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

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.193 by root, Thu May 26 04:15:37 2011 UTC vs.
Revision 1.219 by root, Tue Mar 27 18:54:45 2012 UTC

 use common::sense;
 use base 'Exporter';
 BEGIN {
-   our $VERSION = '3.8';
+   our $VERSION = '4.12';
    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_readdirx
-                     aio_scandir aio_symlink aio_readlink aio_sync aio_fsync
+                     aio_scandir aio_symlink aio_readlink aio_realpath aio_sync
-                     aio_fdatasync aio_sync_file_range aio_pathsync aio_readahead
+                     aio_fsync aio_syncfs aio_fdatasync aio_sync_file_range aio_fallocate
+                     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_msync aio_mtouch aio_mlock aio_mlockall
-                     aio_statvfs);
+                     aio_statvfs
+                     aio_wd);
    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 idle_timeout
                        nreqs nready npending nthreads
 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_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 $path, $mode, $dev, $callback->($status)
+   aio_mknod $pathname, $mode, $dev, $callback->($status)
    aio_link $srcpath, $dstpath, $callback->($status)
    aio_symlink $srcpath, $dstpath, $callback->($status)
-   aio_readlink $path, $callback->($link)
+   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_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
-   aio_load $path, $data, $callback->($status)
+   aio_load $pathname, $data, $callback->($status)
    aio_copy $srcpath, $dstpath, $callback->($status)
    aio_move $srcpath, $dstpath, $callback->($status)
-   aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
-   aio_rmtree $path, $callback->($status)
+   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 $path, $callback->($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->(...)
    IO::AIO::madvise $scalar, $offset, $length, $advice
    IO::AIO::mprotect $scalar, $offset, $length, $protect
    IO::AIO::munlock $scalar, $offset = 0, $length = undef
    IO::AIO::munlockall
-=head2 AIO REQUEST FUNCTIONS
+=head2 API NOTES
 All the C<aio_*> calls are more or less thin wrappers around the syscall
 with the same name (sans C<aio_>). The arguments are similar or identical,
 and they all accept an additional (and optional) C<$callback> argument
-which must be a code reference. This code reference will get called with
+which must be a code reference. This code reference will be called after
-the syscall return code (e.g. most syscalls return C<-1> on error, unlike
+the syscall has been executed in an asynchronous fashion. The results
-perl, which usually delivers "false") as its sole argument after the given
+of the request will be passed as arguments to the callback (and, if an
-syscall has been executed asynchronously.
+error occured, in C<$!>) - for most requests the syscall return code (e.g.
+most syscalls return C<-1> on error, unlike perl, which usually delivers
+"false").
+Some requests (such as C<aio_readdir>) pass the actual results and
+communicate failures by passing C<undef>.
 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
-changed. Alternatively, you can make sure that you never change the
+make sure that you never change the current working directory anywhere
-current working directory anywhere in the program and then use relative
+in the program and then use relative paths. You can also take advantage
-paths.
+of IO::AIOs working directory abstraction, that lets you specify paths
+relative to some previously-opened "working directory object" - 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
+tinkering, b) are in your native filesystem encoding, c) use the Encode
-your pathnames to the locale (or other) encoding in effect in the user
+module and encode your pathnames to the locale (or other) encoding in
-environment, d) use Glib::filename_from_unicode on unicode filenames or e)
+effect in the user environment, d) use Glib::filename_from_unicode on
-use something else to ensure your scalar has the correct contents.
+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 whether it is set or not.
+=head2 AIO REQUEST FUNCTIONS
 =over 4
 =item $prev_pri = aioreq_pri [$pri]
       } 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.
 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<$in_fh> than
-are written, and there is no way to find out how many bytes have been read
+are written, and there is no way to find out how many more bytes have been
-from C<aio_sendfile> alone, as C<aio_sendfile> only provides the number of
+read from C<aio_sendfile> alone, as C<aio_sendfile> only provides the
-bytes written to C<$out_fh>. Only if the result value equals C<$length>
+number of bytes written to C<$out_fh>. Only if the result value equals
-one can assume that C<$length> bytes have been read.
+C<$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
+the socket I/O will be non-blocking. Note, however, that you can run
-a trap where C<aio_sendfile> reads some data with readahead, then fails
+into a trap where C<aio_sendfile> reads some data with readahead, then
-to write all data, and when the socket is ready the next time, the data
+fails to write all data, and when the socket is ready the next time, the
-in the cache is already lost, forcing C<aio_sendfile> to again hit the
+data in the cache is already lost, forcing C<aio_sendfile> to again hit
-disk. Explicit C<aio_read> + C<aio_write> let's you control resource usage
+the disk. Explicit C<aio_read> + C<aio_write> let's you better control
-much better.
+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<$in_fh> should refer to an mmap'able file.
+a socket, and C<$in_fh> should refer to an mmap'able file.
 If a native sendfile cannot be found or it fails with C<ENOSYS>,
-C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or C<ENOTSOCK>,
+C<EINVAL>, C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or
-it will be emulated, so you can call C<aio_sendfile> on any type of
+C<ENOTSOCK>, it will be emulated, so you can call C<aio_sendfile> on any
-filehandle regardless of the limitations of the operating system.
+type of filehandle regardless of the limitations of the operating system.
+As native sendfile syscalls (as practically any non-POSIX interface hacked
+together in a hurry to improve benchmark numbers) tend to be rather buggy
+on many systems, this implementation tries to work around some known bugs
+in Linux and FreeBSD kernels (probably others, too), but that might fail,
+so you really really should check the return value of C<aio_sendfile> -
+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
 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 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.
 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 to tune
+Quite similar to C<aio_readdir>, but the C<$flags> argument allows one to
-behaviour and output format. In case of an error, C<$entries> will be
+tune behaviour and output format. In case of an error, C<$entries> will be
 C<undef>.
 The flags are a combination of the following constants, ORed together (the
 flags will also be passed to the callback, possibly modified):
 =item IO::AIO::READDIR_FOUND_UNKNOWN
 This flag should not be set when calling C<aio_readdirx>. Instead, it
 is being set by C<aio_readdirx>, when any of the C<$type>'s found were
-C<IO::AIO::DT_UNKNOWN>. The absense of this flag therefore indicates that all
+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
       if ($_[0] && $! == EXDEV) {
          aioreq_pri $pri;
          add $grp aio_copy $src, $dst, sub {
             $grp->result ($_[0]);
-            if (!$_[0]) {
+            unless ($_[0]) {
                aioreq_pri $pri;
                add $grp aio_unlink $src;
             }
          };
       } else {
    };
    $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).
 Then entries will be sorted into likely directories a non-initial dot
 currently) and likely non-directories (see C<aio_readdirx>). Then every
 entry plus an appended C</.> will be C<stat>'ed, likely directories first,
 in order of their inode numbers. If that succeeds, it assumes that the
 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), even on systems that cannot return
 the filetype information on readdir.
 If the known number of directories (link count - 2) has been reached, the
    my $grp = aio_group $cb;
    $maxreq = 4 if $maxreq <= 0;
-   # stat once
+   # get a wd object
    aioreq_pri $pri;
-   add $grp aio_stat $path, sub {
+   add $grp aio_wd $path, sub {
+      $_[0]
-      return $grp->result () if $_[0];
+         or return $grp->result ();
-      my $now = time;
-      my $hash1 = join ":", (stat _)[0,1,3,7,9];
-      # read the directory entries
+      my $wd = [shift, "."];
+      # stat once
       aioreq_pri $pri;
-      add $grp aio_readdirx $path, READDIR_DIRS_FIRST, sub {
+      add $grp aio_stat $wd, sub {
-         my $entries = shift
-            or return $grp->result ();
+         return $grp->result () if $_[0];
+         my $now = time;
+         my $hash1 = join ":", (stat _)[0,1,3,7,9];
-         # stat the dir another time
+         # read the directory entries
          aioreq_pri $pri;
+         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 $hash2 = join ":", (stat _)[0,1,3,7,9];
-            my $ndirs;
+               my $ndirs;
-            # take the slow route if anything looks fishy
+               # take the slow route if anything looks fishy
-            if ($hash1 ne $hash2 or (stat _)[9] == $now) {
+               if ($hash1 ne $hash2 or (stat _)[9] == $now) {
-               $ndirs = -1;
+                  $ndirs = -1;
-            } else {
+               } else {
-               # if nlink == 2, we are finished
+                  # if nlink == 2, we are finished
-               # for non-posix-fs's, we rely on nlink < 2
+                  # for non-posix-fs's, we rely on nlink < 2
-               $ndirs = (stat _)[3] - 2
+                  $ndirs = (stat _)[3] - 2
-                  or return $grp->result ([], $entries);
+                     or return $grp->result ([], $entries);
-            }
+               }
-            my (@dirs, @nondirs);
+               my (@dirs, @nondirs);
-            my $statgrp = add $grp aio_group sub {
+               my $statgrp = add $grp aio_group sub {
-               $grp->result (\@dirs, \@nondirs);
+                  $grp->result (\@dirs, \@nondirs);
-            };
+               };
-            limit $statgrp $maxreq;
+               limit $statgrp $maxreq;
-            feed $statgrp sub {
+               feed $statgrp sub {
-               return unless @$entries;
+                  return unless @$entries;
-               my $entry = shift @$entries;
+                  my $entry = shift @$entries;
-               aioreq_pri $pri;
+                  aioreq_pri $pri;
+                  $wd->[1] = "$entry/.";
-               add $statgrp aio_stat "$path/$entry/.", sub {
+                  add $statgrp aio_stat $wd, sub {
-                  if ($_[0] < 0) {
+                     if ($_[0] < 0) {
-                     push @nondirs, $entry;
+                        push @nondirs, $entry;
-                  } else {
+                     } else {
-                     # need to check for real directory
+                        # need to check for real directory
-                     aioreq_pri $pri;
+                        aioreq_pri $pri;
+                        $wd->[1] = $entry;
-                     add $statgrp aio_lstat "$path/$entry", sub {
+                        add $statgrp aio_lstat $wd, sub {
-                        if (-d _) {
+                           if (-d _) {
-                           push @dirs, $entry;
+                              push @dirs, $entry;
-                           unless (--$ndirs) {
+                              unless (--$ndirs) {
-                              push @nondirs, @$entries;
+                                 push @nondirs, @$entries;
-                              feed $statgrp;
+                                 feed $statgrp;
+                              }
+                           } else {
+                              push @nondirs, $entry;
                            }
-                        } else {
-                           push @nondirs, $entry;
                         }
                      }
-                  }
+                  };
                };
             };
          };
       };
    };
    $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.
 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
 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 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
 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 (or the IO::AIO::WD object alone, which
+gets interpreted as C<[$wd, "."]>). If the pathname is absolute, the
+IO::AIO::WD object 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
+      };
+   };
+That C<aio_wd> is a request and not a normal function shows that creating
+an IO::AIO::WD object is itself a potentially blocking operation, which is
+why it is done asynchronously.
+To stat the directory obtained with C<aio_wd> above, one could write
+either of the following three request calls:
+   aio_lstat "/etc"    , sub { ...  # pathname as normal string
+   aio_lstat [$wd, "."], sub { ...  # "." relative to $wd (i.e. $wd itself)
+   aio_lstat $wd       , sub { ...  # shorthand for the previous
+As with normal pathnames, IO::AIO keeps a copy of the working directory
+object and the pathname string, so you could write the following without
+causing any issues due to C<$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.
 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 example,
-C<aio_scandir> might generate hundreds of thousands C<aio_stat> requests,
+C<aio_scandir> might generate hundreds of thousands of C<aio_stat>
-delaying any later requests for a long time.
+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>,
 below) requests active in the group itself and is expected to queue more
 Sets the minimum idle timeout (default 10) after which worker threads are
 allowed to exit. SEe C<IO::AIO::max_idle>.
 =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_outstanding> 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
 =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
-avaiable: C<IO::AIO::FADV_NORMAL>, C<IO::AIO::FADV_SEQUENTIAL>,
+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
-avaiable: C<IO::AIO::MADV_NORMAL>, C<IO::AIO::MADV_SEQUENTIAL>,
+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 avaiable: C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_READ>,
+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>.
  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:

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Revision 1.219 by root, Tue Mar 27 18:54:45 2012 UTC