[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).

        Under normal circumstances you don't need to call this function, as
        this module automatically starts a single async thread.

    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.

    $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:	1.2
Committed:	Sun Jul 10 18:16:49 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_1
Changes since 1.1:	+26 -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	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).
49
50	Under normal circumstances you don't need to call this function, as
51	this module automatically starts a single async thread.
52
53	IO::AIO::max_parallel $nthreads
54	Sets the maximum number of AIO threads to $nthreads. If more than
55	the specified number of threads are currently running, kill them.
56	This function blocks until the limit is reached.
57
58	This module automatically runs "max_parallel 0" at program end, to
59	ensure that all threads are killed and that there are no outstanding
60	requests.
61
62	Under normal circumstances you don't need to call this function.
63
64	$fileno = IO::AIO::poll_fileno
65	Return the request result pipe filehandle. This filehandle must be
66	polled for reading by some mechanism outside this module (e.g. Event
67	or select, see below). If the pipe becomes readable you have to call
68	"poll_cb" to check the results.
69
70	See "poll_cb" for an example.
71
72	IO::AIO::poll_cb
73	Process all outstanding events on the result pipe. You have to call
74	this regularly. Returns the number of events processed. Returns
75	immediately when no events are outstanding.
76
77	You can use Event to multiplex, e.g.:
78
79	Event->io (fd => IO::AIO::poll_fileno,
80	poll => 'r', async => 1,
81	cb => \&IO::AIO::poll_cb);
82
83	IO::AIO::poll_wait
84	Wait till the result filehandle becomes ready for reading (simply
85	does a select on the filehandle. This is useful if you want to
86	synchronously wait for some requests to finish).
87
88	See "nreqs" for an example.
89
90	IO::AIO::nreqs
91	Returns the number of requests currently outstanding.
92
93	Example: wait till there are no outstanding requests anymore:
94
95	IO::AIO::poll_wait, IO::AIO::poll_cb
96	while IO::AIO::nreqs;
97
98	aio_open $pathname, $flags, $mode, $callback
99	Asynchronously open or create a file and call the callback with a
100	newly created filehandle for the file.
101
102	The pathname passed to "aio_open" must be absolute. See API NOTES,
103	above, for an explanation.
104
105	The $mode argument is a bitmask. See the "Fcntl" module for a list.
106	They are the same as used in "sysopen".
107
108	Example:
109
110	aio_open "/etc/passwd", O_RDONLY, 0, sub {
111	if ($_[0]) {
112	print "open successful, fh is $_[0]\n";
113	...
114	} else {
115	die "open failed: $!\n";
116	}
117	};
118
119	aio_close $fh, $callback
120	Asynchronously close a file and call the callback with the result
121	code. WARNING: although accepted, you should not pass in a perl
122	filehandle here, as perl will likely close the file descriptor
123	itself when the filehandle is destroyed. Normally, you can safely
124	call perls "close" or just let filehandles go out of scope.
125
126	aio_read $fh,$offset,$length, $data,$dataoffset,$callback
127	aio_write $fh,$offset,$length, $data,$dataoffset,$callback
128	Reads or writes "length" bytes from the specified "fh" and "offset"
129	into the scalar given by "data" and offset "dataoffset" and calls
130	the callback without the actual number of bytes read (or -1 on
131	error, just like the syscall).
132
133	Example: Read 15 bytes at offset 7 into scalar $buffer, strating at
134	offset 0 within the scalar:
135
136	aio_read $fh, 7, 15, $buffer, 0, sub {
137	$_[0] >= 0 or die "read error: $!";
138	print "read <$buffer>\n";
139	};
140
141	aio_readahead $fh,$offset,$length, $callback
142	Asynchronously reads the specified byte range into the page cache,
143	using the "readahead" syscall. If that syscall doesn't exist the
144	status will be -1 and $! is set to ENOSYS.
145
146	readahead() populates the page cache with data from a file so that
147	subsequent reads from that file will not block on disk I/O. The
148	$offset argument specifies the starting point from which data is to
149	be read and $length specifies the number of bytes to be read. I/O is
150	performed in whole pages, so that offset is effectively rounded down
151	to a page boundary and bytes are read up to the next page boundary
152	greater than or equal to (off-set+length). aio_readahead() does not
153	read beyond the end of the file. The current file offset of the file
154	is left unchanged.
155
156	aio_stat $fh_or_path, $callback
157	aio_lstat $fh, $callback
158	Works like perl's "stat" or "lstat" in void context. The callback
159	will be called after the stat and the results will be available
160	using "stat _" or "-s _" etc...
161
162	The pathname passed to "aio_stat" must be absolute. See API NOTES,
163	above, for an explanation.
164
165	Currently, the stats are always 64-bit-stats, i.e. instead of
166	returning an error when stat'ing a large file, the results will be
167	silently truncated unless perl itself is compiled with large file
168	support.
169
170	Example: Print the length of /etc/passwd:
171
172	aio_stat "/etc/passwd", sub {
173	$_[0] and die "stat failed: $!";
174	print "size is ", -s _, "\n";
175	};
176
177	aio_unlink $pathname, $callback
178	Asynchronously unlink (delete) a file and call the callback with the
179	result code.
180
181	aio_fsync $fh, $callback
182	Asynchronously call fsync on the given filehandle and call the
183	callback with the fsync result code.
184
185	aio_fdatasync $fh, $callback
186	Asynchronously call fdatasync on the given filehandle and call the
187	callback with the fdatasync result code.
188
189	BUGS
190	- could be optimized to use more semaphores instead of filehandles.
191
192	SEE ALSO
193	Coro, Linux::AIO.
194
195	AUTHOR
196	Marc Lehmann <schmorp@schmorp.de>
197	http://home.schmorp.de/
198