50
46 Under normal circumstances you don't need to call this function, as 51 Under normal circumstances you don't need to call this function, as
47 this module automatically starts a single async thread. 52 this module automatically starts some threads (the exact number
53 might change, and is currently 4).
48 54
49 IO::AIO::max_parallel $nthreads 55 IO::AIO::max_parallel $nthreads
50 Sets the maximum number of AIO threads to $nthreads. If more than 56 Sets the maximum number of AIO threads to $nthreads. If more than
51 the specified number of threads are currently running, kill them. 57 the specified number of threads are currently running, kill them.
52 This function blocks until the limit is reached. 58 This function blocks until the limit is reached.
53 59
54 This module automatically runs "max_parallel 0" at program end, to 60 This module automatically runs "max_parallel 0" at program end, to
55 ensure that all threads are killed and that there are no outstanding 61 ensure that all threads are killed and that there are no outstanding
56 requests. 62 requests.
63
64 Under normal circumstances you don't need to call this function.
65
66 $oldnreqs = IO::AIO::max_outstanding $nreqs
67 Sets the maximum number of outstanding requests to $nreqs. If you
68 try to queue up more than this number of requests, the caller will
69 block until some requests have been handled.
70
71 The default is very large, so normally there is no practical limit.
72 If you queue up many requests in a loop it it often improves speed
73 if you set this to a relatively low number, such as 100.
57 74
58 Under normal circumstances you don't need to call this function. 75 Under normal circumstances you don't need to call this function.
59 76
60 $fileno = IO::AIO::poll_fileno 77 $fileno = IO::AIO::poll_fileno
61 Return the *request result pipe filehandle*. This filehandle must be 78 Return the *request result pipe filehandle*. This filehandle must be
… …
90 107
91 IO::AIO::poll_wait, IO::AIO::poll_cb 108 IO::AIO::poll_wait, IO::AIO::poll_cb
92 while IO::AIO::nreqs; 109 while IO::AIO::nreqs;
93 110
94 aio_open $pathname, $flags, $mode, $callback 111 aio_open $pathname, $flags, $mode, $callback
95 Asynchronously open or create a file and call the callback with the 112 Asynchronously open or create a file and call the callback with a
96 filedescriptor (NOT a perl filehandle, sorry for that, but watch 113 newly created filehandle for the file.
97 out, this might change in the future). 114
115 The pathname passed to "aio_open" must be absolute. See API NOTES,
116 above, for an explanation.
98 117
99 The $mode argument is a bitmask. See the "Fcntl" module for a list. 118 The $mode argument is a bitmask. See the "Fcntl" module for a list.
100 They are the same as used in "sysopen". 119 They are the same as used in "sysopen".
101 120
102 Example: 121 Example:
103 122
104 aio_open "/etc/passwd", O_RDONLY, 0, sub { 123 aio_open "/etc/passwd", O_RDONLY, 0, sub {
105 if ($_[0] >= 0) { 124 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"; 125 print "open successful, fh is $_[0]\n";
109 ... 126 ...
110 } else { 127 } else {
111 die "open failed: $!\n"; 128 die "open failed: $!\n";
112 } 129 }
113 }; 130 };
114 131
115 aio_close $fh, $callback 132 aio_close $fh, $callback
116 Asynchronously close a file and call the callback with the result 133 Asynchronously close a file and call the callback with the result
117 code. 134 code. *WARNING:* although accepted, you should not pass in a perl
135 filehandle here, as perl will likely close the file descriptor
136 itself when the filehandle is destroyed. Normally, you can safely
137 call perls "close" or just let filehandles go out of scope.
118 138
119 aio_read $fh,$offset,$length, $data,$dataoffset,$callback 139 aio_read $fh,$offset,$length, $data,$dataoffset,$callback
120 aio_write $fh,$offset,$length, $data,$dataoffset,$callback 140 aio_write $fh,$offset,$length, $data,$dataoffset,$callback
121 Reads or writes "length" bytes from the specified "fh" and "offset" 141 Reads or writes "length" bytes from the specified "fh" and "offset"
122 into the scalar given by "data" and offset "dataoffset" and calls 142 into the scalar given by "data" and offset "dataoffset" and calls
… …
131 print "read <$buffer>\n"; 151 print "read <$buffer>\n";
132 }; 152 };
133 153
134 aio_readahead $fh,$offset,$length, $callback 154 aio_readahead $fh,$offset,$length, $callback
135 Asynchronously reads the specified byte range into the page cache, 155 Asynchronously reads the specified byte range into the page cache,
136 using the "readahead" syscall. 156 using the "readahead" syscall. If that syscall doesn't exist the
157 status will be -1 and $! is set to ENOSYS.
137 158
138 readahead() populates the page cache with data from a file so that 159 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 160 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 161 $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 162 be read and $length specifies the number of bytes to be read. I/O is
… …
177 aio_fdatasync $fh, $callback 198 aio_fdatasync $fh, $callback
178 Asynchronously call fdatasync on the given filehandle and call the 199 Asynchronously call fdatasync on the given filehandle and call the
179 callback with the fdatasync result code. 200 callback with the fdatasync result code.
180 201
181BUGS 202BUGS
182 This module has been extensively tested in a large and very busy 203 - could be optimized to use more semaphores instead of filehandles.
183 webserver for many years now.
184
185 - aio_open gives a fd, but all other functions expect a perl filehandle.
186 204
187SEE ALSO 205SEE ALSO
188 Coro. 206 Coro, Linux::AIO.
189 207
190AUTHOR 208AUTHOR
191 Marc Lehmann <schmorp@schmorp.de> 209 Marc Lehmann <schmorp@schmorp.de>
192 http://home.schmorp.de/ 210 http://home.schmorp.de/
193 211

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