[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, always
    call "poll_cb" from within the same thread, or never call "poll_cb" (or
    other "aio_" functions) recursively.

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 expecting a filehandle keep a copy of the filehandle
    internally until the request has finished.

    The pathnames you pass to these routines *must* be absolute and encoded
    in byte form. The reason for the former 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.

    To encode pathnames to byte form, either make sure you either: a) always
    pass in filenames you got from outside (command line, readdir etc.), b)
    are ASCII or ISO 8859-1, c) use the Encode module and encode your
    pathnames to the locale (or other) encoding in effect in the user
    environment, d) use Glib::filename_from_unicode on unicode filenames or
    e) use something else.

    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 $flags argument is a bitmask. See the "Fcntl" module for a list.
        They are the same as used by "sysopen".

        Likewise, $mode specifies the mode of the newly created file, if it
        didn't exist and "O_CREAT" has been given, just like perl's
        "sysopen", except that it is mandatory (i.e. use 0 if you don't
        create new files, and 0666 or 0777 if you do).

        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
        another time when the filehandle is destroyed. Normally, you can
        safely call perls "close" or just let filehandles go out of scope.

        This is supposed to be a bug in the API, so that might change. It's
        therefore best to avoid this function.

    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).

        The $data scalar *MUST NOT* be modified in any way while the request
        is outstanding. Modifying it can result in segfaults or WW3 (if the
        necessary/optional hardware is installed).

        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
        "aio_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.

        If that syscall doesn't exist (likely if your OS isn't Linux) it
        will be emulated by simply reading the data, which would have a
        similar effect.

    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_rmdir $pathname, $callback
        Asynchronously rmdir (delete) a directory 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.

        If this call isn't available because your OS lacks it or it couldn't
        be detected, it will be emulated by calling "fsync" instead.

  SUPPORT FUNCTIONS
    $fileno = IO::AIO::poll_fileno
        Return the *request result pipe file descriptor*. This filehandle
        must be polled for reading by some mechanism outside this module
        (e.g. Event or select, see below or the SYNOPSIS). 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.

        Example: Install an Event watcher that automatically calls
        IO::AIO::poll_cb with high priority:

           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 (i.e. for which
        their callback has not been invoked yet).

        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.

  FORK BEHAVIOUR
    Before the fork IO::AIO enters a quiescent state where no requests can
    be added in other threads and no results will be processed. After the
    fork the parent simply leaves the quiescent state and continues
    request/result processing, while the child clears the request/result
    queue and starts the same number of threads as were in use by the
    parent.

SEE ALSO
    Coro, Linux::AIO.

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

Revision:	1.10
Committed:	Wed Aug 17 05:26:20 2005 UTC (18 years, 9 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_3, rel-1_4
Changes since 1.9:	+10 -3 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, always
51	call "poll_cb" from within the same thread, or never call "poll_cb" (or
52	other "aio_" functions) recursively.
53
54	FUNCTIONS
55	AIO FUNCTIONS
56	All the "aio_*" calls are more or less thin wrappers around the syscall
57	with the same name (sans "aio_"). The arguments are similar or
58	identical, and they all accept an additional (and optional) $callback
59	argument which must be a code reference. This code reference will get
60	called with the syscall return code (e.g. most syscalls return -1 on
61	error, unlike perl, which usually delivers "false") as it's sole
62	argument when the given syscall has been executed asynchronously.
63
64	All functions expecting a filehandle keep a copy of the filehandle
65	internally until the request has finished.
66
67	The pathnames you pass to these routines must be absolute and encoded
68	in byte form. The reason for the former is that at the time the request
69	is being executed, the current working directory could have changed.
70	Alternatively, you can make sure that you never change the current
71	working directory.
72
73	To encode pathnames to byte form, either make sure you either: a) always
74	pass in filenames you got from outside (command line, readdir etc.), b)
75	are ASCII or ISO 8859-1, c) use the Encode module and encode your
76	pathnames to the locale (or other) encoding in effect in the user
77	environment, d) use Glib::filename_from_unicode on unicode filenames or
78	e) use something else.
79
80	aio_open $pathname, $flags, $mode, $callback
81	Asynchronously open or create a file and call the callback with a
82	newly created filehandle for the file.
83
84	The pathname passed to "aio_open" must be absolute. See API NOTES,
85	above, for an explanation.
86
87	The $flags argument is a bitmask. See the "Fcntl" module for a list.
88	They are the same as used by "sysopen".
89
90	Likewise, $mode specifies the mode of the newly created file, if it
91	didn't exist and "O_CREAT" has been given, just like perl's
92	"sysopen", except that it is mandatory (i.e. use 0 if you don't
93	create new files, and 0666 or 0777 if you do).
94
95	Example:
96
97	aio_open "/etc/passwd", O_RDONLY, 0, sub {
98	if ($_[0]) {
99	print "open successful, fh is $_[0]\n";
100	...
101	} else {
102	die "open failed: $!\n";
103	}
104	};
105
106	aio_close $fh, $callback
107	Asynchronously close a file and call the callback with the result
108	code. WARNING: although accepted, you should not pass in a perl
109	filehandle here, as perl will likely close the file descriptor
110	another time when the filehandle is destroyed. Normally, you can
111	safely call perls "close" or just let filehandles go out of scope.
112
113	This is supposed to be a bug in the API, so that might change. It's
114	therefore best to avoid this function.
115
116	aio_read $fh,$offset,$length, $data,$dataoffset,$callback
117	aio_write $fh,$offset,$length, $data,$dataoffset,$callback
118	Reads or writes "length" bytes from the specified "fh" and "offset"
119	into the scalar given by "data" and offset "dataoffset" and calls
120	the callback without the actual number of bytes read (or -1 on
121	error, just like the syscall).
122
123	The $data scalar MUST NOT be modified in any way while the request
124	is outstanding. Modifying it can result in segfaults or WW3 (if the
125	necessary/optional hardware is installed).
126
127	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
128	offset 0 within the scalar:
129
130	aio_read $fh, 7, 15, $buffer, 0, sub {
131	$_[0] > 0 or die "read error: $!";
132	print "read $_[0] bytes: <$buffer>\n";
133	};
134
135	aio_readahead $fh,$offset,$length, $callback
136	"aio_readahead" populates the page cache with data from a file so
137	that subsequent reads from that file will not block on disk I/O. The
138	$offset argument specifies the starting point from which data is to
139	be read and $length specifies the number of bytes to be read. I/O is
140	performed in whole pages, so that offset is effectively rounded down
141	to a page boundary and bytes are read up to the next page boundary
142	greater than or equal to (off-set+length). "aio_readahead" does not
143	read beyond the end of the file. The current file offset of the file
144	is left unchanged.
145
146	If that syscall doesn't exist (likely if your OS isn't Linux) it
147	will be emulated by simply reading the data, which would have a
148	similar effect.
149
150	aio_stat $fh_or_path, $callback
151	aio_lstat $fh, $callback
152	Works like perl's "stat" or "lstat" in void context. The callback
153	will be called after the stat and the results will be available
154	using "stat _" or "-s _" etc...
155
156	The pathname passed to "aio_stat" must be absolute. See API NOTES,
157	above, for an explanation.
158
159	Currently, the stats are always 64-bit-stats, i.e. instead of
160	returning an error when stat'ing a large file, the results will be
161	silently truncated unless perl itself is compiled with large file
162	support.
163
164	Example: Print the length of /etc/passwd:
165
166	aio_stat "/etc/passwd", sub {
167	$_[0] and die "stat failed: $!";
168	print "size is ", -s _, "\n";
169	};
170
171	aio_unlink $pathname, $callback
172	Asynchronously unlink (delete) a file and call the callback with the
173	result code.
174
175	aio_rmdir $pathname, $callback
176	Asynchronously rmdir (delete) a directory and call the callback with
177	the result code.
178
179	aio_fsync $fh, $callback
180	Asynchronously call fsync on the given filehandle and call the
181	callback with the fsync result code.
182
183	aio_fdatasync $fh, $callback
184	Asynchronously call fdatasync on the given filehandle and call the
185	callback with the fdatasync result code.
186
187	If this call isn't available because your OS lacks it or it couldn't
188	be detected, it will be emulated by calling "fsync" instead.
189
190	SUPPORT FUNCTIONS
191	$fileno = IO::AIO::poll_fileno
192	Return the request result pipe file descriptor. This filehandle
193	must be polled for reading by some mechanism outside this module
194	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
195	becomes readable you have to call "poll_cb" to check the results.
196
197	See "poll_cb" for an example.
198
199	IO::AIO::poll_cb
200	Process all outstanding events on the result pipe. You have to call
201	this regularly. Returns the number of events processed. Returns
202	immediately when no events are outstanding.
203
204	Example: Install an Event watcher that automatically calls
205	IO::AIO::poll_cb with high priority:
206
207	Event->io (fd => IO::AIO::poll_fileno,
208	poll => 'r', async => 1,
209	cb => \&IO::AIO::poll_cb);
210
211	IO::AIO::poll_wait
212	Wait till the result filehandle becomes ready for reading (simply
213	does a "select" on the filehandle. This is useful if you want to
214	synchronously wait for some requests to finish).
215
216	See "nreqs" for an example.
217
218	IO::AIO::nreqs
219	Returns the number of requests currently outstanding (i.e. for which
220	their callback has not been invoked yet).
221
222	Example: wait till there are no outstanding requests anymore:
223
224	IO::AIO::poll_wait, IO::AIO::poll_cb
225	while IO::AIO::nreqs;
226
227	IO::AIO::flush
228	Wait till all outstanding AIO requests have been handled.
229
230	Strictly equivalent to:
231
232	IO::AIO::poll_wait, IO::AIO::poll_cb
233	while IO::AIO::nreqs;
234
235	IO::AIO::poll
236	Waits until some requests have been handled.
237
238	Strictly equivalent to:
239
240	IO::AIO::poll_wait, IO::AIO::poll_cb
241	if IO::AIO::nreqs;
242
243	IO::AIO::min_parallel $nthreads
244	Set the minimum number of AIO threads to $nthreads. The default is
245	1, which means a single asynchronous operation can be done at one
246	time (the number of outstanding operations, however, is unlimited).
247
248	It is recommended to keep the number of threads low, as some Linux
249	kernel versions will scale negatively with the number of threads
250	(higher parallelity => MUCH higher latency). With current Linux 2.6
251	versions, 4-32 threads should be fine.
252
253	Under normal circumstances you don't need to call this function, as
254	this module automatically starts some threads (the exact number
255	might change, and is currently 4).
256
257	IO::AIO::max_parallel $nthreads
258	Sets the maximum number of AIO threads to $nthreads. If more than
259	the specified number of threads are currently running, kill them.
260	This function blocks until the limit is reached.
261
262	This module automatically runs "max_parallel 0" at program end, to
263	ensure that all threads are killed and that there are no outstanding
264	requests.
265
266	Under normal circumstances you don't need to call this function.
267
268	$oldnreqs = IO::AIO::max_outstanding $nreqs
269	Sets the maximum number of outstanding requests to $nreqs. If you
270	try to queue up more than this number of requests, the caller will
271	block until some requests have been handled.
272
273	The default is very large, so normally there is no practical limit.
274	If you queue up many requests in a loop it it often improves speed
275	if you set this to a relatively low number, such as 100.
276
277	Under normal circumstances you don't need to call this function.
278
279	FORK BEHAVIOUR
280	Before the fork IO::AIO enters a quiescent state where no requests can
281	be added in other threads and no results will be processed. After the
282	fork the parent simply leaves the quiescent state and continues
283	request/result processing, while the child clears the request/result
284	queue and starts the same number of threads as were in use by the
285	parent.
286
287	SEE ALSO
288	Coro, Linux::AIO.
289
290	AUTHOR
291	Marc Lehmann <schmorp@schmorp.de>
292	http://home.schmorp.de/
293