[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,
               \&IO::AIO::poll_cb;

     # Tk
     Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
                               readable => \&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 $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, strating 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 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::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:	1.5
Committed:	Sun Jul 10 23:45:16 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.4:	+26 -2 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			\&IO::AIO::poll_cb;
26
27			# Tk
28			Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
29			readable => \&IO::AIO::poll_cb);
30
31	root	1.1	DESCRIPTION
32			This module implements asynchronous I/O using whatever means your
33	root	1.2	operating system supports.
34	root	1.1
35	root	1.2	Currently, a number of threads are started that execute your read/writes
36			and signal their completion. You don't need thread support in your libc
37			or perl, and the threads created by this module will not be visible to
38			the pthreads library. In the future, this module might make use of the
39			native aio functions available on many operating systems. However, they
40			are often not well-supported (Linux doesn't allow them on normal files
41			currently, for example), and they would only support aio_read and
42			aio_write, so the remaining functionality would have to be implemented
43			using threads anyway.
44	root	1.1
45			Although the module will work with in the presence of other threads, it
46	root	1.2	is currently not reentrant, so use appropriate locking yourself.
47	root	1.1
48	root	1.4	FUNCTIONS
49			AIO FUNCTIONS
50	root	1.1	All the "aio_*" calls are more or less thin wrappers around the syscall
51			with the same name (sans "aio_"). The arguments are similar or
52			identical, and they all accept an additional $callback argument which
53			must be a code reference. This code reference will get called with the
54			syscall return code (e.g. most syscalls return -1 on error, unlike perl,
55			which usually delivers "false") as it's sole argument when the given
56			syscall has been executed asynchronously.
57
58			All functions that expect a filehandle will also accept a file
59			descriptor.
60
61			The filenames you pass to these routines must be absolute. The reason
62			is that at the time the request is being executed, the current working
63			directory could have changed. Alternatively, you can make sure that you
64			never change the current working directory.
65
66			aio_open $pathname, $flags, $mode, $callback
67	root	1.2	Asynchronously open or create a file and call the callback with a
68			newly created filehandle for the file.
69
70			The pathname passed to "aio_open" must be absolute. See API NOTES,
71			above, for an explanation.
72	root	1.1
73			The $mode argument is a bitmask. See the "Fcntl" module for a list.
74			They are the same as used in "sysopen".
75
76			Example:
77
78			aio_open "/etc/passwd", O_RDONLY, 0, sub {
79	root	1.2	if ($_[0]) {
80			print "open successful, fh is $_[0]\n";
81	root	1.1	...
82			} else {
83			die "open failed: $!\n";
84			}
85			};
86
87			aio_close $fh, $callback
88			Asynchronously close a file and call the callback with the result
89	root	1.2	code. WARNING: although accepted, you should not pass in a perl
90			filehandle here, as perl will likely close the file descriptor
91			itself when the filehandle is destroyed. Normally, you can safely
92			call perls "close" or just let filehandles go out of scope.
93	root	1.1
94			aio_read $fh,$offset,$length, $data,$dataoffset,$callback
95			aio_write $fh,$offset,$length, $data,$dataoffset,$callback
96			Reads or writes "length" bytes from the specified "fh" and "offset"
97			into the scalar given by "data" and offset "dataoffset" and calls
98			the callback without the actual number of bytes read (or -1 on
99			error, just like the syscall).
100
101			Example: Read 15 bytes at offset 7 into scalar $buffer, strating at
102			offset 0 within the scalar:
103
104			aio_read $fh, 7, 15, $buffer, 0, sub {
105	root	1.5	$_[0] > 0 or die "read error: $!";
106			print "read $_[0] bytes: <$buffer>\n";
107	root	1.1	};
108
109			aio_readahead $fh,$offset,$length, $callback
110			Asynchronously reads the specified byte range into the page cache,
111	root	1.2	using the "readahead" syscall. If that syscall doesn't exist the
112			status will be -1 and $! is set to ENOSYS.
113	root	1.1
114			readahead() populates the page cache with data from a file so that
115			subsequent reads from that file will not block on disk I/O. The
116			$offset argument specifies the starting point from which data is to
117			be read and $length specifies the number of bytes to be read. I/O is
118			performed in whole pages, so that offset is effectively rounded down
119			to a page boundary and bytes are read up to the next page boundary
120			greater than or equal to (off-set+length). aio_readahead() does not
121			read beyond the end of the file. The current file offset of the file
122			is left unchanged.
123
124			aio_stat $fh_or_path, $callback
125			aio_lstat $fh, $callback
126			Works like perl's "stat" or "lstat" in void context. The callback
127			will be called after the stat and the results will be available
128			using "stat _" or "-s _" etc...
129
130			The pathname passed to "aio_stat" must be absolute. See API NOTES,
131			above, for an explanation.
132
133			Currently, the stats are always 64-bit-stats, i.e. instead of
134			returning an error when stat'ing a large file, the results will be
135			silently truncated unless perl itself is compiled with large file
136			support.
137
138			Example: Print the length of /etc/passwd:
139
140			aio_stat "/etc/passwd", sub {
141			$_[0] and die "stat failed: $!";
142			print "size is ", -s _, "\n";
143			};
144
145			aio_unlink $pathname, $callback
146			Asynchronously unlink (delete) a file and call the callback with the
147			result code.
148
149			aio_fsync $fh, $callback
150			Asynchronously call fsync on the given filehandle and call the
151			callback with the fsync result code.
152
153			aio_fdatasync $fh, $callback
154			Asynchronously call fdatasync on the given filehandle and call the
155			callback with the fdatasync result code.
156
157	root	1.4	SUPPORT FUNCTIONS
158			$fileno = IO::AIO::poll_fileno
159			Return the request result pipe filehandle. This filehandle must be
160			polled for reading by some mechanism outside this module (e.g. Event
161			or select, see below). If the pipe becomes readable you have to call
162			"poll_cb" to check the results.
163
164			See "poll_cb" for an example.
165
166			IO::AIO::poll_cb
167			Process all outstanding events on the result pipe. You have to call
168			this regularly. Returns the number of events processed. Returns
169			immediately when no events are outstanding.
170
171			You can use Event to multiplex, e.g.:
172
173			Event->io (fd => IO::AIO::poll_fileno,
174			poll => 'r', async => 1,
175			cb => \&IO::AIO::poll_cb);
176
177			IO::AIO::poll_wait
178			Wait till the result filehandle becomes ready for reading (simply
179			does a select on the filehandle. This is useful if you want to
180			synchronously wait for some requests to finish).
181
182			See "nreqs" for an example.
183
184			IO::AIO::nreqs
185			Returns the number of requests currently outstanding.
186
187			Example: wait till there are no outstanding requests anymore:
188
189			IO::AIO::poll_wait, IO::AIO::poll_cb
190			while IO::AIO::nreqs;
191
192			IO::AIO::min_parallel $nthreads
193			Set the minimum number of AIO threads to $nthreads. The default is
194			1, which means a single asynchronous operation can be done at one
195			time (the number of outstanding operations, however, is unlimited).
196
197			It is recommended to keep the number of threads low, as some Linux
198			kernel versions will scale negatively with the number of threads
199			(higher parallelity => MUCH higher latency). With current Linux 2.6
200			versions, 4-32 threads should be fine.
201
202			Under normal circumstances you don't need to call this function, as
203			this module automatically starts some threads (the exact number
204			might change, and is currently 4).
205
206			IO::AIO::max_parallel $nthreads
207			Sets the maximum number of AIO threads to $nthreads. If more than
208			the specified number of threads are currently running, kill them.
209			This function blocks until the limit is reached.
210
211			This module automatically runs "max_parallel 0" at program end, to
212			ensure that all threads are killed and that there are no outstanding
213			requests.
214
215			Under normal circumstances you don't need to call this function.
216
217			$oldnreqs = IO::AIO::max_outstanding $nreqs
218			Sets the maximum number of outstanding requests to $nreqs. If you
219			try to queue up more than this number of requests, the caller will
220			block until some requests have been handled.
221
222			The default is very large, so normally there is no practical limit.
223			If you queue up many requests in a loop it it often improves speed
224			if you set this to a relatively low number, such as 100.
225
226			Under normal circumstances you don't need to call this function.
227	root	1.1
228			SEE ALSO
229	root	1.2	Coro, Linux::AIO.
230	root	1.1
231			AUTHOR
232			Marc Lehmann <schmorp@schmorp.de>
233			http://home.schmorp.de/
234