威廉·斯托尔斯《操作系统：精髓与设计原理》第五版课后答案解析

操作系统

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《操作系统：精髓与设计原理》第五版课后答案详解本书由威廉·斯托林斯（William Stallings）编著，版权日期为2004年。该教材针对操作系统的核心概念和设计原理进行了深入探讨，适用于计算机科学专业的学生和专业人员进行学习和研究。以下章节概述了书中的一些关键知识点： 1. **计算机系统概述**：这一章介绍了计算机系统的组成，包括硬件、软件和它们之间的交互。内容可能涵盖了体系结构的基本概念，如处理器、内存、输入输出设备等，并讨论了操作系统在系统中的地位。 2. **操作系统概述**：本章着重于解释操作系统的定义、主要功能（如进程管理、内存管理、设备管理等）以及它如何作为计算机系统的核心，提供接口和服务给其他软件。 3. **进程描述与控制**：讲解了进程的基本概念，如创建、状态转换、并发执行和同步机制，以及进程调度算法的重要性。通过理解这个部分，读者可以深入理解操作系统如何管理多个并行运行的任务。 4. **线程、SMP和微内核**：这一节讨论了多线程技术，如何提高程序的并发性能，以及对SMP（对称多处理器）架构的支持。同时，微内核模型的特点和优点也会被阐述，它是现代操作系统设计中的一个重要课题。 5. **并发：互斥与同步**：讲解了并发编程中的核心问题，如互斥锁、信号量、条件变量等同步机制，以及如何避免数据竞争和死锁，确保资源的有效共享。 6. **并发：死锁与饥饿**：深入分析死锁的成因、检测和预防策略，以及如何处理饥饿问题，使并发环境下的程序运行更加稳定和高效。 7. **内存管理**：讨论内存分配、回收、内存碎片以及虚拟内存的概念，涉及物理内存和虚拟地址空间的映射关系，以及内存保护和权限管理。 8. **虚拟内存**：讲解了虚拟内存技术如何扩展可用内存，以及页式、段式、段页式等不同的虚拟存储管理方法，这对于理解现代操作系统如何高效地利用硬件资源至关重要。 9. **无服务器计算（Uniprocessor Systems）**：最后一章可能会深入讨论单处理器系统的特点和限制，以及如何通过优化算法和设计来克服这些局限性，提升单处理器环境下的性能。《操作系统：精髓与设计原理》第五版的课后答案提供了丰富的实践解答和理论解析，帮助读者巩固理论知识并解决实际问题，对于操作系统的学习者来说是一份宝贵的参考资料。在阅读和学习过程中，遇到任何疑问或发现错误，请联系作者ws@shore.net进行反馈，以便不断更新和完善教材内容。

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-14-

NSWERS TO

UESTIONS

3.1 An instruction trace for a program is the sequence of instructions that execute for

that process.

3.2 New batch job; interactive logon; created by OS to provide a service; spawned by

existing process. See Table 3.1 for details.

3.3 Running: The process that is currently being executed. Ready: A process that is

prepared to execute when given the opportunity. Blocked: A process that cannot

execute until some event occurs, such as the completion of an I/O operation. New:

A process that has just been created but has not yet been admitted to the pool of

executable processes by the operating system. Exit: A process that has been released

from the pool of executable processes by the operating system, either because it

halted or because it aborted for some reason.

3.4 Process preemption occurs when an executing process is interrupted by the

processor so that another process can be executed.

3.5 Swapping involves moving part or all of a process from main memory to disk.

When none of the processes in main memory is in the Ready state, the operating

system swaps one of the blocked processes out onto disk into a suspend queue, so

that another process may be brought into main memory to execute.

3.6 There are two independent concepts: whether a process is waiting on an event

(blocked or not), and whether a process has been swapped out of main memory

(suspended or not). To accommodate this 2 × 2 combination, we need two Ready

states and two Blocked states.

3.7 1. The process is not immediately available for execution. 2. The process may or

may not be waiting on an event. If it is, this blocked condition is independent of the

suspend condition, and occurrence of the blocking event does not enable the

process to be executed. 3. The process was placed in a suspended state by an agent;

either itself, a parent process, or the operating system, for the purpose of

preventing its execution. 4. The process may not be removed from this state until

the agent explicitly orders the removal.

3.8 The OS maintains tables for entities related to memory, I/O, files, and processes.

See Table 3.10 for details.

3.9 Process identification, processor state information, and process control information.

3.10 The user mode has restrictions on the instructions that can be executed and the

memory areas that can be accessed. This is to protect the operating system from

CHAPTER 3

PROCESS DESCRIPTION AND CONTROL

-15-

damage or alteration. In kernel mode, the operating system does not have these

restrictions, so that it can perform its tasks.

3.11 1. Assign a unique process identifier to the new process. 2. Allocate space for the

process. 3. Initialize the process control block. 4. Set the appropriate linkages. 5.

Create or expand other data structures.

3.12 An interrupt is due to some sort of event that is external to and independent of the

currently running process, such as the completion of an I/O operation. A trap

relates to an error or exception condition generated within the currently running

process, such as an illegal file access attempt.

3.13 Clock interrupt, I/O interrupt, memory fault.

3.14 A mode switch may occur without changing the state of the process that is

currently in the Running state. A process switch involves taking the currently

executing process out of the Running state in favor of another process. The process

switch involves saving more state information.

NSWERS TO

ROBLEMS

3.1 •Creation and deletion of both user and system processes. The processes in the

system can execute concurrently for information sharing, computation speedup,

modularity, and convenience. Concurrent execution requires a mechanism for

process creation and deletion. The required resources are given to the process

when it is created, or allocated to it while it is running. When the process

terminates, the OS needs to reclaim any reusable resources.

•Suspension and resumption of processes. In process scheduling, the OS needs to

change the process's state to waiting or ready state when it is waiting for some

resources. When the required resources are available, OS needs to change its

state to running state to resume its execution.

•Provision of mechanism for process synchronization. Cooperating processes

may share data. Concurrent access to shared data may result in data

inconsistency. OS has to provide mechanisms for processes synchronization to

ensure the orderly execution of cooperating processes, so that data consistency is

maintained.

•Provision of mechanism for process communication. The processes executing

under the OS may be either independent processes or cooperating processes.

Cooperating processes must have the means to communicate with each other.

•Provision of mechanisms for deadlock handling. In a multiprogramming

environment, several processes may compete for a finite number of resources. If

a deadlock occurs, all waiting processes will never change their waiting state to

running state again, resources are wasted and jobs will never be completed.

3.2 The following example is used in [PINK89] to clarify their definition of block and

suspend:

Suppose a process has been executing for a while and needs an additional

magnetic tape drive so that it can write out a temporary file. Before it can

initiate a write to tape, it must be given permission to use one of the drives.

When it makes its request, a tape drive may not be available, and if that is the

-16-

case, the process will be placed in the blocked state. At some point, we assume

the system will allocate the tape drive to the process; at that time the process

will be moved back to the active state. When the process is placed into the

execute state again it will request a write operation to its newly acquired tape

drive. At this point, the process will be move to the suspend state, where it

waits for the completion of the current write on the tape drive that it now

owns.

The distinction made between two different reasons for waiting for a device could

be useful to the operating system in organizing its work. However, it is no

substitute for a knowledge of which processes are swapped out and which

processes are swapped in. This latter distinction is a necessity and must be reflected

in some fashion in the process state.

3.3 Figure 9.3 shows the result for a single blocked queue. The figure readily

generalizes to multiple blocked queues.

3.4 Penalize the Ready, suspend processes by some fixed amount, such as one or two

priority levels, so that a Ready, suspend process is chosen next only if it has a

higher priority than the highest-priority Ready process by several levels of priority.

3.5 a. A separate queue is associated with each wait state. The differentiation of

waiting processes into queues reduces the work needed to locate a waiting

process when an event occurs that affects it. For example, when a page fault

completes, the scheduler know that the waiting process can be found on the

Page Fault Wait queue.

b. In each case, it would be less efficient to allow the process to be swapped out

while in this state. For example, on a page fault wait, it makes no sense to swap

out a process when we are waiting to bring in another page so that it can

execute.

c. The state transition diagram can be derived from the following state transition

table:

Next State

Current State

Currently

Executing

Computable

(resident)

Computable

(outswapped)

Variety of wait

states (resident)

Variety of wait

states

(outswapped)

Currently

Executing

Rescheduled

Wait

Computable

(resident)

Scheduled

Outswap

Computable

(outswapped)

Inswap

Variety of wait

states (resident)

Event satisfied

Outswap

Variety of wait

states

(outswapped)

Event satisfied

-17-

3.6 a. The advantage of four modes is that there is more flexibility to control access to

memory, allowing finer tuning of memory protection. The disadvantage is

complexity and processing overhead. For example, procedures running at each

of the access modes require separate stacks with appropriate accessibility.

b. In principle, the more modes, the more flexibility, but it seems difficult to

justify going beyond four.

3.7 a. With j < i, a process running in D

is prevented from accessing objects in D

Thus, if D

contains information that is more privileged or is to be kept more

secure than information in D

, this restriction is appropriate. However, this

security policy can be circumvented in the following way. A process running in

could read data in D

and then copy that data into D

. Subsequently, a

process running in D

could access the information.

b. An approach to dealing with this problem, known as a trusted system, is

discussed in Chapter 16.

3.8 a. A application may be processing data received from another process and

storing the results on disk. If there is data waiting to be taken from the other

process, the application may proceed to get that data and process it. If a

previous disk write has completed and there is processed data to write out, the

application may proceed to write to disk. There may be a point where the

process is waiting both for additional data from the input process and for disk

availability.

b. There are several ways that could be handled. A special type of either/or queue

could be used. Or the process could be put in two separate queues. In either

case, the operating system would have to handle the details of alerting the

process to the occurrence of both events, one after the other.

3.9 This technique is based on the assumption that an interrupted process A will

continue to run after the response to an interrupt. But, in general, an interrupt may

cause the basic monitor to preempt a process A in favor of another process B. It is

now necessary to copy the execution state of process A from the location associated

with the interrupt to the process description associated with A. The machine might

as well have stored them there in the first place. Source: [BRIN73].

3.10 Because there are circumstances under which a process may not be preempted (i.e.,

it is executing in kernel mode), it is impossible for the operating system to respond

rapidly to real-time requirements.

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