public final class Logger
        implements org.slf4j.Logger, LocationAwareLogger, LoggingEventAware, AppenderAttachable<ILoggingEvent>, Serializable {
    //......
    public boolean isDebugEnabled() {
        return isDebugEnabled(null);
    }
    public boolean isDebugEnabled(Marker marker) {
        final FilterReply decision = callTurboFilters(marker, Level.DEBUG);
        if (decision == FilterReply.NEUTRAL) {
            return effectiveLevelInt <= Level.DEBUG_INT;
        } else if (decision == FilterReply.DENY) {
            return false;
        } else if (decision == FilterReply.ACCEPT) {
            return true;
        } else {
            throw new IllegalStateException("Unknown FilterReply value: " + decision);
        }
    }        
}

/**
     * Method that calls the attached TurboFilter objects based on the logger and
     * the level.
     * 
     * It is used by isYYYEnabled() methods.
     * 
     * It returns the typical FilterReply values: ACCEPT, NEUTRAL or DENY.
     * 
     * @param level
     * @return the reply given by the TurboFilters
     */
    private FilterReply callTurboFilters(Marker marker, Level level) {
        return loggerContext.getTurboFilterChainDecision_0_3OrMore(marker, this, level, null, null, null);
    }

final FilterReply getTurboFilterChainDecision_0_3OrMore(final Marker marker, final Logger logger, final Level level,
            final String format, final Object[] params, final Throwable t) {
        if (turboFilterList.size() == 0) {
            return FilterReply.NEUTRAL;
        }
        return turboFilterList.getTurboFilterChainDecision(marker, logger, level, format, params, t);
    }

public FilterReply getTurboFilterChainDecision(final Marker marker, final Logger logger, final Level level,
            final String format, final Object[] params, final Throwable t) {
        final int size = size();
        // if (size == 0) {
        // return FilterReply.NEUTRAL;
        // }
        if (size == 1) {
            try {
                TurboFilter tf = get(0);
                return tf.decide(marker, logger, level, format, params, t);
            } catch (IndexOutOfBoundsException iobe) {
                return FilterReply.NEUTRAL;
            }
        }
        Object[] tfa = toArray();
        final int len = tfa.length;
        for (int i = 0; i < len; i++) {
            // for (TurboFilter tf : this) {
            final TurboFilter tf = (TurboFilter) tfa[i];
            final FilterReply r = tf.decide(marker, logger, level, format, params, t);
            if (r == FilterReply.DENY || r == FilterReply.ACCEPT) {
                return r;
            }
        }
        return FilterReply.NEUTRAL;
    }