HW #3 Part III Solution

Introduction



The goal of this homework is to get your hands dirty with more C programming but more importantly, to help you to familiarize yourself with such concepts as creating new processes using fork(), using signals and how to block them, and how to run programs using execve(). This homework consists of three parts.




In the third part, you need to implement a relatively small program that will combine various concepts that you have seen in the applications from the second part of this homework.




Programming Assignment



In this part of the homework, you need to implement an application called artist manager. This application imitates hiring/ ring artists and tracking which of them are busy doing work or available for work. You will need to implement this application using the concepts we have gone through in the recent lectures and that you were using in the previous part of this homework.







Your program should start with the shell and please put a shell prompt to make it more visible, e.g. \ " or \shell "will do just ne. Your program should support the following list of commands:




help date hire N re X reall




assign X




withdraw X







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list exit




Let’s now discuss what each command should do.




help. This command should print some reasonable help message describing available commands. You don’t have to produce a huge print out as something concise will be enough. You can also check the examples of help messages of the Linux tools to get an idea of how such a message may look like.




date. This command should print the current date by executing \date" application, which absolute path is usually \/bin/date". After executing it, your program should return back to the shell prompt.




hire N. This command imitates hiring N artists that may be assigned to some jobs later. Code-wise, you need to spawn N child processes that will keep running and do nothing (think of in nite loop inside of their code) unless some speci c events described later will happen. Please note that this command can be called multiple times.




re X. This command imitates ring a given artist X. By X we will understand PID of one of the child processes. Please note that this command can be called multiple times.




reall. This command imitates ring all currently hired artists.




assign X. This command imitates assigning a given artist X to a job whereby X we will understand PID of one of the child processes. When this happens, the child process with PID equals to X should print \ARTIST X IS ASSIGNED TO A JOB" where you need to substitute X with the PID of that child process.




withdraw X. This command imitates withdrawing a given artist X from job whereby X we will understand PID of one of the child processes. When this happens, the child process with PID equals to X should print \ARTIST X IS WITHDRAWN FROM A JOB" where you need to substitute X with the PID of that child process.




list. This command should list all the current artists’ PIDs and statuses in the following form:




PID STATUS




where the PID is a PID of a child process and status may be either \AS-SIGNED" or \WAITING". What data structure to use to track that information is up to you.




exit. This command exits the shell and your program. Don’t forget to free memory/data structures, close les, etc.




For most of the commands, after each command, your program should return back to the shell prompt. Let’s go now through the internals of some commands. Firing an artist means that you need to gracefully terminate respective child and clean up associated data structures. Please note that all code for manipulating data structures to track artists and their statuses should be located in the artist ds.c le. If you are about to re an artist who is assigned a job then you need to withdraw the artist from the job rst and then re. If for some










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reason child process died by itself (simulating an artist that decided to leave your company) then you need to possibly withdraw that artist from a job and then clean respective data structures.




For communicating with children processes you need to use signals. To assign a job to an artist you need to send SIGUSR1 signal and to withdraw from a job you need to send a SIGUSR2 signal to a particular child process.




Printing Output



To make the grading process faster and easier we introduce a REQUIRE-MENT how you should produce output in your program for anything except your shell prompt. Please also don’t print anything in your nal version of sub-mission, which was not speci cally asked as it may severely a ect your grade.




We provide you with a function cse320 print(char *message), which will print given message to the stdout. During the grading, we will modify this function to test your results by performing the exact string comparison. It also means that it is important to develop your code inside the VM to avoid possi-ble di erences between newline characters between di erent operating systems. Basically, that function just prints a given text.







Please note, that printf() is a formatted print function. Thus, if you need to print formatted string then you may need rst to construct it and then pass the resultant string to provided cse320 print(char *message) function.







So far we only saw functions that have a strict number of parameters. In programming languages such as C++ and Java you have an option of having functions with the same name but the di erent number of parameters. This technique is called function/method overloading but it is not supported in C. But in the case of printf() function, the number of parameters is not just unknown but also may vary drastically. Thus, you may become curious how does functions like printf() and scanf() work. In short, there is a special class of functions called variadic functions that accepts a variable number of arguments. Please refer to the readings at the end of the document to nd more information about these functions.




Implementing/Testing Your Program



When you write your code try to split it into some logical blocks/steps. So every time such piece of code is complete you can test it and once testing is done, push it to the GitHub. Trying to complete the whole program all at once and debug only after will require much more e orts and will negatively a ect the amount of time being spent on this homework.




It is also a good idea to write documentation for your program and put the important decisions about your design into the README le.
















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Requirements



You need to follow the naming conventions and the asked way to implement these exercises. If you are asked for some output then you need to print only what was asked and nothing else. Otherwise, your grade may be severely af-fected. Please nd the list of the requirements for this part of the homework below:




You need to use cse320 print(char *message) for any output except shell prompt.




You should print only what was asked and nothing else.




The Makefile should be located in the root directory of your repository. The executable should be called artist manager.




We should be able to compile your program by typing \make" in the root directory of your repository.




All source code les should be in the \src" folder. All header les should be in the \inc" folder.




You should not include \*.c" les into other \*.c" les.




All code for manipulating data structures to track artists should be located in the artist ds.c le.







And, similar to the previous assignments, no zombies, no memory leaks/er-rors, no crashes.




Submission



Please click on the link below that will set up a repository for you for this homework. In case, it will take more than a few minutes please contact me so I can set up the repository for you manually.




https://classroom.github.com/a/KrHM1LpH




For the second part please create a folder \part 2" and put all les related to the Part II into that folder.




As before, we grade the latest submission.




Interesting Readings



Links below are not necessary to complete this homework but you may nd them interesting.




https://linuxconfig.org/bash-prompt-basics https://en.wikipedia.org/wiki/Function_overloading







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https://en.wikipedia.org/wiki/Variadic_function C functions with variable number of arguments printf() and scanf() examples




Extra Credit I



In our homework when we need to re an artist who is currently assigned to a job we will withdraw the artist rst. Let’s modify this behavior now. Instead of ring right away you need to introduce a timer that will check every 5 seconds if that artist was withdrawn from a job and re the artist only then. You may nd SIGARLM useful for this extra credit.




Extra Credit II



You can see that every time we assign a job we assign it to a particular artist. However, we lack the functionality of just assigning the job and system being able to assign it to the rst available artist. Let’s x it by creating a new command \assignjob". This command should pick the rst available artist and assign a job to that artist. If all of the artists are assigned jobs then \assignjob" command should hire one to do this job.






























































































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