Книга: Distributed operating systems

PROBLEMS

PROBLEMS

1. Name one difference between a process with two threads and two processes each with one thread that share the same address space, that is, the same set of pages.

2. What happens if you join on yourself?

3. A Mach thread creates two new threads as its children, A and B. Thread A does a detach call; B does not. Both threads exit and the parent does a join. What happens?

4. The global run queues of Fig. 8-6 must be locked before being searched. Do the local run queues (not shown in the figure) also have to be locked before being searched? Why or why not?

5. Each of the global run queues has a single mutex for locking it. Suppose that a particular multiprocessor has a global clock that causes clock interrupts on all the CPUs simultaneously. What implications does this have for the Mach scheduler?

6. Mach supports the concept of a processor set. On what class of machines does this concept make the most sense? What is it used for?

7. Mach supports three inheritance attributes for regions of virtual address space. Which ones are needed to make UNIX FORK work correctly?

8. A small process has all its pages in memory. There is enough free memory available for ten more copies of the process. It forks off a child. Is it possible for the child to get a page or protection fault?

9. Why do you think there is a call to copy a region of virtual memory (see Fig. 8-8)? After all, any thread can just copy it by sitting in a tight copy loop.

10. Why is the page replacement algorithm run in the kernel instead of in an external memory manager?

11. Give an example when it is desirable for a thread to deallocate an object in its virtual address space.

12. Can two processes simultaneously have RECEIVE capabilities for the same port? How about SEND capabilities?

13. Does a process know that a port it is reading from is actually a port set? Does it matter?

14. Mach supports two types of messages: simple and complex. Are the complex messages actually required, or is this merely an optimization?

15. Now answer the previous question about SEND-ONCE capabilities and out-of-line messages. Are either of these essential to the correct functioning of Mach?

16. In Fig. 8-15 the same port has a different name in different processes. What problems might this cause?

17. Mach has a system call that allows a process to request that non-Mach traps be given to a special handler, rather than causing the process to be killed. What is this system call good for?

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