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Revision 1.1 by root, Tue Mar 8 20:19:00 2005 UTC vs.
Revision 1.7 by root, Wed Aug 17 16:57:53 2005 UTC

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2 Linux::AIO - linux-specific aio implemented using clone 2 Linux::AIO - linux-specific aio implemented using clone
3 3
4SYNOPSIS 4SYNOPSIS
5 use Linux::AIO; 5 use Linux::AIO;
6 6
7 # This module has been mostly superseded by IO::AIO.
8
7DESCRIPTION 9DESCRIPTION
10 *This module has been mostly superseded by IO::AIO, which is API
11 compatible.*
12
8 This module implements asynchronous i/o using the means available to 13 This module implements asynchronous I/O using the means available to
9 linux - clone. It does not hook into the POSIX aio_* functions because 14 Linux - clone. It does not hook into the POSIX aio_* functions because
10 linux does not yet support these in the kernel (and even if, it would 15 Linux does not yet support these in the kernel (even as of 2.6.12, only
11 only allow aio_read and write, not open and stat). 16 O_DIRECT files are supported) and even if, it would only allow aio_read
17 and write, not open, stat and so on.
12 18
13 Instead, in this module a number of (non-posix) threads are started that 19 Instead, in this module a number of (non-posix) threads are started that
14 execute your read/writes and signal their completion. You don't need 20 execute your read/writes and signal their completion. You don't need
15 thread support in your libc or perl, and the threads created by this 21 thread support in your libc or perl, and the threads created by this
16 module will not be visible to the pthreads library. 22 module will not be visible to the pthreads library.
17 23
18 NOTICE: the threads created by this module will automatically be killed 24 NOTICE: the threads created by this module will automatically be killed
19 when the thread calling min_parallel exits. Make sure you only ever call 25 when the thread calling min_parallel exits. Make sure you only ever call
20 min_parallel from the same thread that loaded this module. 26 min_parallel from the same thread that loaded this module.
21 27
22 Although the module will work with threads, it is not reentrant, so use 28 Although the module will work with in the presence of other threads, it
23 appropriate locking yourself. 29 is not reentrant, so use appropriate locking yourself.
30
31 API NOTES
32 All the "aio_*" calls are more or less thin wrappers around the syscall
33 with the same name (sans "aio_"). The arguments are similar or
34 identical, and they all accept an additional $callback argument which
35 must be a code reference. This code reference will get called with the
36 syscall return code (e.g. most syscalls return -1 on error, unlike perl,
37 which usually delivers "false") as it's sole argument when the given
38 syscall has been executed asynchronously.
39
40 All functions that expect a filehandle will also accept a file
41 descriptor.
42
43 The filenames you pass to these routines *must* be absolute. The reason
44 is that at the time the request is being executed, the current working
45 directory could have changed. Alternatively, you can make sure that you
46 never change the current working directory.
24 47
25 Linux::AIO::min_parallel $nthreads 48 Linux::AIO::min_parallel $nthreads
26 Set the minimum number of AIO threads to $nthreads. The default is 49 Set the minimum number of AIO threads to $nthreads. The default is
27 1, which means a single asynchronous operation can be done at one 50 1, which means a single asynchronous operation can be done at one
28 time (the number of outstanding operations, however, is unlimited). 51 time (the number of outstanding operations, however, is unlimited).
29 52
30 It is recommended to keep the number of threads low, as many linux 53 It is recommended to keep the number of threads low, as some linux
31 kernel versions will scale negatively with the number of threads 54 kernel versions will scale negatively with the number of threads
32 (higher parallelity => MUCH higher latency). 55 (higher parallelity => MUCH higher latency).
56
57 Under normal circumstances you don't need to call this function, as
58 this module automatically starts a single async thread.
59
60 Linux::AIO::max_parallel $nthreads
61 Sets the maximum number of AIO threads to $nthreads. If more than
62 the specified number of threads are currently running, kill them.
63 This function blocks until the limit is reached.
64
65 This module automatically runs "max_parallel 0" at program end, to
66 ensure that all threads are killed and that there are no outstanding
67 requests.
68
69 Under normal circumstances you don't need to call this function.
33 70
34 $fileno = Linux::AIO::poll_fileno 71 $fileno = Linux::AIO::poll_fileno
35 Return the *request result pipe filehandle*. This filehandle must be 72 Return the *request result pipe filehandle*. This filehandle must be
36 polled for reading by some mechanism outside this module (e.g. Event 73 polled for reading by some mechanism outside this module (e.g. Event
37 or select, see below). If the pipe becomes readable you have to call 74 or select, see below). If the pipe becomes readable you have to call
38 "poll_cb" to check the results. 75 "poll_cb" to check the results.
39 76
77 See "poll_cb" for an example.
78
40 Linux::AIO::poll_cb 79 Linux::AIO::poll_cb
41 Process all outstanding events on the result pipe. You have to call 80 Process all outstanding events on the result pipe. You have to call
42 this regularly. Returns the number of events processed. Returns 81 this regularly. Returns the number of events processed. Returns
43 immediately when no events are outstanding. 82 immediately when no events are outstanding.
44 83
45 You can use Event to multiplex, e.g.: 84 You can use Event to multiplex, e.g.:
46 85
47 Event->io (fd => Linux::AIO::poll_fileno, 86 Event->io (fd => Linux::AIO::poll_fileno,
48 poll => 'r', async => 1, 87 poll => 'r', async => 1,
49 cb => \&Linux::AIO::poll_cb ); 88 cb => \&Linux::AIO::poll_cb);
89
90 Linux::AIO::poll_wait
91 Wait till the result filehandle becomes ready for reading (simply
92 does a select on the filehandle. This is useful if you want to
93 synchronously wait for some requests to finish).
94
95 See "nreqs" for an example.
50 96
51 Linux::AIO::nreqs 97 Linux::AIO::nreqs
52 Returns the number of requests currently outstanding. 98 Returns the number of requests currently outstanding.
99
100 Example: wait till there are no outstanding requests anymore:
101
102 Linux::AIO::poll_wait, Linux::AIO::poll_cb
103 while Linux::AIO::nreqs;
53 104
54 aio_open $pathname, $flags, $mode, $callback 105 aio_open $pathname, $flags, $mode, $callback
55 Asynchronously open or create a file and call the callback with the 106 Asynchronously open or create a file and call the callback with the
56 filedescriptor (NOT a perl filehandle, sorry for that, but watch 107 filedescriptor (NOT a perl filehandle, sorry for that, but watch
57 out, this might change in the future). 108 out, this might change in the future).
58 109
110 The pathname passed to "aio_open" must be absolute. See API NOTES,
111 above, for an explanation.
112
113 The $mode argument is a bitmask. See the "Fcntl" module for a list.
114 They are the same as used in "sysopen".
115
116 Example:
117
118 aio_open "/etc/passwd", O_RDONLY, 0, sub {
119 if ($_[0] >= 0) {
120 open my $fh, "<&=$_[0]";
121 print "open successful, fh is $fh\n";
122 ...
123 } else {
124 die "open failed: $!\n";
125 }
126 };
127
59 aio_close $fh, $callback 128 aio_close $fh, $callback
60 Asynchronously close a file and call the callback with the result 129 Asynchronously close a file and call the callback with the result
61 code. 130 code.
62 131
63 aio_read $fh,$offset,$length, $data,$dataoffset,$callback 132 aio_read $fh,$offset,$length, $data,$dataoffset,$callback
64 aio_write $fh,$offset,$length, $data,$dataoffset,$callback 133 aio_write $fh,$offset,$length, $data,$dataoffset,$callback
65 Reads or writes "length" bytes from the specified "fh" and "offset" 134 Reads or writes "length" bytes from the specified "fh" and "offset"
66 into the scalar given by "data" and offset "dataoffset" and calls 135 into the scalar given by "data" and offset "dataoffset" and calls
67 the callback without the actual number of bytes read (or "undef" on 136 the callback without the actual number of bytes read (or -1 on
68 error). 137 error, just like the syscall).
138
139 Example: Read 15 bytes at offset 7 into scalar $buffer, strating at
140 offset 0 within the scalar:
141
142 aio_read $fh, 7, 15, $buffer, 0, sub {
143 $_[0] >= 0 or die "read error: $!";
144 print "read <$buffer>\n";
145 };
146
147 aio_readahead $fh,$offset,$length, $callback
148 Asynchronously reads the specified byte range into the page cache,
149 using the "readahead" syscall.
150
151 readahead() populates the page cache with data from a file so that
152 subsequent reads from that file will not block on disk I/O. The
153 $offset argument specifies the starting point from which data is to
154 be read and $length specifies the number of bytes to be read. I/O is
155 performed in whole pages, so that offset is effectively rounded down
156 to a page boundary and bytes are read up to the next page boundary
157 greater than or equal to (off-set+length). aio_readahead() does not
158 read beyond the end of the file. The current file offset of the file
159 is left unchanged.
69 160
70 aio_stat $fh_or_path, $callback 161 aio_stat $fh_or_path, $callback
71 aio_lstat $fh, $callback 162 aio_lstat $fh, $callback
72 Works like perl's "stat" or "lstat" in void context. The callback 163 Works like perl's "stat" or "lstat" in void context. The callback
73 will be called after the stat and the results will be available 164 will be called after the stat and the results will be available
74 using "stat _" or "-s _" etc... 165 using "stat _" or "-s _" etc...
75 166
167 The pathname passed to "aio_stat" must be absolute. See API NOTES,
168 above, for an explanation.
169
76 Currently, the stats are always 64-bit-stats, i.e. instead of 170 Currently, the stats are always 64-bit-stats, i.e. instead of
77 returning an error when stat'ing a large file, the results will be 171 returning an error when stat'ing a large file, the results will be
78 silently truncated unless perl itself is compiled with large file 172 silently truncated unless perl itself is compiled with large file
79 support. 173 support.
80 174
175 Example: Print the length of /etc/passwd:
176
177 aio_stat "/etc/passwd", sub {
178 $_[0] and die "stat failed: $!";
179 print "size is ", -s _, "\n";
180 };
181
81 aio_unlink $pathname, $callback 182 aio_unlink $pathname, $callback
82 Asynchronously unlink a file. 183 Asynchronously unlink (delete) a file and call the callback with the
184 result code.
185
186 aio_fsync $fh, $callback
187 Asynchronously call fsync on the given filehandle and call the
188 callback with the fsync result code.
189
190 aio_fdatasync $fh, $callback
191 Asynchronously call fdatasync on the given filehandle and call the
192 callback with the fdatasync result code.
83 193
84BUGS 194BUGS
85 This module has been extensively tested in a large and very busy 195 This module has been extensively tested in a large and very busy
86 webserver for many years now. 196 webserver for many years now.
87 197
88 - aio_open gives a fd, but all other functions expect a perl filehandle. 198 - aio_open gives a fd, but all other functions expect a perl filehandle.
89 199
90SEE ALSO 200SEE ALSO
91 Coro. 201 Coro, IO::AIO.
92 202
93AUTHOR 203AUTHOR
94 Marc Lehmann <schmorp@schmorp.de> 204 Marc Lehmann <schmorp@schmorp.de>
95 http://home.schmorp.de/ 205 http://home.schmorp.de/
96 206

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