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               # now get raw message, unless we have it already
               unless ($now) {
                  $format = $format->() if ref $format;
                  $format = sprintf $format, @args if @args;
                  $format =~ s/\n$//;
                  $now = _ts;
               };

               # format msg
               my $str = $ctx->[4]
                  ? $ctx->[4]($now, $_[0], $level, $format)
                  : ($fmt[$level] ||= default_format $now, $_[0], $level, $format);

               $success = 1;

               $ctx->[3]($str)
                  or push @ctx, values %{ $ctx->[2] }; # not consumed - propagate
            } else {
               push @ctx, values %{ $ctx->[2] }; # not masked - propagate
            }
         }
      }
   while $ctx = pop @ctx;

   fatal_exit if $level <= 1;

   $success
}

sub log($$;@) {
   _log
      $CTX{ (caller)[0] } ||= _pkg_ctx +(caller)[0],
      @_;
}

=item $logger = AnyEvent::Log::logger $level[, \$enabled]

Creates a code reference that, when called, acts as if the
C<AnyEvent::Log::log> function was called at this point with the given
level. C<$logger> is passed a C<$msg> and optional C<@args>, just as with
the C<AnyEvent::Log::log> function:

   my $debug_log = AnyEvent::Log::logger "debug";

   $debug_log->("debug here");
   $debug_log->("%06d emails processed", 12345);
   $debug_log->(sub { $obj->as_string });

The idea behind this function is to decide whether to log before actually
logging - when the C<logger> function is called once, but the returned
logger callback often, then this can be a tremendous speed win.

Despite this speed advantage, changes in logging configuration will
still be reflected by the logger callback, even if configuration changes
I<after> it was created.

To further speed up logging, you can bind a scalar variable to the logger,
which contains true if the logger should be called or not - if it is
false, calling the logger can be safely skipped. This variable will be
updated as long as C<$logger> is alive.

Full example:

   # near the init section
   use AnyEvent::Log;

   my $debug_log = AnyEvent:Log::logger debug => \my $debug;

   # and later in your program
   $debug_log->("yo, stuff here") if $debug;

   $debug and $debug_log->("123");

=cut

our %LOGGER;

# re-assess logging status for all loggers
sub _reassess {
   local $SIG{__DIE__};
   my $die = sub { die };

   for (@_ ? $LOGGER{$_[0]} : values %LOGGER) {
      my ($ctx, $level, $renabled) = @$_;

      # to detect whether a message would be logged, we actually
      # try to log one and die. this isn't fast, but we can be
      # sure that the logging decision is correct :)

      $$renabled = !eval {
         _log $ctx, $level, $die;

         1
      };
   }
}

sub _logger {
   my ($ctx, $level, $renabled) = @_;

   $$renabled = 1;

   my $logger = [$ctx, $level, $renabled];

   $LOGGER{$logger+0} = $logger;

   _reassess $logger+0;

   require AnyEvent::Util unless $AnyEvent::Util::VERSION;
   my $guard = AnyEvent::Util::guard (sub {
      # "clean up"
      delete $LOGGER{$logger+0};
   });

   sub {
      $guard if 0; # keep guard alive, but don't cause runtime overhead

      _log $ctx, $level, @_
         if $$renabled;
   }