private static long now() {
        return System.currentTimeMillis();
    }
Attempts to invoke the specified {@code runnable} if no other action with
the same specifier has been called recently. Otherwise, the method will
return with no effect.

@param action    the action specifier
@param runnable  the callable action to invoke
tool-parent/tool-core/src/main/java/com/speedment/tool/core/internal/util/Throttler.java