Finally, many packets are only a few hundred bytes, in which case it is doubtful that mapping will beat copying. Still, it is an interesting idea that is certainly worth thinking about.Timer Management. 13. The usual sequence of steps in an RPC involves trapping to the kernel to have the message sent from the client to the server. Suppose that a special co-processor chip for doing network I/O exists and that this chip is directly addressable from user space. Would it be worth having? What steps would an RPC consist of in that case?. An obvious question is: What happens when a department head, or worse yet, a big cheese, stops functioning (crashes)? One answer is to promote one of the direct subordinates of the faulty manager to fill in for the boss. The choice of which can be made by the subordinates themselves, by the deceased’s peers, or in a more autocratic system, by the sick manager’s boss.. While many real-time systems and applications are programmed in general-purpose languages such as C, specialized real-time languages can potentially be of great assistance. For example, in such a language, it should be easy to express the work as a collection of short tasks (e.g., lightweight processes or threads) that can be scheduled independently, subject to user-defined precedence and mutual exclusion constraints.. 3. The entire algorithm is performed in well under a memory cycle.. Fig. 6-28. Ownership location using a central manager. (a) Four-message protocol. (b) Three-message protocol.. The rest of this chapter is structured as follows. First we will describe objects and capabilities, since these are the heart of the entire system. Then we will look at the kernel, focusing on process management, memory management, and communication. Finally, we will
examine some of the main servers, including the bullet server, the directory server, the replication server, and the run server.. DescriptionDirectionInitAllocate a table slot?EndReturn a table slot?RegisterListen to a FLIP address?UnregisterStop listening?UnicastSend a point-to-point message?MulticostSend a multicost message?BroadcastSend a broadcast message?ReceivePacket received?NotdeliverUndeliverable packet received?. 4. Ports.. [Картинка: any2fbimgloader212]. [Картинка: any2fbimgloader228]. Mach has a single server that runs BSD UNIX as an application program. It provides 100 percent binary-compatible emulation, a great boon for running existing software for which the source code is not available. General object replication is not supported. Other servers also exist.. The next step is for the application writer to write the client and server code. Both of these are then compiled, as are the two stub procedures. The resulting client code and client stub object files are then linked with the runtime library to produce the executable binary for the client. Similarly, the server code and server stub are compiled and linked to produce the server’s binary. At runtime, the client and server are started to make the application run.. CDS permits entries to be replicated to provide higher availability and better fault tolerance. The directory is the unit of replication, with an entire directory either being replicated or not. For this reason, directories are a heavier weight concept than in say, UNIX. CDS directories cannot be created and deleted from the usual programmer’s interface. Special administrative programs are used.. Fig. 10-22. An X.500 directory information tree..