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Revision 1.5 by root, Sun Jul 10 17:11:54 2005 UTC

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

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