[ViewVC] Annotation 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 *
#	User	Rev	Content
1	root	1.1	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	root	1.2	operating system supports.
10	root	1.1
11	root	1.2	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	root	1.1
21			Although the module will work with in the presence of other threads, it
22	root	1.2	is currently not reentrant, so use appropriate locking yourself.
23	root	1.1
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	root	1.3	It is recommended to keep the number of threads low, as some Linux
47	root	1.1	kernel versions will scale negatively with the number of threads
48	root	1.3	(higher parallelity => MUCH higher latency). With current Linux 2.6
49			versions, 4-32 threads should be fine.
50	root	1.1
51			Under normal circumstances you don't need to call this function, as
52	root	1.3	this module automatically starts some threads (the exact number
53			might change, and is currently 4).
54	root	1.1
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	root	1.3	$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	root	1.1	$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	root	1.2	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	root	1.1
118			The $mode argument is a bitmask. See the "Fcntl" module for a list.
119			They are the same as used in "sysopen".
120
121			Example:
122
123			aio_open "/etc/passwd", O_RDONLY, 0, sub {
124	root	1.2	if ($_[0]) {
125			print "open successful, fh is $_[0]\n";
126	root	1.1	...
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	root	1.2	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	root	1.1
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	root	1.2	using the "readahead" syscall. If that syscall doesn't exist the
157			status will be -1 and $! is set to ENOSYS.
158	root	1.1
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	root	1.2	- could be optimized to use more semaphores instead of filehandles.
204	root	1.1
205			SEE ALSO
206	root	1.2	Coro, Linux::AIO.
207	root	1.1
208			AUTHOR
209			Marc Lehmann <schmorp@schmorp.de>
210			http://home.schmorp.de/
211