[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: $!";
     };

     # AnyEvent
     open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
     my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });

     # 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,
               in => sub { IO::AIO::poll_cb; 1 };

     # Tk
     Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
                               readable => \&IO::AIO::poll_cb);

     # Danga::Socket
     Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
                                 \&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, always
    call "poll_cb" from within the same thread, or never call "poll_cb" (or
    other "aio_" functions) recursively.

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 (and optional) $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 expecting a filehandle keep a copy of the filehandle
    internally until the request has finished.

    The pathnames you pass to these routines *must* be absolute and encoded
    in byte form. The reason for the former 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.

    To encode pathnames to byte form, either make sure you either: a) always
    pass in filenames you got from outside (command line, readdir etc.), b)
    are ASCII or ISO 8859-1, c) use the Encode module and encode your
    pathnames to the locale (or other) encoding in effect in the user
    environment, d) use Glib::filename_from_unicode on unicode filenames or
    e) use something else.

    aio_open $pathname, $flags, $mode, $callback->($fh)
        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 $flags argument is a bitmask. See the "Fcntl" module for a list.
        They are the same as used by "sysopen".

        Likewise, $mode specifies the mode of the newly created file, if it
        didn't exist and "O_CREAT" has been given, just like perl's
        "sysopen", except that it is mandatory (i.e. use 0 if you don't
        create new files, and 0666 or 0777 if you do).

        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, $callback->($status)
        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
        another time when the filehandle is destroyed. Normally, you can
        safely call perls "close" or just let filehandles go out of scope.

        This is supposed to be a bug in the API, so that might change. It's
        therefore best to avoid this function.

    aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
    aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
        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).

        The $data scalar *MUST NOT* be modified in any way while the request
        is outstanding. Modifying it can result in segfaults or WW3 (if the
        necessary/optional hardware is installed).

        Example: Read 15 bytes at offset 7 into scalar $buffer, starting 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_move $srcpath, $dstpath, $callback->($status)
        [EXPERIMENTAL]

        Try to move the *file* (directories not supported as either source
        or destination) from $srcpath to $dstpath and call the callback with
        the 0 (error) or -1 ok.

        This is a composite request that tries to rename(2) the file first.
        If rename files with "EXDEV", it creates the destination file with
        mode 0200 and copies the contents of the source file into it using
        "aio_sendfile", followed by restoring atime, mtime, access mode and
        uid/gid, in that order, and unlinking the $srcpath.

        If an error occurs, the partial destination file will be unlinked,
        if possible, except when setting atime, mtime, access mode and
        uid/gid, where errors are being ignored.

    aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
        Tries to copy $length bytes from $in_fh to $out_fh. It starts
        reading at byte offset $in_offset, and starts writing at the current
        file offset of $out_fh. Because of that, it is not safe to issue
        more than one "aio_sendfile" per $out_fh, as they will interfere
        with each other.

        This call tries to make use of a native "sendfile" syscall to
        provide zero-copy operation. For this to work, $out_fh should refer
        to a socket, and $in_fh should refer to mmap'able file.

        If the native sendfile call fails or is not implemented, it will be
        emulated, so you can call "aio_sendfile" on any type of filehandle
        regardless of the limitations of the operating system.

        Please note, however, that "aio_sendfile" can read more bytes from
        $in_fh than are written, and there is no way to find out how many
        bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
        only provides the number of bytes written to $out_fh. Only if the
        result value equals $length one can assume that $length bytes have
        been read.

    aio_readahead $fh,$offset,$length, $callback->($retval)
        "aio_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.

        If that syscall doesn't exist (likely if your OS isn't Linux) it
        will be emulated by simply reading the data, which would have a
        similar effect.

    aio_stat $fh_or_path, $callback->($status)
    aio_lstat $fh, $callback->($status)
        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, $callback->($status)
        Asynchronously unlink (delete) a file and call the callback with the
        result code.

    aio_link $srcpath, $dstpath, $callback->($status)
        Asynchronously create a new link to the existing object at $srcpath
        at the path $dstpath and call the callback with the result code.

    aio_symlink $srcpath, $dstpath, $callback->($status)
        Asynchronously create a new symbolic link to the existing object at
        $srcpath at the path $dstpath and call the callback with the result
        code.

    aio_rename $srcpath, $dstpath, $callback->($status)
        Asynchronously rename the object at $srcpath to $dstpath, just as
        rename(2) and call the callback with the result code.

    aio_rmdir $pathname, $callback->($status)
        Asynchronously rmdir (delete) a directory and call the callback with
        the result code.

    aio_readdir $pathname, $callback->($entries)
        Unlike the POSIX call of the same name, "aio_readdir" reads an
        entire directory (i.e. opendir + readdir + closedir). The entries
        will not be sorted, and will NOT include the "." and ".." entries.

        The callback a single argument which is either "undef" or an
        array-ref with the filenames.

    aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
        Scans a directory (similar to "aio_readdir") and tries to separate
        the entries of directory $path into two sets of names, ones you can
        recurse into (directories), and ones you cannot recurse into
        (everything else).

        "aio_scandir" is a composite request that consists of many
        aio-primitives. $maxreq specifies the maximum number of outstanding
        aio requests that this function generates. If it is "<= 0", then a
        suitable default will be chosen (currently 8).

        On error, the callback is called without arguments, otherwise it
        receives two array-refs with path-relative entry names.

        Example:

           aio_scandir $dir, 0, sub {
              my ($dirs, $nondirs) = @_;
              print "real directories: @$dirs\n";
              print "everything else: @$nondirs\n";
           };

        Implementation notes.

        The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
        can.

        After reading the directory, the modification time, size etc. of the
        directory before and after the readdir is checked, and if they
        match, the link count will be used to decide how many entries are
        directories (if >= 2). Otherwise, no knowledge of the number of
        subdirectories will be assumed.

        Then entires will be sorted into likely directories (everything
        without a non-initial dot) and likely non-directories (everything
        else). Then every entry + "/." will be "stat"'ed, likely directories
        first. This is often faster because filesystems might detect the
        type of the entry without reading the inode data (e.g. ext2fs
        filetype feature). If that succeeds, it assumes that the entry is a
        directory or a symlink to directory (which will be checked
        seperately).

        If the known number of directories has been reached, the rest of the
        entries is assumed to be non-directories.

    aio_fsync $fh, $callback->($status)
        Asynchronously call fsync on the given filehandle and call the
        callback with the fsync result code.

    aio_fdatasync $fh, $callback->($status)
        Asynchronously call fdatasync on the given filehandle and call the
        callback with the fdatasync result code.

        If this call isn't available because your OS lacks it or it couldn't
        be detected, it will be emulated by calling "fsync" instead.

  SUPPORT FUNCTIONS
    $fileno = IO::AIO::poll_fileno
        Return the *request result pipe file descriptor*. This filehandle
        must be polled for reading by some mechanism outside this module
        (e.g. Event or select, see below or the SYNOPSIS). 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.

        Example: Install an Event watcher that automatically calls
        IO::AIO::poll_cb with high priority:

           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 (i.e. for which
        their callback has not been invoked yet).

        Example: wait till there are no outstanding requests anymore:

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

    IO::AIO::flush
        Wait till all outstanding AIO requests have been handled.

        Strictly equivalent to:

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

    IO::AIO::poll
        Waits until some requests have been handled.

        Strictly equivalent to:

           IO::AIO::poll_wait, IO::AIO::poll_cb
              if IO::AIO::nreqs;

    IO::AIO::min_parallel $nthreads
        Set the minimum number of AIO threads to $nthreads. The current
        default is 4, which means four asynchronous operations can be done
        at one time (the number of outstanding operations, however, is
        unlimited).

        IO::AIO starts threads only on demand, when an AIO request is queued
        and no free thread exists.

        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 most circumstances you don't need to call this function, as
        the module selects a default that is suitable for low to moderate
        load.

    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, this function
        kills them. This function blocks until the limit is reached.

        While $nthreads are zero, aio requests get queued but not executed
        until the number of threads has been increased again.

        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 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.

  FORK BEHAVIOUR
    Before the fork, IO::AIO enters a quiescent state where no requests can
    be added in other threads and no results will be processed. After the
    fork the parent simply leaves the quiescent state and continues
    request/result processing, while the child clears the request/result
    queue (so the requests started before the fork will only be handled in
    the parent). Threats will be started on demand until the limit ste in
    the parent process has been reached again.

SEE ALSO
    Coro, Linux::AIO.

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

Revision:	1.17
Committed:	Mon Jun 26 14:53:55 2006 UTC (17 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.16:	+30 -0 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	root	1.14	# AnyEvent
19			open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
20			my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
21
22	root	1.5	# Event
23			Event->io (fd => IO::AIO::poll_fileno,
24			poll => 'r',
25			cb => \&IO::AIO::poll_cb);
26
27			# Glib/Gtk2
28			add_watch Glib::IO IO::AIO::poll_fileno,
29	root	1.7	in => sub { IO::AIO::poll_cb; 1 };
30	root	1.5
31			# Tk
32			Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
33			readable => \&IO::AIO::poll_cb);
34
35	root	1.6	# Danga::Socket
36			Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
37			\&IO::AIO::poll_cb);
38
39	root	1.1	DESCRIPTION
40			This module implements asynchronous I/O using whatever means your
41	root	1.2	operating system supports.
42	root	1.1
43	root	1.2	Currently, a number of threads are started that execute your read/writes
44			and signal their completion. You don't need thread support in your libc
45			or perl, and the threads created by this module will not be visible to
46			the pthreads library. In the future, this module might make use of the
47			native aio functions available on many operating systems. However, they
48			are often not well-supported (Linux doesn't allow them on normal files
49			currently, for example), and they would only support aio_read and
50			aio_write, so the remaining functionality would have to be implemented
51			using threads anyway.
52	root	1.1
53			Although the module will work with in the presence of other threads, it
54	root	1.7	is currently not reentrant, so use appropriate locking yourself, always
55			call "poll_cb" from within the same thread, or never call "poll_cb" (or
56			other "aio_" functions) recursively.
57	root	1.1
58	root	1.4	FUNCTIONS
59			AIO FUNCTIONS
60	root	1.1	All the "aio_*" calls are more or less thin wrappers around the syscall
61			with the same name (sans "aio_"). The arguments are similar or
62	root	1.6	identical, and they all accept an additional (and optional) $callback
63			argument which must be a code reference. This code reference will get
64			called with the syscall return code (e.g. most syscalls return -1 on
65			error, unlike perl, which usually delivers "false") as it's sole
66			argument when the given syscall has been executed asynchronously.
67	root	1.1
68	root	1.8	All functions expecting a filehandle keep a copy of the filehandle
69			internally until the request has finished.
70	root	1.1
71	root	1.9	The pathnames you pass to these routines must be absolute and encoded
72			in byte form. The reason for the former is that at the time the request
73			is being executed, the current working directory could have changed.
74			Alternatively, you can make sure that you never change the current
75			working directory.
76
77			To encode pathnames to byte form, either make sure you either: a) always
78			pass in filenames you got from outside (command line, readdir etc.), b)
79			are ASCII or ISO 8859-1, c) use the Encode module and encode your
80			pathnames to the locale (or other) encoding in effect in the user
81			environment, d) use Glib::filename_from_unicode on unicode filenames or
82			e) use something else.
83	root	1.1
84	root	1.13	aio_open $pathname, $flags, $mode, $callback->($fh)
85	root	1.2	Asynchronously open or create a file and call the callback with a
86			newly created filehandle for the file.
87
88			The pathname passed to "aio_open" must be absolute. See API NOTES,
89			above, for an explanation.
90	root	1.1
91	root	1.7	The $flags argument is a bitmask. See the "Fcntl" module for a list.
92			They are the same as used by "sysopen".
93
94			Likewise, $mode specifies the mode of the newly created file, if it
95			didn't exist and "O_CREAT" has been given, just like perl's
96			"sysopen", except that it is mandatory (i.e. use 0 if you don't
97			create new files, and 0666 or 0777 if you do).
98	root	1.1
99			Example:
100
101			aio_open "/etc/passwd", O_RDONLY, 0, sub {
102	root	1.2	if ($_[0]) {
103			print "open successful, fh is $_[0]\n";
104	root	1.1	...
105			} else {
106			die "open failed: $!\n";
107			}
108			};
109
110	root	1.13	aio_close $fh, $callback->($status)
111	root	1.1	Asynchronously close a file and call the callback with the result
112	root	1.2	code. WARNING: although accepted, you should not pass in a perl
113			filehandle here, as perl will likely close the file descriptor
114	root	1.7	another time when the filehandle is destroyed. Normally, you can
115			safely call perls "close" or just let filehandles go out of scope.
116
117			This is supposed to be a bug in the API, so that might change. It's
118			therefore best to avoid this function.
119	root	1.1
120	root	1.13	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
121			aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
122	root	1.1	Reads or writes "length" bytes from the specified "fh" and "offset"
123			into the scalar given by "data" and offset "dataoffset" and calls
124			the callback without the actual number of bytes read (or -1 on
125			error, just like the syscall).
126
127	root	1.10	The $data scalar MUST NOT be modified in any way while the request
128			is outstanding. Modifying it can result in segfaults or WW3 (if the
129			necessary/optional hardware is installed).
130
131	root	1.6	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
132	root	1.1	offset 0 within the scalar:
133
134			aio_read $fh, 7, 15, $buffer, 0, sub {
135	root	1.5	$_[0] > 0 or die "read error: $!";
136			print "read $_[0] bytes: <$buffer>\n";
137	root	1.1	};
138
139	root	1.17	aio_move $srcpath, $dstpath, $callback->($status)
140			[EXPERIMENTAL]
141
142			Try to move the file (directories not supported as either source
143			or destination) from $srcpath to $dstpath and call the callback with
144			the 0 (error) or -1 ok.
145
146			This is a composite request that tries to rename(2) the file first.
147			If rename files with "EXDEV", it creates the destination file with
148			mode 0200 and copies the contents of the source file into it using
149			"aio_sendfile", followed by restoring atime, mtime, access mode and
150			uid/gid, in that order, and unlinking the $srcpath.
151
152			If an error occurs, the partial destination file will be unlinked,
153			if possible, except when setting atime, mtime, access mode and
154			uid/gid, where errors are being ignored.
155
156	root	1.13	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
157	root	1.12	Tries to copy $length bytes from $in_fh to $out_fh. It starts
158			reading at byte offset $in_offset, and starts writing at the current
159			file offset of $out_fh. Because of that, it is not safe to issue
160			more than one "aio_sendfile" per $out_fh, as they will interfere
161			with each other.
162
163			This call tries to make use of a native "sendfile" syscall to
164			provide zero-copy operation. For this to work, $out_fh should refer
165			to a socket, and $in_fh should refer to mmap'able file.
166
167			If the native sendfile call fails or is not implemented, it will be
168			emulated, so you can call "aio_sendfile" on any type of filehandle
169			regardless of the limitations of the operating system.
170
171			Please note, however, that "aio_sendfile" can read more bytes from
172			$in_fh than are written, and there is no way to find out how many
173			bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
174			only provides the number of bytes written to $out_fh. Only if the
175			result value equals $length one can assume that $length bytes have
176			been read.
177
178	root	1.13	aio_readahead $fh,$offset,$length, $callback->($retval)
179	root	1.7	"aio_readahead" populates the page cache with data from a file so
180			that subsequent reads from that file will not block on disk I/O. The
181	root	1.1	$offset argument specifies the starting point from which data is to
182			be read and $length specifies the number of bytes to be read. I/O is
183			performed in whole pages, so that offset is effectively rounded down
184			to a page boundary and bytes are read up to the next page boundary
185	root	1.7	greater than or equal to (off-set+length). "aio_readahead" does not
186	root	1.1	read beyond the end of the file. The current file offset of the file
187			is left unchanged.
188
189	root	1.9	If that syscall doesn't exist (likely if your OS isn't Linux) it
190			will be emulated by simply reading the data, which would have a
191			similar effect.
192
193	root	1.13	aio_stat $fh_or_path, $callback->($status)
194			aio_lstat $fh, $callback->($status)
195	root	1.1	Works like perl's "stat" or "lstat" in void context. The callback
196			will be called after the stat and the results will be available
197			using "stat _" or "-s _" etc...
198
199			The pathname passed to "aio_stat" must be absolute. See API NOTES,
200			above, for an explanation.
201
202			Currently, the stats are always 64-bit-stats, i.e. instead of
203			returning an error when stat'ing a large file, the results will be
204			silently truncated unless perl itself is compiled with large file
205			support.
206
207			Example: Print the length of /etc/passwd:
208
209			aio_stat "/etc/passwd", sub {
210			$_[0] and die "stat failed: $!";
211			print "size is ", -s _, "\n";
212			};
213
214	root	1.13	aio_unlink $pathname, $callback->($status)
215	root	1.1	Asynchronously unlink (delete) a file and call the callback with the
216			result code.
217
218	root	1.17	aio_link $srcpath, $dstpath, $callback->($status)
219			Asynchronously create a new link to the existing object at $srcpath
220			at the path $dstpath and call the callback with the result code.
221
222			aio_symlink $srcpath, $dstpath, $callback->($status)
223			Asynchronously create a new symbolic link to the existing object at
224			$srcpath at the path $dstpath and call the callback with the result
225			code.
226
227			aio_rename $srcpath, $dstpath, $callback->($status)
228			Asynchronously rename the object at $srcpath to $dstpath, just as
229			rename(2) and call the callback with the result code.
230
231	root	1.13	aio_rmdir $pathname, $callback->($status)
232	root	1.9	Asynchronously rmdir (delete) a directory and call the callback with
233			the result code.
234
235	root	1.15	aio_readdir $pathname, $callback->($entries)
236	root	1.13	Unlike the POSIX call of the same name, "aio_readdir" reads an
237			entire directory (i.e. opendir + readdir + closedir). The entries
238			will not be sorted, and will NOT include the "." and ".." entries.
239
240			The callback a single argument which is either "undef" or an
241			array-ref with the filenames.
242
243			aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
244			Scans a directory (similar to "aio_readdir") and tries to separate
245			the entries of directory $path into two sets of names, ones you can
246			recurse into (directories), and ones you cannot recurse into
247			(everything else).
248
249			"aio_scandir" is a composite request that consists of many
250			aio-primitives. $maxreq specifies the maximum number of outstanding
251			aio requests that this function generates. If it is "<= 0", then a
252			suitable default will be chosen (currently 8).
253
254			On error, the callback is called without arguments, otherwise it
255			receives two array-refs with path-relative entry names.
256
257			Example:
258
259			aio_scandir $dir, 0, sub {
260			my ($dirs, $nondirs) = @_;
261			print "real directories: @$dirs\n";
262			print "everything else: @$nondirs\n";
263			};
264
265			Implementation notes.
266
267			The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
268			can.
269
270			After reading the directory, the modification time, size etc. of the
271			directory before and after the readdir is checked, and if they
272			match, the link count will be used to decide how many entries are
273			directories (if >= 2). Otherwise, no knowledge of the number of
274			subdirectories will be assumed.
275
276			Then entires will be sorted into likely directories (everything
277			without a non-initial dot) and likely non-directories (everything
278			else). Then every entry + "/." will be "stat"'ed, likely directories
279			first. This is often faster because filesystems might detect the
280	root	1.16	type of the entry without reading the inode data (e.g. ext2fs
281	root	1.13	filetype feature). If that succeeds, it assumes that the entry is a
282			directory or a symlink to directory (which will be checked
283			seperately).
284
285			If the known number of directories has been reached, the rest of the
286			entries is assumed to be non-directories.
287
288			aio_fsync $fh, $callback->($status)
289	root	1.1	Asynchronously call fsync on the given filehandle and call the
290			callback with the fsync result code.
291
292	root	1.13	aio_fdatasync $fh, $callback->($status)
293	root	1.1	Asynchronously call fdatasync on the given filehandle and call the
294	root	1.9	callback with the fdatasync result code.
295
296			If this call isn't available because your OS lacks it or it couldn't
297			be detected, it will be emulated by calling "fsync" instead.
298	root	1.1
299	root	1.4	SUPPORT FUNCTIONS
300			$fileno = IO::AIO::poll_fileno
301	root	1.7	Return the request result pipe file descriptor. This filehandle
302			must be polled for reading by some mechanism outside this module
303			(e.g. Event or select, see below or the SYNOPSIS). If the pipe
304			becomes readable you have to call "poll_cb" to check the results.
305	root	1.4
306			See "poll_cb" for an example.
307
308			IO::AIO::poll_cb
309			Process all outstanding events on the result pipe. You have to call
310			this regularly. Returns the number of events processed. Returns
311			immediately when no events are outstanding.
312
313	root	1.7	Example: Install an Event watcher that automatically calls
314			IO::AIO::poll_cb with high priority:
315	root	1.4
316			Event->io (fd => IO::AIO::poll_fileno,
317			poll => 'r', async => 1,
318			cb => \&IO::AIO::poll_cb);
319
320			IO::AIO::poll_wait
321			Wait till the result filehandle becomes ready for reading (simply
322	root	1.7	does a "select" on the filehandle. This is useful if you want to
323	root	1.4	synchronously wait for some requests to finish).
324
325			See "nreqs" for an example.
326
327			IO::AIO::nreqs
328	root	1.7	Returns the number of requests currently outstanding (i.e. for which
329			their callback has not been invoked yet).
330	root	1.4
331			Example: wait till there are no outstanding requests anymore:
332
333			IO::AIO::poll_wait, IO::AIO::poll_cb
334			while IO::AIO::nreqs;
335
336	root	1.6	IO::AIO::flush
337			Wait till all outstanding AIO requests have been handled.
338
339			Strictly equivalent to:
340
341			IO::AIO::poll_wait, IO::AIO::poll_cb
342			while IO::AIO::nreqs;
343
344			IO::AIO::poll
345			Waits until some requests have been handled.
346
347			Strictly equivalent to:
348
349			IO::AIO::poll_wait, IO::AIO::poll_cb
350			if IO::AIO::nreqs;
351
352	root	1.4	IO::AIO::min_parallel $nthreads
353	root	1.11	Set the minimum number of AIO threads to $nthreads. The current
354			default is 4, which means four asynchronous operations can be done
355			at one time (the number of outstanding operations, however, is
356			unlimited).
357
358			IO::AIO starts threads only on demand, when an AIO request is queued
359			and no free thread exists.
360	root	1.4
361			It is recommended to keep the number of threads low, as some Linux
362			kernel versions will scale negatively with the number of threads
363			(higher parallelity => MUCH higher latency). With current Linux 2.6
364			versions, 4-32 threads should be fine.
365
366	root	1.11	Under most circumstances you don't need to call this function, as
367			the module selects a default that is suitable for low to moderate
368			load.
369	root	1.4
370			IO::AIO::max_parallel $nthreads
371			Sets the maximum number of AIO threads to $nthreads. If more than
372	root	1.11	the specified number of threads are currently running, this function
373			kills them. This function blocks until the limit is reached.
374
375			While $nthreads are zero, aio requests get queued but not executed
376			until the number of threads has been increased again.
377	root	1.4
378			This module automatically runs "max_parallel 0" at program end, to
379			ensure that all threads are killed and that there are no outstanding
380			requests.
381
382			Under normal circumstances you don't need to call this function.
383
384			$oldnreqs = IO::AIO::max_outstanding $nreqs
385			Sets the maximum number of outstanding requests to $nreqs. If you
386			try to queue up more than this number of requests, the caller will
387			block until some requests have been handled.
388
389			The default is very large, so normally there is no practical limit.
390	root	1.11	If you queue up many requests in a loop it often improves speed if
391			you set this to a relatively low number, such as 100.
392	root	1.4
393			Under normal circumstances you don't need to call this function.
394	root	1.1
395	root	1.9	FORK BEHAVIOUR
396	root	1.11	Before the fork, IO::AIO enters a quiescent state where no requests can
397	root	1.10	be added in other threads and no results will be processed. After the
398			fork the parent simply leaves the quiescent state and continues
399			request/result processing, while the child clears the request/result
400	root	1.11	queue (so the requests started before the fork will only be handled in
401			the parent). Threats will be started on demand until the limit ste in
402			the parent process has been reached again.
403	root	1.9
404	root	1.1	SEE ALSO
405	root	1.2	Coro, Linux::AIO.
406	root	1.1
407			AUTHOR
408			Marc Lehmann <schmorp@schmorp.de>
409			http://home.schmorp.de/
410