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

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.72 by root, Tue Oct 24 14:25:53 2006 UTC vs.
Revision 1.89 by root, Sun Oct 29 11:03:18 2006 UTC

 =head1 DESCRIPTION
 This module implements asynchronous I/O using whatever means your
 operating system supports.
+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
+when doing heavy I/O (GUI programs, high performance network servers
+etc.), but can also be used to easily do operations in parallel that are
+normally done sequentially, e.g. stat'ing many files, which is much faster
+on a RAID volume or over NFS when you do a number of stat operations
+concurrently.
+While 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 inefficient. Use an event
+loop for that (such as the L<Event|Event> 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
 to perl. In the future, this module might make use of the native aio
 functions available on many operating systems. However, they are often
-not well-supported or restricted (Linux doesn't allow them on normal
+not well-supported or restricted (GNU/Linux doesn't allow them on normal
 files currently, for example), and they would only support aio_read and
 aio_write, so the remaining functionality would have to be implemented
 using threads anyway.
 Although the module will work with in the presence of other (Perl-)
 threads, it is currently not reentrant in any way, so use appropriate
 locking yourself, always call C<poll_cb> from within the same thread, or
 never call C<poll_cb> (or other C<aio_> functions) recursively.
+=head2 EXAMPLE
+This is a simple example that uses the Event module and loads
+F</etc/passwd> asynchronously:
+   use Fcntl;
+   use Event;
+   use IO::AIO;
+   # register the IO::AIO callback with Event
+   Event->io (fd => IO::AIO::poll_fileno,
+              poll => 'r',
+              cb => \&IO::AIO::poll_cb);
+   # queue the request to open /etc/passwd
+   aio_open "/etc/passwd", O_RDONLY, 0, sub {
+      my $fh = $_[0]
+         or die "error while opening: $!";
+      # stat'ing filehandles is generally non-blocking
+      my $size = -s $fh;
+      # queue a request to read the file
+      my $contents;
+      aio_read $fh, 0, $size, $contents, 0, sub {
+         $_[0] == $size
+            or die "short read: $!";
+         close $fh;
+         # file contents now in $contents
+         print $contents;
+         # exit event loop and program
+         Event::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;
 =head1 REQUEST ANATOMY AND LIFETIME
 Every C<aio_*> function creates a request. which is a C data structure not
 directly visible to Perl.
 Request has reached the end of its lifetime and holds no resources anymore
 (except possibly for the Perl object, but its connection to the actual
 aio request is severed and calling its methods will either do nothing or
 result in a runtime error).
+=back
 =cut
 package IO::AIO;
 no warnings;
 use strict 'vars';
 use base 'Exporter';
 BEGIN {
-   our $VERSION = '2.0';
+   our $VERSION = '2.1';
    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_scandir aio_symlink
                      aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move
-                     aio_group aio_nop);
+                     aio_copy aio_group aio_nop aio_mknod);
    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_outstanding nreqs);
+                       min_parallel max_parallel max_idle
+                       nreqs nready npending nthreads
+                       max_poll_time max_poll_reqs);
    @IO::AIO::GRP::ISA = 'IO::AIO::REQ';
    require XSLoader;
    XSLoader::load ("IO::AIO", $VERSION);
 }
 =head1 FUNCTIONS
-=head2 AIO FUNCTIONS
+=head2 AIO REQUEST FUNCTIONS
 All the C<aio_*> calls are more or less thin wrappers around the syscall
 with the same name (sans C<aio_>). The arguments are similar or identical,
 and they all accept an additional (and optional) C<$callback> argument
 which must be a code reference. This code reference will get called with
 syscall has been executed asynchronously.
 All functions expecting a filehandle keep a copy of the filehandle
 internally until the request has finished.
-All requests return objects of type L<IO::AIO::REQ> that allow further
+All functions return request objects of type L<IO::AIO::REQ> that allow
-manipulation of those requests while they are in-flight.
+further manipulation of those requests while they are in-flight.
 The pathnames you pass to these routines I<must> be absolute and
-encoded in byte form. The reason for the former is that at the time the
+encoded as octets. The reason for the former is that at the time the
 request is being executed, the current working directory could have
 changed. Alternatively, you can make sure that you never change the
-current working directory.
+current working directory anywhere in the program and then use relative
+paths.
-To encode pathnames to byte form, either make sure you either: a)
+To encode pathnames as octets, either make sure you either: a) always pass
-always pass in filenames you got from outside (command line, readdir
+in filenames you got from outside (command line, readdir etc.) without
-etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode
+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.
+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.
 =over 4
-=item aioreq_pri $pri
+=item $prev_pri = aioreq_pri [$pri]
-Sets the priority for the next aio request. The default priority
+Returns the priority value that would be used for the next request and, if
+C<$pri> is given, sets the priority for the next aio request.
-is C<0>, the minimum and maximum priorities are C<-4> and C<4>,
+The default priority is C<0>, the minimum and maximum priorities are C<-4>
-respectively. Requests with higher priority will be serviced first.
+and C<4>, respectively. Requests with higher priority will be serviced
+first.
-The priority will be reset to C<0> after each call to one of the C<aio_>
+The priority will be reset to C<0> after each call to one of the C<aio_*>
 functions.
 Example: open a file with low priority, then read something from it with
 higher priority so the read request is serviced before other low priority
 open requests (potentially spamming the cache):
    };
 =item aioreq_nice $pri_adjust
 Similar to C<aioreq_pri>, but subtracts the given value from the current
-priority, so effects are cumulative.
+priority, so the effect is cumulative.
 =item aio_open $pathname, $flags, $mode, $callback->($fh)
 Asynchronously open or create a file and call the callback with a newly
 created filehandle for the file.
    aio_read $fh, 7, 15, $buffer, 0, sub {
       $_[0] > 0 or die "read error: $!";
       print "read $_[0] bytes: <$buffer>\n";
    };
-=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.
-This is a composite request that tries to rename(2) the file first. If
-rename files with C<EXDEV>, it 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, and unlinking the C<$srcpath>.
-If an error occurs, the partial destination file will be unlinked, if
-possible, except when setting atime, mtime, access mode and uid/gid, where
-errors are being ignored.
-=cut
-sub aio_move($$$) {
-   my ($src, $dst, $cb) = @_;
-   my $grp = aio_group $cb;
-   add $grp aio_rename $src, $dst, sub {
-      if ($_[0] && $! == EXDEV) {
-         add $grp aio_open $src, O_RDONLY, 0, sub {
-            if (my $src_fh = $_[0]) {
-               my @stat = stat $src_fh;
-               add $grp aio_open $dst, O_WRONLY, 0200, sub {
-                  if (my $dst_fh = $_[0]) {
-                     add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
-                        close $src_fh;
-                        if ($_[0] == $stat[7]) {
-                           utime $stat[8], $stat[9], $dst;
-                           chmod $stat[2] & 07777, $dst_fh;
-                           chown $stat[4], $stat[5], $dst_fh;
-                           close $dst_fh;
-                           add $grp aio_unlink $src, sub {
-                              $grp->result ($_[0]);
-                           };
-                        } else {
-                           my $errno = $!;
-                           add $grp aio_unlink $dst, sub {
-                              $! = $errno;
-                              $grp->result (-1);
-                           };
-                        }
-                     };
-                  } else {
-                     $grp->result (-1);
-                  }
-               },
-            } else {
-               $grp->result (-1);
-            }
-         };
-      } else {
-         $grp->result ($_[0]);
-      }
-   };
-   $grp
-}
 =item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
 Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
 reading at byte offset C<$in_offset>, and starts writing at the current
 =item aio_unlink $pathname, $callback->($status)
 Asynchronously unlink (delete) a file and call the callback with the
 result code.
+=item aio_mknod $path, $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 { ...
 =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.
 sorted, and will B<NOT> include the C<.> and C<..> entries.
 The callback a single argument which is either C<undef> or an array-ref
 with the filenames.
+=item aio_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.
+This is a composite request that it 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
+possible, except when setting atime, mtime, access mode and uid/gid, where
+errors are being ignored.
+=cut
+sub aio_copy($$;$) {
+   my ($src, $dst, $cb) = @_;
+   my $pri = aioreq_pri;
+   my $grp = aio_group $cb;
+   aioreq_pri $pri;
+   add $grp aio_open $src, O_RDONLY, 0, sub {
+      if (my $src_fh = $_[0]) {
+         my @stat = stat $src_fh;
+         aioreq_pri $pri;
+         add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
+            if (my $dst_fh = $_[0]) {
+               aioreq_pri $pri;
+               add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
+                  if ($_[0] == $stat[7]) {
+                     $grp->result (0);
+                     close $src_fh;
+                     # those should not normally block. should. should.
+                     utime $stat[8], $stat[9], $dst;
+                     chmod $stat[2] & 07777, $dst_fh;
+                     chown $stat[4], $stat[5], $dst_fh;
+                     close $dst_fh;
+                  } 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);
+      }
+   };
+   $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.
+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
+that is successful, unlinking the C<$srcpath>.
+=cut
+sub aio_move($$;$) {
+   my ($src, $dst, $cb) = @_;
+   my $pri = aioreq_pri;
+   my $grp = aio_group $cb;
+   aioreq_pri $pri;
+   add $grp aio_rename $src, $dst, sub {
+      if ($_[0] && $! == EXDEV) {
+         aioreq_pri $pri;
+         add $grp aio_copy $src, $dst, sub {
+            $grp->result ($_[0]);
+            if (!$_[0]) {
+               aioreq_pri $pri;
+               add $grp aio_unlink $src;
+            }
+         };
+      } else {
+         $grp->result ($_[0]);
+      }
+   };
+   $grp
+}
 =item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
 Scans a directory (similar to C<aio_readdir>) but additionally tries to
-separate the entries of directory C<$path> into two sets of names, ones
+efficiently separate the entries of directory C<$path> into two sets of
-you can recurse into (directories or links to them), and ones you cannot
+names, directories you can recurse into (directories), and ones you cannot
-recurse into (everything else).
+recurse into (everything else, including symlinks to directories).
 C<aio_scandir> is a composite request that creates of many sub requests_
 C<$maxreq> specifies the maximum number of outstanding aio requests that
 this function generates. If it is C<< <= 0 >>, then a suitable default
-will be chosen (currently 6).
+will be chosen (currently 4).
 On error, the callback is called without arguments, otherwise it receives
 two array-refs with path-relative entry names.
 Example:
 =cut
 sub aio_scandir($$$) {
    my ($path, $maxreq, $cb) = @_;
+   my $pri = aioreq_pri;
    my $grp = aio_group $cb;
-   $maxreq = 6 if $maxreq <= 0;
+   $maxreq = 4 if $maxreq <= 0;
    # stat once
+   aioreq_pri $pri;
    add $grp aio_stat $path, 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 {
          my $entries = shift
             or return $grp->result ();
          # stat the dir another time
+         aioreq_pri $pri;
          add $grp aio_stat $path, sub {
             my $hash2 = join ":", (stat _)[0,1,3,7,9];
             my $ndirs;
                               map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
                                  @$entries];
             my (@dirs, @nondirs);
-            my ($statcb, $schedcb);
-            my $nreq = 0;
-            my $statgrp = add $grp aio_group;
+            my $statgrp = add $grp aio_group sub {
+               $grp->result (\@dirs, \@nondirs);
+            };
-            $schedcb = sub {
+            limit $statgrp $maxreq;
-               if (@$entries) {
+            feed $statgrp sub {
-                  if ($nreq < $maxreq) {
+               return unless @$entries;
-                     my $ent = pop @$entries;
+               my $entry = pop @$entries;
+               aioreq_pri $pri;
+               add $statgrp aio_stat "$path/$entry/.", sub {
+                  if ($_[0] < 0) {
+                     push @nondirs, $entry;
+                  } else {
+                     # need to check for real directory
+                     aioreq_pri $pri;
+                     add $statgrp aio_lstat "$path/$entry", sub {
+                        if (-d _) {
+                           push @dirs, $entry;
+                           unless (--$ndirs) {
+                              push @nondirs, @$entries;
+                              feed $statgrp;
+                           }
+                        } else {
+                           push @nondirs, $entry;
+                        }
-                     $nreq++;
+                     }
-                     add $statgrp aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
                   }
-               } elsif (!$nreq) {
-                  # finished
-                  $statgrp->cancel;
-                  undef $statcb;
-                  undef $schedcb;
-                  $grp->result (\@dirs, \@nondirs);
-               }
+               };
             };
-            $statcb = sub {
-               my ($status, $entry) = @_;
-               if ($status < 0) {
-                  $nreq--;
-                  push @nondirs, $entry;
-                  &$schedcb;
-               } else {
-                  # need to check for real directory
-                  add $grp aio_lstat "$path/$entry", sub {
-                     $nreq--;
-                     if (-d _) {
-                        push @dirs, $entry;
-                        if (!--$ndirs) {
-                           push @nondirs, @$entries;
-                           $entries = [];
-                        }
-                     } else {
-                        push @nondirs, $entry;
-                     }
-                     &$schedcb;
-                  }
-               }
-            };
-            &$schedcb while @$entries && $nreq < $maxreq;
          };
       };
    };
    $grp
 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_group $callback->(...)
-[EXPERIMENTAL]
 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
 many requests into a single, composite, request with a definite callback
 and the ability to cancel the whole request with its subrequests.
 =item * They can also can also be added to other IO::AIO::GRP objects.
 =item * You must not add requests to a group from within the group callback (or
 any later time).
-=item * This does not harmonise well with C<max_outstanding>, so best do
-not combine C<aio_group> with it. Groups and feeders are recommended for
-this kind of concurrency-limiting.
 =back
 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
 be added, including other groups, as long as you do not create circular
 dependencies.
 Returns all its arguments.
+=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.
 =item $grp->result (...)
 Set the result value(s) that will be passed to the group callback when all
-subrequests have finished. By default, no argument will be passed.
+subrequests have finished and set thre groups errno to the current value
+of errno (just like calling C<errno> without an error number). By default,
+no argument will be passed and errno is zero.
+=item $grp->errno ([$errno])
+Sets the group errno value to C<$errno>, or the current value of errno
+when the argument is missing.
+Every aio request has an associated errno value that is restored when
+the callback is invoked. This method lets you change this value from its
+default (0).
+Calling C<result> will also set errno, so make sure you either set C<$!>
+before the call to C<result>, or call c<errno> after it.
 =item feed $grp $callback->($grp)
-[VERY EXPERIMENTAL]
 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
 =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
 See C<poll_cb> for an example.
 =item IO::AIO::poll_cb
-Process all outstanding events on the result pipe. You have to call this
+Process some outstanding events on the result pipe. You have to call this
 regularly. Returns the number of events processed. Returns immediately
-when no events are outstanding.
+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.
 Example: Install an Event watcher that automatically calls
 IO::AIO::poll_cb with high priority:
    Event->io (fd => IO::AIO::poll_fileno,
               poll => 'r', async => 1,
               cb => \&IO::AIO::poll_cb);
+=item IO::AIO::max_poll_reqs $nreqs
+=item IO::AIO::max_poll_time $seconds
+These set the maximum number of requests (default C<0>, meaning infinity)
+that are being processed by C<IO::AIO::poll_cb> in one call, respectively
+the maximum amount of time (default C<0>, meaning infinity) spent in
+C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
+of time C<poll_cb> is allowed to use).
+Setting C<max_poll_time> to a non-zero value creates an overhead of one
+syscall per request processed, which is not normally a problem unless your
+callbacks are really really fast or your OS is really really slow (I am
+not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
+Setting these is useful if you want to ensure some level of
+interactiveness when perl is not fast enough to process all requests in
+time.
+For interactive programs, values such as C<0.01> to C<0.1> should be fine.
+Example: Install an Event watcher that automatically calls
+IO::AIO::poll_cb with low priority, to ensure that other parts of the
+program get the CPU sometimes even under high AIO load.
+   # try not to spend much more than 0.1s in poll_cb
+   IO::AIO::max_poll_time 0.1;
+   # 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
 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
+C<select> on the filehandle. This is useful if you want to synchronously
-for some requests to finish).
+wait for some requests to finish).
 See C<nreqs> for an example.
+=item IO::AIO::poll
+Waits until some requests have been handled.
+Strictly equivalent to:
+   IO::AIO::poll_wait, IO::AIO::poll_cb
+      if IO::AIO::nreqs;
-=item IO::AIO::nreqs
+=item IO::AIO::flush
-Returns the number of requests currently outstanding (i.e. for which their
+Wait till all outstanding AIO requests have been handled.
-callback has not been invoked yet).
-Example: wait till there are no outstanding requests anymore:
+Strictly equivalent to:
    IO::AIO::poll_wait, IO::AIO::poll_cb
       while IO::AIO::nreqs;
-=item IO::AIO::flush
+=head3 CONTROLLING THE NUMBER OF THREADS
-Wait till all outstanding AIO requests have been handled.
-Strictly equivalent to:
-   IO::AIO::poll_wait, IO::AIO::poll_cb
-      while IO::AIO::nreqs;
-=item IO::AIO::poll
-Waits until some requests have been handled.
-Strictly equivalent to:
-   IO::AIO::poll_wait, IO::AIO::poll_cb
-      if IO::AIO::nreqs;
 =item IO::AIO::min_parallel $nthreads
 Set the minimum number of AIO threads to C<$nthreads>. The current
 default is C<8>, which means eight asynchronous operations can execute
 concurrently at any one time (the number of outstanding requests,
 however, is unlimited).
 IO::AIO starts threads only on demand, when an AIO request is queued and
-no free thread exists.
+no free thread exists. Please note that queueing up a hundred requests can
+create demand for a hundred threads, even if it turns out that everything
+is in the cache and could have been processed faster by a single thread.
 It is recommended to keep the number of threads relatively low, as some
 Linux kernel versions will scale negatively with the number of threads
 (higher parallelity => MUCH higher latency). With current Linux 2.6
 versions, 4-32 threads should be fine.
 This module automatically runs C<max_parallel 0> at program end, to ensure
 that all threads are killed and that there are no outstanding requests.
 Under normal circumstances you don't need to call this function.
+=item IO::AIO::max_idle $nthreads
+Limit the number of threads (default: 4) that are allowed to idle (i.e.,
+threads that did not get a request to process within 10 seconds). That
+means if a thread becomes idle while C<$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 $oldnreqs = IO::AIO::max_outstanding $nreqs
+=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
-[DEPRECATED]
+This is a very bad function to use in interactive programs because it
+blocks, and a bad way to reduce concurrency because it is inexact: Better
+use an C<aio_group> together with a feed callback.
 Sets the maximum number of outstanding requests to C<$nreqs>. If you
-try to queue up more than this number of requests, the caller will block until
+to queue up more than this number of requests, the next call to the
-some requests have been handled.
+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 is very large, so normally there is no practical limit. If you
+The default value is very large, so there is no practical limit on the
-queue up many requests in a loop it often improves speed if you set
+number of outstanding requests.
-this to a relatively low number, such as C<100>.
-This function does not work well together with C<aio_group>'s, and their
+You can still queue as many requests as you want. Therefore,
-feeder interface is better suited to limiting concurrency, so do not use
+C<max_oustsanding> is mainly useful in simple scripts (with low values) or
-this function.
+as a stop gap to shield against fatal memory overflow (with large values).
-Under normal circumstances you don't need to call this function.
+=head3 STATISTICAL INFORMATION
+=item IO::AIO::nreqs
+Returns the number of requests currently in the ready, execute or pending
+states (i.e. for which their callback has not been invoked yet).
+Example: wait till there are no outstanding requests anymore:
+   IO::AIO::poll_wait, IO::AIO::poll_cb
+      while IO::AIO::nreqs;
+=item IO::AIO::nready
+Returns the number of requests currently in the ready state (not yet
+executed).
+=item IO::AIO::npending
+Returns the number of requests currently in the pending state (executed,
+but not yet processed by poll_cb).
 =back
 =cut
 }
 min_parallel 8;
 END {
-   max_parallel 0;
+   min_parallel 1;
-}
+   flush;
+};
 1;
 =head2 FORK BEHAVIOUR
 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.
-Temporary memory that was allocated for request processing is not
-reclaimed in the child, however. While this is possible in some cases, it
-is almost impossible in others (threads are evil you know), so you will
-have to live with it. This is around 64k buffer (for sendfile, readahead
-emulation) + the size of the directory being scanned (readdir).
 In short: the parent will, after a short pause, continue as if fork had
 not been called, while the child will act as if IO::AIO has not been used
 yet.
 =head2 MEMORY USAGE
 temporary buffers, and each thread requires a stack and other data
 structures (usually around 16k-128k, depending on the OS).
 =head1 KNOWN BUGS
-See FORK BEHAVIOUR, above.
+Known bugs will be fixed in the next release.
 =head1 SEE ALSO
 L<Coro::AIO>.

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Comparing IO-AIO/AIO.pm (file contents):
Revision 1.72 by root, Tue Oct 24 14:25:53 2006 UTC vs.
Revision 1.89 by root, Sun Oct 29 11:03:18 2006 UTC