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

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.58 by root, Sun Oct 22 10:33:19 2006 UTC vs.
Revision 1.85 by root, Sat Oct 28 01:40:30 2006 UTC

  };
  # version 2+ has request and group objects
  use IO::AIO 2;
+ aioreq_pri 4; # give next request a very high priority
  my $req = aio_unlink "/tmp/file", sub { };
  $req->cancel; # cancel request if still in queue
  my $grp = aio_group sub { print "all stats done\n" };
  add $grp aio_stat "..." for ...;
 =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.
-Currently, a number of threads are started that execute your read/writes
+In this version, a number of threads are started that execute your
-and signal their completion. You don't need thread support in your libc or
+requests and signal their completion. You don't need thread support
-perl, and the threads created by this module will not be visible to the
+in perl, and the threads created by this module will not be visible
-pthreads library. In the future, this module might make use of the native
+to perl. In the future, this module might make use of the native aio
-aio functions available on many operating systems. However, they are often
+functions available on many operating systems. However, they are often
-not well-supported (Linux doesn't allow them on normal files currently,
+not well-supported or restricted (GNU/Linux doesn't allow them on normal
-for example), and they would only support aio_read and aio_write, so the
+files currently, for example), and they would only support aio_read and
-remaining functionality would have to be implemented using threads anyway.
+aio_write, so the remaining functionality would have to be implemented
+using threads anyway.
-Although the module will work with in the presence of other threads, it is
+Although the module will work with in the presence of other (Perl-)
-currently not reentrant, so use appropriate locking yourself, always call
+threads, it is currently not reentrant in any way, so use appropriate
-C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
+locking yourself, always call C<poll_cb> from within the same thread, or
-C<aio_> functions) recursively.
+never call C<poll_cb> (or other C<aio_> functions) recursively.
+=head1 REQUEST ANATOMY AND LIFETIME
+Every C<aio_*> function creates a request. which is a C data structure not
+directly visible to Perl.
+If called in non-void context, every request function returns a Perl
+object representing the request. In void context, nothing is returned,
+which saves a bit of memory.
+The perl object is a fairly standard ref-to-hash object. The hash contents
+are not used by IO::AIO so you are free to store anything you like in it.
+During their existance, aio requests travel through the following states,
+in order:
+=over 4
+=item ready
+Immediately after a request is created it is put into the ready state,
+waiting for a thread to execute it.
+=item execute
+A thread has accepted the request for processing and is currently
+executing it (e.g. blocking in read).
+=item pending
+The request has been executed and is waiting for result processing.
+While request submission and execution is fully asynchronous, result
+processing is not and relies on the perl interpreter calling C<poll_cb>
+(or another function with the same effect).
+=item result
+The request results are processed synchronously by C<poll_cb>.
+The C<poll_cb> function will process all outstanding aio requests by
+calling their callbacks, freeing memory associated with them and managing
+any groups they are contained in.
+=item done
+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).
 =cut
 package IO::AIO;
 use base 'Exporter';
 BEGIN {
    our $VERSION = '2.0';
-   our @EXPORT = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
+   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_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
-                    aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move
+                     aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move
-                    aio_group);
+                     aio_copy aio_group aio_nop aio_mknod);
-   our @EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
+   our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
+   our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
+                       min_parallel max_parallel nreqs nready npending);
    @IO::AIO::GRP::ISA = 'IO::AIO::REQ';
    require XSLoader;
    XSLoader::load ("IO::AIO", $VERSION);
 environment, d) use Glib::filename_from_unicode on unicode filenames or e)
 use something else.
 =over 4
+=item $prev_pri = aioreq_pri [$pri]
+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.
+The default priority is C<0>, the minimum and maximum priorities are C<-4>
+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_*>
+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):
+   aioreq_pri -3;
+   aio_open ..., sub {
+      return unless $_[0];
+      aioreq_pri -2;
+      aio_read $_[0], ..., sub {
+         ...
+      };
+   };
+=item aioreq_nice $pri_adjust
+Similar to C<aioreq_pri>, but subtracts the given value from the current
+priority, so effects are 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)
-[EXPERIMENTAL due to internal aio_group use]
-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)
+Asynchronously create a device node (or fifo). See mknod(2).
+The only portable (POSIX) 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($$;$) {
+   my ($src, $dst, $cb) = @_;
+   my $pri = aioreq_pri;
+   my $grp = aio_group $cb;
+   aioreq_pri $pri;
+   add $grp aio_rename $src, $dst, sub {
+      if ($_[0] && $! == EXDEV) {
+         aioreq_pri $pri;
+         add $grp aio_copy $src, $dst, sub {
+            $grp->result ($_[0]);
+            if (!$_[0]) {
+               aioreq_pri $pri;
+               add $grp aio_unlink $src;
+            }
+         };
+      } else {
+         $grp->result ($_[0]);
+      }
+   };
+   $grp
+}
 =item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
-[EXPERIMENTAL due to internal aio_group use]
 Scans a directory (similar to C<aio_readdir>) but additionally tries to
-separate the entries of directory C<$path> into two sets of names, ones
+efficiently separate the entries of directory C<$path> into two sets of
-you can recurse into (directories or links to them), and ones you cannot
+names, directories you can recurse into (directories), and ones you cannot
-recurse into (everything else).
+recurse into (everything else, including symlinks to directories).
-C<aio_scandir> is a composite request that consists of many sub
+C<aio_scandir> is a composite request that creates of many sub requests_
-requests. C<$maxreq> specifies the maximum number of outstanding aio
+C<$maxreq> specifies the maximum number of outstanding aio requests that
-requests that this function generates. If it is C<< <= 0 >>, then a
+this function generates. If it is C<< <= 0 >>, then a suitable default
-suitable default will be chosen (currently 8).
+will be chosen (currently 4).
 On error, the callback is called without arguments, otherwise it receives
 two array-refs with path-relative entry names.
 Example:
 =cut
 sub aio_scandir($$$) {
    my ($path, $maxreq, $cb) = @_;
+   my $pri = aioreq_pri;
    my $grp = aio_group $cb;
-   $maxreq = 8 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 $statgrp = add $grp aio_group sub {
-            my $nreq = 0;
+               $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 $grp aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
                   }
-               } elsif (!$nreq) {
-                  # finished
-                  undef $statcb;
-                  undef $schedcb;
-                  $grp->result (\@dirs, \@nondirs) if $cb;
-                  undef $cb;
-               }
+               };
             };
-            $statcb = sub {
-               my ($status, $entry) = @_;
-               if ($status < 0) {
-                  $nreq--;
-                  push @nondirs, $entry;
-                  &$schedcb;
-               } else {
-                  # need to check for real directory
-                  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.
+many requests into a single, composite, request with a definite callback
+and the ability to cancel the whole request with its subrequests.
 Returns an object of class L<IO::AIO::GRP>. See its documentation below
 for more info.
 Example:
    add $grp
       (aio_stat ...),
       (aio_stat ...),
       ...;
+=item aio_nop $callback->()
+This is a special request - it does nothing in itself and is only used for
+side effects, such as when you want to add a dummy request to a group so
+that finishing the requests in the group depends on executing the given
+code.
+While this request does nothing, it still goes through the execution
+phase and still requires a worker thread. Thus, the callback will not
+be executed immediately but only after other requests in the queue have
+entered their execution phase. This can be used to measure request
+latency.
-=item IO::AIO::aio_sleep $fractional_seconds, $callback->()  *NOT EXPORTED*
+=item IO::AIO::aio_busy $fractional_seconds, $callback->()  *NOT EXPORTED*
 Mainly used for debugging and benchmarking, this aio request puts one of
 the request workers to sleep for the given time.
 While it is theoretically handy to have simple I/O scheduling requests
-like sleep and file handle readable/writable, the overhead this creates
+like sleep and file handle readable/writable, the overhead this creates is
-is immense, so do not use this function except to put your application
+immense (it blocks a thread for a long time) so do not use this function
-under artificial I/O pressure.
+except to put your application under artificial I/O pressure.
 =back
 =head2 IO::AIO::REQ CLASS
 All non-aggregate C<aio_*> functions return an object of this class when
 called in non-void context.
-A request always moves through the following five states in its lifetime,
-in order: B<ready> (request has been created, but has not been executed
-yet), B<execute> (request is currently being executed), B<pending>
-(request has been executed but callback has not been called yet),
-B<result> (results are being processed synchronously, includes calling the
-callback) and B<done> (request has reached the end of its lifetime and
-holds no resources anymore).
 =over 4
-=item $req->cancel
+=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
 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.
 =back
 =head2 IO::AIO::GRP CLASS
 This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
    };
 This makes it very easy to create composite requests (see the source of
 C<aio_move> for an application) that work and feel like simple requests.
+=over 4
-The IO::AIO::GRP objects will be cleaned up during calls to
+=item * The IO::AIO::GRP objects will be cleaned up during calls to
 C<IO::AIO::poll_cb>, just like any other request.
-They can be canceled like any other request. Canceling will cancel not
+=item * They can be canceled like any other request. Canceling will cancel not
-just the request itself, but also all requests it contains.
+only the request itself, but also all requests it contains.
-They can also can also be added to other IO::AIO::GRP objects.
+=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).
+=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
 exist.
 group. And only when all those requests have finished will the the group
 itself finish.
 =over 4
+=item add $grp ...
 =item $grp->add (...)
-=item add $grp ...
 Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
 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)
+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, 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
+requests.
+The feed callback can queue as many requests as it likes (i.e. C<add> does
+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.
+Example:
+   # stat all files in @files, but only ever use four aio requests concurrently:
+   my $grp = aio_group sub { print "finished\n" };
+   limit $grp 4;
+   feed $grp sub {
+      my $file = pop @files
+         or return;
+      add $grp aio_stat $file, sub { ... };
+   };
+=item limit $grp $num
+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.
 =back
 =head2 SUPPORT FUNCTIONS
 Process all outstanding events on the result pipe. You have to call this
 regularly. Returns the number of events processed. Returns immediately
 when no events are outstanding.
+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::poll_some $max_requests
+Similar to C<poll_cb>, but only processes up to C<$max_requests> requests
+at a time.
+Useful if you want to ensure some level of interactiveness when perl is
+not fast enough to process all requests in time.
+Example: Install an Event watcher that automatically calls
+IO::AIO::poll_some with low priority, to ensure that other parts of the
+program get the CPU sometimes even under high AIO load.
+   Event->io (fd => IO::AIO::poll_fileno,
+              poll => 'r', nice => 1,
+              cb => sub { IO::AIO::poll_some 256 });
 =item IO::AIO::poll_wait
 Wait till the result filehandle becomes ready for reading (simply does a
 C<select> on the filehandle. This is useful if you want to synchronously wait
 for some requests to finish).
 See C<nreqs> for an example.
 =item IO::AIO::nreqs
-Returns the number of requests currently outstanding (i.e. for which their
+Returns the number of requests currently in the ready, execute or pending
-callback has not been invoked yet).
+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).
 =item IO::AIO::flush
 Wait till all outstanding AIO 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
+Set the minimum number of AIO threads to C<$nthreads>. The current
-is C<4>, which means four asynchronous operations can be done at one time
+default is C<8>, which means eight asynchronous operations can execute
-(the number of outstanding operations, however, is unlimited).
+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.
-It is recommended to keep the number of threads low, as some Linux
+It is recommended to keep the number of threads relatively low, as some
-kernel versions will scale negatively with the number of threads (higher
+Linux kernel versions will scale negatively with the number of threads
-parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
+(higher parallelity => MUCH higher latency). With current Linux 2.6
-threads should be fine.
+versions, 4-32 threads should be fine.
 Under most circumstances you don't need to call this function, as the
 module selects a default that is suitable for low to moderate load.
 =item IO::AIO::max_parallel $nthreads
 This module automatically runs C<max_parallel 0> at program end, to ensure
 that all threads are killed and that there are no outstanding requests.
 Under normal circumstances you don't need to call this function.
-=item $oldnreqs = IO::AIO::max_outstanding $nreqs
+=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
+This is a very bad function to use in interactive programs because it
+blocks, and a bad way to reduce concurrency because it is inexact: Better
+use an C<aio_group> together with a feed callback.
 Sets the maximum number of outstanding requests to C<$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>.
-Under normal circumstances you don't need to call this function.
+You can still queue as many requests as you want. Therefore,
+C<max_oustsanding> is mainly useful in simple scripts (with low values) or
+as a stop gap to shield against fatal memory overflow (with large values).
 =back
 =cut
       or return undef;
    *$sym
 }
-min_parallel 4;
+min_parallel 8;
 END {
-   max_parallel 0;
+   min_parallel 1;
-}
+   flush;
+};
 1;
 =head2 FORK BEHAVIOUR
 This module should do "the right thing" when the process using it forks:
 Before the fork, IO::AIO enters a quiescent state where no requests
 can be added in other threads and no results will be processed. After
 the fork the parent simply leaves the quiescent state and continues
-request/result processing, while the child clears the request/result
+request/result processing, while the child frees the request/result queue
-queue (so the requests started before the fork will only be handled in
+(so that the requests started before the fork will only be handled in the
-the parent). Threads will be started on demand until the limit ste 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
 not been called, while the child will act as if IO::AIO has not been used
 yet.
+=head2 MEMORY USAGE
+Per-request usage:
+Each aio request uses - depending on your architecture - around 100-200
+bytes of memory. In addition, stat requests need a stat buffer (possibly
+a few hundred bytes), readdir requires a result buffer and so on. Perl
+scalars and other data passed into aio requests will also be locked and
+will consume memory till the request has entered the done state.
+This is now awfully much, so queuing lots of requests is not usually a
+problem.
+Per-thread usage:
+In the execution phase, some aio requests require more memory for
+temporary buffers, and each thread requires a stack and other data
+structures (usually around 16k-128k, depending on the OS).
+=head1 KNOWN BUGS
+Known bugs will be fixed in the next release.
 =head1 SEE ALSO
-L<Coro>, L<Linux::AIO> (obsolete).
+L<Coro::AIO>.
 =head1 AUTHOR
  Marc Lehmann <schmorp@schmorp.de>
  http://home.schmorp.de/

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Revision 1.85 by root, Sat Oct 28 01:40:30 2006 UTC