4. The termsloosely-coupled system andtightly-coupled system are often used to described distributed computer systems. What is the different between them?. 3. Nonblocking send with interrupt (makes programming difficult).. [Картинка: any2fbimgloader50]. In the absence of any other information, the best estimate of the message propagation time is (T1–T0)/2. When the reply comes in, the value in the message can be increased by this amount to give an estimate of the server’s current time. If the theoretical minimum propagation time is known, other properties of the time estimate can be calculated.. 4. Avoidance (avoid deadlocks by allocating resources carefully).. Once activated like this, the runtime system can reschedule its threads, typically by marking the current thread as blocked and taking another thread from the ready list, setting up its registers, and restarting it. Later, when the kernel learns that the original thread can run again (e.g., the pipe it was trying to read from now contains data, or the page it faulted over has been brought in from disk), it makes another upcall to the runtime system to inform it of this event. The runtime system, at its own discretion, can either restart the blocked thread immediately, or put it on the ready list to be run later.. Fig. 4-19. A processor hierarchy can be modeled as an organizational hierarchy.. [Картинка: any2fbimgloader129]. LaRowe and Ellis (1991) have compared a large number of algorithms and concluded that no single policy is best. The machine architecture, the size of the penalty for a remote access, and the reference pattern of the program in question all play a large role in determining which algorithm is best.. 6.3.7. Entry Consistency. Packets passed by the RPC layer or the group communication layer (see Fig. 7-16) to the FLIP layer are addressed by FLIP addresses, so the FLIP layer must be able to convert these addresses to network addresses for actual transmission. In order to perform this function, the FLIP layer maintains the routing table shown in Fig. 7-18. Currently this table is maintained in software, but chip designers could implement it in hardware in the future.. [Картинка: any2fbimgloader227]. Logically, when a process reads from a file, that request should be caught by the process manager and then forwarded to the object manager using the normal RPC mechanism. However, since reads and writes are so important, an optimized strategy is used to improve their performance. The process manager maintains a table with the segment capabilities for all the open files. It makes ansgRead call to the kernel to get the required data. If the data are available, the kernel copies them directly to the user’s buffer. If they are not, the kernel makes anMpPullIn upcall to the appropriate mapper (usually, the object manager). The mapper issues one or more disk reads, as needed. When the pages are available, the mapper gives them to the kernel, which copies the required data to the user’s buffer and completes the system call.The Streams Manager. PROBLEMS. 21. The authentication protocol described in the text allows an intruder to send arbitrarily many messages to the authentication server in an attempt to get a reply containing an initial session key. What weakness does this observation introduce into the system? (Hint: You may assume that all messages contain a timestamp and other information, so it is easy to tell a valid mes sage from random junk.).