操作系统设计原理习题解析

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"这是一本关于操作系统操作精髓与设计原理的习题解答手册，由William Stallings编写。手册包含了第五版教材的所有复习问题和作业问题的解决方案，旨在帮助读者理解和掌握操作系统的核心概念和技术。" 该资源是操作系统学习的重要辅助资料，涵盖了多个关键章节的内容： 1. **第一章：计算机系统概述** (Chapter 1: Computer System Overview) 这一章通常会介绍计算机硬件的基本结构，包括处理器、内存和I/O设备，以及它们如何协同工作执行指令。还会涉及计算机系统的层次结构，从底层硬件到上层软件的交互。 2. **第二章：操作系统概述** (Chapter 2: Operating System Overview) 操作系统的定义、功能和类型（如批处理、分时、实时、网络操作系统等）会在这一章讨论。同时，可能会讲解操作系统在计算机系统中的角色，以及其对资源管理和用户服务的职责。 3. **第三章：进程描述与控制** (Chapter 3: Process Description and Control) 这一章深入探讨进程的概念，包括进程的状态模型（新建、就绪、运行、等待），进程间的通信，以及调度算法，如FCFS（先来先服务）、SJF（最短作业优先）、优先级调度等。 4. **第四章：线程、SMP和微内核** (Chapter 4: Threads, SMP, and Microkernels) 线程作为轻量级进程，如何提升系统并发性和效率，多处理器系统（SMP, Symmetric Multiprocessing）下的并发执行，以及微内核架构的优缺点和实现方式将在这章中阐述。 5. **第五章：并发：互斥与同步** (Chapter 5: Concurrency: Mutual Exclusion and Synchronization) 介绍互斥锁、信号量、管程等并发控制机制，用于解决资源竞争和数据一致性问题。 6. **第六章：并发：死锁与饥饿** (Chapter 6: Concurrency: Deadlock and Starvation) 解析死锁的定义、产生条件，以及避免和检测死锁的方法。同时，会讨论饥饿现象及其解决方案。 7. **第七章：内存管理** (Chapter 7: Memory Management) 讲述虚拟地址与物理地址的映射，页面和段的内存划分，以及页面替换算法（如LRU, FIFO等）和内存分配策略。 8. **第八章：虚拟内存** (Chapter 8: Virtual Memory) 虚拟内存的原理，如分页和分段技术，以及需求调页、预调页等策略，如何实现内存的按需加载和交换。 9. **第九章：单处理器系统** (Chapter 9: Uniprocessor Systems) 在这一章中，可能涉及单处理器环境下的系统设计和优化，以及相对于多处理器系统的不同挑战和解决方案。这本习题解答手册通过解决实际问题，帮助读者巩固操作系统理论知识，提升实践能力，对于学习和理解操作系统原理非常有帮助。如果你发现任何错误或问题，可以通过邮件向作者报告，以便更新和改进。

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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

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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

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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

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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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