CSc 360编程代写、C++程序代写

日期：2021-10-01 10:57

1 CSc 360: Operating Systems

2 (Fall 2020)

Programming Assignment 1

P1: A Process Manager (PMan)

3

4 Spec Out: Sept. 13, 2021

5 Code Due: Oct. 4, 2021 (23:55 pm)

6 1 Goals

7 This assignment is designed to help you:

8 1. get familiar with C programming,

9 2. get familiar with system calls related to process management,

10 3. get familiar with the process control block (PCB).

11 You are required to implement your solution in C (other languages are not allowed). Your work

12 will be tested on linux.csc.uvic.ca.

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14 Note: linux.csc.uvic.ca is a particular machine at the UVic Department of Computer Sci-

15 ence. It does not mean “any Linux machine” at UVic. Even more importantly, it does not mean any

16 “Unix-like” machine, such as a Mac OS X machine—many students have developed their programs

17 for their Mac OS X laptops only to find that their code works differently on linux.csc.uvic.ca

18 resulting in a substantial loss of marks.

19 You can remote access linux.csc.uvic.ca by ssh username@linux.csc.uvic.ca. SSH clients

20 are available for a wide variety of operating systems including Linux, Mac OS and Windows.

21 Be sure to study the man pages for the various systems calls and functions suggested in this

22 assignment. The system calls are in Section 2 of the man pages, so you should type (for example):

23 ? man 2 waitpid

24 2 Schedule

25 In order to help you finish this programming assignment on time, the schedule of this assignment

26 has been synchronized with both the lectures and the tutorials. There are three tutorials arranged

27 during the course of this assignment.

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Tutorial No. Tutorial Milestones

First system programming in C, P1 spec go-through, design hints design and code skeleton

Second more on system programming and testing alpha code done

Third final testing and last-minute help final deliverable

28 3 Requirements

29 3.1 Prompt for user input

30 Your PMan needs to show the prompt for user input. For example, when you run PMan by type in

31 linux.csc.uvic.ca:/home/user? ./PMan

32 It prompts

33 PMan: >

34 for user input.

35 3.2 Background Execution of Programs

36 PMan allows a program to be started in the background—that is, the program is running, but PMan

37 continues to accept input from the user. You will implement a simplified version of background

38 execution that supports executing processes in the background.

39 If the user types: bg foo, your PMan will start the program foo in the background. That is,

40 the program foo will execute and PMan will also continue to execute and give the prompt to accept

41 more commands.

42 The command bglist will have PMan display a list of all the programs currently executing in

43 the background, e.g.,:

44 123: /home/user/a1/foo

45 456: /home/user/a1/foo

46 Total background jobs: 2

47 In this case, there are 2 background jobs, both running the program foo, the first one with

48 process ID 123 and the second one with 456.

49 Your PMan needs to support the following commands:

50 1. The command bgkill pid will send the TERM signal to the job with process ID pid to terminate

51 that job.

52 2. The command bgstop pid will send the STOP signal to the job pid to stop (temporarily) that

53 job.

54 3. The command bgstart pid will send the CONT signal to the job pid to re-start that job (which

55 has been previously stopped).

56 See the man page for the kill() system call for details.

57 Your PMan must indicate to the user when background jobs have terminated. Read the man

58 page for the waitpid() system call. You are suggested to use the WNOHANG option.

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59 3.3 Status of Process

60 Your PMan needs to support a command pstat pid to list the following information related to

61 process pid, where pid is the Process ID.

62 1. comm : The filename of the executable, in parentheses. This is visible whether or not the

63 executable is swapped out.

64 2. state : One of the following characters, indicating process state: R (Running), S (Sleeping

65 in an interruptible wait), D (Waiting in uninterruptible disk sleep), Z (Zombie), T (Stopped

66 (on a signal) or (before Linux 2.6.33) trace stopped ), t (Tracing stop (Linux 2.6.33 onward)),

67 W (Paging (only before Linux 2.6.0)), X (Dead (from Linux 2.6.0 onward)), x (Dead (Linux

68 2.6.33 to 3.13 only)), K (Wakekill (Linux 2.6.33 to 3.13 only)), W (Waking (Linux 2.6.33 to

69 3.13 only)), P (Parked (Linux 3.9 to 3.13 only)).

70 3. utime: Amount of time that this process has been scheduled in user mode, measured in clock

71 ticks (divide by sysconf( SC CLK TCK)). This includes guest time, guest time (time spent

72 running a virtual CPU, see below), so that applications that are not aware of the guest time

73 field do not lose that time from their calculations.

74 4. stime: Amount of time that this process has been scheduled in kernel mode, measured in

75 clock ticks (divide by sysconf( SC CLK TCK)).

76 5. rss: Resident Set Size: number of pages the process has in real memory. This is just the pages

77 which count toward text, data, or stack space. This does not include pages which have not

78 been demand-loaded in, or which are swapped out.

79 6. voluntary ctxt switches: Number of voluntary context switches (since Linux 2.6.23).

80 7. nonvoluntary ctxt switches: Number of involuntary context switches (since Linux 2.6.23).

81 If process pid does not exist, PMan returns an error like:

82 Error: Process 1245 does not exist.

83 In the above example, 1245 is the pid value.

84 To summarize, your PMan should support the following commands: bg, bglist, bgkill,

85 bgstop, bgstart, and pstat. If the user types an unrecognized command, an error message is

86 given by PMan, e.g.,

87 PMan:> ttest

88 PMan:> ttest: command not found

89 4 Deliveries and Marking Scheme

90 For your final submission of each assignment you are required to submit your source code to connex

91 dropbox. You should include a readme file to tell TA how to compile and run your code. TAs are not

92 supposed to fix the bugs, either in your source code or in your make file. If following your readme

93 file, the TAs cannot compile and run your code, you may get a zero mark for the assignment.

94 The marking scheme is as follows:

3

Components Weight

Make file 5

Error handling 10

bg 10

bglist 10

bgkill 10

bgstop 10

bgstart 15

pstat 20

Code style 5

Readme.txt 5

Total Weight 100

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96 5 Odds and Ends

97 5.1 Implementation Hints

98 1. Use fork() and execvp() so that the parent process accepts user input and the child process

99 executes arbitrary commands.

100 2. Use a data structure (e.g., a linked list) to record the background processes.

101 3. Use the \proc pseudo-file system to find out the information required by pstat. Note that

102 \proc is not a real file system, because all files have a size zero. The files just include a pointer

103 to process control block (PCB) in the OS kernel. Due to this reason, never try to write

104 anything into \proc!

105 5.2 Warning

106 Since you will use fork() in your assignment, it is important that you do not create a fork()

107 bomb, which easily eats up all the pid resources allocated to you. If this happens, you cannot log

108 into your account any more, even from a different machine. Both the instructor and the TAs cannot

109 help you out. You have to go to IT support asking them to kill your buggy process. Clearly, IT

110 support will not be happy if many students ask for such a help.

111 To avoid the mishap, you MUST use ulimit -u in bash to find out the default max number

112 of user processes allocated to you (it is normally 50), and reduce this number to a safe value. For

113 instance, if the default max number of user processes is 50, you can use

114 % ulimit -u 35

115 to reduce this number to 35. Therefore, even if your code has a bug and has created a fork()

116 bomb, you still have unused 15 processes left and you can log in from a different machine to kill

117 the buggy process.

118 Please take this warning seriously!

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119 5.3 Compilation

120 You’ve been provided with a Makefile that builds the sample code (in p1s.tar.gz). It takes care

121 of linking-in the GNU readline library for you. The sample code shows you how to use readline()

122 to get input from the user, only if you choose to use the readline library.

123 5.4 Helper Programs

124 5.4.1 inf.c

125 This program takes two parameters:

126 tag: a single word which is printed repeatedly

127 interval: the interval, in seconds, between two printings of the tag

128 The purpose of this program is to help you with debugging background processes. It acts a trivial

129 background process, whose presence can be “felt” since it prints a tag (specified by you) every few

130 seconds (as specified by you). This program takes a tag so that even when multiple instances of it

131 are executing, you can tell the difference between each instance.

132 This program considerably simplifies the programming of PMan which deals with re-starting,

133 stopping, and killing programs.

134 5.4.2 args.c

135 This is a very trivial program which prints out a list of all arguments passed to it.

136 This program is provided so that you can verify that your PMan passes all arguments supplied

137 on the command line—often, people have off-by-1 errors in their code and pass one argument less.

138 5.5 Code Quality

139 We cannot specify completely the coding style that we would like to see but it includes the following:

140 1. Proper decomposition of a program into subroutines (and multiple source code files when

141 necessary)—A 500 line program as a single routine won’t suffice.

142 2. Comment—judiciously, but not profusely. Comments also serve to help a marker, in addition

143 to yourself. To further elaborate:

144 (a) Your favorite quote from Star Wars or Douglas Adams’ Hitch-hiker’s Guide to the Galaxy

145 does not count as comments. In fact, they simply count as anti-comments, and will result

146 in a loss of marks.

147 (b) Comment your code in English. It is the official language of this university.

148 3. Proper variable names—leia is not a good variable name, it never was and never will be.

149 4. Small number of global variables, if any. Most programs need a very small number of global

150 variables, if any. (If you have a global variable named temp, think again.)

151 5. The return values from all system calls and function calls listed in the assignment

152 specification should be checked and all values should be dealt with appropriately.

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153 5.6 Plagiarism

154 This assignment is to be done individually. You are encouraged to discuss the design of your solution

155 with your classmates, but each person must implement their own assignment.

156 Your markers will submit the code to an automated plagiarism detection program.

157 We add archived solutions from previous semesters (a few years worth) to the plagia-

158 rism detector, in order to catch “recycled” solutions.

159

160 The End

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