Facing the kindergarten synchronization problem (\"Kindergarten\"), where regula
ID: 3600366 • Letter: F
Question
Facing the kindergarten synchronization problem ("Kindergarten"), where regulations require that one teacher per R children is always present, where R is an integer (e.g., child / teacher ratio 3: 1) to ensure proper supervision of children Moreover, we would wish for our configuration to have the following characteristics 1. If a teacher attempts to leave but this is not possible, he should returns in office (and not block while waiting for the exit condition to be met) 2. Every parent should be able to enter the nursery area to verify whether the regulation is met Please provide the synchronized processes: Teacher, Children, Parents, which satisfy the requirements above, by further defining functions enter 0, _exit O and verify compliance 0 that are subsequently used, or replace them (their call) with the appropriate code within: Teachers, Children and Parents. You may use mutexes/ locks, semaphores, shared variables) void Teacher() void Child() void Parent() for G;)f for (;) for (G;) f teacher_enter; ...critical section... teach); teacher_exit); go home(); child enter; .. .critical section... learn) child exit); go_home(O; parent_enter) ...critical section.. verify_compliance); parent_exit); go_home(O; SolutionExplanation / Answer
//main.c
#include <stdio.h> // for standard input/output
#include <stdbool.h> // required to use bool in C
#include <pthread.h> // for threads
#include <stdlib.h> // for atoi() function
#include <semaphore.h> // for semaphores
#include <unistd.h> // for sleep function
/
sem_t t;
sem_t c;
float R;
float curr_R;
sem_t r_mutex;
sem_t t_mutex;
int inf = 100000000;
void teacher_enter(){
sem_post(&t); // increment the number of teachers, if another was waiting to leave, it will be released
printf("Teacher %u just arrived. ", (int) pthread_self());
}
void teach(){
printf("Teacher %u is teaching. ", (int) pthread_self());
sleep(10); // teachers teach for 10 seconds
}
void teacher_exit(){
int curr_teach; // current number of teachers
sem_getvalue(&t, &curr_teach);
int curr_child; // current number of children
sem_getvalue(&c, &curr_child);
float temp_R;
if ( (curr_teach - 1) != 0 ){
temp_R = curr_child/(curr_teach-1);
}
else{
if (curr_child == 0){
temp_R = 0;
}
else{
temp_R = inf;
}
}
// if when the teacher leaves the ratio will still be met, the teacher can leave freely
if (temp_R <= R){
sem_wait(&t); // decrement number of teachers
printf("Teacher %u just left. ", (int) pthread_self());
}
// else, teacher can't leave until another joins
else {
printf("Teacher %u wants to leave but can't. Will go back to work and then try again later. ", (int) pthread_self());
teach(); // teacher is teaching again
teacher_exit(); // teacher attempts to leave again
}
}
void go_home(){
printf("%u is going home now. ", (int) pthread_self());
pthread_exit(0); // person leaves
}
void child_enter(){
sem_post(&c); // increment the number of children
printf("Child %u just arrived. ", (int) pthread_self());
}
void child_exit(){
sem_wait(&c); // decrement number of children
printf("Child %u just left. ", (int) pthread_self());
}
void learn(){
printf("Child %u is learning. ", (int) pthread_self());
sleep(10); // children learn for 10 seconds
}
void parent_enter(){
printf("Parent %u just arrived. ", (int) pthread_self());
}
void verify_compliance(){
int curr_teach; // current number of teachers
sem_getvalue(&t, &curr_teach);
int curr_child; // current number of children
sem_getvalue(&c, &curr_child);
if ( curr_teach!= 0 ){
curr_R = curr_child/curr_teach;
}
else{
if (curr_child == 0){
curr_R = 0;
}
else{
curr_R == inf;
}
}
sem_post(&r_mutex); // unlock the resources
if (curr_R <= R){ // if the compliance is verified
printf("Parent %u has verified compliance! ", (int) pthread_self());
}
else{
printf("Parent %u is unsatisfied because the regulation is not met! ", (int) pthread_self());
}
}
void parent_exit(){
printf("Parent %u just left. ", (int) pthread_self());
}
void Teacher(){
for (;;) {
teacher_enter();
// ... critical section ... //
teach();
sem_wait(&t_mutex); // locking so that only one teacher can leave at a time
teacher_exit();
sem_post(&t_mutex);
go_home();
}
}
void Child(){
for (;;) {
child_enter();
// ... critical section ... //
learn();
child_exit();
go_home();
}
}
void Parent(){
for (;;) {
parent_enter();
// ... critical section ... //
verify_compliance();
parent_exit();
go_home();
}
}
int main(int argc, char ** argv){
//first arg = # of teach
//2nd arg = # of children
sem_init(&c, 0, 0); // initialize semaphore for children to 0
sem_init(&t, 0, 0); // initialize semaphore for teachers to 0
sem_init(&r_mutex, 0, 1); // initialize semaphore for teachers to 0
sem_init(&t_mutex, 0, 1); // initialize semaphore for teachers to 0
R = 3.0; // arbitrary number for ratio required
int count_child = 9;
int count_teacher = 5;
int count_parent = 4;
//threads instantiated here
pthread_t child_tid[count_child];
pthread_t teacher_tid[count_teacher];
pthread_t parent_tid[count_parent];
pthread_attr_t attr;
pthread_attr_init(&attr); // get the default attributes
//creating all of the threads here
for(int i = 0;i<count_teacher;i++){
pthread_create(&teacher_tid[i],&attr,(void*) Teacher, NULL);
}
sleep(1);
for(int i = 0;i<count_child;i++){
pthread_create(&child_tid[i],&attr,(void *) Child, NULL);
}
for(int i = 0; i<count_parent;i++){
pthread_create(&parent_tid[i],&attr,(void*) Parent, NULL);
sleep(3);
}
//joining the thread here
for(int i = 0;i<count_teacher;i++){
pthread_join(teacher_tid[i],NULL);
}
for(int i = 0;i<count_child;i++){
pthread_join(child_tid[i], NULL);
}
for(int i = 0; i<count_parent;i++){
pthread_join(parent_tid[i], NULL);
}
sem_destroy(&c);
sem_destroy(&t);
sem_destroy(&r_mutex);
sem_destroy(&t_mutex);
return 0;
}
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