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      if( HAS_BROKEN_TRAMPOLINES ) {
         return $cv->( $self, @_[1..$#_] );
      }
      else {
         # Don't assign to $_[0] directly or we will change caller's first argument
         shift @_;
         unshift @_, $self;
         goto &$cv;
      }
   };
}

=head2 can_event

   $code = $notifier->can_event( $event_name )

Returns a C<CODE> reference if the object can perform the given event name,
either by a configured C<CODE> reference parameter, or by implementing a
method. If the object is unable to handle this event, C<undef> is returned.

=cut

sub can_event
{
   my $self = shift;
   my ( $event_name ) = @_;

   return $self->{$event_name} || $self->can( $event_name );
}

=head2 make_event_cb

   $callback = $notifier->make_event_cb( $event_name )

Returns a C<CODE> reference which, when invoked, will execute the given event
handler. Event handlers may either be subclass methods, or parameters given to
the C<new> or C<configure> method.

The event handler can be passed extra arguments by giving them to the C<CODE>
reference; the first parameter received will be a reference to the notifier
itself. This is stored weakly in the closure, so it is safe to store the
resulting C<CODE> reference in the object itself without causing a reference
cycle.

=cut

sub make_event_cb
{
   my $self = shift;
   my ( $event_name ) = @_;

   my $code = $self->can_event( $event_name )
      or croak "$self cannot handle $event_name event";

   my $caller = caller;

   return $self->_capture_weakself( 
      !$IO::Async::Debug::DEBUG ? $code : sub {
         my $self = $_[0];
         $self->_debug_printf_event( $caller, $event_name );
         goto &$code;
      }
   );
}

=head2 maybe_make_event_cb

   $callback = $notifier->maybe_make_event_cb( $event_name )

Similar to C<make_event_cb> but will return C<undef> if the object cannot
handle the named event, rather than throwing an exception.

=cut

sub maybe_make_event_cb
{
   my $self = shift;
   my ( $event_name ) = @_;

   my $code = $self->can_event( $event_name )
      or return undef;

   my $caller = caller;

   return $self->_capture_weakself(
      !$IO::Async::Debug::DEBUG ? $code : sub {
         my $self = $_[0];
         $self->_debug_printf_event( $caller, $event_name );
         goto &$code;
      }
   );
}

=head2 invoke_event

   @ret = $notifier->invoke_event( $event_name, @args )

Invokes the given event handler, passing in the given arguments. Event
handlers may either be subclass methods, or parameters given to the C<new> or
C<configure> method. Returns whatever the underlying method or CODE reference
returned.

=cut

sub invoke_event
{
   my $self = shift;
   my ( $event_name, @args ) = @_;

   my $code = $self->can_event( $event_name )
      or croak "$self cannot handle $event_name event";

   $self->_debug_printf_event( scalar caller, $event_name ) if $IO::Async::Debug::DEBUG;
   return $code->( $self, @args );
}

=head2 maybe_invoke_event

   $retref = $notifier->maybe_invoke_event( $event_name, @args )

Similar to C<invoke_event> but will return C<undef> if the object cannot
handle the name event, rather than throwing an exception. In order to
distinguish this from an event-handling function that simply returned
C<undef>, if the object does handle the event, the list that it returns will
be returned in an ARRAY reference.

=cut

sub maybe_invoke_event
{
   my $self = shift;
   my ( $event_name, @args ) = @_;

   my $code = $self->can_event( $event_name )
      or return undef;

   $self->_debug_printf_event( scalar caller, $event_name ) if $IO::Async::Debug::DEBUG;
   return [ $code->( $self, @args ) ];
}

=head1 DEBUGGING SUPPORT

=cut

=head2 debug_printf

   $notifier->debug_printf( $format, @args )

Conditionally print a debugging message to C<STDERR> if debugging is enabled.
If such a message is printed, it will be printed using C<printf> using the
given format and arguments. The message will be prefixed with an string, in
square brackets, to help identify the C<$notifier> instance. This string will
be the class name of the notifier, and any parent notifiers it is contained
by, joined by an arrow C<< <- >>. To ensure this string does not grow too
long, certain prefixes are abbreviated:

 IO::Async::Protocol::  =>  IaP:
 IO::Async::            =>  Ia:
 Net::Async::           =>  Na:

Finally, each notifier that has a name defined using the C<notifier_name>
parameter has that name appended in braces.

For example, invoking

 $stream->debug_printf( "EVENT on_read" )

On an L<IO::Async::Stream> instance reading and writing a file descriptor
whose C<fileno> is 4, which is a child of an L<IO::Async::Protocol::Stream>,
will produce a line of output:

 [Ia:Stream{rw=4}<-IaP:Stream] EVENT on_read

=cut

sub debug_printf
{
   $IO::Async::Debug::DEBUG or return;

   my $self = shift;
   my ( $format, @args ) = @_;

   my @id;
   while( $self ) {
      push @id, ref $self;

      my $name = $self->notifier_name;
      $id[-1] .= "{$name}" if defined $name and length $name;

      $self = $self->parent;
   }

   s/^IO::Async::Protocol::/IaP:/,
   s/^IO::Async::/Ia:/,
   s/^Net::Async::/Na:/ for @id;

   IO::Async::Debug::logf "[%s] $format\n", join("<-", @id), @args;
}

sub _debug_printf_event
{
   my $self = shift;
   my ( $caller, $event_name ) = @_;

   my $class = ref $self;

   if( $IO::Async::Debug::DEBUG > 1 or $class eq $caller ) {
      s/^IO::Async::Protocol::/IaP:/,
      s/^IO::Async::/Ia:/,
      s/^Net::Async::/Na:/ for my $str_caller = $caller;

      $self->debug_printf( "EVENT %s",
         ( $class eq $caller ? $event_name : "${str_caller}::$event_name" )
      );
   }
}

=head2 invoke_error

   $notifier->invoke_error( $message, $name, @details )

Invokes the stored C<on_error> event handler, passing in the given arguments.
If no handler is defined, it will be passed up to the containing parent
notifier, if one exists. If no parent exists, the error message will be thrown
as an exception by using C<die()> and this method will not return.

If a handler is found to handle this error, the method will return as normal.
However, as the expected use-case is to handle "fatal" errors that now render
the notifier unsuitable to continue, code should be careful not to perform any
further work after invoking it. Specifically, sockets may become disconnected,
or the entire notifier may now be removed from its containing loop.

The C<$name> and C<@details> list should follow similar semantics to L<Future>
failures. That is, the C<$name> should be a string giving a category of
failure, and the C<@details> list should contain additional arguments that
relate to that kind of failure.

=cut

sub invoke_error
{
   my $self = shift;
   my ( $message, $name, @details ) = @_;

   if( my $code = $self->{IO_Async_Notifier__on_error} || $self->can( "on_error" ) ) {
      return $code->( $self, $message, $name, @details );
   }

   if( my $parent = $self->parent ) {
      return $parent->invoke_error( @_ );
   }

   die "$message\n";
}

=head1 AUTHOR

Paul Evans <leonerd@leonerd.org.uk>

=cut

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