[ViewVC] Contents of: cvs/IO-AIO/README

NAME
    IO::AIO - Asynchronous Input/Output

SYNOPSIS
     use IO::AIO;

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.

  API NOTES
    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 $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.

    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.

    $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;

    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, strating at
        offset 0 within the scalar:

           aio_read $fh, 7, 15, $buffer, 0, sub {
              $_[0] >= 0 or die "read error: $!";
              print "read <$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 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.

BUGS
       - could be optimized to use more semaphores instead of filehandles.

SEE ALSO
    Coro, Linux::AIO.

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

Revision:	1.3
Committed:	Sun Jul 10 20:57:36 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_2
Changes since 1.2:	+16 -3 lines
Log Message:	* empty log message *
#	Content
1	NAME
2	IO::AIO - Asynchronous Input/Output
3
4	SYNOPSIS
5	use IO::AIO;
6
7	DESCRIPTION
8	This module implements asynchronous I/O using whatever means your
9	operating system supports.
10
11	Currently, a number of threads are started that execute your read/writes
12	and signal their completion. You don't need thread support in your libc
13	or perl, and the threads created by this module will not be visible to
14	the pthreads library. In the future, this module might make use of the
15	native aio functions available on many operating systems. However, they
16	are often not well-supported (Linux doesn't allow them on normal files
17	currently, for example), and they would only support aio_read and
18	aio_write, so the remaining functionality would have to be implemented
19	using threads anyway.
20
21	Although the module will work with in the presence of other threads, it
22	is currently not reentrant, so use appropriate locking yourself.
23
24	API NOTES
25	All the "aio_*" calls are more or less thin wrappers around the syscall
26	with the same name (sans "aio_"). The arguments are similar or
27	identical, and they all accept an additional $callback argument which
28	must be a code reference. This code reference will get called with the
29	syscall return code (e.g. most syscalls return -1 on error, unlike perl,
30	which usually delivers "false") as it's sole argument when the given
31	syscall has been executed asynchronously.
32
33	All functions that expect a filehandle will also accept a file
34	descriptor.
35
36	The filenames you pass to these routines must be absolute. The reason
37	is that at the time the request is being executed, the current working
38	directory could have changed. Alternatively, you can make sure that you
39	never change the current working directory.
40
41	IO::AIO::min_parallel $nthreads
42	Set the minimum number of AIO threads to $nthreads. The default is
43	1, which means a single asynchronous operation can be done at one
44	time (the number of outstanding operations, however, is unlimited).
45
46	It is recommended to keep the number of threads low, as some Linux
47	kernel versions will scale negatively with the number of threads
48	(higher parallelity => MUCH higher latency). With current Linux 2.6
49	versions, 4-32 threads should be fine.
50
51	Under normal circumstances you don't need to call this function, as
52	this module automatically starts some threads (the exact number
53	might change, and is currently 4).
54
55	IO::AIO::max_parallel $nthreads
56	Sets the maximum number of AIO threads to $nthreads. If more than
57	the specified number of threads are currently running, kill them.
58	This function blocks until the limit is reached.
59
60	This module automatically runs "max_parallel 0" at program end, to
61	ensure that all threads are killed and that there are no outstanding
62	requests.
63
64	Under normal circumstances you don't need to call this function.
65
66	$oldnreqs = IO::AIO::max_outstanding $nreqs
67	Sets the maximum number of outstanding requests to $nreqs. If you
68	try to queue up more than this number of requests, the caller will
69	block until some requests have been handled.
70
71	The default is very large, so normally there is no practical limit.
72	If you queue up many requests in a loop it it often improves speed
73	if you set this to a relatively low number, such as 100.
74
75	Under normal circumstances you don't need to call this function.
76
77	$fileno = IO::AIO::poll_fileno
78	Return the request result pipe filehandle. This filehandle must be
79	polled for reading by some mechanism outside this module (e.g. Event
80	or select, see below). If the pipe becomes readable you have to call
81	"poll_cb" to check the results.
82
83	See "poll_cb" for an example.
84
85	IO::AIO::poll_cb
86	Process all outstanding events on the result pipe. You have to call
87	this regularly. Returns the number of events processed. Returns
88	immediately when no events are outstanding.
89
90	You can use Event to multiplex, e.g.:
91
92	Event->io (fd => IO::AIO::poll_fileno,
93	poll => 'r', async => 1,
94	cb => \&IO::AIO::poll_cb);
95
96	IO::AIO::poll_wait
97	Wait till the result filehandle becomes ready for reading (simply
98	does a select on the filehandle. This is useful if you want to
99	synchronously wait for some requests to finish).
100
101	See "nreqs" for an example.
102
103	IO::AIO::nreqs
104	Returns the number of requests currently outstanding.
105
106	Example: wait till there are no outstanding requests anymore:
107
108	IO::AIO::poll_wait, IO::AIO::poll_cb
109	while IO::AIO::nreqs;
110
111	aio_open $pathname, $flags, $mode, $callback
112	Asynchronously open or create a file and call the callback with a
113	newly created filehandle for the file.
114
115	The pathname passed to "aio_open" must be absolute. See API NOTES,
116	above, for an explanation.
117
118	The $mode argument is a bitmask. See the "Fcntl" module for a list.
119	They are the same as used in "sysopen".
120
121	Example:
122
123	aio_open "/etc/passwd", O_RDONLY, 0, sub {
124	if ($_[0]) {
125	print "open successful, fh is $_[0]\n";
126	...
127	} else {
128	die "open failed: $!\n";
129	}
130	};
131
132	aio_close $fh, $callback
133	Asynchronously close a file and call the callback with the result
134	code. WARNING: although accepted, you should not pass in a perl
135	filehandle here, as perl will likely close the file descriptor
136	itself when the filehandle is destroyed. Normally, you can safely
137	call perls "close" or just let filehandles go out of scope.
138
139	aio_read $fh,$offset,$length, $data,$dataoffset,$callback
140	aio_write $fh,$offset,$length, $data,$dataoffset,$callback
141	Reads or writes "length" bytes from the specified "fh" and "offset"
142	into the scalar given by "data" and offset "dataoffset" and calls
143	the callback without the actual number of bytes read (or -1 on
144	error, just like the syscall).
145
146	Example: Read 15 bytes at offset 7 into scalar $buffer, strating at
147	offset 0 within the scalar:
148
149	aio_read $fh, 7, 15, $buffer, 0, sub {
150	$_[0] >= 0 or die "read error: $!";
151	print "read <$buffer>\n";
152	};
153
154	aio_readahead $fh,$offset,$length, $callback
155	Asynchronously reads the specified byte range into the page cache,
156	using the "readahead" syscall. If that syscall doesn't exist the
157	status will be -1 and $! is set to ENOSYS.
158
159	readahead() populates the page cache with data from a file so that
160	subsequent reads from that file will not block on disk I/O. The
161	$offset argument specifies the starting point from which data is to
162	be read and $length specifies the number of bytes to be read. I/O is
163	performed in whole pages, so that offset is effectively rounded down
164	to a page boundary and bytes are read up to the next page boundary
165	greater than or equal to (off-set+length). aio_readahead() does not
166	read beyond the end of the file. The current file offset of the file
167	is left unchanged.
168
169	aio_stat $fh_or_path, $callback
170	aio_lstat $fh, $callback
171	Works like perl's "stat" or "lstat" in void context. The callback
172	will be called after the stat and the results will be available
173	using "stat _" or "-s _" etc...
174
175	The pathname passed to "aio_stat" must be absolute. See API NOTES,
176	above, for an explanation.
177
178	Currently, the stats are always 64-bit-stats, i.e. instead of
179	returning an error when stat'ing a large file, the results will be
180	silently truncated unless perl itself is compiled with large file
181	support.
182
183	Example: Print the length of /etc/passwd:
184
185	aio_stat "/etc/passwd", sub {
186	$_[0] and die "stat failed: $!";
187	print "size is ", -s _, "\n";
188	};
189
190	aio_unlink $pathname, $callback
191	Asynchronously unlink (delete) a file and call the callback with the
192	result code.
193
194	aio_fsync $fh, $callback
195	Asynchronously call fsync on the given filehandle and call the
196	callback with the fsync result code.
197
198	aio_fdatasync $fh, $callback
199	Asynchronously call fdatasync on the given filehandle and call the
200	callback with the fdatasync result code.
201
202	BUGS
203	- could be optimized to use more semaphores instead of filehandles.
204
205	SEE ALSO
206	Coro, Linux::AIO.
207
208	AUTHOR
209	Marc Lehmann <schmorp@schmorp.de>
210	http://home.schmorp.de/
211