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

NAME
    Linux::AIO - linux-specific aio implemented using clone

SYNOPSIS
     use Linux::AIO;

DESCRIPTION
    This module implements asynchronous I/O using the means available to
    Linux - clone. It does not hook into the POSIX aio_* functions because
    Linux does not yet support these in the kernel (even as of 2.6.12, only
    O_DIRECT files are supported) and even if, it would only allow aio_read
    and write, not open, stat and so on.

    Instead, in this module a number of (non-posix) 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.

    NOTICE: the threads created by this module will automatically be killed
    when the thread calling min_parallel exits. Make sure you only ever call
    min_parallel from the same thread that loaded this module.

    Although the module will work with in the presence of other threads, it
    is 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.

    Linux::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.

    Linux::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 = Linux::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.

    Linux::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 => Linux::AIO::poll_fileno,
                      poll => 'r', async => 1,
                      cb => \&Linux::AIO::poll_cb);

    Linux::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.

    Linux::AIO::nreqs
        Returns the number of requests currently outstanding.

        Example: wait till there are no outstanding requests anymore:

           Linux::AIO::poll_wait, Linux::AIO::poll_cb
              while Linux::AIO::nreqs;

    aio_open $pathname, $flags, $mode, $callback
        Asynchronously open or create a file and call the callback with the
        filedescriptor (NOT a perl filehandle, sorry for that, but watch
        out, this might change in the future).

        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] >= 0) {
                 open my $fh, "<&$_[0]";   # create a copy for perl
                 aio_close $_[0], sub { }; # close the aio handle
                 print "open successful, fh is $fh\n";
                 ...
              } else {
                 die "open failed: $!\n";
              }
           };

    aio_close $fh, $callback
        Asynchronously close a file and call the callback with the result
        code.

    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.

        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
    This module has been extensively tested in a large and very busy
    webserver for many years now.

       - aio_open gives a fd, but all other functions expect a perl filehandle.

SEE ALSO
    Coro, IO::AIO.

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

Revision:	1.5
Committed:	Sun Jul 10 17:11:54 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_71
Changes since 1.4:	+14 -2 lines
Log Message:	* empty log message *
#	Content
1	NAME
2	Linux::AIO - linux-specific aio implemented using clone
3
4	SYNOPSIS
5	use Linux::AIO;
6
7	DESCRIPTION
8	This module implements asynchronous I/O using the means available to
9	Linux - clone. It does not hook into the POSIX aio_* functions because
10	Linux does not yet support these in the kernel (even as of 2.6.12, only
11	O_DIRECT files are supported) and even if, it would only allow aio_read
12	and write, not open, stat and so on.
13
14	Instead, in this module a number of (non-posix) threads are started that
15	execute your read/writes and signal their completion. You don't need
16	thread support in your libc or perl, and the threads created by this
17	module will not be visible to the pthreads library.
18
19	NOTICE: the threads created by this module will automatically be killed
20	when the thread calling min_parallel exits. Make sure you only ever call
21	min_parallel from the same thread that loaded this module.
22
23	Although the module will work with in the presence of other threads, it
24	is not reentrant, so use appropriate locking yourself.
25
26	API NOTES
27	All the "aio_*" calls are more or less thin wrappers around the syscall
28	with the same name (sans "aio_"). The arguments are similar or
29	identical, and they all accept an additional $callback argument which
30	must be a code reference. This code reference will get called with the
31	syscall return code (e.g. most syscalls return -1 on error, unlike perl,
32	which usually delivers "false") as it's sole argument when the given
33	syscall has been executed asynchronously.
34
35	All functions that expect a filehandle will also accept a file
36	descriptor.
37
38	The filenames you pass to these routines must be absolute. The reason
39	is that at the time the request is being executed, the current working
40	directory could have changed. Alternatively, you can make sure that you
41	never change the current working directory.
42
43	Linux::AIO::min_parallel $nthreads
44	Set the minimum number of AIO threads to $nthreads. The default is
45	1, which means a single asynchronous operation can be done at one
46	time (the number of outstanding operations, however, is unlimited).
47
48	It is recommended to keep the number of threads low, as some linux
49	kernel versions will scale negatively with the number of threads
50	(higher parallelity => MUCH higher latency).
51
52	Under normal circumstances you don't need to call this function, as
53	this module automatically starts a single async thread.
54
55	Linux::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	$fileno = Linux::AIO::poll_fileno
67	Return the request result pipe filehandle. This filehandle must be
68	polled for reading by some mechanism outside this module (e.g. Event
69	or select, see below). If the pipe becomes readable you have to call
70	"poll_cb" to check the results.
71
72	See "poll_cb" for an example.
73
74	Linux::AIO::poll_cb
75	Process all outstanding events on the result pipe. You have to call
76	this regularly. Returns the number of events processed. Returns
77	immediately when no events are outstanding.
78
79	You can use Event to multiplex, e.g.:
80
81	Event->io (fd => Linux::AIO::poll_fileno,
82	poll => 'r', async => 1,
83	cb => \&Linux::AIO::poll_cb);
84
85	Linux::AIO::poll_wait
86	Wait till the result filehandle becomes ready for reading (simply
87	does a select on the filehandle. This is useful if you want to
88	synchronously wait for some requests to finish).
89
90	See "nreqs" for an example.
91
92	Linux::AIO::nreqs
93	Returns the number of requests currently outstanding.
94
95	Example: wait till there are no outstanding requests anymore:
96
97	Linux::AIO::poll_wait, Linux::AIO::poll_cb
98	while Linux::AIO::nreqs;
99
100	aio_open $pathname, $flags, $mode, $callback
101	Asynchronously open or create a file and call the callback with the
102	filedescriptor (NOT a perl filehandle, sorry for that, but watch
103	out, this might change in the future).
104
105	The pathname passed to "aio_open" must be absolute. See API NOTES,
106	above, for an explanation.
107
108	The $mode argument is a bitmask. See the "Fcntl" module for a list.
109	They are the same as used in "sysopen".
110
111	Example:
112
113	aio_open "/etc/passwd", O_RDONLY, 0, sub {
114	if ($_[0] >= 0) {
115	open my $fh, "<&$_[0]"; # create a copy for perl
116	aio_close $_[0], sub { }; # close the aio handle
117	print "open successful, fh is $fh\n";
118	...
119	} else {
120	die "open failed: $!\n";
121	}
122	};
123
124	aio_close $fh, $callback
125	Asynchronously close a file and call the callback with the result
126	code.
127
128	aio_read $fh,$offset,$length, $data,$dataoffset,$callback
129	aio_write $fh,$offset,$length, $data,$dataoffset,$callback
130	Reads or writes "length" bytes from the specified "fh" and "offset"
131	into the scalar given by "data" and offset "dataoffset" and calls
132	the callback without the actual number of bytes read (or -1 on
133	error, just like the syscall).
134
135	Example: Read 15 bytes at offset 7 into scalar $buffer, strating at
136	offset 0 within the scalar:
137
138	aio_read $fh, 7, 15, $buffer, 0, sub {
139	$_[0] >= 0 or die "read error: $!";
140	print "read <$buffer>\n";
141	};
142
143	aio_readahead $fh,$offset,$length, $callback
144	Asynchronously reads the specified byte range into the page cache,
145	using the "readahead" syscall.
146
147	readahead() populates the page cache with data from a file so that
148	subsequent reads from that file will not block on disk I/O. The
149	$offset argument specifies the starting point from which data is to
150	be read and $length specifies the number of bytes to be read. I/O is
151	performed in whole pages, so that offset is effectively rounded down
152	to a page boundary and bytes are read up to the next page boundary
153	greater than or equal to (off-set+length). aio_readahead() does not
154	read beyond the end of the file. The current file offset of the file
155	is left unchanged.
156
157	aio_stat $fh_or_path, $callback
158	aio_lstat $fh, $callback
159	Works like perl's "stat" or "lstat" in void context. The callback
160	will be called after the stat and the results will be available
161	using "stat _" or "-s _" etc...
162
163	The pathname passed to "aio_stat" must be absolute. See API NOTES,
164	above, for an explanation.
165
166	Currently, the stats are always 64-bit-stats, i.e. instead of
167	returning an error when stat'ing a large file, the results will be
168	silently truncated unless perl itself is compiled with large file
169	support.
170
171	Example: Print the length of /etc/passwd:
172
173	aio_stat "/etc/passwd", sub {
174	$_[0] and die "stat failed: $!";
175	print "size is ", -s _, "\n";
176	};
177
178	aio_unlink $pathname, $callback
179	Asynchronously unlink (delete) a file and call the callback with the
180	result code.
181
182	aio_fsync $fh, $callback
183	Asynchronously call fsync on the given filehandle and call the
184	callback with the fsync result code.
185
186	aio_fdatasync $fh, $callback
187	Asynchronously call fdatasync on the given filehandle and call the
188	callback with the fdatasync result code.
189
190	BUGS
191	This module has been extensively tested in a large and very busy
192	webserver for many years now.
193
194	- aio_open gives a fd, but all other functions expect a perl filehandle.
195
196	SEE ALSO
197	Coro, IO::AIO.
198
199	AUTHOR
200	Marc Lehmann <schmorp@schmorp.de>
201	http://home.schmorp.de/
202