[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.

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: $!";
              print "read <$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:	1.4
Committed:	Sun Jul 10 21:04:46 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.3:	+72 -73 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	root	1.4	FUNCTIONS
25			AIO FUNCTIONS
26	root	1.1	All the "aio_*" calls are more or less thin wrappers around the syscall
27			with the same name (sans "aio_"). The arguments are similar or
28			identical, and they all accept an additional $callback argument which
29			must be a code reference. This code reference will get called with the
30			syscall return code (e.g. most syscalls return -1 on error, unlike perl,
31			which usually delivers "false") as it's sole argument when the given
32			syscall has been executed asynchronously.
33
34			All functions that expect a filehandle will also accept a file
35			descriptor.
36
37			The filenames you pass to these routines must be absolute. The reason
38			is that at the time the request is being executed, the current working
39			directory could have changed. Alternatively, you can make sure that you
40			never change the current working directory.
41
42			aio_open $pathname, $flags, $mode, $callback
43	root	1.2	Asynchronously open or create a file and call the callback with a
44			newly created filehandle for the file.
45
46			The pathname passed to "aio_open" must be absolute. See API NOTES,
47			above, for an explanation.
48	root	1.1
49			The $mode argument is a bitmask. See the "Fcntl" module for a list.
50			They are the same as used in "sysopen".
51
52			Example:
53
54			aio_open "/etc/passwd", O_RDONLY, 0, sub {
55	root	1.2	if ($_[0]) {
56			print "open successful, fh is $_[0]\n";
57	root	1.1	...
58			} else {
59			die "open failed: $!\n";
60			}
61			};
62
63			aio_close $fh, $callback
64			Asynchronously close a file and call the callback with the result
65	root	1.2	code. WARNING: although accepted, you should not pass in a perl
66			filehandle here, as perl will likely close the file descriptor
67			itself when the filehandle is destroyed. Normally, you can safely
68			call perls "close" or just let filehandles go out of scope.
69	root	1.1
70			aio_read $fh,$offset,$length, $data,$dataoffset,$callback
71			aio_write $fh,$offset,$length, $data,$dataoffset,$callback
72			Reads or writes "length" bytes from the specified "fh" and "offset"
73			into the scalar given by "data" and offset "dataoffset" and calls
74			the callback without the actual number of bytes read (or -1 on
75			error, just like the syscall).
76
77			Example: Read 15 bytes at offset 7 into scalar $buffer, strating at
78			offset 0 within the scalar:
79
80			aio_read $fh, 7, 15, $buffer, 0, sub {
81			$_[0] >= 0 or die "read error: $!";
82			print "read <$buffer>\n";
83			};
84
85			aio_readahead $fh,$offset,$length, $callback
86			Asynchronously reads the specified byte range into the page cache,
87	root	1.2	using the "readahead" syscall. If that syscall doesn't exist the
88			status will be -1 and $! is set to ENOSYS.
89	root	1.1
90			readahead() populates the page cache with data from a file so that
91			subsequent reads from that file will not block on disk I/O. The
92			$offset argument specifies the starting point from which data is to
93			be read and $length specifies the number of bytes to be read. I/O is
94			performed in whole pages, so that offset is effectively rounded down
95			to a page boundary and bytes are read up to the next page boundary
96			greater than or equal to (off-set+length). aio_readahead() does not
97			read beyond the end of the file. The current file offset of the file
98			is left unchanged.
99
100			aio_stat $fh_or_path, $callback
101			aio_lstat $fh, $callback
102			Works like perl's "stat" or "lstat" in void context. The callback
103			will be called after the stat and the results will be available
104			using "stat _" or "-s _" etc...
105
106			The pathname passed to "aio_stat" must be absolute. See API NOTES,
107			above, for an explanation.
108
109			Currently, the stats are always 64-bit-stats, i.e. instead of
110			returning an error when stat'ing a large file, the results will be
111			silently truncated unless perl itself is compiled with large file
112			support.
113
114			Example: Print the length of /etc/passwd:
115
116			aio_stat "/etc/passwd", sub {
117			$_[0] and die "stat failed: $!";
118			print "size is ", -s _, "\n";
119			};
120
121			aio_unlink $pathname, $callback
122			Asynchronously unlink (delete) a file and call the callback with the
123			result code.
124
125			aio_fsync $fh, $callback
126			Asynchronously call fsync on the given filehandle and call the
127			callback with the fsync result code.
128
129			aio_fdatasync $fh, $callback
130			Asynchronously call fdatasync on the given filehandle and call the
131			callback with the fdatasync result code.
132
133	root	1.4	SUPPORT FUNCTIONS
134			$fileno = IO::AIO::poll_fileno
135			Return the request result pipe filehandle. This filehandle must be
136			polled for reading by some mechanism outside this module (e.g. Event
137			or select, see below). If the pipe becomes readable you have to call
138			"poll_cb" to check the results.
139
140			See "poll_cb" for an example.
141
142			IO::AIO::poll_cb
143			Process all outstanding events on the result pipe. You have to call
144			this regularly. Returns the number of events processed. Returns
145			immediately when no events are outstanding.
146
147			You can use Event to multiplex, e.g.:
148
149			Event->io (fd => IO::AIO::poll_fileno,
150			poll => 'r', async => 1,
151			cb => \&IO::AIO::poll_cb);
152
153			IO::AIO::poll_wait
154			Wait till the result filehandle becomes ready for reading (simply
155			does a select on the filehandle. This is useful if you want to
156			synchronously wait for some requests to finish).
157
158			See "nreqs" for an example.
159
160			IO::AIO::nreqs
161			Returns the number of requests currently outstanding.
162
163			Example: wait till there are no outstanding requests anymore:
164
165			IO::AIO::poll_wait, IO::AIO::poll_cb
166			while IO::AIO::nreqs;
167
168			IO::AIO::min_parallel $nthreads
169			Set the minimum number of AIO threads to $nthreads. The default is
170			1, which means a single asynchronous operation can be done at one
171			time (the number of outstanding operations, however, is unlimited).
172
173			It is recommended to keep the number of threads low, as some Linux
174			kernel versions will scale negatively with the number of threads
175			(higher parallelity => MUCH higher latency). With current Linux 2.6
176			versions, 4-32 threads should be fine.
177
178			Under normal circumstances you don't need to call this function, as
179			this module automatically starts some threads (the exact number
180			might change, and is currently 4).
181
182			IO::AIO::max_parallel $nthreads
183			Sets the maximum number of AIO threads to $nthreads. If more than
184			the specified number of threads are currently running, kill them.
185			This function blocks until the limit is reached.
186
187			This module automatically runs "max_parallel 0" at program end, to
188			ensure that all threads are killed and that there are no outstanding
189			requests.
190
191			Under normal circumstances you don't need to call this function.
192
193			$oldnreqs = IO::AIO::max_outstanding $nreqs
194			Sets the maximum number of outstanding requests to $nreqs. If you
195			try to queue up more than this number of requests, the caller will
196			block until some requests have been handled.
197
198			The default is very large, so normally there is no practical limit.
199			If you queue up many requests in a loop it it often improves speed
200			if you set this to a relatively low number, such as 100.
201
202			Under normal circumstances you don't need to call this function.
203	root	1.1
204			SEE ALSO
205	root	1.2	Coro, Linux::AIO.
206	root	1.1
207			AUTHOR
208			Marc Lehmann <schmorp@schmorp.de>
209			http://home.schmorp.de/
210