[ViewVC] Contents of: cvs/IO-AIO/README

NAME
    IO::AIO - Asynchronous Input/Output

SYNOPSIS
     use IO::AIO;

     aio_open "/etc/passwd", O_RDONLY, 0, sub {
        my ($fh) = @_;
        ...
     };

     aio_unlink "/tmp/file", sub { };

     aio_read $fh, 30000, 1024, $buffer, 0, sub {
        $_[0] > 0 or die "read error: $!";
     };

     # Event
     Event->io (fd => IO::AIO::poll_fileno,
                poll => 'r',
                cb => \&IO::AIO::poll_cb);

     # Glib/Gtk2
     add_watch Glib::IO IO::AIO::poll_fileno,
               in => sub { IO::AIO::poll_cb, 1 };

     # Tk
     Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
                               readable => \&IO::AIO::poll_cb);

     # Danga::Socket
     Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
                                 \&IO::AIO::poll_cb);

DESCRIPTION
    This module implements asynchronous I/O using whatever means your
    operating system supports.

    Currently, a number of threads are started that execute your read/writes
    and signal their completion. You don't need thread support in your libc
    or perl, and the threads created by this module will not be visible to
    the pthreads library. In the future, this module might make use of the
    native aio functions available on many operating systems. However, they
    are often not well-supported (Linux doesn't allow them on normal files
    currently, for example), and they would only support aio_read and
    aio_write, so the remaining functionality would have to be implemented
    using threads anyway.

    Although the module will work with in the presence of other threads, it
    is currently not reentrant, so use appropriate locking yourself.

FUNCTIONS
  AIO FUNCTIONS
    All the "aio_*" calls are more or less thin wrappers around the syscall
    with the same name (sans "aio_"). The arguments are similar or
    identical, and they all accept an additional (and optional) $callback
    argument which must be a code reference. This code reference will get
    called with the syscall return code (e.g. most syscalls return -1 on
    error, unlike perl, which usually delivers "false") as it's sole
    argument when the given syscall has been executed asynchronously.

    All functions that expect a filehandle will also accept a file
    descriptor.

    The filenames you pass to these routines *must* be absolute. The reason
    is that at the time the request is being executed, the current working
    directory could have changed. Alternatively, you can make sure that you
    never change the current working directory.

    aio_open $pathname, $flags, $mode, $callback
        Asynchronously open or create a file and call the callback with a
        newly created filehandle for the file.

        The pathname passed to "aio_open" must be absolute. See API NOTES,
        above, for an explanation.

        The $mode argument is a bitmask. See the "Fcntl" module for a list.
        They are the same as used in "sysopen".

        Example:

           aio_open "/etc/passwd", O_RDONLY, 0, sub {
              if ($_[0]) {
                 print "open successful, fh is $_[0]\n";
                 ...
              } else {
                 die "open failed: $!\n";
              }
           };

    aio_close $fh, $callback
        Asynchronously close a file and call the callback with the result
        code. *WARNING:* although accepted, you should not pass in a perl
        filehandle here, as perl will likely close the file descriptor
        itself when the filehandle is destroyed. Normally, you can safely
        call perls "close" or just let filehandles go out of scope.

    aio_read $fh,$offset,$length, $data,$dataoffset,$callback
    aio_write $fh,$offset,$length, $data,$dataoffset,$callback
        Reads or writes "length" bytes from the specified "fh" and "offset"
        into the scalar given by "data" and offset "dataoffset" and calls
        the callback without the actual number of bytes read (or -1 on
        error, just like the syscall).

        Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
        offset 0 within the scalar:

           aio_read $fh, 7, 15, $buffer, 0, sub {
              $_[0] > 0 or die "read error: $!";
              print "read $_[0] bytes: <$buffer>\n";
           };

    aio_readahead $fh,$offset,$length, $callback
        Asynchronously reads the specified byte range into the page cache,
        using the "readahead" syscall. If that syscall doesn't exist (likely
        if your OS isn't Linux) the status will be -1 and $! is set to
        ENOSYS.

        readahead() populates the page cache with data from a file so that
        subsequent reads from that file will not block on disk I/O. The
        $offset argument specifies the starting point from which data is to
        be read and $length specifies the number of bytes to be read. I/O is
        performed in whole pages, so that offset is effectively rounded down
        to a page boundary and bytes are read up to the next page boundary
        greater than or equal to (off-set+length). aio_readahead() does not
        read beyond the end of the file. The current file offset of the file
        is left unchanged.

    aio_stat $fh_or_path, $callback
    aio_lstat $fh, $callback
        Works like perl's "stat" or "lstat" in void context. The callback
        will be called after the stat and the results will be available
        using "stat _" or "-s _" etc...

        The pathname passed to "aio_stat" must be absolute. See API NOTES,
        above, for an explanation.

        Currently, the stats are always 64-bit-stats, i.e. instead of
        returning an error when stat'ing a large file, the results will be
        silently truncated unless perl itself is compiled with large file
        support.

        Example: Print the length of /etc/passwd:

           aio_stat "/etc/passwd", sub {
              $_[0] and die "stat failed: $!";
              print "size is ", -s _, "\n";
           };

    aio_unlink $pathname, $callback
        Asynchronously unlink (delete) a file and call the callback with the
        result code.

    aio_fsync $fh, $callback
        Asynchronously call fsync on the given filehandle and call the
        callback with the fsync result code.

    aio_fdatasync $fh, $callback
        Asynchronously call fdatasync on the given filehandle and call the
        callback with the fdatasync result code.

  SUPPORT FUNCTIONS
    $fileno = IO::AIO::poll_fileno
        Return the *request result pipe filehandle*. This filehandle must be
        polled for reading by some mechanism outside this module (e.g. Event
        or select, see below). If the pipe becomes readable you have to call
        "poll_cb" to check the results.

        See "poll_cb" for an example.

    IO::AIO::poll_cb
        Process all outstanding events on the result pipe. You have to call
        this regularly. Returns the number of events processed. Returns
        immediately when no events are outstanding.

        You can use Event to multiplex, e.g.:

           Event->io (fd => IO::AIO::poll_fileno,
                      poll => 'r', async => 1,
                      cb => \&IO::AIO::poll_cb);

    IO::AIO::poll_wait
        Wait till the result filehandle becomes ready for reading (simply
        does a select on the filehandle. This is useful if you want to
        synchronously wait for some requests to finish).

        See "nreqs" for an example.

    IO::AIO::nreqs
        Returns the number of requests currently outstanding.

        Example: wait till there are no outstanding requests anymore:

           IO::AIO::poll_wait, IO::AIO::poll_cb
              while IO::AIO::nreqs;

    IO::AIO::flush
        Wait till all outstanding AIO requests have been handled.

        Strictly equivalent to:

           IO::AIO::poll_wait, IO::AIO::poll_cb
              while IO::AIO::nreqs;

    IO::AIO::poll
        Waits until some requests have been handled.

        Strictly equivalent to:

           IO::AIO::poll_wait, IO::AIO::poll_cb
              if IO::AIO::nreqs;

    IO::AIO::min_parallel $nthreads
        Set the minimum number of AIO threads to $nthreads. The default is
        1, which means a single asynchronous operation can be done at one
        time (the number of outstanding operations, however, is unlimited).

        It is recommended to keep the number of threads low, as some Linux
        kernel versions will scale negatively with the number of threads
        (higher parallelity => MUCH higher latency). With current Linux 2.6
        versions, 4-32 threads should be fine.

        Under normal circumstances you don't need to call this function, as
        this module automatically starts some threads (the exact number
        might change, and is currently 4).

    IO::AIO::max_parallel $nthreads
        Sets the maximum number of AIO threads to $nthreads. If more than
        the specified number of threads are currently running, kill them.
        This function blocks until the limit is reached.

        This module automatically runs "max_parallel 0" at program end, to
        ensure that all threads are killed and that there are no outstanding
        requests.

        Under normal circumstances you don't need to call this function.

    $oldnreqs = IO::AIO::max_outstanding $nreqs
        Sets the maximum number of outstanding requests to $nreqs. If you
        try to queue up more than this number of requests, the caller will
        block until some requests have been handled.

        The default is very large, so normally there is no practical limit.
        If you queue up many requests in a loop it it often improves speed
        if you set this to a relatively low number, such as 100.

        Under normal circumstances you don't need to call this function.

SEE ALSO
    Coro, Linux::AIO.

AUTHOR
     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de/

Revision:	1.6
Committed:	Mon Jul 11 03:29:39 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_4, rel-0_5
Changes since 1.5:	+30 -9 lines
Log Message:	* empty log message *
#	Content
1	NAME
2	IO::AIO - Asynchronous Input/Output
3
4	SYNOPSIS
5	use IO::AIO;
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	in => sub { IO::AIO::poll_cb, 1 };
26
27	# Tk
28	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
29	readable => \&IO::AIO::poll_cb);
30
31	# Danga::Socket
32	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
33	\&IO::AIO::poll_cb);
34
35	DESCRIPTION
36	This module implements asynchronous I/O using whatever means your
37	operating system supports.
38
39	Currently, a number of threads are started that execute your read/writes
40	and signal their completion. You don't need thread support in your libc
41	or perl, and the threads created by this module will not be visible to
42	the pthreads library. In the future, this module might make use of the
43	native aio functions available on many operating systems. However, they
44	are often not well-supported (Linux doesn't allow them on normal files
45	currently, for example), and they would only support aio_read and
46	aio_write, so the remaining functionality would have to be implemented
47	using threads anyway.
48
49	Although the module will work with in the presence of other threads, it
50	is currently not reentrant, so use appropriate locking yourself.
51
52	FUNCTIONS
53	AIO FUNCTIONS
54	All the "aio_*" calls are more or less thin wrappers around the syscall
55	with the same name (sans "aio_"). The arguments are similar or
56	identical, and they all accept an additional (and optional) $callback
57	argument which must be a code reference. This code reference will get
58	called with the syscall return code (e.g. most syscalls return -1 on
59	error, unlike perl, which usually delivers "false") as it's sole
60	argument when the given syscall has been executed asynchronously.
61
62	All functions that expect a filehandle will also accept a file
63	descriptor.
64
65	The filenames you pass to these routines must be absolute. The reason
66	is that at the time the request is being executed, the current working
67	directory could have changed. Alternatively, you can make sure that you
68	never change the current working directory.
69
70	aio_open $pathname, $flags, $mode, $callback
71	Asynchronously open or create a file and call the callback with a
72	newly created filehandle for the file.
73
74	The pathname passed to "aio_open" must be absolute. See API NOTES,
75	above, for an explanation.
76
77	The $mode argument is a bitmask. See the "Fcntl" module for a list.
78	They are the same as used in "sysopen".
79
80	Example:
81
82	aio_open "/etc/passwd", O_RDONLY, 0, sub {
83	if ($_[0]) {
84	print "open successful, fh is $_[0]\n";
85	...
86	} else {
87	die "open failed: $!\n";
88	}
89	};
90
91	aio_close $fh, $callback
92	Asynchronously close a file and call the callback with the result
93	code. WARNING: although accepted, you should not pass in a perl
94	filehandle here, as perl will likely close the file descriptor
95	itself when the filehandle is destroyed. Normally, you can safely
96	call perls "close" or just let filehandles go out of scope.
97
98	aio_read $fh,$offset,$length, $data,$dataoffset,$callback
99	aio_write $fh,$offset,$length, $data,$dataoffset,$callback
100	Reads or writes "length" bytes from the specified "fh" and "offset"
101	into the scalar given by "data" and offset "dataoffset" and calls
102	the callback without the actual number of bytes read (or -1 on
103	error, just like the syscall).
104
105	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
106	offset 0 within the scalar:
107
108	aio_read $fh, 7, 15, $buffer, 0, sub {
109	$_[0] > 0 or die "read error: $!";
110	print "read $_[0] bytes: <$buffer>\n";
111	};
112
113	aio_readahead $fh,$offset,$length, $callback
114	Asynchronously reads the specified byte range into the page cache,
115	using the "readahead" syscall. If that syscall doesn't exist (likely
116	if your OS isn't Linux) the status will be -1 and $! is set to
117	ENOSYS.
118
119	readahead() populates the page cache with data from a file so that
120	subsequent reads from that file will not block on disk I/O. The
121	$offset argument specifies the starting point from which data is to
122	be read and $length specifies the number of bytes to be read. I/O is
123	performed in whole pages, so that offset is effectively rounded down
124	to a page boundary and bytes are read up to the next page boundary
125	greater than or equal to (off-set+length). aio_readahead() does not
126	read beyond the end of the file. The current file offset of the file
127	is left unchanged.
128
129	aio_stat $fh_or_path, $callback
130	aio_lstat $fh, $callback
131	Works like perl's "stat" or "lstat" in void context. The callback
132	will be called after the stat and the results will be available
133	using "stat _" or "-s _" etc...
134
135	The pathname passed to "aio_stat" must be absolute. See API NOTES,
136	above, for an explanation.
137
138	Currently, the stats are always 64-bit-stats, i.e. instead of
139	returning an error when stat'ing a large file, the results will be
140	silently truncated unless perl itself is compiled with large file
141	support.
142
143	Example: Print the length of /etc/passwd:
144
145	aio_stat "/etc/passwd", sub {
146	$_[0] and die "stat failed: $!";
147	print "size is ", -s _, "\n";
148	};
149
150	aio_unlink $pathname, $callback
151	Asynchronously unlink (delete) a file and call the callback with the
152	result code.
153
154	aio_fsync $fh, $callback
155	Asynchronously call fsync on the given filehandle and call the
156	callback with the fsync result code.
157
158	aio_fdatasync $fh, $callback
159	Asynchronously call fdatasync on the given filehandle and call the
160	callback with the fdatasync result code.
161
162	SUPPORT FUNCTIONS
163	$fileno = IO::AIO::poll_fileno
164	Return the request result pipe filehandle. This filehandle must be
165	polled for reading by some mechanism outside this module (e.g. Event
166	or select, see below). If the pipe becomes readable you have to call
167	"poll_cb" to check the results.
168
169	See "poll_cb" for an example.
170
171	IO::AIO::poll_cb
172	Process all outstanding events on the result pipe. You have to call
173	this regularly. Returns the number of events processed. Returns
174	immediately when no events are outstanding.
175
176	You can use Event to multiplex, e.g.:
177
178	Event->io (fd => IO::AIO::poll_fileno,
179	poll => 'r', async => 1,
180	cb => \&IO::AIO::poll_cb);
181
182	IO::AIO::poll_wait
183	Wait till the result filehandle becomes ready for reading (simply
184	does a select on the filehandle. This is useful if you want to
185	synchronously wait for some requests to finish).
186
187	See "nreqs" for an example.
188
189	IO::AIO::nreqs
190	Returns the number of requests currently outstanding.
191
192	Example: wait till there are no outstanding requests anymore:
193
194	IO::AIO::poll_wait, IO::AIO::poll_cb
195	while IO::AIO::nreqs;
196
197	IO::AIO::flush
198	Wait till all outstanding AIO requests have been handled.
199
200	Strictly equivalent to:
201
202	IO::AIO::poll_wait, IO::AIO::poll_cb
203	while IO::AIO::nreqs;
204
205	IO::AIO::poll
206	Waits until some requests have been handled.
207
208	Strictly equivalent to:
209
210	IO::AIO::poll_wait, IO::AIO::poll_cb
211	if IO::AIO::nreqs;
212
213	IO::AIO::min_parallel $nthreads
214	Set the minimum number of AIO threads to $nthreads. The default is
215	1, which means a single asynchronous operation can be done at one
216	time (the number of outstanding operations, however, is unlimited).
217
218	It is recommended to keep the number of threads low, as some Linux
219	kernel versions will scale negatively with the number of threads
220	(higher parallelity => MUCH higher latency). With current Linux 2.6
221	versions, 4-32 threads should be fine.
222
223	Under normal circumstances you don't need to call this function, as
224	this module automatically starts some threads (the exact number
225	might change, and is currently 4).
226
227	IO::AIO::max_parallel $nthreads
228	Sets the maximum number of AIO threads to $nthreads. If more than
229	the specified number of threads are currently running, kill them.
230	This function blocks until the limit is reached.
231
232	This module automatically runs "max_parallel 0" at program end, to
233	ensure that all threads are killed and that there are no outstanding
234	requests.
235
236	Under normal circumstances you don't need to call this function.
237
238	$oldnreqs = IO::AIO::max_outstanding $nreqs
239	Sets the maximum number of outstanding requests to $nreqs. If you
240	try to queue up more than this number of requests, the caller will
241	block until some requests have been handled.
242
243	The default is very large, so normally there is no practical limit.
244	If you queue up many requests in a loop it it often improves speed
245	if you set this to a relatively low number, such as 100.
246
247	Under normal circumstances you don't need to call this function.
248
249	SEE ALSO
250	Coro, Linux::AIO.
251
252	AUTHOR
253	Marc Lehmann <schmorp@schmorp.de>
254	http://home.schmorp.de/
255