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Revision: 1.4
Committed: Sun Jul 10 01:02:51 2005 UTC (19 years, 4 months ago) by root
Branch: MAIN
Changes since 1.3: +83 -4 lines
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# Content
1 NAME
2 Linux::AIO - linux-specific aio implemented using clone
3
4 SYNOPSIS
5 use Linux::AIO;
6
7 DESCRIPTION
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
10 Linux does not yet support these in the kernel (even as of 2.6.12, only
11 O_DIRECT files are supported) and even if, it would only allow aio_read
12 and write, not open, stat and so on.
13
14 Instead, in this module a number of (non-posix) threads are started that
15 execute your read/writes and signal their completion. You don't need
16 thread support in your libc or perl, and the threads created by this
17 module will not be visible to the pthreads library.
18
19 NOTICE: the threads created by this module will automatically be killed
20 when the thread calling min_parallel exits. Make sure you only ever call
21 min_parallel from the same thread that loaded this module.
22
23 Although the module will work with in the presence of other threads, it
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 Linux::AIO::min_parallel $nthreads
39 Set the minimum number of AIO threads to $nthreads. The default is
40 1, which means a single asynchronous operation can be done at one
41 time (the number of outstanding operations, however, is unlimited).
42
43 It is recommended to keep the number of threads low, as some linux
44 kernel versions will scale negatively with the number of threads
45 (higher parallelity => MUCH higher latency).
46
47 Under normal circumstances you don't need to call this function, as
48 this module automatically starts a single async thread.
49
50 Linux::AIO::max_parallel $nthreads
51 Sets the maximum number of AIO threads to $nthreads. If more than
52 the specified number of threads are currently running, kill them.
53 This function blocks until the limit is reached.
54
55 This module automatically runs "max_parallel 0" at program end, to
56 ensure that all threads are killed and that there are no outstanding
57 requests.
58
59 Under normal circumstances you don't need to call this function.
60
61 $fileno = Linux::AIO::poll_fileno
62 Return the *request result pipe filehandle*. This filehandle must be
63 polled for reading by some mechanism outside this module (e.g. Event
64 or select, see below). If the pipe becomes readable you have to call
65 "poll_cb" to check the results.
66
67 See "poll_cb" for an example.
68
69 Linux::AIO::poll_cb
70 Process all outstanding events on the result pipe. You have to call
71 this regularly. Returns the number of events processed. Returns
72 immediately when no events are outstanding.
73
74 You can use Event to multiplex, e.g.:
75
76 Event->io (fd => Linux::AIO::poll_fileno,
77 poll => 'r', async => 1,
78 cb => \&Linux::AIO::poll_cb);
79
80 Linux::AIO::poll_wait
81 Wait till the result filehandle becomes ready for reading (simply
82 does a select on the filehandle. This is useful if you want to
83 synchronously wait for some requests to finish).
84
85 See "nreqs" for an example.
86
87 Linux::AIO::nreqs
88 Returns the number of requests currently outstanding.
89
90 Example: wait till there are no outstanding requests anymore:
91
92 Linux::AIO::poll_wait while Linux::AIO::nreqs;
93
94 aio_open $pathname, $flags, $mode, $callback
95 Asynchronously open or create a file and call the callback with the
96 filedescriptor (NOT a perl filehandle, sorry for that, but watch
97 out, this might change in the future).
98
99 The $mode argument is a bitmask. See the "Fcntl" module for a list.
100 They are the same as used in "sysopen".
101
102 Example:
103
104 aio_open "/etc/passwd", O_RDONLY, 0, sub {
105 if ($_[0] >= 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";
109 ...
110 } else {
111 die "open failed: $!\n";
112 }
113 };
114
115 aio_close $fh, $callback
116 Asynchronously close a file and call the callback with the result
117 code.
118
119 aio_read $fh,$offset,$length, $data,$dataoffset,$callback
120 aio_write $fh,$offset,$length, $data,$dataoffset,$callback
121 Reads or writes "length" bytes from the specified "fh" and "offset"
122 into the scalar given by "data" and offset "dataoffset" and calls
123 the callback without the actual number of bytes read (or -1 on
124 error, just like the syscall).
125
126 Example: Read 15 bytes at offset 7 into scalar $buffer, strating at
127 offset 0 within the scalar:
128
129 aio_read $fh, 7, 15, $buffer, 0, sub {
130 $_[0] >= 0 or die "read error: $!";
131 print "read <$buffer>\n";
132 };
133
134 aio_readahead $fh,$offset,$length, $callback
135 Asynchronously reads the specified byte range into the page cache,
136 using the "readahead" syscall.
137
138 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
140 $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
142 performed in whole pages, so that offset is effectively rounded down
143 to a page boundary and bytes are read up to the next page boundary
144 greater than or equal to (off-set+length). aio_readahead() does not
145 read beyond the end of the file. The current file offset of the file
146 is left unchanged.
147
148 aio_stat $fh_or_path, $callback
149 aio_lstat $fh, $callback
150 Works like perl's "stat" or "lstat" in void context. The callback
151 will be called after the stat and the results will be available
152 using "stat _" or "-s _" etc...
153
154 Currently, the stats are always 64-bit-stats, i.e. instead of
155 returning an error when stat'ing a large file, the results will be
156 silently truncated unless perl itself is compiled with large file
157 support.
158
159 Example: Print the length of /etc/passwd:
160
161 aio_stat "/etc/passwd", sub {
162 $_[0] and die "stat failed: $!";
163 print "size is ", -s _, "\n";
164 };
165
166 aio_unlink $pathname, $callback
167 Asynchronously unlink (delete) a file and call the callback with the
168 result code.
169
170 aio_fsync $fh, $callback
171 Asynchronously call fsync on the given filehandle and call the
172 callback with the fsync result code.
173
174 aio_fdatasync $fh, $callback
175 Asynchronously call fdatasync on the given filehandle and call the
176 callback with the fdatasync result code.
177
178 BUGS
179 This module has been extensively tested in a large and very busy
180 webserver for many years now.
181
182 - aio_open gives a fd, but all other functions expect a perl filehandle.
183
184 SEE ALSO
185 Coro.
186
187 AUTHOR
188 Marc Lehmann <schmorp@schmorp.de>
189 http://home.schmorp.de/
190