Answered Essay: You have been hired by the CS Department to write code to help synchronize a professor and his/her students dur

You have been hired by the CS Department to write code to help synchronize a professor and his/her students during office hours. The professor, of course, wants to take a nap if no students are around to ask questions; if there are students who want to ask questions, they must synchronize with each other and with the professor so that

– only one person is speaking at any one time,

– each student question is answered by the professor, and

– no student asks another question before the professor is done answering the previous one.

You are to write four procedures: AnswerStart(), AnswerDone(), QuestionStart() and QuestionDone().

The professor loops running the code: AnswerStart(); give answer; AnswerDone(). AnswerStart doesn’t return until a question has been asked. Each student loops running the code: QuestionStart(); ask question; QuestionDone(). QuestionStart() does not return until it is the student’s turn to ask a question. Since professors consider it rude for a student not to wait for an answer, QuestionEnd() should not return until the professor has finished answering the question. You can use a command line interface for this program. You are free to make other design choices and be creative in your implementation. You may use any programming language of your choice.

Expert Answer


#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <time.h>
#include <stdlib.h>
#include <semaphore.h>
struct student{

        int id;
        int numQuestions; //number of questions to ask
        int questionNum;        //number of questions that have been answered


int totalStudents;
int inOffice, studentZ;  //in office - students in office; studentZ keeps track of students enter and leave
sem_t readyForQuestion, questionWait, answerWait, capacity;
//pthread_cond_t stud, prof;
pthread_t professor;
pthread_mutex_t question_lock; /*lock, lock2,*/ 
//int professorWait = 0, studentWait;
int identification;

void Professor();
void *StartProfessor();
void AnswerStart();
void AnswerDone();
void Student(int id);
void * StartStudent(void * student);
void QuestionStart();
void QuestionDone();
void nap();
void EnterOffice();
void LeaveOffice();

void Professor()
        //pthread_mutex_init(&lock, NULL);
        //pthread_mutex_init(&lock2, NULL);
        pthread_mutex_init(&question_lock, NULL);
        //initialize semaphores
        //second parameter signifies whether it is shared(1) or not(0)
        sem_init(&capacity,0,inOffice);//not using yet
//      pthread_cond_init(&prof, NULL);
//      pthread_cond_init(&stud, NULL);
        studentZ = 0;

        pthread_create(&professor, NULL, StartProfessor, NULL);

//does professor things
void * StartProfessor()
                //if no students nap
                //if(inOffice == 0) //totalStudents
                //if(inOffice > 0)
                        //sem wait for question
                        AnswerStart();//answer start
                        AnswerDone();//answer done
void AnswerStart()
        //struct student * std = student;
        printf("Professor starts to answer question for student %dn", identification);

void AnswerDone()
        printf("Professor is done with answer for student %dn", identification);

//makes a thread for 1 student
void Student(int id)
//printf("you no make student");
        struct student * newStd = malloc(sizeof(struct student));
        newStd->id = id;
        newStd->numQuestions = (id % 4) + 1;
        newStd->questionNum = 0;
        pthread_t stack;
        pthread_create(&stack, NULL, (void *) StartStudent, (void *) newStd);


//work for student thread
void *StartStudent(void * student)
        struct student * std = student;
        while(std->numQuestions > std->questionNum)
                        identification = std->id;
                        //semaphore answer question (post)
                        //sem wait for answer
                        //pthread_mutex_unlock(&lock);  //professor starts answering
                        //pthread_mutex_lock(&lock2);       //professor done answering
                        //printf("%d %d %dn ", std->questionNum,std->numQuestions, inOffice);
                        if(std->questionNum == std->numQuestions)
                                if(studentZ == 0) //this is new here

void QuestionStart()
        printf("Student %d asks a questionn", identification);

void QuestionDone()
        printf("Student %d is satisfiedn", identification);

void nap()
        printf("professor is napping...n");

void EnterOffice()
        printf("student %d shows up in the officen", identification);

void LeaveOffice()
        printf("Student %d leaves the officen", identification);

int main(int argc, char *argv[])
        totalStudents = atoi(argv[1]);
        inOffice = atoi(argv[2]);
        int i;
        for(i = 0 ; i < totalStudents; i++)
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