[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).

        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 *
#	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			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	root	1.2	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	root	1.1
105			The $mode argument is a bitmask. See the "Fcntl" module for a list.
106			They are the same as used in "sysopen".
107
108			Example:
109
110			aio_open "/etc/passwd", O_RDONLY, 0, sub {
111	root	1.2	if ($_[0]) {
112			print "open successful, fh is $_[0]\n";
113	root	1.1	...
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	root	1.2	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	root	1.1
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	root	1.2	using the "readahead" syscall. If that syscall doesn't exist the
144			status will be -1 and $! is set to ENOSYS.
145	root	1.1
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	root	1.2	- could be optimized to use more semaphores instead of filehandles.
191	root	1.1
192			SEE ALSO
193	root	1.2	Coro, Linux::AIO.
194	root	1.1
195			AUTHOR
196			Marc Lehmann <schmorp@schmorp.de>
197			http://home.schmorp.de/
198