As a second example, consider a factory full of robots, each containing a powerful computer for handling vision, planning, communication, and other tasks. When a robot on the assembly line notices that a part it is supposed to install is defective, it asks another robot in the parts department to bring it a replacement. If all the robots act like peripheral devices attached to the same central computer and the system can be programmed that way, it too counts as a distributed system.. #define MAX_PATH 255 /* maximum length of a file name */. specification of file_server, version 3.1:. Real timers do not interrupt exactlyHtimes a second. Theoretically, a timer withH= 60 should generate 216,000 ticks per hour. In practice, the relative error obtainable with modern timer chips is about 10-5, meaning that a particular machine can get a value in the range 215,998 to 216,002 ticks per hour. More precisely, if there exists some constant ? such that [Картинка: any2fbimgloader60]. The third property says that transactions areisolatedorserializable.What it means is that if two or more transactions are running at the same time, to each of them and to other processes, the final result looks as though all transactions ran sequentially in some (system dependent) order.. In some systems the workstations have local disks and in others they do not. The latter are universally calleddiskless workstations,but the former are variously known asdiskful workstations,ordisky workstations,or even stranger names. If the workstations are diskless, the file system must be implemented by one or more remote file servers. Requests to read and write files are sent to a file server, which performs the work and sends back the replies.. On the other hand, when the kernel manages the cache, it can dynamically decide how much memory to reserve for programs and how much for the cache.. W(x)a andR(y)b. [Картинка: any2fbimgloader151]. Whereas these two strategies are approximately equally easy to implement in a multiprocessor, they differ radically in a DSM system. Unlike in a multiprocessor, where the MMU knows which word is to be written and what the new value is, in a DSM system the software does not know which word is to be written or what the new value will be. To find out, it could make a secret copy of the page about to be changed (the page number is known), make the page writable, set the hardware trap bit, which forces a trap after every instruction, and restart the faulting process. One instruction later, it catches the trap and compares the current page with the secret copy it just made, to see which word has been changed. It could then broadcast a short packet giving the address and new value on the network. The processors receiving this packet could then check to see if they have the page in question, and if so, update it.. 6.6.2. Linda. 2. put_reply — done by a server when it has a reply to send.. 9. Why does thetrans call have parameters for both sending and receiving? Would it not have been better and simpler to have two calls,send_requestandget_reply, one for sending and one for receiving?. 2. Security.. Third, authentication must work both ways. That is, not only must the server be convinced who the client is, but the client must also be convinced who the server is. This requirement is necessary to prevent an intruder from capturing messages from the client and pretending that it is, say, the file server..