An operating systems can also be classified by the extent of the support for real-time services. Most operating systems support priorities, which may be used to allow applications with nearer deadlines to get precedence. Real-time operating systems provide more elaborate, higher-level support for meeting deadlines that automatically schedules processes based on task durations and deadlines. Things get tricky when shared objects are accessed by real-time processes, since ideally, we do not want a process with a later deadline to block a process with an earlier deadline. Solutions exist if we make certain assumptions about behaviors of real-time systems.