[ViewVC] Annotation 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).

        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
    IO::AIO handles all outstanding AIO requests before the fork, destroys
    all AIO threads, and recreates them in both the parent and the child
    after the fork.

SEE ALSO
    Coro, Linux::AIO.

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

Revision:	1.9
Committed:	Tue Aug 16 23:33:38 2005 UTC (18 years, 9 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_2
Changes since 1.8:	+29 -11 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	NAME
2			IO::AIO - Asynchronous Input/Output
3
4			SYNOPSIS
5			use IO::AIO;
6
7	root	1.5	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	root	1.7	in => sub { IO::AIO::poll_cb; 1 };
26	root	1.5
27			# Tk
28			Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
29			readable => \&IO::AIO::poll_cb);
30
31	root	1.6	# Danga::Socket
32			Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
33			\&IO::AIO::poll_cb);
34
35	root	1.1	DESCRIPTION
36			This module implements asynchronous I/O using whatever means your
37	root	1.2	operating system supports.
38	root	1.1
39	root	1.2	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	root	1.1
49			Although the module will work with in the presence of other threads, it
50	root	1.7	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	root	1.1
54	root	1.4	FUNCTIONS
55			AIO FUNCTIONS
56	root	1.1	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	root	1.6	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	root	1.1
64	root	1.8	All functions expecting a filehandle keep a copy of the filehandle
65			internally until the request has finished.
66	root	1.1
67	root	1.9	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	root	1.1
80			aio_open $pathname, $flags, $mode, $callback
81	root	1.2	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	root	1.1
87	root	1.7	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, $mode specifies the mode of the newly created file, if it
91			didn't exist and "O_CREAT" has been given, just like perl's
92			"sysopen", except that it is mandatory (i.e. use 0 if you don't
93			create new files, and 0666 or 0777 if you do).
94	root	1.1
95			Example:
96
97			aio_open "/etc/passwd", O_RDONLY, 0, sub {
98	root	1.2	if ($_[0]) {
99			print "open successful, fh is $_[0]\n";
100	root	1.1	...
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	root	1.2	code. WARNING: although accepted, you should not pass in a perl
109			filehandle here, as perl will likely close the file descriptor
110	root	1.7	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	root	1.1
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	root	1.6	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
124	root	1.1	offset 0 within the scalar:
125
126			aio_read $fh, 7, 15, $buffer, 0, sub {
127	root	1.5	$_[0] > 0 or die "read error: $!";
128			print "read $_[0] bytes: <$buffer>\n";
129	root	1.1	};
130
131			aio_readahead $fh,$offset,$length, $callback
132	root	1.7	"aio_readahead" populates the page cache with data from a file so
133			that subsequent reads from that file will not block on disk I/O. The
134	root	1.1	$offset argument specifies the starting point from which data is to
135			be read and $length specifies the number of bytes to be read. I/O is
136			performed in whole pages, so that offset is effectively rounded down
137			to a page boundary and bytes are read up to the next page boundary
138	root	1.7	greater than or equal to (off-set+length). "aio_readahead" does not
139	root	1.1	read beyond the end of the file. The current file offset of the file
140			is left unchanged.
141
142	root	1.9	If that syscall doesn't exist (likely if your OS isn't Linux) it
143			will be emulated by simply reading the data, which would have a
144			similar effect.
145
146	root	1.1	aio_stat $fh_or_path, $callback
147			aio_lstat $fh, $callback
148			Works like perl's "stat" or "lstat" in void context. The callback
149			will be called after the stat and the results will be available
150			using "stat _" or "-s _" etc...
151
152			The pathname passed to "aio_stat" must be absolute. See API NOTES,
153			above, for an explanation.
154
155			Currently, the stats are always 64-bit-stats, i.e. instead of
156			returning an error when stat'ing a large file, the results will be
157			silently truncated unless perl itself is compiled with large file
158			support.
159
160			Example: Print the length of /etc/passwd:
161
162			aio_stat "/etc/passwd", sub {
163			$_[0] and die "stat failed: $!";
164			print "size is ", -s _, "\n";
165			};
166
167			aio_unlink $pathname, $callback
168			Asynchronously unlink (delete) a file and call the callback with the
169			result code.
170
171	root	1.9	aio_rmdir $pathname, $callback
172			Asynchronously rmdir (delete) a directory and call the callback with
173			the result code.
174
175	root	1.1	aio_fsync $fh, $callback
176			Asynchronously call fsync on the given filehandle and call the
177			callback with the fsync result code.
178
179			aio_fdatasync $fh, $callback
180			Asynchronously call fdatasync on the given filehandle and call the
181	root	1.9	callback with the fdatasync result code.
182
183			If this call isn't available because your OS lacks it or it couldn't
184			be detected, it will be emulated by calling "fsync" instead.
185	root	1.1
186	root	1.4	SUPPORT FUNCTIONS
187			$fileno = IO::AIO::poll_fileno
188	root	1.7	Return the request result pipe file descriptor. This filehandle
189			must be polled for reading by some mechanism outside this module
190			(e.g. Event or select, see below or the SYNOPSIS). If the pipe
191			becomes readable you have to call "poll_cb" to check the results.
192	root	1.4
193			See "poll_cb" for an example.
194
195			IO::AIO::poll_cb
196			Process all outstanding events on the result pipe. You have to call
197			this regularly. Returns the number of events processed. Returns
198			immediately when no events are outstanding.
199
200	root	1.7	Example: Install an Event watcher that automatically calls
201			IO::AIO::poll_cb with high priority:
202	root	1.4
203			Event->io (fd => IO::AIO::poll_fileno,
204			poll => 'r', async => 1,
205			cb => \&IO::AIO::poll_cb);
206
207			IO::AIO::poll_wait
208			Wait till the result filehandle becomes ready for reading (simply
209	root	1.7	does a "select" on the filehandle. This is useful if you want to
210	root	1.4	synchronously wait for some requests to finish).
211
212			See "nreqs" for an example.
213
214			IO::AIO::nreqs
215	root	1.7	Returns the number of requests currently outstanding (i.e. for which
216			their callback has not been invoked yet).
217	root	1.4
218			Example: wait till there are no outstanding requests anymore:
219
220			IO::AIO::poll_wait, IO::AIO::poll_cb
221			while IO::AIO::nreqs;
222
223	root	1.6	IO::AIO::flush
224			Wait till all outstanding AIO requests have been handled.
225
226			Strictly equivalent to:
227
228			IO::AIO::poll_wait, IO::AIO::poll_cb
229			while IO::AIO::nreqs;
230
231			IO::AIO::poll
232			Waits until some requests have been handled.
233
234			Strictly equivalent to:
235
236			IO::AIO::poll_wait, IO::AIO::poll_cb
237			if IO::AIO::nreqs;
238
239	root	1.4	IO::AIO::min_parallel $nthreads
240			Set the minimum number of AIO threads to $nthreads. The default is
241			1, which means a single asynchronous operation can be done at one
242			time (the number of outstanding operations, however, is unlimited).
243
244			It is recommended to keep the number of threads low, as some Linux
245			kernel versions will scale negatively with the number of threads
246			(higher parallelity => MUCH higher latency). With current Linux 2.6
247			versions, 4-32 threads should be fine.
248
249			Under normal circumstances you don't need to call this function, as
250			this module automatically starts some threads (the exact number
251			might change, and is currently 4).
252
253			IO::AIO::max_parallel $nthreads
254			Sets the maximum number of AIO threads to $nthreads. If more than
255			the specified number of threads are currently running, kill them.
256			This function blocks until the limit is reached.
257
258			This module automatically runs "max_parallel 0" at program end, to
259			ensure that all threads are killed and that there are no outstanding
260			requests.
261
262			Under normal circumstances you don't need to call this function.
263
264			$oldnreqs = IO::AIO::max_outstanding $nreqs
265			Sets the maximum number of outstanding requests to $nreqs. If you
266			try to queue up more than this number of requests, the caller will
267			block until some requests have been handled.
268
269			The default is very large, so normally there is no practical limit.
270			If you queue up many requests in a loop it it often improves speed
271			if you set this to a relatively low number, such as 100.
272
273			Under normal circumstances you don't need to call this function.
274	root	1.1
275	root	1.9	FORK BEHAVIOUR
276			IO::AIO handles all outstanding AIO requests before the fork, destroys
277			all AIO threads, and recreates them in both the parent and the child
278			after the fork.
279
280	root	1.1	SEE ALSO
281	root	1.2	Coro, Linux::AIO.
282	root	1.1
283			AUTHOR
284			Marc Lehmann <schmorp@schmorp.de>
285			http://home.schmorp.de/
286