-操作系统精髓与设计原理(第五版)+课后题答案1
CHAPTER 4
PROCESS DESCRIPTION AND
CONTROL
Review Questions
4.2 Less state information is involved.
4.5 Address space, file resources, execution privileges are examples.
4.6 1. Thread switching does not require kernel mode privileges because all
of the thread management data structures are within the user address space of a single process. Therefore, the process does not switch to the kernel mode to do thread management. This saves the overhead of two mode switches (user to kernel; kernel back to user). 2. Scheduling can be application specific. One application may benefit most from a simple round-robin scheduling algorithm, while another might benefit from a priority-based scheduling algorithm. The scheduling algorithm can be tailored to the application without disturbing the underlying OS scheduler. 3. ULTs can run on any operating system. No changes are required to the underlying kernel to support ULTs. The threads library is a set of application-level utilities shared by all applications.
4.7 1. In a typical operating system, many system calls are blocking. Thus,
when a ULT executes a system call, not only is that thread blocked, but also all of the threads within the process are blocked. 2. In a pure ULT strategy, a multithreaded application cannot take advantage of
multiprocessing. A kernel assigns one process to only one processor at a time. Therefore, only a single thread within a process can execute at a time. Problems
4.2 Because, with ULTs, the thread structure of a process is not visible to the operating system, which only schedules on the basis of processes.