[ViewVC] Diff of: cvs/IO-AIO/AIO.pm

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.120 by root, Sun Dec 2 21:51:36 2007 UTC vs.
Revision 1.211 by root, Tue Sep 27 12:10:29 2011 UTC

 =head1 SYNOPSIS
  use IO::AIO;
- aio_open "/etc/passwd", O_RDONLY, 0, sub {
+ aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
     my $fh = shift
        or die "/etc/passwd: $!";
     ...
  };
  $req->cancel; # cancel request if still in queue
  my $grp = aio_group sub { print "all stats done\n" };
  add $grp aio_stat "..." for ...;
- # AnyEvent integration (EV, Event, Glib, Tk, urxvt, pureperl...)
- open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
- my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
- # EV integration
- my $w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
- # Event integration
- Event->io (fd => IO::AIO::poll_fileno,
-            poll => 'r',
-            cb => \&IO::AIO::poll_cb);
- # Glib/Gtk2 integration
- add_watch Glib::IO IO::AIO::poll_fileno,
-           in => sub { IO::AIO::poll_cb; 1 };
- # Tk integration
- Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
-                           readable => \&IO::AIO::poll_cb);
- # Danga::Socket integration
- 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.
+operating system supports. It is implemented as an interface to C<libeio>
+(L<http://software.schmorp.de/pkg/libeio.html>).
 Asynchronous means that operations that can normally block your program
 (e.g. reading from disk) will be done asynchronously: the operation
 will still block, but you can do something else in the meantime. This
 is extremely useful for programs that need to stay interactive even
 on a RAID volume or over NFS when you do a number of stat operations
 concurrently.
 While most of this works on all types of file descriptors (for
 example sockets), using these functions on file descriptors that
-support nonblocking operation (again, sockets, pipes etc.) is very
+support nonblocking operation (again, sockets, pipes etc.) is
-inefficient. Use an event loop for that (such as the L<Event|Event>
+very inefficient. Use an event loop for that (such as the L<EV>
 module): IO::AIO will naturally fit into such an event loop itself.
 In this version, a number of threads are started that execute your
 requests and signal their completion. You don't need thread support
 in perl, and the threads created by this module will not be visible
 yourself, always call C<poll_cb> from within the same thread, or never
 call C<poll_cb> (or other C<aio_> functions) recursively.
 =head2 EXAMPLE
-This is a simple example that uses the Event module and loads
+This is a simple example that uses the EV module and loads
 F</etc/passwd> asynchronously:
    use Fcntl;
-   use Event;
+   use EV;
    use IO::AIO;
-   # register the IO::AIO callback with Event
+   # register the IO::AIO callback with EV
-   Event->io (fd => IO::AIO::poll_fileno,
+   my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
-              poll => 'r',
-              cb => \&IO::AIO::poll_cb);
    # queue the request to open /etc/passwd
-   aio_open "/etc/passwd", O_RDONLY, 0, sub {
+   aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
       my $fh = shift
          or die "error while opening: $!";
       # stat'ing filehandles is generally non-blocking
       my $size = -s $fh;
          # file contents now in $contents
          print $contents;
          # exit event loop and program
-         Event::unloop;
+         EV::unloop;
       };
    };
    # possibly queue up other requests, or open GUI windows,
    # check for sockets etc. etc.
    # process events as long as there are some:
-   Event::loop;
+   EV::loop;
 =head1 REQUEST ANATOMY AND LIFETIME
 Every C<aio_*> function creates a request. which is a C data structure not
 directly visible to Perl.
 package IO::AIO;
 use Carp ();
-no warnings;
+use common::sense;
-use strict 'vars';
 use base 'Exporter';
 BEGIN {
-   our $VERSION = '2.6';
+   our $VERSION = '4.0';
    our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close
-                     aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir
+                     aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx
-                     aio_scandir aio_symlink aio_readlink aio_sync aio_fsync
+                     aio_scandir aio_symlink aio_readlink aio_realpath aio_sync
+                     aio_fsync aio_syncfs aio_fdatasync aio_sync_file_range aio_fallocate
-                     aio_fdatasync aio_pathsync aio_readahead
+                     aio_pathsync aio_readahead
                      aio_rename aio_link aio_move aio_copy aio_group
                      aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown
-                     aio_chmod aio_utime aio_truncate);
+                     aio_chmod aio_utime aio_truncate
+                     aio_msync aio_mtouch aio_mlock aio_mlockall
+                     aio_statvfs
+                     aio_wd);
-   our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice aio_block));
+   our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
    our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
-                       min_parallel max_parallel max_idle
+                       min_parallel max_parallel max_idle idle_timeout
                        nreqs nready npending nthreads
-                       max_poll_time max_poll_reqs);
+                       max_poll_time max_poll_reqs
+                       sendfile fadvise madvise
+                       mmap munmap munlock munlockall);
+   push @AIO_REQ, qw(aio_busy); # not exported
    @IO::AIO::GRP::ISA = 'IO::AIO::REQ';
    require XSLoader;
    XSLoader::load ("IO::AIO", $VERSION);
 }
 =head1 FUNCTIONS
+=head2 QUICK OVERVIEW
+This section simply lists the prototypes of the most important functions
+for quick reference. See the following sections for function-by-function
+documentation.
+   aio_wd $pathname, $callback->($wd)
+   aio_open $pathname, $flags, $mode, $callback->($fh)
+   aio_close $fh, $callback->($status)
+   aio_read  $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
+   aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
+   aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
+   aio_readahead $fh,$offset,$length, $callback->($retval)
+   aio_stat  $fh_or_path, $callback->($status)
+   aio_lstat $fh, $callback->($status)
+   aio_statvfs $fh_or_path, $callback->($statvfs)
+   aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
+   aio_chown $fh_or_path, $uid, $gid, $callback->($status)
+   aio_truncate $fh_or_path, $offset, $callback->($status)
+   aio_chmod $fh_or_path, $mode, $callback->($status)
+   aio_unlink $pathname, $callback->($status)
+   aio_mknod $pathname, $mode, $dev, $callback->($status)
+   aio_link $srcpath, $dstpath, $callback->($status)
+   aio_symlink $srcpath, $dstpath, $callback->($status)
+   aio_readlink $pathname, $callback->($link)
+   aio_realpath $pathname, $callback->($link)
+   aio_rename $srcpath, $dstpath, $callback->($status)
+   aio_mkdir $pathname, $mode, $callback->($status)
+   aio_rmdir $pathname, $callback->($status)
+   aio_readdir $pathname, $callback->($entries)
+   aio_readdirx $pathname, $flags, $callback->($entries, $flags)
+      IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
+      IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
+   aio_load $pathname, $data, $callback->($status)
+   aio_copy $srcpath, $dstpath, $callback->($status)
+   aio_move $srcpath, $dstpath, $callback->($status)
+   aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
+   aio_rmtree $pathname, $callback->($status)
+   aio_sync $callback->($status)
+   aio_syncfs $fh, $callback->($status)
+   aio_fsync $fh, $callback->($status)
+   aio_fdatasync $fh, $callback->($status)
+   aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
+   aio_pathsync $pathname, $callback->($status)
+   aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
+   aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
+   aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
+   aio_mlockall $flags, $callback->($status)
+   aio_group $callback->(...)
+   aio_nop $callback->()
+   $prev_pri = aioreq_pri [$pri]
+   aioreq_nice $pri_adjust
+   IO::AIO::poll_wait
+   IO::AIO::poll_cb
+   IO::AIO::poll
+   IO::AIO::flush
+   IO::AIO::max_poll_reqs $nreqs
+   IO::AIO::max_poll_time $seconds
+   IO::AIO::min_parallel $nthreads
+   IO::AIO::max_parallel $nthreads
+   IO::AIO::max_idle $nthreads
+   IO::AIO::idle_timeout $seconds
+   IO::AIO::max_outstanding $maxreqs
+   IO::AIO::nreqs
+   IO::AIO::nready
+   IO::AIO::npending
+   IO::AIO::sendfile $ofh, $ifh, $offset, $count
+   IO::AIO::fadvise $fh, $offset, $len, $advice
+   IO::AIO::madvise $scalar, $offset, $length, $advice
+   IO::AIO::mprotect $scalar, $offset, $length, $protect
+   IO::AIO::munlock $scalar, $offset = 0, $length = undef
+   IO::AIO::munlockall
 =head2 AIO REQUEST FUNCTIONS
 All the C<aio_*> calls are more or less thin wrappers around the syscall
 with the same name (sans C<aio_>). The arguments are similar or identical,
 and they all accept an additional (and optional) C<$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
+perl, which usually delivers "false") as its sole argument after the given
 syscall has been executed asynchronously.
 All functions expecting a filehandle keep a copy of the filehandle
 internally until the request has finished.
 All functions return request objects of type L<IO::AIO::REQ> that allow
 further manipulation of those requests while they are in-flight.
-The pathnames you pass to these routines I<must> be absolute and
+The pathnames you pass to these routines I<should> be absolute. The
-encoded as octets. The reason for the former is that at the time the
+reason for this is that at the time the request is being executed, the
-request is being executed, the current working directory could have
+current working directory could have changed. Alternatively, you can make
-changed. Alternatively, you can make sure that you never change the
+sure that you never change the current working directory anywhere in
-current working directory anywhere in the program and then use relative
+the program and then use relative paths. Lastly, you can take advantage
-paths.
+of IO::AIOs working directory abstraction - see the description of the
+C<IO::AIO::WD> class later in this document.
 To encode pathnames as octets, either make sure you either: a) always pass
 in filenames you got from outside (command line, readdir etc.) without
 tinkering, 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 to ensure your scalar has the correct contents.
 This works, btw. independent of the internal UTF-8 bit, which IO::AIO
-handles correctly wether it is set or not.
+handles correctly whether it is set or not.
 =over 4
 =item $prev_pri = aioreq_pri [$pri]
 by the umask in effect then the request is being executed, so better never
 change the umask.
 Example:
-   aio_open "/etc/passwd", O_RDONLY, 0, sub {
+   aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
       if ($_[0]) {
          print "open successful, fh is $_[0]\n";
          ...
       } else {
          die "open failed: $!\n";
       }
    };
+In addition to all the common open modes/flags (C<O_RDONLY>, C<O_WRONLY>,
+C<O_RDWR>, C<O_CREAT>, C<O_TRUNC>, C<O_EXCL> and C<O_APPEND>), the
+following POSIX and non-POSIX constants are available (missing ones on
+your system are, as usual, C<0>):
+C<O_ASYNC>, C<O_DIRECT>, C<O_NOATIME>, C<O_CLOEXEC>, C<O_NOCTTY>, C<O_NOFOLLOW>,
+C<O_NONBLOCK>, C<O_EXEC>, C<O_SEARCH>, C<O_DIRECTORY>, C<O_DSYNC>,
+C<O_RSYNC>, C<O_SYNC> and C<O_TTY_INIT>.
 =item aio_close $fh, $callback->($status)
 Asynchronously close a file and call the callback with the result
 code.
 Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
-closing the file descriptor associated with the filehandle itself. Here is
+closing the file descriptor associated with the filehandle itself.
-what aio_close will try:
-   1. dup()licate the fd
+Therefore, C<aio_close> will not close the filehandle - instead it will
-   2. asynchronously close() the duplicated fd
+use dup2 to overwrite the file descriptor with the write-end of a pipe
-   3. dup()licate the fd once more
+(the pipe fd will be created on demand and will be cached).
-   4. let perl close() the filehandle
-   5. asynchronously close the duplicated fd
-The idea is that the first close() flushes stuff to disk that closing an
+Or in other words: the file descriptor will be closed, but it will not be
-fd will flush, so when perl closes the fd, nothing much will need to be
+free for reuse until the perl filehandle is closed.
-flushed.  The second async. close() will then flush stuff to disk that
-closing the last fd to the file will flush.
-Just FYI, SuSv3 has this to say on close:
-   All outstanding record locks owned by the process on the file
-   associated with the file descriptor shall be removed.
-   If fildes refers to a socket, close() shall cause the socket to be
-   destroyed. ... close() shall block for up to the current linger
-   interval until all data is transmitted.
-   [this actually sounds like a specification bug, but who knows]
-And at least Linux additionally actually flushes stuff on every close,
-even when the file itself is still open.
-Sounds enourmously inefficient and complicated? Yes... please show me how
-to nuke perl's fd out of existence...
 =cut
-sub aio_close($;$) {
-   aio_block {
-      my ($fh, $cb) = @_;
-      my $pri = aioreq_pri;
-      my $grp = aio_group $cb;
-      my $fd = fileno $fh;
-      defined $fd or Carp::croak "aio_close called with fd-less filehandle";
-      # if the dups fail we will simply get EBADF
-      my $fd2 = _dup $fd;
-      aioreq_pri $pri;
-      add $grp _aio_close $fd2, sub {
-         my $fd2 = _dup $fd;
-         close $fh;
-         aioreq_pri $pri;
-         add $grp _aio_close $fd2, sub {
-            $grp->result ($_[0]);
-         };
-      };
-      $grp
-   }
-}
 =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<$offset>
+Reads or writes C<$length> bytes from or to the specified C<$fh> and
-into the scalar given by C<$data> and offset C<$dataoffset> and calls the
+C<$offset> into the scalar given by C<$data> and offset C<$dataoffset>
-callback without the actual number of bytes read (or -1 on error, just
+and calls the callback without the actual number of bytes read (or -1 on
-like the syscall).
+error, just like the syscall).
+C<aio_read> will, like C<sysread>, shrink or grow the C<$data> scalar to
+offset plus the actual number of bytes read.
 If C<$offset> is undefined, then the current file descriptor offset will
 be used (and updated), otherwise the file descriptor offset will not be
 changed by these calls.
-If C<$length> is undefined in C<aio_write>, use the remaining length of C<$data>.
+If C<$length> is undefined in C<aio_write>, use the remaining length of
+C<$data>.
 If C<$dataoffset> is less than zero, it will be counted from the end of
 C<$data>.
 The C<$data> scalar I<MUST NOT> be modified in any way while the request
 Tries to copy C<$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<$out_fh>, as they will interfere with each
-other.
+other. The same C<$in_fh> works fine though, as this function does not
+move or use the file offset of C<$in_fh>.
+Please note that C<aio_sendfile> can read more bytes from C<$in_fh> than
+are written, and there is no way to find out how many more 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<$length> bytes have been read.
+Unlike with other C<aio_> functions, it makes a lot of sense to use
+C<aio_sendfile> on non-blocking sockets, as long as one end (typically
+the C<$in_fh>) is a file - the file I/O will then be asynchronous, while
+the socket I/O will be non-blocking. Note, however, that you can run
+into a trap where C<aio_sendfile> reads some data with readahead, then
+fails to write all data, and when the socket is ready the next time, the
+data in the cache is already lost, forcing C<aio_sendfile> to again hit
+the disk. Explicit C<aio_read> + C<aio_write> let's you better control
+resource usage.
-This call tries to make use of a native C<sendfile> syscall to provide
+This call tries to make use of a native C<sendfile>-like syscall to
-zero-copy operation. For this to work, C<$out_fh> should refer to a
+provide zero-copy operation. For this to work, C<$out_fh> should refer to
-socket, and C<$in_fh> should refer to mmap'able file.
+a socket, and C<$in_fh> should refer to an mmap'able file.
-If the native sendfile call fails or is not implemented, it will be
+If a native sendfile cannot be found or it fails with C<ENOSYS>,
-emulated, so you can call C<aio_sendfile> on any type of filehandle
+C<EINVAL>, C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or
+C<ENOTSOCK>, it will be emulated, so you can call C<aio_sendfile> on any
-regardless of the limitations of the operating system.
+type of filehandle regardless of the limitations of the operating system.
-Please note, however, that C<aio_sendfile> can read more bytes from
+As native sendfile syscalls (as practically any non-POSIX interface hacked
-C<$in_fh> than are written, and there is no way to find out how many
+together in a hurry to improve benchmark numbers) tend to be rather buggy
-bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
+on many systems, this implementation tries to work around some known bugs
-provides the number of bytes written to C<$out_fh>. Only if the result
+in Linux and FreeBSD kernels (probably others, too), but that might fail,
-value equals C<$length> one can assume that C<$length> bytes have been
+so you really really should check the return value of C<aio_sendfile> -
-read.
+fewre bytes than expected might have been transferred.
 =item aio_readahead $fh,$offset,$length, $callback->($retval)
 C<aio_readahead> populates the page cache with data from a file so that
 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.
+To help interpret the mode and dev/rdev stat values, IO::AIO offers the
+following constants and functions (if not implemented, the constants will
+be C<0> and the functions will either C<croak> or fall back on traditional
+behaviour).
+C<S_IFMT>, C<S_IFIFO>, C<S_IFCHR>, C<S_IFBLK>, C<S_IFLNK>, C<S_IFREG>,
+C<S_IFDIR>, C<S_IFWHT>, C<S_IFSOCK>, C<IO::AIO::major $dev_t>,
+C<IO::AIO::minor $dev_t>, C<IO::AIO::makedev $major, $minor>.
 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_statvfs $fh_or_path, $callback->($statvfs)
+Works like the POSIX C<statvfs> or C<fstatvfs> syscalls, depending on
+whether a file handle or path was passed.
+On success, the callback is passed a hash reference with the following
+members: C<bsize>, C<frsize>, C<blocks>, C<bfree>, C<bavail>, C<files>,
+C<ffree>, C<favail>, C<fsid>, C<flag> and C<namemax>. On failure, C<undef>
+is passed.
+The following POSIX IO::AIO::ST_* constants are defined: C<ST_RDONLY> and
+C<ST_NOSUID>.
+The following non-POSIX IO::AIO::ST_* flag masks are defined to
+their correct value when available, or to C<0> on systems that do
+not support them:  C<ST_NODEV>, C<ST_NOEXEC>, C<ST_SYNCHRONOUS>,
+C<ST_MANDLOCK>, C<ST_WRITE>, C<ST_APPEND>, C<ST_IMMUTABLE>, C<ST_NOATIME>,
+C<ST_NODIRATIME> and C<ST_RELATIME>.
+Example: stat C</wd> and dump out the data if successful.
+   aio_statvfs "/wd", sub {
+      my $f = $_[0]
+         or die "statvfs: $!";
+      use Data::Dumper;
+      say Dumper $f;
+   };
+   # result:
+   {
+      bsize   => 1024,
+      bfree   => 4333064312,
+      blocks  => 10253828096,
+      files   => 2050765568,
+      flag    => 4096,
+      favail  => 2042092649,
+      bavail  => 4333064312,
+      ffree   => 2042092649,
+      namemax => 255,
+      frsize  => 1024,
+      fsid    => 1810
+   }
 =item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
 Works like perl's C<utime> function (including the special case of $atime
 and $mtime being undef). Fractional times are supported if the underlying
 syscalls support them.
 Asynchronously unlink (delete) a file and call the callback with the
 result code.
-=item aio_mknod $path, $mode, $dev, $callback->($status)
+=item aio_mknod $pathname, $mode, $dev, $callback->($status)
 [EXPERIMENTAL]
 Asynchronously create a device node (or fifo). See mknod(2).
 The only (POSIX-) portable way of calling this function is:
-   aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
+   aio_mknod $pathname, IO::AIO::S_IFIFO | $mode, 0, sub { ...
+See C<aio_stat> for info about some potentially helpful extra constants
+and functions.
 =item aio_link $srcpath, $dstpath, $callback->($status)
 Asynchronously create a new link to the existing object at C<$srcpath> at
 the path C<$dstpath> and call the callback with the result code.
 Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
 the path C<$dstpath> and call the callback with the result code.
-=item aio_readlink $path, $callback->($link)
+=item aio_readlink $pathname, $callback->($link)
 Asynchronously read the symlink specified by C<$path> and pass it to
 the callback. If an error occurs, nothing or undef gets passed to the
 callback.
+=item aio_realpath $pathname, $callback->($path)
+Asynchronously make the path absolute and resolve any symlinks in
+C<$path>. The resulting path only consists of directories (Same as
+L<Cwd::realpath>).
+This request can be used to get the absolute path of the current working
+directory by passing it a path of F<.> (a single dot).
 =item aio_rename $srcpath, $dstpath, $callback->($status)
 Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
 rename(2) and call the callback with the result code.
 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
+The callback is passed a single argument which is either C<undef> or an
-with the filenames.
+array-ref with the filenames.
+=item aio_readdirx $pathname, $flags, $callback->($entries, $flags)
+Quite similar to C<aio_readdir>, but the C<$flags> argument allows one to
+tune behaviour and output format. In case of an error, C<$entries> will be
+C<undef>.
+The flags are a combination of the following constants, ORed together (the
+flags will also be passed to the callback, possibly modified):
+=over 4
+=item IO::AIO::READDIR_DENTS
+When this flag is off, then the callback gets an arrayref consisting of
+names only (as with C<aio_readdir>), otherwise it gets an arrayref with
+C<[$name, $type, $inode]> arrayrefs, each describing a single directory
+entry in more detail.
+C<$name> is the name of the entry.
+C<$type> is one of the C<IO::AIO::DT_xxx> constants:
+C<IO::AIO::DT_UNKNOWN>, C<IO::AIO::DT_FIFO>, C<IO::AIO::DT_CHR>, C<IO::AIO::DT_DIR>,
+C<IO::AIO::DT_BLK>, C<IO::AIO::DT_REG>, C<IO::AIO::DT_LNK>, C<IO::AIO::DT_SOCK>,
+C<IO::AIO::DT_WHT>.
+C<IO::AIO::DT_UNKNOWN> means just that: readdir does not know. If you need to
+know, you have to run stat yourself. Also, for speed reasons, the C<$type>
+scalars are read-only: you can not modify them.
+C<$inode> is the inode number (which might not be exact on systems with 64
+bit inode numbers and 32 bit perls). This field has unspecified content on
+systems that do not deliver the inode information.
+=item IO::AIO::READDIR_DIRS_FIRST
+When this flag is set, then the names will be returned in an order where
+likely directories come first, in optimal stat order. This is useful when
+you need to quickly find directories, or you want to find all directories
+while avoiding to stat() each entry.
+If the system returns type information in readdir, then this is used
+to find directories directly. Otherwise, likely directories are names
+beginning with ".", or otherwise names with no dots, of which names with
+short names are tried first.
+=item IO::AIO::READDIR_STAT_ORDER
+When this flag is set, then the names will be returned in an order
+suitable for stat()'ing each one. That is, when you plan to stat()
+all files in the given directory, then the returned order will likely
+be fastest.
+If both this flag and C<IO::AIO::READDIR_DIRS_FIRST> are specified, then
+the likely dirs come first, resulting in a less optimal stat order.
+=item IO::AIO::READDIR_FOUND_UNKNOWN
+This flag should not be set when calling C<aio_readdirx>. Instead, it
+is being set by C<aio_readdirx>, when any of the C<$type>'s found were
+C<IO::AIO::DT_UNKNOWN>. The absence of this flag therefore indicates that all
+C<$type>'s are known, which can be used to speed up some algorithms.
+=back
-=item aio_load $path, $data, $callback->($status)
+=item aio_load $pathname, $data, $callback->($status)
 This is a composite request that tries to fully load the given file into
 memory. Status is the same as with aio_read.
 =cut
 sub aio_load($$;$) {
-   aio_block {
-      my ($path, undef, $cb) = @_;
+   my ($path, undef, $cb) = @_;
-      my $data = \$_[1];
+   my $data = \$_[1];
-      my $pri = aioreq_pri;
+   my $pri = aioreq_pri;
-      my $grp = aio_group $cb;
+   my $grp = aio_group $cb;
+   aioreq_pri $pri;
+   add $grp aio_open $path, O_RDONLY, 0, sub {
+      my $fh = shift
+         or return $grp->result (-1);
       aioreq_pri $pri;
-      add $grp aio_open $path, O_RDONLY, 0, sub {
-         my $fh = shift
-            or return $grp->result (-1);
-         aioreq_pri $pri;
-         add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
+      add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
-            $grp->result ($_[0]);
+         $grp->result ($_[0]);
-         };
       };
-      $grp
-   }
+   };
+   $grp
 }
 =item aio_copy $srcpath, $dstpath, $callback->($status)
 Try to copy the I<file> (directories not supported as either source or
 destination) from C<$srcpath> to C<$dstpath> and call the callback with
-the C<0> (error) or C<-1> ok.
+a status of C<0> (ok) or C<-1> (error, see C<$!>).
-This is a composite request that it creates the destination file with
+This is a composite request that creates the destination file with
 mode 0200 and copies the contents of the source file into it using
 C<aio_sendfile>, followed by restoring atime, mtime, access mode and
 uid/gid, in that order.
 If an error occurs, the partial destination file will be unlinked, if
 errors are being ignored.
 =cut
 sub aio_copy($$;$) {
-   aio_block {
-      my ($src, $dst, $cb) = @_;
+   my ($src, $dst, $cb) = @_;
-      my $pri = aioreq_pri;
+   my $pri = aioreq_pri;
-      my $grp = aio_group $cb;
+   my $grp = aio_group $cb;
-      aioreq_pri $pri;
+   aioreq_pri $pri;
-      add $grp aio_open $src, O_RDONLY, 0, sub {
+   add $grp aio_open $src, O_RDONLY, 0, sub {
-         if (my $src_fh = $_[0]) {
+      if (my $src_fh = $_[0]) {
-            my @stat = stat $src_fh;
+         my @stat = stat $src_fh; # hmm, might block over nfs?
-            aioreq_pri $pri;
+         aioreq_pri $pri;
-            add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
+         add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
-               if (my $dst_fh = $_[0]) {
+            if (my $dst_fh = $_[0]) {
-                  aioreq_pri $pri;
+               aioreq_pri $pri;
-                  add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
+               add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
-                     if ($_[0] == $stat[7]) {
+                  if ($_[0] == $stat[7]) {
-                        $grp->result (0);
+                     $grp->result (0);
-                        close $src_fh;
+                     close $src_fh;
-                        # those should not normally block. should. should.
+                     my $ch = sub {
-                        utime $stat[8], $stat[9], $dst;
-                        chmod $stat[2] & 07777, $dst_fh;
-                        chown $stat[4], $stat[5], $dst_fh;
                         aioreq_pri $pri;
+                        add $grp aio_chmod $dst_fh, $stat[2] & 07777, sub {
+                           aioreq_pri $pri;
+                           add $grp aio_chown $dst_fh, $stat[4], $stat[5], sub {
+                              aioreq_pri $pri;
-                        add $grp aio_close $dst_fh;
+                              add $grp aio_close $dst_fh;
-                     } else {
+                           }
-                        $grp->result (-1);
-                        close $src_fh;
-                        close $dst_fh;
-                        aioreq $pri;
+                        };
-                        add $grp aio_unlink $dst;
-                     }
+                     };
+                     aioreq_pri $pri;
+                     add $grp aio_utime $dst_fh, $stat[8], $stat[9], sub {
+                        if ($_[0] < 0 && $! == ENOSYS) {
+                           aioreq_pri $pri;
+                           add $grp aio_utime $dst, $stat[8], $stat[9], $ch;
+                        } else {
+                           $ch->();
+                        }
+                     };
+                  } else {
+                     $grp->result (-1);
+                     close $src_fh;
+                     close $dst_fh;
+                     aioreq $pri;
+                     add $grp aio_unlink $dst;
-                  };
+                  }
-               } else {
-                  $grp->result (-1);
-               }
+               };
+            } else {
+               $grp->result (-1);
-            },
+            }
-         } else {
-            $grp->result (-1);
-         }
+         },
+      } else {
+         $grp->result (-1);
-      };
+      }
-      $grp
-   }
+   };
+   $grp
 }
 =item aio_move $srcpath, $dstpath, $callback->($status)
 Try to move the I<file> (directories not supported as either source or
 destination) from C<$srcpath> to C<$dstpath> and call the callback with
-the C<0> (error) or C<-1> ok.
+a status of C<0> (ok) or C<-1> (error, see C<$!>).
-This is a composite request that tries to rename(2) the file first. If
+This is a composite request that tries to rename(2) the file first; if
-rename files with C<EXDEV>, it copies the file with C<aio_copy> and, if
+rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
-that is successful, unlinking the C<$srcpath>.
+that is successful, unlinks the C<$srcpath>.
 =cut
 sub aio_move($$;$) {
-   aio_block {
-      my ($src, $dst, $cb) = @_;
+   my ($src, $dst, $cb) = @_;
-      my $pri = aioreq_pri;
+   my $pri = aioreq_pri;
-      my $grp = aio_group $cb;
+   my $grp = aio_group $cb;
-      aioreq_pri $pri;
+   aioreq_pri $pri;
-      add $grp aio_rename $src, $dst, sub {
+   add $grp aio_rename $src, $dst, sub {
-         if ($_[0] && $! == EXDEV) {
+      if ($_[0] && $! == EXDEV) {
-            aioreq_pri $pri;
+         aioreq_pri $pri;
-            add $grp aio_copy $src, $dst, sub {
+         add $grp aio_copy $src, $dst, sub {
-               $grp->result ($_[0]);
-               if (!$_[0]) {
-                  aioreq_pri $pri;
-                  add $grp aio_unlink $src;
-               }
-            };
-         } else {
             $grp->result ($_[0]);
+            unless ($_[0]) {
+               aioreq_pri $pri;
+               add $grp aio_unlink $src;
+            }
-         }
+         };
+      } else {
+         $grp->result ($_[0]);
-      };
+      }
-      $grp
-   }
+   };
+   $grp
 }
-=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
+=item aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
 Scans a directory (similar to C<aio_readdir>) but additionally tries to
 efficiently separate the entries of directory C<$path> into two sets of
 names, directories you can recurse into (directories), and ones you cannot
 recurse into (everything else, including symlinks to directories).
 Implementation notes.
 The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
+If readdir returns file type information, then this is used directly to
+find directories.
-After reading the directory, the modification time, size etc. of the
+Otherwise, after reading the directory, the modification time, size etc.
-directory before and after the readdir is checked, and if they match (and
+of the directory before and after the readdir is checked, and if they
-isn't the current time), the link count will be used to decide how many
+match (and isn't the current time), the link count will be used to decide
-entries are directories (if >= 2). Otherwise, no knowledge of the number
+how many entries are directories (if >= 2). Otherwise, no knowledge of the
-of subdirectories will be assumed.
+number of subdirectories will be assumed.
-Then entries will be sorted into likely directories (everything without
+Then entries will be sorted into likely directories a non-initial dot
-a non-initial dot currently) and likely non-directories (everything
+currently) and likely non-directories (see C<aio_readdirx>). Then every
-else). Then every entry plus an appended C</.> will be C<stat>'ed,
+entry plus an appended C</.> will be C<stat>'ed, likely directories first,
-likely directories first. If that succeeds, it assumes that the entry
+in order of their inode numbers. If that succeeds, it assumes that the
-is a directory or a symlink to directory (which will be checked
+entry is a directory or a symlink to directory (which will be checked
-seperately). This is often faster than stat'ing the entry itself because
+separately). This is often faster than stat'ing the entry itself because
 filesystems might detect the type of the entry without reading the inode
-data (e.g. ext2fs filetype feature).
+data (e.g. ext2fs filetype feature), even on systems that cannot return
+the filetype information on readdir.
 If the known number of directories (link count - 2) has been reached, the
 rest of the entries is assumed to be non-directories.
 This only works with certainty on POSIX (= UNIX) filesystems, which
 directory counting heuristic.
 =cut
 sub aio_scandir($$;$) {
-   aio_block {
-      my ($path, $maxreq, $cb) = @_;
+   my ($path, $maxreq, $cb) = @_;
-      my $pri = aioreq_pri;
+   my $pri = aioreq_pri;
-      my $grp = aio_group $cb;
+   my $grp = aio_group $cb;
-      $maxreq = 4 if $maxreq <= 0;
+   $maxreq = 4 if $maxreq <= 0;
+   # get a wd object
+   aioreq_pri $pri;
+   add $grp aio_wd $path, sub {
+      my $wd = [shift, "."];
       # stat once
       aioreq_pri $pri;
-      add $grp aio_stat $path, sub {
+      add $grp aio_stat $wd, sub {
          return $grp->result () if $_[0];
          my $now = time;
          my $hash1 = join ":", (stat _)[0,1,3,7,9];
          # read the directory entries
          aioreq_pri $pri;
-         add $grp aio_readdir $path, sub {
+         add $grp aio_readdirx $wd, READDIR_DIRS_FIRST, sub {
             my $entries = shift
                or return $grp->result ();
             # stat the dir another time
             aioreq_pri $pri;
-            add $grp aio_stat $path, sub {
+            add $grp aio_stat $wd, sub {
                my $hash2 = join ":", (stat _)[0,1,3,7,9];
                my $ndirs;
                # take the slow route if anything looks fishy
                if ($hash1 ne $hash2 or (stat _)[9] == $now) {
                   $ndirs = -1;
                } else {
                   # if nlink == 2, we are finished
-                  # on non-posix-fs's, we rely on nlink < 2
+                  # for non-posix-fs's, we rely on nlink < 2
                   $ndirs = (stat _)[3] - 2
                      or return $grp->result ([], $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 $statgrp = add $grp aio_group sub {
                   $grp->result (\@dirs, \@nondirs);
                };
                limit $statgrp $maxreq;
                feed $statgrp sub {
                   return unless @$entries;
-                  my $entry = pop @$entries;
+                  my $entry = shift @$entries;
                   aioreq_pri $pri;
+                  $wd->[1] = "$entry/.";
-                  add $statgrp aio_stat "$path/$entry/.", sub {
+                  add $statgrp aio_stat $wd, sub {
                      if ($_[0] < 0) {
                         push @nondirs, $entry;
                      } else {
                         # need to check for real directory
                         aioreq_pri $pri;
+                        $wd->[1] = $entry;
-                        add $statgrp aio_lstat "$path/$entry", sub {
+                        add $statgrp aio_lstat $wd, sub {
                            if (-d _) {
                               push @dirs, $entry;
                               unless (--$ndirs) {
                                  push @nondirs, @$entries;
                   };
                };
             };
          };
       };
-      $grp
-   }
+   };
+   $grp
 }
-=item aio_rmtree $path, $callback->($status)
+=item aio_rmtree $pathname, $callback->($status)
 Delete a directory tree starting (and including) C<$path>, return the
 status of the final C<rmdir> only.  This is a composite request that
 uses C<aio_scandir> to recurse into and rmdir directories, and unlink
 everything else.
 =cut
 sub aio_rmtree;
 sub aio_rmtree($;$) {
-   aio_block {
-      my ($path, $cb) = @_;
+   my ($path, $cb) = @_;
-      my $pri = aioreq_pri;
+   my $pri = aioreq_pri;
-      my $grp = aio_group $cb;
+   my $grp = aio_group $cb;
-      aioreq_pri $pri;
+   aioreq_pri $pri;
-      add $grp aio_scandir $path, 0, sub {
+   add $grp aio_scandir $path, 0, sub {
-         my ($dirs, $nondirs) = @_;
+      my ($dirs, $nondirs) = @_;
-         my $dirgrp = aio_group sub {
+      my $dirgrp = aio_group sub {
-            add $grp aio_rmdir $path, sub {
+         add $grp aio_rmdir $path, sub {
-               $grp->result ($_[0]);
+            $grp->result ($_[0]);
-            };
          };
-         (aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
-         (aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
-         add $grp $dirgrp;
       };
-      $grp
+      (aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
+      (aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
+      add $grp $dirgrp;
-   }
+   };
+   $grp
 }
 =item aio_sync $callback->($status)
 Asynchronously call sync and call the callback when finished.
 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.
+=item aio_syncfs $fh, $callback->($status)
+Asynchronously call the syncfs syscall to sync the filesystem associated
+to the given filehandle and call the callback with the syncfs result
+code. If syncfs is not available, calls sync(), but returns C<-1> and sets
+errno to C<ENOSYS> nevertheless.
+=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
+Sync the data portion of the file specified by C<$offset> and C<$length>
+to disk (but NOT the metadata), by calling the Linux-specific
+sync_file_range call. If sync_file_range is not available or it returns
+ENOSYS, then fdatasync or fsync is being substituted.
+C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
+C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
+C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
+manpage for details.
-=item aio_pathsync $path, $callback->($status)
+=item aio_pathsync $pathname, $callback->($status)
 This request tries to open, fsync and close the given path. This is a
-composite request intended tosync directories after directory operations
+composite request intended to sync directories after directory operations
 (E.g. rename). This might not work on all operating systems or have any
 specific effect, but usually it makes sure that directory changes get
 written to disc. It works for anything that can be opened for read-only,
 not just directories.
+Future versions of this function might fall back to other methods when
+C<fsync> on the directory fails (such as calling C<sync>).
 Passes C<0> when everything went ok, and C<-1> on error.
 =cut
 sub aio_pathsync($;$) {
-   aio_block {
-      my ($path, $cb) = @_;
+   my ($path, $cb) = @_;
-      my $pri = aioreq_pri;
+   my $pri = aioreq_pri;
-      my $grp = aio_group $cb;
+   my $grp = aio_group $cb;
-      aioreq_pri $pri;
+   aioreq_pri $pri;
-      add $grp aio_open $path, O_RDONLY, 0, sub {
+   add $grp aio_open $path, O_RDONLY, 0, sub {
-         my ($fh) = @_;
+      my ($fh) = @_;
-         if ($fh) {
+      if ($fh) {
+         aioreq_pri $pri;
+         add $grp aio_fsync $fh, sub {
+            $grp->result ($_[0]);
             aioreq_pri $pri;
-            add $grp aio_fsync $fh, sub {
-               $grp->result ($_[0]);
-               aioreq_pri $pri;
-               add $grp aio_close $fh;
+            add $grp aio_close $fh;
-            };
-         } else {
-            $grp->result (-1);
-         }
+         };
+      } else {
+         $grp->result (-1);
-      };
+      }
-      $grp
-   }
+   };
+   $grp
 }
+=item aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
+This is a rather advanced IO::AIO call, which only works on mmap(2)ed
+scalars (see the C<IO::AIO::mmap> function, although it also works on data
+scalars managed by the L<Sys::Mmap> or L<Mmap> modules, note that the
+scalar must only be modified in-place while an aio operation is pending on
+it).
+It calls the C<msync> function of your OS, if available, with the memory
+area starting at C<$offset> in the string and ending C<$length> bytes
+later. If C<$length> is negative, counts from the end, and if C<$length>
+is C<undef>, then it goes till the end of the string. The flags can be
+a combination of C<IO::AIO::MS_ASYNC>, C<IO::AIO::MS_INVALIDATE> and
+C<IO::AIO::MS_SYNC>.
+=item aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
+This is a rather advanced IO::AIO call, which works best on mmap(2)ed
+scalars.
+It touches (reads or writes) all memory pages in the specified
+range inside the scalar.  All caveats and parameters are the same
+as for C<aio_msync>, above, except for flags, which must be either
+C<0> (which reads all pages and ensures they are instantiated) or
+C<IO::AIO::MT_MODIFY>, which modifies the memory page s(by reading and
+writing an octet from it, which dirties the page).
+=item aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
+This is a rather advanced IO::AIO call, which works best on mmap(2)ed
+scalars.
+It reads in all the pages of the underlying storage into memory (if any)
+and locks them, so they are not getting swapped/paged out or removed.
+If C<$length> is undefined, then the scalar will be locked till the end.
+On systems that do not implement C<mlock>, this function returns C<-1>
+and sets errno to C<ENOSYS>.
+Note that the corresponding C<munlock> is synchronous and is
+documented under L<MISCELLANEOUS FUNCTIONS>.
+Example: open a file, mmap and mlock it - both will be undone when
+C<$data> gets destroyed.
+   open my $fh, "<", $path or die "$path: $!";
+   my $data;
+   IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
+   aio_mlock $data; # mlock in background
+=item aio_mlockall $flags, $callback->($status)
+Calls the C<mlockall> function with the given C<$flags> (a combination of
+C<IO::AIO::MCL_CURRENT> and C<IO::AIO::MCL_FUTURE>).
+On systems that do not implement C<mlockall>, this function returns C<-1>
+and sets errno to C<ENOSYS>.
+Note that the corresponding C<munlockall> is synchronous and is
+documented under L<MISCELLANEOUS FUNCTIONS>.
+Example: asynchronously lock all current and future pages into memory.
+   aio_mlockall IO::AIO::MCL_FUTURE;
 =item aio_group $callback->(...)
 This is a very special aio request: Instead of doing something, it is a
 container for other aio requests, which is useful if you want to bundle
 immense (it blocks a thread for a long time) so do not use this function
 except to put your application under artificial I/O pressure.
 =back
+=head2 IO::AIO::WD - multiple working directories
+Your process only has one current working directory, which is used by all
+threads. This makes it hard to use relative paths (some other component
+could call C<chdir> at any time, and it is hard to control when the path
+will be used by IO::AIO).
+One solution for this is to always use absolute paths. This usually works,
+but can be quite slow (the kernel has to walk the whole path on every
+access), and can also be a hassle to implement.
+Newer POSIX systems have a number of functions (openat, fdopendir,
+futimensat and so on) that make it possible to specify working directories
+per operation.
+For portability, and because the clowns who "designed", or shall I write,
+perpetrated this new interface were obviously half-drunk, this abstraction
+cannot be perfect, though.
+IO::AIO allows you to convert directory paths into a so-called IO::AIO::WD
+object. This object stores the canonicalised, absolute version of the
+path, and on systems that allow it, also a directory file descriptor.
+Everywhere where a pathname is accepted by IO::AIO (e.g. in C<aio_stat>
+or C<aio_unlink>), one can specify an array reference with an IO::AIO::WD
+object and a pathname instead. If the pathname is absolute, the
+IO::AIO::WD objetc is ignored, otherwise the pathname is resolved relative
+to that IO::AIO::WD object.
+For example, to get a wd object for F</etc> and then stat F<passwd>
+inside, you would write:
+   aio_wd "/etc", sub {
+      my $etcdir = shift;
+      # although $etcdir can be undef on error, there is generally no reason
+      # to check for errors here, as aio_stat will fail with ENOENT
+      # when $etcdir is undef.
+      aio_stat [$etcdir, "passwd"], sub {
+         # yay
+      };
+   };
+This shows that creating an IO::AIO::WD object is itself a potentially
+blocking operation, which is why it is done asynchronously.
+As with normal pathnames, IO::AIO keeps a copy of the working directory
+object and the pathname string, so you could write the following without
+causing any issues due to C<$path> getting reused:
+   my $path = [$wd, undef];
+   for my $name (qw(abc def ghi)) {
+      $path->[1] = $name;
+      aio_stat $path, sub {
+         # ...
+      };
+   }
+There are some caveats: when directories get renamed (or deleted), the
+pathname string doesn't change, so will point to the new directory (or
+nowhere at all), while the directory fd, if available on the system,
+will still point to the original directory. Most functions accepting a
+pathname will use the directory fd on newer systems, and the string on
+older systems. Some functions (such as realpath) will always rely on the
+string form of the pathname.
+So this fucntionality is mainly useful to get some protection against
+C<chdir>, to easily get an absolute path out of a relative path for future
+reference, and to speed up doing many operations in the same directory
+(e.g. when stat'ing all files in a directory).
+The following functions implement this working directory abstraction:
+=over 4
+=item aio_wd $pathname, $callback->($wd)
+Asynchonously canonicalise the given pathname and convert it to an
+IO::AIO::WD object representing it. If possible and supported on the
+system, also open a directory fd to speed up pathname resolution relative
+to this working directory.
+If something goes wrong, then C<undef> is passwd to the callback instead
+of a working directory object and C<$!> is set appropriately. Since
+passing C<undef> as working directory component of a pathname fails the
+request with C<ENOENT>, there is often no need for error checking in the
+C<aio_wd> callback, as future requests using the value will fail in the
+expected way.
+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.
+=item IO::AIO::CWD
+This is a compiletime constant (object) that represents the process
+current working directory.
+Specifying this object as working directory object for a pathname is as
+if the pathname would be specified directly, without a directory object,
+e.g., these calls are functionally identical:
+   aio_stat "somefile", sub { ... };
+   aio_stat [IO::AIO::CWD, "somefile"], sub { ... };
+=back
 =head2 IO::AIO::REQ CLASS
 All non-aggregate C<aio_*> functions return an object of this class when
 called in non-void context.
 =item cancel $req
 Cancels the request, if possible. Has the effect of skipping execution
 when entering the B<execute> state and skipping calling the callback when
 entering the the B<result> state, but will leave the request otherwise
-untouched. That means that requests that currently execute will not be
+untouched (with the exception of readdir). That means that requests that
-stopped and resources held by the request will not be freed prematurely.
+currently execute will not be stopped and resources held by the request
+will not be freed prematurely.
 =item cb $req $callback->(...)
 Replace (or simply set) the callback registered to the request.
 Their lifetime, simplified, looks like this: when they are empty, they
 will finish very quickly. If they contain only requests that are in the
 C<done> state, they will also finish. Otherwise they will continue to
 exist.
-That means after creating a group you have some time to add requests. And
+That means after creating a group you have some time to add requests
-in the callbacks of those requests, you can add further requests to the
+(precisely before the callback has been invoked, which is only done within
-group. And only when all those requests have finished will the the group
+the C<poll_cb>). And in the callbacks of those requests, you can add
-itself finish.
+further requests to the group. And only when all those requests have
+finished will the the group itself finish.
 =over 4
 =item add $grp ...
 =item $grp->cancel_subs
 Cancel all subrequests and clears any feeder, but not the group request
 itself. Useful when you queued a lot of events but got a result early.
+The group request will finish normally (you cannot add requests to the
+group).
 =item $grp->result (...)
 Set the result value(s) that will be passed to the group callback when all
 subrequests have finished and set the groups errno to the current value
 =item feed $grp $callback->($grp)
 Sets a feeder/generator on this group: every group can have an attached
 generator that generates requests if idle. The idea behind this is that,
 although you could just queue as many requests as you want in a group,
-this might starve other requests for a potentially long time.  For
+this might starve other requests for a potentially long time. For example,
-example, C<aio_scandir> might generate hundreds of thousands C<aio_stat>
+C<aio_scandir> might generate hundreds of thousands of C<aio_stat>
 requests, delaying any later requests for a long time.
 To avoid this, and allow incremental generation of requests, you can
 instead a group and set a feeder on it that generates those requests. The
 feed callback will be called whenever there are few enough (see C<limit>,
 not impose any limits).
 If the feed does not queue more requests when called, it will be
 automatically removed from the group.
-If the feed limit is C<0>, it will be set to C<2> automatically.
+If the feed limit is C<0> when this method is called, it will be set to
+C<2> automatically.
 Example:
    # stat all files in @files, but only ever use four aio requests concurrently:
 Sets the feeder limit for the group: The feeder will be called whenever
 the group contains less than this many requests.
 Setting the limit to C<0> will pause the feeding process.
+The default value for the limit is C<0>, but note that setting a feeder
+automatically bumps it up to C<2>.
 =back
 =head2 SUPPORT FUNCTIONS
 =head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
 =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
+polled for reading by some mechanism outside this module (e.g. EV, Glib,
-select, see below or the SYNOPSIS). If the pipe becomes readable you have
+select and so on, see below or the SYNOPSIS). If the pipe becomes readable
-to call C<poll_cb> to check the results.
+you have to call C<poll_cb> to check the results.
 See C<poll_cb> for an example.
 =item IO::AIO::poll_cb
-Process some outstanding events on the result pipe. You have to call this
+Process some outstanding events on the result pipe. You have to call
-regularly. Returns the number of events processed. Returns immediately
+this regularly. Returns C<0> if all events could be processed (or there
-when no events are outstanding. The amount of events processed depends on
+were no events to process), or C<-1> if it returned earlier for whatever
-the settings of C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
+reason. Returns immediately when no events are outstanding. The amount of
+events processed depends on the settings of C<IO::AIO::max_poll_req> and
+C<IO::AIO::max_poll_time>.
 If not all requests were processed for whatever reason, the filehandle
-will still be ready when C<poll_cb> returns.
+will still be ready when C<poll_cb> returns, so normally you don't have to
+do anything special to have it called later.
+Apart from calling C<IO::AIO::poll_cb> when the event filehandle becomes
+ready, it can be beneficial to call this function from loops which submit
+a lot of requests, to make sure the results get processed when they become
+available and not just when the loop is finished and the event loop takes
+over again. This function returns very fast when there are no outstanding
+requests.
 Example: Install an Event watcher that automatically calls
-IO::AIO::poll_cb with high priority:
+IO::AIO::poll_cb with high priority (more examples can be found in the
+SYNOPSIS section, at the top of this document):
    Event->io (fd => IO::AIO::poll_fileno,
               poll => 'r', async => 1,
               cb => \&IO::AIO::poll_cb);
+=item IO::AIO::poll_wait
+If there are any outstanding requests and none of them in the result
+phase, 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::poll
+Waits until some requests have been handled.
+Returns the number of requests processed, but is otherwise strictly
+equivalent to:
+   IO::AIO::poll_wait, IO::AIO::poll_cb
+=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::max_poll_reqs $nreqs
 =item IO::AIO::max_poll_time $seconds
    # use a low priority so other tasks have priority
    Event->io (fd => IO::AIO::poll_fileno,
               poll => 'r', nice => 1,
               cb => &IO::AIO::poll_cb);
-=item IO::AIO::poll_wait
-If there are any outstanding requests and none of them in the result
-phase, 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::poll
-Waits until some requests have been handled.
-Returns the number of requests processed, but is otherwise strictly
-equivalent to:
-   IO::AIO::poll_wait, IO::AIO::poll_cb
-=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;
 =back
 =head3 CONTROLLING THE NUMBER OF THREADS
 =over
 Under normal circumstances you don't need to call this function.
 =item IO::AIO::max_idle $nthreads
-Limit the number of threads (default: 4) that are allowed to idle (i.e.,
+Limit the number of threads (default: 4) that are allowed to idle
-threads that did not get a request to process within 10 seconds). That
+(i.e., threads that did not get a request to process within the idle
-means if a thread becomes idle while C<$nthreads> other threads are also
+timeout (default: 10 seconds). That means if a thread becomes idle while
-idle, it will free its resources and exit.
+C<$nthreads> other threads are also idle, it will free its resources and
+exit.
 This is useful when you allow a large number of threads (e.g. 100 or 1000)
 to allow for extremely high load situations, but want to free resources
 under normal circumstances (1000 threads can easily consume 30MB of RAM).
 The default is probably ok in most situations, especially if thread
 creation is fast. If thread creation is very slow on your system you might
 want to use larger values.
+=item IO::AIO::idle_timeout $seconds
+Sets the minimum idle timeout (default 10) after which worker threads are
+allowed to exit. SEe C<IO::AIO::max_idle>.
-=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
+=item IO::AIO::max_outstanding $maxreqs
+Sets the maximum number of outstanding requests to C<$nreqs>. If
+you do queue up more than this number of requests, the next call to
+C<IO::AIO::poll_cb> (and other functions calling C<poll_cb>, such as
+C<IO::AIO::flush> or C<IO::AIO::poll>) will block until the limit is no
+longer exceeded.
+In other words, this setting does not enforce a queue limit, but can be
+used to make poll functions block if the limit is exceeded.
 This is a very bad function to use in interactive programs because it
 blocks, and a bad way to reduce concurrency because it is inexact: Better
 use an C<aio_group> together with a feed callback.
-Sets the maximum number of outstanding requests to C<$nreqs>. If you
+It's main use is in scripts without an event loop - when you want to stat
-do queue up more than this number of requests, the next call to the
+a lot of files, you can write somehting like this:
-C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
-function will block until the limit is no longer exceeded.
-The default value is very large, so there is no practical limit on the
+   IO::AIO::max_outstanding 32;
-number of outstanding requests.
-You can still queue as many requests as you want. Therefore,
+   for my $path (...) {
-C<max_oustsanding> is mainly useful in simple scripts (with low values) or
+      aio_stat $path , ...;
-as a stop gap to shield against fatal memory overflow (with large values).
+      IO::AIO::poll_cb;
+   }
+   IO::AIO::flush;
+The call to C<poll_cb> inside the loop will normally return instantly, but
+as soon as more thna C<32> reqeusts are in-flight, it will block until
+some requests have been handled. This keeps the loop from pushing a large
+number of C<aio_stat> requests onto the queue.
+The default value for C<max_outstanding> is very large, so there is no
+practical limit on the number of outstanding requests.
 =back
 =head3 STATISTICAL INFORMATION
 Returns the number of requests currently in the pending state (executed,
 but not yet processed by poll_cb).
 =back
+=head3 MISCELLANEOUS FUNCTIONS
+IO::AIO implements some functions that might be useful, but are not
+asynchronous.
+=over 4
+=item IO::AIO::sendfile $ofh, $ifh, $offset, $count
+Calls the C<eio_sendfile_sync> function, which is like C<aio_sendfile>,
+but is blocking (this makes most sense if you know the input data is
+likely cached already and the output filehandle is set to non-blocking
+operations).
+Returns the number of bytes copied, or C<-1> on error.
+=item IO::AIO::fadvise $fh, $offset, $len, $advice
+Simply calls the C<posix_fadvise> function (see its
+manpage for details). The following advice constants are
+available: C<IO::AIO::FADV_NORMAL>, C<IO::AIO::FADV_SEQUENTIAL>,
+C<IO::AIO::FADV_RANDOM>, C<IO::AIO::FADV_NOREUSE>,
+C<IO::AIO::FADV_WILLNEED>, C<IO::AIO::FADV_DONTNEED>.
+On systems that do not implement C<posix_fadvise>, this function returns
+ENOSYS, otherwise the return value of C<posix_fadvise>.
+=item IO::AIO::madvise $scalar, $offset, $len, $advice
+Simply calls the C<posix_madvise> function (see its
+manpage for details). The following advice constants are
+available: C<IO::AIO::MADV_NORMAL>, C<IO::AIO::MADV_SEQUENTIAL>,
+C<IO::AIO::MADV_RANDOM>, C<IO::AIO::MADV_WILLNEED>, C<IO::AIO::MADV_DONTNEED>.
+On systems that do not implement C<posix_madvise>, this function returns
+ENOSYS, otherwise the return value of C<posix_madvise>.
+=item IO::AIO::mprotect $scalar, $offset, $len, $protect
+Simply calls the C<mprotect> function on the preferably AIO::mmap'ed
+$scalar (see its manpage for details). The following protect
+constants are available: C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_READ>,
+C<IO::AIO::PROT_WRITE>, C<IO::AIO::PROT_EXEC>.
+On systems that do not implement C<mprotect>, this function returns
+ENOSYS, otherwise the return value of C<mprotect>.
+=item IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
+Memory-maps a file (or anonymous memory range) and attaches it to the
+given C<$scalar>, which will act like a string scalar.
+The only operations allowed on the scalar are C<substr>/C<vec> that don't
+change the string length, and most read-only operations such as copying it
+or searching it with regexes and so on.
+Anything else is unsafe and will, at best, result in memory leaks.
+The memory map associated with the C<$scalar> is automatically removed
+when the C<$scalar> is destroyed, or when the C<IO::AIO::mmap> or
+C<IO::AIO::munmap> functions are called.
+This calls the C<mmap>(2) function internally. See your system's manual
+page for details on the C<$length>, C<$prot> and C<$flags> parameters.
+The C<$length> must be larger than zero and smaller than the actual
+filesize.
+C<$prot> is a combination of C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_EXEC>,
+C<IO::AIO::PROT_READ> and/or C<IO::AIO::PROT_WRITE>,
+C<$flags> can be a combination of C<IO::AIO::MAP_SHARED> or
+C<IO::AIO::MAP_PRIVATE>, or a number of system-specific flags (when
+not available, the are defined as 0): C<IO::AIO::MAP_ANONYMOUS>
+(which is set to C<MAP_ANON> if your system only provides this
+constant), C<IO::AIO::MAP_HUGETLB>, C<IO::AIO::MAP_LOCKED>,
+C<IO::AIO::MAP_NORESERVE>, C<IO::AIO::MAP_POPULATE> or
+C<IO::AIO::MAP_NONBLOCK>
+If C<$fh> is C<undef>, then a file descriptor of C<-1> is passed.
+C<$offset> is the offset from the start of the file - it generally must be
+a multiple of C<IO::AIO::PAGESIZE> and defaults to C<0>.
+Example:
+   use Digest::MD5;
+   use IO::AIO;
+   open my $fh, "<verybigfile"
+      or die "$!";
+   IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
+      or die "verybigfile: $!";
+   my $fast_md5 = md5 $data;
+=item IO::AIO::munmap $scalar
+Removes a previous mmap and undefines the C<$scalar>.
+=item IO::AIO::munlock $scalar, $offset = 0, $length = undef
+Calls the C<munlock> function, undoing the effects of a previous
+C<aio_mlock> call (see its description for details).
+=item IO::AIO::munlockall
+Calls the C<munlockall> function.
+On systems that do not implement C<munlockall>, this function returns
+ENOSYS, otherwise the return value of C<munlockall>.
+=back
 =cut
 min_parallel 8;
 END { flush }
 1;
+=head1 EVENT LOOP INTEGRATION
+It is recommended to use L<AnyEvent::AIO> to integrate IO::AIO
+automatically into many event loops:
+ # AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
+ use AnyEvent::AIO;
+You can also integrate IO::AIO manually into many event loops, here are
+some examples of how to do this:
+ # EV integration
+ my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
+ # Event integration
+ Event->io (fd => IO::AIO::poll_fileno,
+            poll => 'r',
+            cb => \&IO::AIO::poll_cb);
+ # Glib/Gtk2 integration
+ add_watch Glib::IO IO::AIO::poll_fileno,
+           in => sub { IO::AIO::poll_cb; 1 };
+ # Tk integration
+ Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
+                           readable => \&IO::AIO::poll_cb);
+ # Danga::Socket integration
+ Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
+                             \&IO::AIO::poll_cb);
 =head2 FORK BEHAVIOUR
-This module should do "the right thing" when the process using it forks:
+Usage of pthreads in a program changes the semantics of fork
+considerably. Specifically, only async-safe functions can be called after
+fork. Perl doesn't know about this, so in general, you cannot call fork
+with defined behaviour in perl if pthreads are involved. IO::AIO uses
+pthreads, so this applies, but many other extensions and (for inexplicable
+reasons) perl itself often is linked against pthreads, so this limitation
+applies to quite a lot of perls.
-Before the fork, IO::AIO enters a quiescent state where no requests
+This module no longer tries to fight your OS, or POSIX. That means IO::AIO
-can be added in other threads and no results will be processed. After
+only works in the process that loaded it. Forking is fully supported, but
-the fork the parent simply leaves the quiescent state and continues
+using IO::AIO in the child is not.
-request/result processing, while the child frees the request/result queue
-(so that the requests started before the fork will only be handled in the
-parent). Threads will be started on demand until the limit set in the
-parent process has been reached again.
-In short: the parent will, after a short pause, continue as if fork had
+You might get around by not I<using> IO::AIO before (or after)
-not been called, while the child will act as if IO::AIO has not been used
+forking. You could also try to call the L<IO::AIO::reinit> function in the
-yet.
+child:
+=over 4
+=item IO::AIO::reinit
+Abandons all current requests and I/O threads and simply reinitialises all
+data structures. This is not an operation supported by any standards, but
+happens to work on GNU/Linux and some newer BSD systems.
+The only reasonable use for this function is to call it after forking, if
+C<IO::AIO> was used in the parent. Calling it while IO::AIO is active in
+the process will result in undefined behaviour. Calling it at any time
+will also result in any undefined (by POSIX) behaviour.
+=back
 =head2 MEMORY USAGE
 Per-request usage:
 Known bugs will be fixed in the next release.
 =head1 SEE ALSO
-L<Coro::AIO>.
+L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
+more natural syntax.
 =head1 AUTHOR
  Marc Lehmann <schmorp@schmorp.de>
  http://home.schmorp.de/

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Revision 1.211 by root, Tue Sep 27 12:10:29 2011 UTC