[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_sendfile $out_fh, $in_fh, $in_offset, $length, $callback
        Tries to copy $length bytes from $in_fh to $out_fh. It starts
        reading at byte offset $in_offset, and starts writing at the current
        file offset of $out_fh. Because of that, it is not safe to issue
        more than one "aio_sendfile" per $out_fh, as they will interfere
        with each other.

        This call tries to make use of a native "sendfile" syscall to
        provide zero-copy operation. For this to work, $out_fh should refer
        to a socket, and $in_fh should refer to mmap'able file.

        If the native sendfile call fails or is not implemented, it will be
        emulated, so you can call "aio_sendfile" on any type of filehandle
        regardless of the limitations of the operating system.

        Please note, however, that "aio_sendfile" can read more bytes from
        $in_fh than are written, and there is no way to find out how many
        bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
        only provides the number of bytes written to $out_fh. Only if the
        result value equals $length one can assume that $length bytes have
        been read.

    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 current
        default is 4, which means four asynchronous operations can be done
        at one time (the number of outstanding operations, however, is
        unlimited).

        IO::AIO starts threads only on demand, when an AIO request is queued
        and no free thread exists.

        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 most circumstances you don't need to call this function, as
        the module selects a default that is suitable for low to moderate
        load.

    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, this function
        kills them. This function blocks until the limit is reached.

        While $nthreads are zero, aio requests get queued but not executed
        until the number of threads has been increased again.

        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 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 (so the requests started before the fork will only be handled in
    the parent). Threats will be started on demand until the limit ste in
    the parent process has been reached again.

SEE ALSO
    Coro, Linux::AIO.

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

Revision:	1.12
Committed:	Tue Aug 23 00:05:00 2005 UTC (18 years, 9 months ago) by root
Branch:	MAIN
Changes since 1.11:	+22 -0 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_sendfile $out_fh, $in_fh, $in_offset, $length, $callback
136	Tries to copy $length bytes from $in_fh to $out_fh. It starts
137	reading at byte offset $in_offset, and starts writing at the current
138	file offset of $out_fh. Because of that, it is not safe to issue
139	more than one "aio_sendfile" per $out_fh, as they will interfere
140	with each other.
141
142	This call tries to make use of a native "sendfile" syscall to
143	provide zero-copy operation. For this to work, $out_fh should refer
144	to a socket, and $in_fh should refer to mmap'able file.
145
146	If the native sendfile call fails or is not implemented, it will be
147	emulated, so you can call "aio_sendfile" on any type of filehandle
148	regardless of the limitations of the operating system.
149
150	Please note, however, that "aio_sendfile" can read more bytes from
151	$in_fh than are written, and there is no way to find out how many
152	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
153	only provides the number of bytes written to $out_fh. Only if the
154	result value equals $length one can assume that $length bytes have
155	been read.
156
157	aio_readahead $fh,$offset,$length, $callback
158	"aio_readahead" populates the page cache with data from a file so
159	that subsequent reads from that file will not block on disk I/O. The
160	$offset argument specifies the starting point from which data is to
161	be read and $length specifies the number of bytes to be read. I/O is
162	performed in whole pages, so that offset is effectively rounded down
163	to a page boundary and bytes are read up to the next page boundary
164	greater than or equal to (off-set+length). "aio_readahead" does not
165	read beyond the end of the file. The current file offset of the file
166	is left unchanged.
167
168	If that syscall doesn't exist (likely if your OS isn't Linux) it
169	will be emulated by simply reading the data, which would have a
170	similar effect.
171
172	aio_stat $fh_or_path, $callback
173	aio_lstat $fh, $callback
174	Works like perl's "stat" or "lstat" in void context. The callback
175	will be called after the stat and the results will be available
176	using "stat _" or "-s _" etc...
177
178	The pathname passed to "aio_stat" must be absolute. See API NOTES,
179	above, for an explanation.
180
181	Currently, the stats are always 64-bit-stats, i.e. instead of
182	returning an error when stat'ing a large file, the results will be
183	silently truncated unless perl itself is compiled with large file
184	support.
185
186	Example: Print the length of /etc/passwd:
187
188	aio_stat "/etc/passwd", sub {
189	$_[0] and die "stat failed: $!";
190	print "size is ", -s _, "\n";
191	};
192
193	aio_unlink $pathname, $callback
194	Asynchronously unlink (delete) a file and call the callback with the
195	result code.
196
197	aio_rmdir $pathname, $callback
198	Asynchronously rmdir (delete) a directory and call the callback with
199	the result code.
200
201	aio_fsync $fh, $callback
202	Asynchronously call fsync on the given filehandle and call the
203	callback with the fsync result code.
204
205	aio_fdatasync $fh, $callback
206	Asynchronously call fdatasync on the given filehandle and call the
207	callback with the fdatasync result code.
208
209	If this call isn't available because your OS lacks it or it couldn't
210	be detected, it will be emulated by calling "fsync" instead.
211
212	SUPPORT FUNCTIONS
213	$fileno = IO::AIO::poll_fileno
214	Return the request result pipe file descriptor. This filehandle
215	must be polled for reading by some mechanism outside this module
216	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
217	becomes readable you have to call "poll_cb" to check the results.
218
219	See "poll_cb" for an example.
220
221	IO::AIO::poll_cb
222	Process all outstanding events on the result pipe. You have to call
223	this regularly. Returns the number of events processed. Returns
224	immediately when no events are outstanding.
225
226	Example: Install an Event watcher that automatically calls
227	IO::AIO::poll_cb with high priority:
228
229	Event->io (fd => IO::AIO::poll_fileno,
230	poll => 'r', async => 1,
231	cb => \&IO::AIO::poll_cb);
232
233	IO::AIO::poll_wait
234	Wait till the result filehandle becomes ready for reading (simply
235	does a "select" on the filehandle. This is useful if you want to
236	synchronously wait for some requests to finish).
237
238	See "nreqs" for an example.
239
240	IO::AIO::nreqs
241	Returns the number of requests currently outstanding (i.e. for which
242	their callback has not been invoked yet).
243
244	Example: wait till there are no outstanding requests anymore:
245
246	IO::AIO::poll_wait, IO::AIO::poll_cb
247	while IO::AIO::nreqs;
248
249	IO::AIO::flush
250	Wait till all outstanding AIO requests have been handled.
251
252	Strictly equivalent to:
253
254	IO::AIO::poll_wait, IO::AIO::poll_cb
255	while IO::AIO::nreqs;
256
257	IO::AIO::poll
258	Waits until some requests have been handled.
259
260	Strictly equivalent to:
261
262	IO::AIO::poll_wait, IO::AIO::poll_cb
263	if IO::AIO::nreqs;
264
265	IO::AIO::min_parallel $nthreads
266	Set the minimum number of AIO threads to $nthreads. The current
267	default is 4, which means four asynchronous operations can be done
268	at one time (the number of outstanding operations, however, is
269	unlimited).
270
271	IO::AIO starts threads only on demand, when an AIO request is queued
272	and no free thread exists.
273
274	It is recommended to keep the number of threads low, as some Linux
275	kernel versions will scale negatively with the number of threads
276	(higher parallelity => MUCH higher latency). With current Linux 2.6
277	versions, 4-32 threads should be fine.
278
279	Under most circumstances you don't need to call this function, as
280	the module selects a default that is suitable for low to moderate
281	load.
282
283	IO::AIO::max_parallel $nthreads
284	Sets the maximum number of AIO threads to $nthreads. If more than
285	the specified number of threads are currently running, this function
286	kills them. This function blocks until the limit is reached.
287
288	While $nthreads are zero, aio requests get queued but not executed
289	until the number of threads has been increased again.
290
291	This module automatically runs "max_parallel 0" at program end, to
292	ensure that all threads are killed and that there are no outstanding
293	requests.
294
295	Under normal circumstances you don't need to call this function.
296
297	$oldnreqs = IO::AIO::max_outstanding $nreqs
298	Sets the maximum number of outstanding requests to $nreqs. If you
299	try to queue up more than this number of requests, the caller will
300	block until some requests have been handled.
301
302	The default is very large, so normally there is no practical limit.
303	If you queue up many requests in a loop it often improves speed if
304	you set this to a relatively low number, such as 100.
305
306	Under normal circumstances you don't need to call this function.
307
308	FORK BEHAVIOUR
309	Before the fork, IO::AIO enters a quiescent state where no requests can
310	be added in other threads and no results will be processed. After the
311	fork the parent simply leaves the quiescent state and continues
312	request/result processing, while the child clears the request/result
313	queue (so the requests started before the fork will only be handled in
314	the parent). Threats will be started on demand until the limit ste in
315	the parent process has been reached again.
316
317	SEE ALSO
318	Coro, Linux::AIO.
319
320	AUTHOR
321	Marc Lehmann <schmorp@schmorp.de>
322	http://home.schmorp.de/
323