[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 that expect a filehandle will also accept a file
    descriptor.

    The filenames you pass to these routines *must* be absolute. The reason
    for this 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 $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).

        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".

        "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.

    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. Might set $! to "ENOSYS" if
        "fdatasync" is not available.

  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.

SEE ALSO
    Coro, Linux::AIO.

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

Revision:	1.7
Committed:	Wed Jul 20 21:55:38 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_9, rel-1_0
Changes since 1.6:	+34 -21 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 that expect a filehandle will also accept a file
65	descriptor.
66
67	The filenames you pass to these routines must be absolute. The reason
68	for this is that at the time the request is being executed, the current
69	working directory could have changed. Alternatively, you can make sure
70	that you never change the current working directory.
71
72	aio_open $pathname, $flags, $mode, $callback
73	Asynchronously open or create a file and call the callback with a
74	newly created filehandle for the file.
75
76	The pathname passed to "aio_open" must be absolute. See API NOTES,
77	above, for an explanation.
78
79	The $flags argument is a bitmask. See the "Fcntl" module for a list.
80	They are the same as used by "sysopen".
81
82	Likewise, $mode specifies the mode of the newly created file, if it
83	didn't exist and "O_CREAT" has been given, just like perl's
84	"sysopen", except that it is mandatory (i.e. use 0 if you don't
85	create new files, and 0666 or 0777 if you do).
86
87	Example:
88
89	aio_open "/etc/passwd", O_RDONLY, 0, sub {
90	if ($_[0]) {
91	print "open successful, fh is $_[0]\n";
92	...
93	} else {
94	die "open failed: $!\n";
95	}
96	};
97
98	aio_close $fh, $callback
99	Asynchronously close a file and call the callback with the result
100	code. WARNING: although accepted, you should not pass in a perl
101	filehandle here, as perl will likely close the file descriptor
102	another time when the filehandle is destroyed. Normally, you can
103	safely call perls "close" or just let filehandles go out of scope.
104
105	This is supposed to be a bug in the API, so that might change. It's
106	therefore best to avoid this function.
107
108	aio_read $fh,$offset,$length, $data,$dataoffset,$callback
109	aio_write $fh,$offset,$length, $data,$dataoffset,$callback
110	Reads or writes "length" bytes from the specified "fh" and "offset"
111	into the scalar given by "data" and offset "dataoffset" and calls
112	the callback without the actual number of bytes read (or -1 on
113	error, just like the syscall).
114
115	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
116	offset 0 within the scalar:
117
118	aio_read $fh, 7, 15, $buffer, 0, sub {
119	$_[0] > 0 or die "read error: $!";
120	print "read $_[0] bytes: <$buffer>\n";
121	};
122
123	aio_readahead $fh,$offset,$length, $callback
124	Asynchronously reads the specified byte range into the page cache,
125	using the "readahead" syscall. If that syscall doesn't exist (likely
126	if your OS isn't Linux) the status will be -1 and $! is set to
127	"ENOSYS".
128
129	"aio_readahead" populates the page cache with data from a file so
130	that subsequent reads from that file will not block on disk I/O. The
131	$offset argument specifies the starting point from which data is to
132	be read and $length specifies the number of bytes to be read. I/O is
133	performed in whole pages, so that offset is effectively rounded down
134	to a page boundary and bytes are read up to the next page boundary
135	greater than or equal to (off-set+length). "aio_readahead" does not
136	read beyond the end of the file. The current file offset of the file
137	is left unchanged.
138
139	aio_stat $fh_or_path, $callback
140	aio_lstat $fh, $callback
141	Works like perl's "stat" or "lstat" in void context. The callback
142	will be called after the stat and the results will be available
143	using "stat _" or "-s _" etc...
144
145	The pathname passed to "aio_stat" must be absolute. See API NOTES,
146	above, for an explanation.
147
148	Currently, the stats are always 64-bit-stats, i.e. instead of
149	returning an error when stat'ing a large file, the results will be
150	silently truncated unless perl itself is compiled with large file
151	support.
152
153	Example: Print the length of /etc/passwd:
154
155	aio_stat "/etc/passwd", sub {
156	$_[0] and die "stat failed: $!";
157	print "size is ", -s _, "\n";
158	};
159
160	aio_unlink $pathname, $callback
161	Asynchronously unlink (delete) a file and call the callback with the
162	result code.
163
164	aio_fsync $fh, $callback
165	Asynchronously call fsync on the given filehandle and call the
166	callback with the fsync result code.
167
168	aio_fdatasync $fh, $callback
169	Asynchronously call fdatasync on the given filehandle and call the
170	callback with the fdatasync result code. Might set $! to "ENOSYS" if
171	"fdatasync" is not available.
172
173	SUPPORT FUNCTIONS
174	$fileno = IO::AIO::poll_fileno
175	Return the request result pipe file descriptor. This filehandle
176	must be polled for reading by some mechanism outside this module
177	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
178	becomes readable you have to call "poll_cb" to check the results.
179
180	See "poll_cb" for an example.
181
182	IO::AIO::poll_cb
183	Process all outstanding events on the result pipe. You have to call
184	this regularly. Returns the number of events processed. Returns
185	immediately when no events are outstanding.
186
187	Example: Install an Event watcher that automatically calls
188	IO::AIO::poll_cb with high priority:
189
190	Event->io (fd => IO::AIO::poll_fileno,
191	poll => 'r', async => 1,
192	cb => \&IO::AIO::poll_cb);
193
194	IO::AIO::poll_wait
195	Wait till the result filehandle becomes ready for reading (simply
196	does a "select" on the filehandle. This is useful if you want to
197	synchronously wait for some requests to finish).
198
199	See "nreqs" for an example.
200
201	IO::AIO::nreqs
202	Returns the number of requests currently outstanding (i.e. for which
203	their callback has not been invoked yet).
204
205	Example: wait till there are no outstanding requests anymore:
206
207	IO::AIO::poll_wait, IO::AIO::poll_cb
208	while IO::AIO::nreqs;
209
210	IO::AIO::flush
211	Wait till all outstanding AIO requests have been handled.
212
213	Strictly equivalent to:
214
215	IO::AIO::poll_wait, IO::AIO::poll_cb
216	while IO::AIO::nreqs;
217
218	IO::AIO::poll
219	Waits until some requests have been handled.
220
221	Strictly equivalent to:
222
223	IO::AIO::poll_wait, IO::AIO::poll_cb
224	if IO::AIO::nreqs;
225
226	IO::AIO::min_parallel $nthreads
227	Set the minimum number of AIO threads to $nthreads. The default is
228	1, which means a single asynchronous operation can be done at one
229	time (the number of outstanding operations, however, is unlimited).
230
231	It is recommended to keep the number of threads low, as some Linux
232	kernel versions will scale negatively with the number of threads
233	(higher parallelity => MUCH higher latency). With current Linux 2.6
234	versions, 4-32 threads should be fine.
235
236	Under normal circumstances you don't need to call this function, as
237	this module automatically starts some threads (the exact number
238	might change, and is currently 4).
239
240	IO::AIO::max_parallel $nthreads
241	Sets the maximum number of AIO threads to $nthreads. If more than
242	the specified number of threads are currently running, kill them.
243	This function blocks until the limit is reached.
244
245	This module automatically runs "max_parallel 0" at program end, to
246	ensure that all threads are killed and that there are no outstanding
247	requests.
248
249	Under normal circumstances you don't need to call this function.
250
251	$oldnreqs = IO::AIO::max_outstanding $nreqs
252	Sets the maximum number of outstanding requests to $nreqs. If you
253	try to queue up more than this number of requests, the caller will
254	block until some requests have been handled.
255
256	The default is very large, so normally there is no practical limit.
257	If you queue up many requests in a loop it it often improves speed
258	if you set this to a relatively low number, such as 100.
259
260	Under normal circumstances you don't need to call this function.
261
262	SEE ALSO
263	Coro, Linux::AIO.
264
265	AUTHOR
266	Marc Lehmann <schmorp@schmorp.de>
267	http://home.schmorp.de/
268