[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,
               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_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_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. ext2s
        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:	1.13
Committed:	Tue Aug 30 15:45:10 2005 UTC (18 years, 8 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_61, rel-1_6
Changes since 1.12:	+65 -12 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	root	1.7	in => sub { IO::AIO::poll_cb; 1 };
26	root	1.5
27			# Tk
28			Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
29			readable => \&IO::AIO::poll_cb);
30
31	root	1.6	# Danga::Socket
32			Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
33			\&IO::AIO::poll_cb);
34
35	root	1.1	DESCRIPTION
36			This module implements asynchronous I/O using whatever means your
37	root	1.2	operating system supports.
38	root	1.1
39	root	1.2	Currently, a number of threads are started that execute your read/writes
40			and signal their completion. You don't need thread support in your libc
41			or perl, and the threads created by this module will not be visible to
42			the pthreads library. In the future, this module might make use of the
43			native aio functions available on many operating systems. However, they
44			are often not well-supported (Linux doesn't allow them on normal files
45			currently, for example), and they would only support aio_read and
46			aio_write, so the remaining functionality would have to be implemented
47			using threads anyway.
48	root	1.1
49			Although the module will work with in the presence of other threads, it
50	root	1.7	is currently not reentrant, so use appropriate locking yourself, always
51			call "poll_cb" from within the same thread, or never call "poll_cb" (or
52			other "aio_" functions) recursively.
53	root	1.1
54	root	1.4	FUNCTIONS
55			AIO FUNCTIONS
56	root	1.1	All the "aio_*" calls are more or less thin wrappers around the syscall
57			with the same name (sans "aio_"). The arguments are similar or
58	root	1.6	identical, and they all accept an additional (and optional) $callback
59			argument which must be a code reference. This code reference will get
60			called with the syscall return code (e.g. most syscalls return -1 on
61			error, unlike perl, which usually delivers "false") as it's sole
62			argument when the given syscall has been executed asynchronously.
63	root	1.1
64	root	1.8	All functions expecting a filehandle keep a copy of the filehandle
65			internally until the request has finished.
66	root	1.1
67	root	1.9	The pathnames you pass to these routines must be absolute and encoded
68			in byte form. The reason for the former is that at the time the request
69			is being executed, the current working directory could have changed.
70			Alternatively, you can make sure that you never change the current
71			working directory.
72
73			To encode pathnames to byte form, either make sure you either: a) always
74			pass in filenames you got from outside (command line, readdir etc.), b)
75			are ASCII or ISO 8859-1, c) use the Encode module and encode your
76			pathnames to the locale (or other) encoding in effect in the user
77			environment, d) use Glib::filename_from_unicode on unicode filenames or
78			e) use something else.
79	root	1.1
80	root	1.13	aio_open $pathname, $flags, $mode, $callback->($fh)
81	root	1.2	Asynchronously open or create a file and call the callback with a
82			newly created filehandle for the file.
83
84			The pathname passed to "aio_open" must be absolute. See API NOTES,
85			above, for an explanation.
86	root	1.1
87	root	1.7	The $flags argument is a bitmask. See the "Fcntl" module for a list.
88			They are the same as used by "sysopen".
89
90			Likewise, $mode specifies the mode of the newly created file, if it
91			didn't exist and "O_CREAT" has been given, just like perl's
92			"sysopen", except that it is mandatory (i.e. use 0 if you don't
93			create new files, and 0666 or 0777 if you do).
94	root	1.1
95			Example:
96
97			aio_open "/etc/passwd", O_RDONLY, 0, sub {
98	root	1.2	if ($_[0]) {
99			print "open successful, fh is $_[0]\n";
100	root	1.1	...
101			} else {
102			die "open failed: $!\n";
103			}
104			};
105
106	root	1.13	aio_close $fh, $callback->($status)
107	root	1.1	Asynchronously close a file and call the callback with the result
108	root	1.2	code. WARNING: although accepted, you should not pass in a perl
109			filehandle here, as perl will likely close the file descriptor
110	root	1.7	another time when the filehandle is destroyed. Normally, you can
111			safely call perls "close" or just let filehandles go out of scope.
112
113			This is supposed to be a bug in the API, so that might change. It's
114			therefore best to avoid this function.
115	root	1.1
116	root	1.13	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
117			aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
118	root	1.1	Reads or writes "length" bytes from the specified "fh" and "offset"
119			into the scalar given by "data" and offset "dataoffset" and calls
120			the callback without the actual number of bytes read (or -1 on
121			error, just like the syscall).
122
123	root	1.10	The $data scalar MUST NOT be modified in any way while the request
124			is outstanding. Modifying it can result in segfaults or WW3 (if the
125			necessary/optional hardware is installed).
126
127	root	1.6	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
128	root	1.1	offset 0 within the scalar:
129
130			aio_read $fh, 7, 15, $buffer, 0, sub {
131	root	1.5	$_[0] > 0 or die "read error: $!";
132			print "read $_[0] bytes: <$buffer>\n";
133	root	1.1	};
134
135	root	1.13	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
136	root	1.12	Tries to copy $length bytes from $in_fh to $out_fh. It starts
137			reading at byte offset $in_offset, and starts writing at the current
138			file offset of $out_fh. Because of that, it is not safe to issue
139			more than one "aio_sendfile" per $out_fh, as they will interfere
140			with each other.
141
142			This call tries to make use of a native "sendfile" syscall to
143			provide zero-copy operation. For this to work, $out_fh should refer
144			to a socket, and $in_fh should refer to mmap'able file.
145
146			If the native sendfile call fails or is not implemented, it will be
147			emulated, so you can call "aio_sendfile" on any type of filehandle
148			regardless of the limitations of the operating system.
149
150			Please note, however, that "aio_sendfile" can read more bytes from
151			$in_fh than are written, and there is no way to find out how many
152			bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
153			only provides the number of bytes written to $out_fh. Only if the
154			result value equals $length one can assume that $length bytes have
155			been read.
156
157	root	1.13	aio_readahead $fh,$offset,$length, $callback->($retval)
158	root	1.7	"aio_readahead" populates the page cache with data from a file so
159			that subsequent reads from that file will not block on disk I/O. The
160	root	1.1	$offset argument specifies the starting point from which data is to
161			be read and $length specifies the number of bytes to be read. I/O is
162			performed in whole pages, so that offset is effectively rounded down
163			to a page boundary and bytes are read up to the next page boundary
164	root	1.7	greater than or equal to (off-set+length). "aio_readahead" does not
165	root	1.1	read beyond the end of the file. The current file offset of the file
166			is left unchanged.
167
168	root	1.9	If that syscall doesn't exist (likely if your OS isn't Linux) it
169			will be emulated by simply reading the data, which would have a
170			similar effect.
171
172	root	1.13	aio_stat $fh_or_path, $callback->($status)
173			aio_lstat $fh, $callback->($status)
174	root	1.1	Works like perl's "stat" or "lstat" in void context. The callback
175			will be called after the stat and the results will be available
176			using "stat _" or "-s _" etc...
177
178			The pathname passed to "aio_stat" must be absolute. See API NOTES,
179			above, for an explanation.
180
181			Currently, the stats are always 64-bit-stats, i.e. instead of
182			returning an error when stat'ing a large file, the results will be
183			silently truncated unless perl itself is compiled with large file
184			support.
185
186			Example: Print the length of /etc/passwd:
187
188			aio_stat "/etc/passwd", sub {
189			$_[0] and die "stat failed: $!";
190			print "size is ", -s _, "\n";
191			};
192
193	root	1.13	aio_unlink $pathname, $callback->($status)
194	root	1.1	Asynchronously unlink (delete) a file and call the callback with the
195			result code.
196
197	root	1.13	aio_rmdir $pathname, $callback->($status)
198	root	1.9	Asynchronously rmdir (delete) a directory and call the callback with
199			the result code.
200
201	root	1.13	aio_readdir $pathname $callback->($entries)
202			Unlike the POSIX call of the same name, "aio_readdir" reads an
203			entire directory (i.e. opendir + readdir + closedir). The entries
204			will not be sorted, and will NOT include the "." and ".." entries.
205
206			The callback a single argument which is either "undef" or an
207			array-ref with the filenames.
208
209			aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
210			Scans a directory (similar to "aio_readdir") and tries to separate
211			the entries of directory $path into two sets of names, ones you can
212			recurse into (directories), and ones you cannot recurse into
213			(everything else).
214
215			"aio_scandir" is a composite request that consists of many
216			aio-primitives. $maxreq specifies the maximum number of outstanding
217			aio requests that this function generates. If it is "<= 0", then a
218			suitable default will be chosen (currently 8).
219
220			On error, the callback is called without arguments, otherwise it
221			receives two array-refs with path-relative entry names.
222
223			Example:
224
225			aio_scandir $dir, 0, sub {
226			my ($dirs, $nondirs) = @_;
227			print "real directories: @$dirs\n";
228			print "everything else: @$nondirs\n";
229			};
230
231			Implementation notes.
232
233			The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
234			can.
235
236			After reading the directory, the modification time, size etc. of the
237			directory before and after the readdir is checked, and if they
238			match, the link count will be used to decide how many entries are
239			directories (if >= 2). Otherwise, no knowledge of the number of
240			subdirectories will be assumed.
241
242			Then entires will be sorted into likely directories (everything
243			without a non-initial dot) and likely non-directories (everything
244			else). Then every entry + "/." will be "stat"'ed, likely directories
245			first. This is often faster because filesystems might detect the
246			type of the entry without reading the inode data (e.g. ext2s
247			filetype feature). If that succeeds, it assumes that the entry is a
248			directory or a symlink to directory (which will be checked
249			seperately).
250
251			If the known number of directories has been reached, the rest of the
252			entries is assumed to be non-directories.
253
254			aio_fsync $fh, $callback->($status)
255	root	1.1	Asynchronously call fsync on the given filehandle and call the
256			callback with the fsync result code.
257
258	root	1.13	aio_fdatasync $fh, $callback->($status)
259	root	1.1	Asynchronously call fdatasync on the given filehandle and call the
260	root	1.9	callback with the fdatasync result code.
261
262			If this call isn't available because your OS lacks it or it couldn't
263			be detected, it will be emulated by calling "fsync" instead.
264	root	1.1
265	root	1.4	SUPPORT FUNCTIONS
266			$fileno = IO::AIO::poll_fileno
267	root	1.7	Return the request result pipe file descriptor. This filehandle
268			must be polled for reading by some mechanism outside this module
269			(e.g. Event or select, see below or the SYNOPSIS). If the pipe
270			becomes readable you have to call "poll_cb" to check the results.
271	root	1.4
272			See "poll_cb" for an example.
273
274			IO::AIO::poll_cb
275			Process all outstanding events on the result pipe. You have to call
276			this regularly. Returns the number of events processed. Returns
277			immediately when no events are outstanding.
278
279	root	1.7	Example: Install an Event watcher that automatically calls
280			IO::AIO::poll_cb with high priority:
281	root	1.4
282			Event->io (fd => IO::AIO::poll_fileno,
283			poll => 'r', async => 1,
284			cb => \&IO::AIO::poll_cb);
285
286			IO::AIO::poll_wait
287			Wait till the result filehandle becomes ready for reading (simply
288	root	1.7	does a "select" on the filehandle. This is useful if you want to
289	root	1.4	synchronously wait for some requests to finish).
290
291			See "nreqs" for an example.
292
293			IO::AIO::nreqs
294	root	1.7	Returns the number of requests currently outstanding (i.e. for which
295			their callback has not been invoked yet).
296	root	1.4
297			Example: wait till there are no outstanding requests anymore:
298
299			IO::AIO::poll_wait, IO::AIO::poll_cb
300			while IO::AIO::nreqs;
301
302	root	1.6	IO::AIO::flush
303			Wait till all outstanding AIO requests have been handled.
304
305			Strictly equivalent to:
306
307			IO::AIO::poll_wait, IO::AIO::poll_cb
308			while IO::AIO::nreqs;
309
310			IO::AIO::poll
311			Waits until some requests have been handled.
312
313			Strictly equivalent to:
314
315			IO::AIO::poll_wait, IO::AIO::poll_cb
316			if IO::AIO::nreqs;
317
318	root	1.4	IO::AIO::min_parallel $nthreads
319	root	1.11	Set the minimum number of AIO threads to $nthreads. The current
320			default is 4, which means four asynchronous operations can be done
321			at one time (the number of outstanding operations, however, is
322			unlimited).
323
324			IO::AIO starts threads only on demand, when an AIO request is queued
325			and no free thread exists.
326	root	1.4
327			It is recommended to keep the number of threads low, as some Linux
328			kernel versions will scale negatively with the number of threads
329			(higher parallelity => MUCH higher latency). With current Linux 2.6
330			versions, 4-32 threads should be fine.
331
332	root	1.11	Under most circumstances you don't need to call this function, as
333			the module selects a default that is suitable for low to moderate
334			load.
335	root	1.4
336			IO::AIO::max_parallel $nthreads
337			Sets the maximum number of AIO threads to $nthreads. If more than
338	root	1.11	the specified number of threads are currently running, this function
339			kills them. This function blocks until the limit is reached.
340
341			While $nthreads are zero, aio requests get queued but not executed
342			until the number of threads has been increased again.
343	root	1.4
344			This module automatically runs "max_parallel 0" at program end, to
345			ensure that all threads are killed and that there are no outstanding
346			requests.
347
348			Under normal circumstances you don't need to call this function.
349
350			$oldnreqs = IO::AIO::max_outstanding $nreqs
351			Sets the maximum number of outstanding requests to $nreqs. If you
352			try to queue up more than this number of requests, the caller will
353			block until some requests have been handled.
354
355			The default is very large, so normally there is no practical limit.
356	root	1.11	If you queue up many requests in a loop it often improves speed if
357			you set this to a relatively low number, such as 100.
358	root	1.4
359			Under normal circumstances you don't need to call this function.
360	root	1.1
361	root	1.9	FORK BEHAVIOUR
362	root	1.11	Before the fork, IO::AIO enters a quiescent state where no requests can
363	root	1.10	be added in other threads and no results will be processed. After the
364			fork the parent simply leaves the quiescent state and continues
365			request/result processing, while the child clears the request/result
366	root	1.11	queue (so the requests started before the fork will only be handled in
367			the parent). Threats will be started on demand until the limit ste in
368			the parent process has been reached again.
369	root	1.9
370	root	1.1	SEE ALSO
371	root	1.2	Coro, Linux::AIO.
372	root	1.1
373			AUTHOR
374			Marc Lehmann <schmorp@schmorp.de>
375			http://home.schmorp.de/
376