An Operating Systems Vade Mecum

320 Co-operating Processes Chapter 9introduce the List and the Sort processes. How does this situation look inDemos/MP?(d) What information passes between the port managers for the three processeswhen the command interpreter introduces List to Sort? (Assume that each of theseprocesses is on a different machine.)5. What information would be useful in deciding if a process should be migrated in amulticomputer operating system?6. WorkEasy Computers is designing a new product in which individual machines areused for predefined functions. For example, one machine is used as a file server,another runs the text editor, and a third runs the compiler. A fourth machine is theuser’s interface into the network. Is this organization reasonable?7. Bandwidth is the number of bits that can be sent from one machine to anotherevery second. Delay is the amount of time between when the writer submits theWritePort call and the reader’s ReadPort call finishes. High bandwidth and lowdelay are important for efficient communication. Suggest a multicomputer applicationin which high bandwidth is more important than low delay. Suggest an applicationwhere low delay is more important.8. Instead of piping List and Sort, as in Figure 9.5, the standard output of List couldbe directed to a file. After List is finished, Sort could be invoked with standardinput coming from the file. Which method is likely to execute faster?9. Ports that buffer unread data require some policy for deciding when to block awriter. For simplicity, assume a uniprocessor operating system. Assume that thereare currently ten ports and buffer space to hold 10,000 bytes. Suggest a blockingstrategy.10. On multiprocessors, some buffer space may be used for messages that are in transit— that is, messages written by a process on a second machine to be read by a processon a third machine. The current machine happens to be in the communicationpath and must therefore buffer messages. How does this situation change youranswer to exercise 9?11. Charlotte uses capabilities to bound ports, for both reading and writing. A link is apair of bound ports such that the reader of one is the writer of the other, and viceversa. Capabilities are always transmitted as a pair and are never separated.(a) What should the CreatePort call return?(b) A client process has a link to a file server process. Suggest a protocol for openinga file for sequential read or sequential write. Try to make file read and filewrite use as few port read and port write operations as possible.12. The Locus operating system has only one file hierarchy, which spans all themachines in the multicomputer. Assuming that each file actually exists on thesecondary storage of only one machine and that each machine has secondarystorage, suggest an allocation design for associating files with machines.13. Your answer to exercise 12 may suffer from a situation in which more files cannotfit on one machine, but other machines still have plenty of file space. Suggest anallocation design that lessens this problem. Do not allow individual files to crossmachine boundaries.