[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).

        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 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:	1.11
Committed:	Sat Aug 20 00:32:42 2005 UTC (18 years, 9 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_5
Changes since 1.10:	+21 -13 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	1.10	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	root	1.6	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
128	root	1.1	offset 0 within the scalar:
129
130			aio_read $fh, 7, 15, $buffer, 0, sub {
131	root	1.5	$_[0] > 0 or die "read error: $!";
132			print "read $_[0] bytes: <$buffer>\n";
133	root	1.1	};
134
135			aio_readahead $fh,$offset,$length, $callback
136	root	1.7	"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	root	1.1	$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	root	1.7	greater than or equal to (off-set+length). "aio_readahead" does not
143	root	1.1	read beyond the end of the file. The current file offset of the file
144			is left unchanged.
145
146	root	1.9	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	root	1.1	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	root	1.9	aio_rmdir $pathname, $callback
176			Asynchronously rmdir (delete) a directory and call the callback with
177			the result code.
178
179	root	1.1	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	root	1.9	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	root	1.1
190	root	1.4	SUPPORT FUNCTIONS
191			$fileno = IO::AIO::poll_fileno
192	root	1.7	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	root	1.4
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	root	1.7	Example: Install an Event watcher that automatically calls
205			IO::AIO::poll_cb with high priority:
206	root	1.4
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	root	1.7	does a "select" on the filehandle. This is useful if you want to
214	root	1.4	synchronously wait for some requests to finish).
215
216			See "nreqs" for an example.
217
218			IO::AIO::nreqs
219	root	1.7	Returns the number of requests currently outstanding (i.e. for which
220			their callback has not been invoked yet).
221	root	1.4
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	root	1.6	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	root	1.4	IO::AIO::min_parallel $nthreads
244	root	1.11	Set the minimum number of AIO threads to $nthreads. The current
245			default is 4, which means four asynchronous operations can be done
246			at one time (the number of outstanding operations, however, is
247			unlimited).
248
249			IO::AIO starts threads only on demand, when an AIO request is queued
250			and no free thread exists.
251	root	1.4
252			It is recommended to keep the number of threads low, as some Linux
253			kernel versions will scale negatively with the number of threads
254			(higher parallelity => MUCH higher latency). With current Linux 2.6
255			versions, 4-32 threads should be fine.
256
257	root	1.11	Under most circumstances you don't need to call this function, as
258			the module selects a default that is suitable for low to moderate
259			load.
260	root	1.4
261			IO::AIO::max_parallel $nthreads
262			Sets the maximum number of AIO threads to $nthreads. If more than
263	root	1.11	the specified number of threads are currently running, this function
264			kills them. This function blocks until the limit is reached.
265
266			While $nthreads are zero, aio requests get queued but not executed
267			until the number of threads has been increased again.
268	root	1.4
269			This module automatically runs "max_parallel 0" at program end, to
270			ensure that all threads are killed and that there are no outstanding
271			requests.
272
273			Under normal circumstances you don't need to call this function.
274
275			$oldnreqs = IO::AIO::max_outstanding $nreqs
276			Sets the maximum number of outstanding requests to $nreqs. If you
277			try to queue up more than this number of requests, the caller will
278			block until some requests have been handled.
279
280			The default is very large, so normally there is no practical limit.
281	root	1.11	If you queue up many requests in a loop it often improves speed if
282			you set this to a relatively low number, such as 100.
283	root	1.4
284			Under normal circumstances you don't need to call this function.
285	root	1.1
286	root	1.9	FORK BEHAVIOUR
287	root	1.11	Before the fork, IO::AIO enters a quiescent state where no requests can
288	root	1.10	be added in other threads and no results will be processed. After the
289			fork the parent simply leaves the quiescent state and continues
290			request/result processing, while the child clears the request/result
291	root	1.11	queue (so the requests started before the fork will only be handled in
292			the parent). Threats will be started on demand until the limit ste in
293			the parent process has been reached again.
294	root	1.9
295	root	1.1	SEE ALSO
296	root	1.2	Coro, Linux::AIO.
297	root	1.1
298			AUTHOR
299			Marc Lehmann <schmorp@schmorp.de>
300			http://home.schmorp.de/
301