IO-AIO/AIO.pm

=head1 NAME

IO::AIO - Asynchronous Input/Output

=head1 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);


=head1 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
C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
C<aio_> functions) recursively.

=cut

package IO::AIO;

no warnings;

use base 'Exporter';

use Fcntl ();

BEGIN {
   $VERSION = '1.72';

   @EXPORT = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
                aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
                aio_fsync aio_fdatasync aio_readahead);
   @EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel
                   max_outstanding nreqs);

   require XSLoader;
   XSLoader::load IO::AIO, $VERSION;
}

=head1 FUNCTIONS

=head2 AIO FUNCTIONS

All the C<aio_*> calls are more or less thin wrappers around the syscall
with the same name (sans C<aio_>). The arguments are similar or identical,
and they all accept an additional (and optional) C<$callback> argument
which must be a code reference. This code reference will get called with
the syscall return code (e.g. most syscalls return C<-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 I<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.

=over 4

=item 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 C<aio_open> must be absolute. See API NOTES, above,
for an explanation.

The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
list. They are the same as used by C<sysopen>.

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

=item aio_close $fh, $callback->($status)

Asynchronously close a file and call the callback with the result
code. I<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
C<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.

=item aio_read  $fh,$offset,$length, $data,$dataoffset, $callback->($retval)

=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)

Reads or writes C<length> bytes from the specified C<fh> and C<offset>
into the scalar given by C<data> and offset C<dataoffset> and calls the
callback without the actual number of bytes read (or -1 on error, just
like the syscall).

The C<$data> scalar I<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 C<$buffer>, starting at
offset C<0> within the scalar:

   aio_read $fh, 7, 15, $buffer, 0, sub {
      $_[0] > 0 or die "read error: $!";
      print "read $_[0] bytes: <$buffer>\n";
   };

=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)

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

This call tries to make use of a native C<sendfile> syscall to provide
zero-copy operation. For this to work, C<$out_fh> should refer to a
socket, and C<$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 C<aio_sendfile> on any type of filehandle
regardless of the limitations of the operating system.

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

=item aio_readahead $fh,$offset,$length, $callback->($retval)

C<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 C<$offset>
argument specifies the starting point from which data is to be read and
C<$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). C<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.

=item aio_stat  $fh_or_path, $callback->($status)

=item aio_lstat $fh, $callback->($status)

Works like perl's C<stat> or C<lstat> in void context. The callback will
be called after the stat and the results will be available using C<stat _>
or C<-s _> etc...

The pathname passed to C<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 F</etc/passwd>:

   aio_stat "/etc/passwd", sub {
      $_[0] and die "stat failed: $!";
      print "size is ", -s _, "\n";
   };

=item aio_unlink $pathname, $callback->($status)

Asynchronously unlink (delete) a file and call the callback with the
result code.

=item aio_rmdir $pathname, $callback->($status)

Asynchronously rmdir (delete) a directory and call the callback with the
result code.

=item aio_readdir $pathname, $callback->($entries)

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

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

=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)

Scans a directory (similar to C<aio_readdir>) and tries to separate the
entries of directory C<$path> into two sets of names, ones you can recurse
into (directories), and ones you cannot recurse into (everything else).

C<aio_scandir> is a composite request that consists of many
aio-primitives. C<$maxreq> specifies the maximum number of outstanding
aio requests that this function generates. If it is C<< <= 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 C<aio_readdir> cannot be avoided, but C<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 + C</.> will be C<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.

=cut

sub aio_scandir($$$) {
   my ($path, $maxreq, $cb) = @_;

   $maxreq = 8 if $maxreq <= 0;

   # stat once
   aio_stat $path, sub {
      return $cb->() if $_[0];
      my $hash1 = join ":", (stat _)[0,1,3,7,9];

      # read the directory entries
      aio_readdir $path, sub {
         my $entries = shift
            or return $cb->();

         # stat the dir another time
         aio_stat $path, sub {
            my $hash2 = join ":", (stat _)[0,1,3,7,9];

            my $ndirs;

            # take the slow route if anything looks fishy
            if ($hash1 ne $hash2) {
               $ndirs = -1;
            } else {
               # if nlink == 2, we are finished
               # on non-posix-fs's, we rely on nlink < 2
               $ndirs = (stat _)[3] - 2
                  or return $cb->([], $entries);
            }

            # sort into likely dirs and likely nondirs
            # dirs == files without ".", short entries first
            $entries = [map $_->[0],
                           sort { $b->[1] cmp $a->[1] }
                              map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
                                 @$entries];

            my (@dirs, @nondirs);

            my ($statcb, $schedcb);
            my $nreq = 0;

            $schedcb = sub {
               if (@$entries) {
                  if ($nreq < $maxreq) {
                     my $ent = pop @$entries;
                     $nreq++;
                     aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
                  }
               } elsif (!$nreq) {
                  # finished
                  undef $statcb;
                  undef $schedcb;
                  $cb->(\@dirs, \@nondirs) if $cb;
                  undef $cb;
               }
            };
            $statcb = sub {
               my ($status, $entry) = @_;

               if ($status < 0) {
                  $nreq--;
                  push @nondirs, $entry;
                  &$schedcb;
               } else {
                  # need to check for real directory
                  aio_lstat "$path/$entry", sub {
                     $nreq--;

                     if (-d _) {
                        push @dirs, $entry;

                        if (!--$ndirs) {
                           push @nondirs, @$entries;
                           $entries = [];
                        }
                     } else {
                        push @nondirs, $entry;
                     }

                     &$schedcb;
                  }
               }
            };

            &$schedcb while @$entries && $nreq < $maxreq;
         };
      };
   };
}

=item aio_fsync $fh, $callback->($status)

Asynchronously call fsync on the given filehandle and call the callback
with the fsync result code.

=item 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 C<fsync> instead.

=back

=head2 SUPPORT FUNCTIONS

=over 4

=item $fileno = IO::AIO::poll_fileno

Return the I<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 C<poll_cb> to check the results.

See C<poll_cb> for an example.

=item 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);

=item IO::AIO::poll_wait

Wait till the result filehandle becomes ready for reading (simply does a
C<select> on the filehandle. This is useful if you want to synchronously wait
for some requests to finish).

See C<nreqs> for an example.

=item 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;

=item 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;

=item 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;

=item IO::AIO::min_parallel $nthreads

Set the minimum number of AIO threads to C<$nthreads>. The current default
is C<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.

=item IO::AIO::max_parallel $nthreads

Sets the maximum number of AIO threads to C<$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 C<$nthreads> are zero, aio requests get queued but not executed
until the number of threads has been increased again.

This module automatically runs C<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.

=item $oldnreqs = IO::AIO::max_outstanding $nreqs

Sets the maximum number of outstanding requests to C<$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 C<100>.

Under normal circumstances you don't need to call this function.

=back

=cut

# support function to convert a fd into a perl filehandle
sub _fd2fh {
   return undef if $_[0] < 0;

   # try to generate nice filehandles
   my $sym = "IO::AIO::fd#$_[0]";
   local *$sym;

   open *$sym, "+<&=$_[0]"      # usually works under any unix
      or open *$sym, "<&=$_[0]" # cygwin needs this
      or open *$sym, ">&=$_[0]" # or this
      or return undef;

   *$sym
}

min_parallel 4;

END {
   max_parallel 0;
}

1;

=head2 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.

=head1 SEE ALSO

L<Coro>, L<Linux::AIO>.

=head1 AUTHOR

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

=cut

Revision:	1.47
Committed:	Thu Dec 29 15:44:13 2005 UTC (18 years, 4 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_72
Changes since 1.46:	+2 -2 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			IO::AIO - Asynchronous Input/Output
4
5			=head1 SYNOPSIS
6
7			use IO::AIO;
8
9	root	1.6	aio_open "/etc/passwd", O_RDONLY, 0, sub {
10			my ($fh) = @_;
11			...
12			};
13
14			aio_unlink "/tmp/file", sub { };
15
16			aio_read $fh, 30000, 1024, $buffer, 0, sub {
17	root	1.8	$_[0] > 0 or die "read error: $!";
18	root	1.6	};
19
20	root	1.42	# AnyEvent
21			open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
22			my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
23
24	root	1.6	# Event
25			Event->io (fd => IO::AIO::poll_fileno,
26	root	1.7	poll => 'r',
27	root	1.6	cb => \&IO::AIO::poll_cb);
28
29			# Glib/Gtk2
30			add_watch Glib::IO IO::AIO::poll_fileno,
31	root	1.22	in => sub { IO::AIO::poll_cb; 1 };
32	root	1.6
33			# Tk
34			Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
35			readable => \&IO::AIO::poll_cb);
36
37	root	1.11	# Danga::Socket
38			Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
39			\&IO::AIO::poll_cb);
40
41
42	root	1.1	=head1 DESCRIPTION
43
44			This module implements asynchronous I/O using whatever means your
45	root	1.2	operating system supports.
46	root	1.1
47	root	1.2	Currently, a number of threads are started that execute your read/writes
48			and signal their completion. You don't need thread support in your libc or
49			perl, and the threads created by this module will not be visible to the
50			pthreads library. In the future, this module might make use of the native
51			aio functions available on many operating systems. However, they are often
52			not well-supported (Linux doesn't allow them on normal files currently,
53			for example), and they would only support aio_read and aio_write, so the
54			remaining functionality would have to be implemented using threads anyway.
55	root	1.1
56			Although the module will work with in the presence of other threads, it is
57	root	1.22	currently not reentrant, so use appropriate locking yourself, always call
58			C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
59			C<aio_> functions) recursively.
60	root	1.1
61			=cut
62
63			package IO::AIO;
64
65	root	1.23	no warnings;
66
67	root	1.1	use base 'Exporter';
68
69	root	1.2	use Fcntl ();
70
71	root	1.1	BEGIN {
72	root	1.47	$VERSION = '1.72';
73	root	1.1
74	root	1.39	@EXPORT = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
75	root	1.40	aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
76	root	1.38	aio_fsync aio_fdatasync aio_readahead);
77			@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel
78			max_outstanding nreqs);
79	root	1.1
80			require XSLoader;
81			XSLoader::load IO::AIO, $VERSION;
82			}
83
84	root	1.5	=head1 FUNCTIONS
85	root	1.1
86	root	1.5	=head2 AIO FUNCTIONS
87	root	1.1
88	root	1.5	All the C<aio_*> calls are more or less thin wrappers around the syscall
89			with the same name (sans C<aio_>). The arguments are similar or identical,
90	root	1.14	and they all accept an additional (and optional) C<$callback> argument
91			which must be a code reference. This code reference will get called with
92			the syscall return code (e.g. most syscalls return C<-1> on error, unlike
93			perl, which usually delivers "false") as it's sole argument when the given
94			syscall has been executed asynchronously.
95	root	1.1
96	root	1.23	All functions expecting a filehandle keep a copy of the filehandle
97			internally until the request has finished.
98	root	1.1
99	root	1.28	The pathnames you pass to these routines I<must> be absolute and
100			encoded in byte form. The reason for the former is that at the time the
101			request is being executed, the current working directory could have
102			changed. Alternatively, you can make sure that you never change the
103			current working directory.
104
105			To encode pathnames to byte form, either make sure you either: a)
106			always pass in filenames you got from outside (command line, readdir
107			etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode
108			your pathnames to the locale (or other) encoding in effect in the user
109			environment, d) use Glib::filename_from_unicode on unicode filenames or e)
110			use something else.
111	root	1.1
112	root	1.5	=over 4
113	root	1.1
114	root	1.40	=item aio_open $pathname, $flags, $mode, $callback->($fh)
115	root	1.1
116	root	1.2	Asynchronously open or create a file and call the callback with a newly
117			created filehandle for the file.
118	root	1.1
119			The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
120			for an explanation.
121
122	root	1.20	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
123			list. They are the same as used by C<sysopen>.
124
125			Likewise, C<$mode> specifies the mode of the newly created file, if it
126			didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
127			except that it is mandatory (i.e. use C<0> if you don't create new files,
128			and C<0666> or C<0777> if you do).
129	root	1.1
130			Example:
131
132			aio_open "/etc/passwd", O_RDONLY, 0, sub {
133	root	1.2	if ($_[0]) {
134			print "open successful, fh is $_[0]\n";
135	root	1.1	...
136			} else {
137			die "open failed: $!\n";
138			}
139			};
140
141	root	1.40	=item aio_close $fh, $callback->($status)
142	root	1.1
143	root	1.2	Asynchronously close a file and call the callback with the result
144			code. I<WARNING:> although accepted, you should not pass in a perl
145	root	1.20	filehandle here, as perl will likely close the file descriptor another
146			time when the filehandle is destroyed. Normally, you can safely call perls
147			C<close> or just let filehandles go out of scope.
148
149			This is supposed to be a bug in the API, so that might change. It's
150			therefore best to avoid this function.
151	root	1.1
152	root	1.40	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
153	root	1.1
154	root	1.40	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
155	root	1.1
156			Reads or writes C<length> bytes from the specified C<fh> and C<offset>
157			into the scalar given by C<data> and offset C<dataoffset> and calls the
158			callback without the actual number of bytes read (or -1 on error, just
159			like the syscall).
160
161	root	1.31	The C<$data> scalar I<MUST NOT> be modified in any way while the request
162			is outstanding. Modifying it can result in segfaults or WW3 (if the
163			necessary/optional hardware is installed).
164
165	root	1.17	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
166	root	1.1	offset C<0> within the scalar:
167
168			aio_read $fh, 7, 15, $buffer, 0, sub {
169	root	1.9	$_[0] > 0 or die "read error: $!";
170			print "read $_[0] bytes: <$buffer>\n";
171	root	1.1	};
172
173	root	1.40	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
174	root	1.35
175			Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
176			reading at byte offset C<$in_offset>, and starts writing at the current
177			file offset of C<$out_fh>. Because of that, it is not safe to issue more
178			than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
179			other.
180
181			This call tries to make use of a native C<sendfile> syscall to provide
182			zero-copy operation. For this to work, C<$out_fh> should refer to a
183			socket, and C<$in_fh> should refer to mmap'able file.
184
185			If the native sendfile call fails or is not implemented, it will be
186	root	1.36	emulated, so you can call C<aio_sendfile> on any type of filehandle
187			regardless of the limitations of the operating system.
188	root	1.35
189			Please note, however, that C<aio_sendfile> can read more bytes from
190			C<$in_fh> than are written, and there is no way to find out how many
191	root	1.36	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
192			provides the number of bytes written to C<$out_fh>. Only if the result
193			value equals C<$length> one can assume that C<$length> bytes have been
194			read.
195	root	1.35
196	root	1.40	=item aio_readahead $fh,$offset,$length, $callback->($retval)
197	root	1.1
198	root	1.20	C<aio_readahead> populates the page cache with data from a file so that
199	root	1.1	subsequent reads from that file will not block on disk I/O. The C<$offset>
200			argument specifies the starting point from which data is to be read and
201			C<$length> specifies the number of bytes to be read. I/O is performed in
202			whole pages, so that offset is effectively rounded down to a page boundary
203			and bytes are read up to the next page boundary greater than or equal to
204	root	1.20	(off-set+length). C<aio_readahead> does not read beyond the end of the
205	root	1.1	file. The current file offset of the file is left unchanged.
206
207	root	1.26	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
208			emulated by simply reading the data, which would have a similar effect.
209
210	root	1.40	=item aio_stat $fh_or_path, $callback->($status)
211	root	1.1
212	root	1.40	=item aio_lstat $fh, $callback->($status)
213	root	1.1
214			Works like perl's C<stat> or C<lstat> in void context. The callback will
215			be called after the stat and the results will be available using C<stat _>
216			or C<-s _> etc...
217
218			The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
219			for an explanation.
220
221			Currently, the stats are always 64-bit-stats, i.e. instead of returning an
222			error when stat'ing a large file, the results will be silently truncated
223			unless perl itself is compiled with large file support.
224
225			Example: Print the length of F</etc/passwd>:
226
227			aio_stat "/etc/passwd", sub {
228			$_[0] and die "stat failed: $!";
229			print "size is ", -s _, "\n";
230			};
231
232	root	1.40	=item aio_unlink $pathname, $callback->($status)
233	root	1.1
234			Asynchronously unlink (delete) a file and call the callback with the
235			result code.
236
237	root	1.40	=item aio_rmdir $pathname, $callback->($status)
238	root	1.27
239			Asynchronously rmdir (delete) a directory and call the callback with the
240			result code.
241
242	root	1.46	=item aio_readdir $pathname, $callback->($entries)
243	root	1.37
244			Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
245			directory (i.e. opendir + readdir + closedir). The entries will not be
246			sorted, and will B<NOT> include the C<.> and C<..> entries.
247
248			The callback a single argument which is either C<undef> or an array-ref
249			with the filenames.
250
251	root	1.40	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
252
253			Scans a directory (similar to C<aio_readdir>) and tries to separate the
254			entries of directory C<$path> into two sets of names, ones you can recurse
255			into (directories), and ones you cannot recurse into (everything else).
256
257			C<aio_scandir> is a composite request that consists of many
258			aio-primitives. C<$maxreq> specifies the maximum number of outstanding
259			aio requests that this function generates. If it is C<< <= 0 >>, then a
260			suitable default will be chosen (currently 8).
261
262			On error, the callback is called without arguments, otherwise it receives
263			two array-refs with path-relative entry names.
264
265			Example:
266
267			aio_scandir $dir, 0, sub {
268			my ($dirs, $nondirs) = @_;
269			print "real directories: @$dirs\n";
270			print "everything else: @$nondirs\n";
271			};
272
273			Implementation notes.
274
275			The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
276
277			After reading the directory, the modification time, size etc. of the
278			directory before and after the readdir is checked, and if they match, the
279			link count will be used to decide how many entries are directories (if
280			>= 2). Otherwise, no knowledge of the number of subdirectories will be
281			assumed.
282
283			Then entires will be sorted into likely directories (everything without a
284			non-initial dot) and likely non-directories (everything else). Then every
285			entry + C</.> will be C<stat>'ed, likely directories first. This is often
286			faster because filesystems might detect the type of the entry without
287			reading the inode data (e.g. ext2s filetype feature). If that succeeds,
288			it assumes that the entry is a directory or a symlink to directory (which
289			will be checked seperately).
290
291			If the known number of directories has been reached, the rest of the
292			entries is assumed to be non-directories.
293
294			=cut
295
296			sub aio_scandir($$$) {
297			my ($path, $maxreq, $cb) = @_;
298
299			$maxreq = 8 if $maxreq <= 0;
300
301			# stat once
302			aio_stat $path, sub {
303	root	1.47	return $cb->() if $_[0];
304	root	1.40	my $hash1 = join ":", (stat _)[0,1,3,7,9];
305
306			# read the directory entries
307			aio_readdir $path, sub {
308			my $entries = shift
309			or return $cb->();
310
311			# stat the dir another time
312			aio_stat $path, sub {
313			my $hash2 = join ":", (stat _)[0,1,3,7,9];
314
315			my $ndirs;
316
317			# take the slow route if anything looks fishy
318			if ($hash1 ne $hash2) {
319			$ndirs = -1;
320			} else {
321			# if nlink == 2, we are finished
322			# on non-posix-fs's, we rely on nlink < 2
323			$ndirs = (stat _)[3] - 2
324	root	1.43	or return $cb->([], $entries);
325	root	1.40	}
326
327			# sort into likely dirs and likely nondirs
328			# dirs == files without ".", short entries first
329			$entries = [map $_->[0],
330			sort { $b->[1] cmp $a->[1] }
331			map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
332			@$entries];
333
334			my (@dirs, @nondirs);
335
336			my ($statcb, $schedcb);
337			my $nreq = 0;
338
339			$schedcb = sub {
340			if (@$entries) {
341			if ($nreq < $maxreq) {
342			my $ent = pop @$entries;
343			$nreq++;
344			aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
345			}
346			} elsif (!$nreq) {
347			# finished
348			undef $statcb;
349			undef $schedcb;
350	root	1.45	$cb->(\@dirs, \@nondirs) if $cb;
351	root	1.40	undef $cb;
352			}
353			};
354			$statcb = sub {
355			my ($status, $entry) = @_;
356
357			if ($status < 0) {
358			$nreq--;
359			push @nondirs, $entry;
360			&$schedcb;
361			} else {
362			# need to check for real directory
363			aio_lstat "$path/$entry", sub {
364			$nreq--;
365
366			if (-d _) {
367			push @dirs, $entry;
368
369			if (!--$ndirs) {
370			push @nondirs, @$entries;
371			$entries = [];
372			}
373			} else {
374			push @nondirs, $entry;
375			}
376
377			&$schedcb;
378			}
379			}
380			};
381
382			&$schedcb while @$entries && $nreq < $maxreq;
383			};
384			};
385			};
386			}
387
388			=item aio_fsync $fh, $callback->($status)
389	root	1.1
390			Asynchronously call fsync on the given filehandle and call the callback
391			with the fsync result code.
392
393	root	1.40	=item aio_fdatasync $fh, $callback->($status)
394	root	1.1
395			Asynchronously call fdatasync on the given filehandle and call the
396	root	1.26	callback with the fdatasync result code.
397
398			If this call isn't available because your OS lacks it or it couldn't be
399			detected, it will be emulated by calling C<fsync> instead.
400	root	1.1
401	root	1.5	=back
402
403			=head2 SUPPORT FUNCTIONS
404
405			=over 4
406
407			=item $fileno = IO::AIO::poll_fileno
408
409	root	1.20	Return the I<request result pipe file descriptor>. This filehandle must be
410			polled for reading by some mechanism outside this module (e.g. Event or
411			select, see below or the SYNOPSIS). If the pipe becomes readable you have
412			to call C<poll_cb> to check the results.
413	root	1.5
414			See C<poll_cb> for an example.
415
416			=item IO::AIO::poll_cb
417
418			Process all outstanding events on the result pipe. You have to call this
419			regularly. Returns the number of events processed. Returns immediately
420			when no events are outstanding.
421
422	root	1.20	Example: Install an Event watcher that automatically calls
423			IO::AIO::poll_cb with high priority:
424	root	1.5
425			Event->io (fd => IO::AIO::poll_fileno,
426			poll => 'r', async => 1,
427			cb => \&IO::AIO::poll_cb);
428
429			=item IO::AIO::poll_wait
430
431			Wait till the result filehandle becomes ready for reading (simply does a
432	root	1.20	C<select> on the filehandle. This is useful if you want to synchronously wait
433	root	1.5	for some requests to finish).
434
435			See C<nreqs> for an example.
436
437			=item IO::AIO::nreqs
438
439	root	1.20	Returns the number of requests currently outstanding (i.e. for which their
440			callback has not been invoked yet).
441	root	1.5
442			Example: wait till there are no outstanding requests anymore:
443
444			IO::AIO::poll_wait, IO::AIO::poll_cb
445			while IO::AIO::nreqs;
446
447	root	1.12	=item IO::AIO::flush
448
449			Wait till all outstanding AIO requests have been handled.
450
451	root	1.13	Strictly equivalent to:
452
453			IO::AIO::poll_wait, IO::AIO::poll_cb
454			while IO::AIO::nreqs;
455
456			=item IO::AIO::poll
457
458			Waits until some requests have been handled.
459
460			Strictly equivalent to:
461
462			IO::AIO::poll_wait, IO::AIO::poll_cb
463			if IO::AIO::nreqs;
464
465	root	1.5	=item IO::AIO::min_parallel $nthreads
466
467	root	1.34	Set the minimum number of AIO threads to C<$nthreads>. The current default
468			is C<4>, which means four asynchronous operations can be done at one time
469	root	1.5	(the number of outstanding operations, however, is unlimited).
470
471	root	1.34	IO::AIO starts threads only on demand, when an AIO request is queued and
472			no free thread exists.
473
474	root	1.5	It is recommended to keep the number of threads low, as some Linux
475			kernel versions will scale negatively with the number of threads (higher
476			parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
477			threads should be fine.
478
479	root	1.34	Under most circumstances you don't need to call this function, as the
480			module selects a default that is suitable for low to moderate load.
481	root	1.5
482			=item IO::AIO::max_parallel $nthreads
483
484	root	1.34	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
485			specified number of threads are currently running, this function kills
486			them. This function blocks until the limit is reached.
487
488			While C<$nthreads> are zero, aio requests get queued but not executed
489			until the number of threads has been increased again.
490	root	1.5
491			This module automatically runs C<max_parallel 0> at program end, to ensure
492			that all threads are killed and that there are no outstanding requests.
493
494			Under normal circumstances you don't need to call this function.
495
496			=item $oldnreqs = IO::AIO::max_outstanding $nreqs
497
498			Sets the maximum number of outstanding requests to C<$nreqs>. If you
499			try to queue up more than this number of requests, the caller will block until
500			some requests have been handled.
501
502			The default is very large, so normally there is no practical limit. If you
503	root	1.34	queue up many requests in a loop it often improves speed if you set
504	root	1.5	this to a relatively low number, such as C<100>.
505
506			Under normal circumstances you don't need to call this function.
507
508			=back
509
510	root	1.1	=cut
511
512	root	1.2	# support function to convert a fd into a perl filehandle
513			sub _fd2fh {
514			return undef if $_[0] < 0;
515
516	root	1.23	# try to generate nice filehandles
517			my $sym = "IO::AIO::fd#$_[0]";
518			local *$sym;
519	root	1.25
520	root	1.27	open *$sym, "+<&=$_[0]" # usually works under any unix
521			or open *$sym, "<&=$_[0]" # cygwin needs this
522			or open *$sym, ">&=$_[0]" # or this
523	root	1.2	or return undef;
524
525	root	1.23	*$sym
526	root	1.2	}
527
528	root	1.1	min_parallel 4;
529
530			END {
531			max_parallel 0;
532			}
533
534			1;
535
536	root	1.27	=head2 FORK BEHAVIOUR
537
538	root	1.34	Before the fork, IO::AIO enters a quiescent state where no requests
539			can be added in other threads and no results will be processed. After
540			the fork the parent simply leaves the quiescent state and continues
541			request/result processing, while the child clears the request/result
542			queue (so the requests started before the fork will only be handled in
543			the parent). Threats will be started on demand until the limit ste in the
544			parent process has been reached again.
545	root	1.27
546	root	1.1	=head1 SEE ALSO
547
548			L<Coro>, L<Linux::AIO>.
549
550			=head1 AUTHOR
551
552			Marc Lehmann <schmorp@schmorp.de>
553			http://home.schmorp.de/
554
555			=cut
556