[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.

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

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

    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.

        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.

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

        You can use Event to multiplex, e.g.:

           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.

        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:	1.6
Committed:	Mon Jul 11 03:29:39 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_4, rel-0_5
Changes since 1.5:	+30 -9 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	1.6	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	1.2	is currently not reentrant, so use appropriate locking yourself.
51	root	1.1
52	root	1.4	FUNCTIONS
53			AIO FUNCTIONS
54	root	1.1	All the "aio_*" calls are more or less thin wrappers around the syscall
55			with the same name (sans "aio_"). The arguments are similar or
56	root	1.6	identical, and they all accept an additional (and optional) $callback
57			argument which must be a code reference. This code reference will get
58			called with the syscall return code (e.g. most syscalls return -1 on
59			error, unlike perl, which usually delivers "false") as it's sole
60			argument when the given syscall has been executed asynchronously.
61	root	1.1
62			All functions that expect a filehandle will also accept a file
63			descriptor.
64
65			The filenames you pass to these routines must be absolute. The reason
66			is that at the time the request is being executed, the current working
67			directory could have changed. Alternatively, you can make sure that you
68			never change the current working directory.
69
70			aio_open $pathname, $flags, $mode, $callback
71	root	1.2	Asynchronously open or create a file and call the callback with a
72			newly created filehandle for the file.
73
74			The pathname passed to "aio_open" must be absolute. See API NOTES,
75			above, for an explanation.
76	root	1.1
77			The $mode argument is a bitmask. See the "Fcntl" module for a list.
78			They are the same as used in "sysopen".
79
80			Example:
81
82			aio_open "/etc/passwd", O_RDONLY, 0, sub {
83	root	1.2	if ($_[0]) {
84			print "open successful, fh is $_[0]\n";
85	root	1.1	...
86			} else {
87			die "open failed: $!\n";
88			}
89			};
90
91			aio_close $fh, $callback
92			Asynchronously close a file and call the callback with the result
93	root	1.2	code. WARNING: although accepted, you should not pass in a perl
94			filehandle here, as perl will likely close the file descriptor
95			itself when the filehandle is destroyed. Normally, you can safely
96			call perls "close" or just let filehandles go out of scope.
97	root	1.1
98			aio_read $fh,$offset,$length, $data,$dataoffset,$callback
99			aio_write $fh,$offset,$length, $data,$dataoffset,$callback
100			Reads or writes "length" bytes from the specified "fh" and "offset"
101			into the scalar given by "data" and offset "dataoffset" and calls
102			the callback without the actual number of bytes read (or -1 on
103			error, just like the syscall).
104
105	root	1.6	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
106	root	1.1	offset 0 within the scalar:
107
108			aio_read $fh, 7, 15, $buffer, 0, sub {
109	root	1.5	$_[0] > 0 or die "read error: $!";
110			print "read $_[0] bytes: <$buffer>\n";
111	root	1.1	};
112
113			aio_readahead $fh,$offset,$length, $callback
114			Asynchronously reads the specified byte range into the page cache,
115	root	1.6	using the "readahead" syscall. If that syscall doesn't exist (likely
116			if your OS isn't Linux) the status will be -1 and $! is set to
117			ENOSYS.
118	root	1.1
119			readahead() populates the page cache with data from a file so that
120			subsequent reads from that file will not block on disk I/O. The
121			$offset argument specifies the starting point from which data is to
122			be read and $length specifies the number of bytes to be read. I/O is
123			performed in whole pages, so that offset is effectively rounded down
124			to a page boundary and bytes are read up to the next page boundary
125			greater than or equal to (off-set+length). aio_readahead() does not
126			read beyond the end of the file. The current file offset of the file
127			is left unchanged.
128
129			aio_stat $fh_or_path, $callback
130			aio_lstat $fh, $callback
131			Works like perl's "stat" or "lstat" in void context. The callback
132			will be called after the stat and the results will be available
133			using "stat _" or "-s _" etc...
134
135			The pathname passed to "aio_stat" must be absolute. See API NOTES,
136			above, for an explanation.
137
138			Currently, the stats are always 64-bit-stats, i.e. instead of
139			returning an error when stat'ing a large file, the results will be
140			silently truncated unless perl itself is compiled with large file
141			support.
142
143			Example: Print the length of /etc/passwd:
144
145			aio_stat "/etc/passwd", sub {
146			$_[0] and die "stat failed: $!";
147			print "size is ", -s _, "\n";
148			};
149
150			aio_unlink $pathname, $callback
151			Asynchronously unlink (delete) a file and call the callback with the
152			result code.
153
154			aio_fsync $fh, $callback
155			Asynchronously call fsync on the given filehandle and call the
156			callback with the fsync result code.
157
158			aio_fdatasync $fh, $callback
159			Asynchronously call fdatasync on the given filehandle and call the
160			callback with the fdatasync result code.
161
162	root	1.4	SUPPORT FUNCTIONS
163			$fileno = IO::AIO::poll_fileno
164			Return the request result pipe filehandle. This filehandle must be
165			polled for reading by some mechanism outside this module (e.g. Event
166			or select, see below). If the pipe becomes readable you have to call
167			"poll_cb" to check the results.
168
169			See "poll_cb" for an example.
170
171			IO::AIO::poll_cb
172			Process all outstanding events on the result pipe. You have to call
173			this regularly. Returns the number of events processed. Returns
174			immediately when no events are outstanding.
175
176			You can use Event to multiplex, e.g.:
177
178			Event->io (fd => IO::AIO::poll_fileno,
179			poll => 'r', async => 1,
180			cb => \&IO::AIO::poll_cb);
181
182			IO::AIO::poll_wait
183			Wait till the result filehandle becomes ready for reading (simply
184			does a select on the filehandle. This is useful if you want to
185			synchronously wait for some requests to finish).
186
187			See "nreqs" for an example.
188
189			IO::AIO::nreqs
190			Returns the number of requests currently outstanding.
191
192			Example: wait till there are no outstanding requests anymore:
193
194			IO::AIO::poll_wait, IO::AIO::poll_cb
195			while IO::AIO::nreqs;
196
197	root	1.6	IO::AIO::flush
198			Wait till all outstanding AIO requests have been handled.
199
200			Strictly equivalent to:
201
202			IO::AIO::poll_wait, IO::AIO::poll_cb
203			while IO::AIO::nreqs;
204
205			IO::AIO::poll
206			Waits until some requests have been handled.
207
208			Strictly equivalent to:
209
210			IO::AIO::poll_wait, IO::AIO::poll_cb
211			if IO::AIO::nreqs;
212
213	root	1.4	IO::AIO::min_parallel $nthreads
214			Set the minimum number of AIO threads to $nthreads. The default is
215			1, which means a single asynchronous operation can be done at one
216			time (the number of outstanding operations, however, is unlimited).
217
218			It is recommended to keep the number of threads low, as some Linux
219			kernel versions will scale negatively with the number of threads
220			(higher parallelity => MUCH higher latency). With current Linux 2.6
221			versions, 4-32 threads should be fine.
222
223			Under normal circumstances you don't need to call this function, as
224			this module automatically starts some threads (the exact number
225			might change, and is currently 4).
226
227			IO::AIO::max_parallel $nthreads
228			Sets the maximum number of AIO threads to $nthreads. If more than
229			the specified number of threads are currently running, kill them.
230			This function blocks until the limit is reached.
231
232			This module automatically runs "max_parallel 0" at program end, to
233			ensure that all threads are killed and that there are no outstanding
234			requests.
235
236			Under normal circumstances you don't need to call this function.
237
238			$oldnreqs = IO::AIO::max_outstanding $nreqs
239			Sets the maximum number of outstanding requests to $nreqs. If you
240			try to queue up more than this number of requests, the caller will
241			block until some requests have been handled.
242
243			The default is very large, so normally there is no practical limit.
244			If you queue up many requests in a loop it it often improves speed
245			if you set this to a relatively low number, such as 100.
246
247			Under normal circumstances you don't need to call this function.
248	root	1.1
249			SEE ALSO
250	root	1.2	Coro, Linux::AIO.
251	root	1.1
252			AUTHOR
253			Marc Lehmann <schmorp@schmorp.de>
254			http://home.schmorp.de/
255