I am writing a program (for homework) that simulates a unisex bathroom. Only 4 people are allowed at a time and men and woman cannot enter if the other sex is already using the bathroom. My problem is with allowing a max of 4 people in the bathroom. As you can see from the output, only 1 person is getting into the restroom at a time. Here is my code:
const int Delayx = 60;
int i;
int restroom = 0;
int Menwaiting = 0;
int Womenwaiting = 0;
semaphore max_capacity;
semaphore woman;
semaphore man;
semaphore mutex;
semaphore restroomcount;
void Delay(void)
{
int DelayTime;
DelayTime = random(Delayx);
for (i = 0; i<DelayTime; i++);
}
void Woman(void)
{
// for(;;){
Womenwaiting++;
//wait(mutex);
wait(woman);
wait(max_capacity);
//wait(woman);
wait(mutex);
wait(restroomcount);
cout << "A Woman has entered Restroom"<<endl;
cout << "People in the Restroom:" << restroom++ <<endl <<endl;
signal(restroomcount);
Womenwaiting--;
Delay();
wait(restroomcount);
cout << "A woman has exited Restroom"<<endl;
cout << "People in the Restroom:" << restroom-- <<endl<<endl;
signal(restroomcount);
signal(mutex);
signal(max_capacity);
if(Menwaiting > Womenwaiting){
signal(man);
}
else{
signal(woman);
}
//signal(max_capacity);
//signal(man);
// }
}
void Man(void)
{
// for(;;){
Menwaiting++;
//wait(mutex);
wait(man);
wait(max_capacity);
//wait(man);
wait(mutex);
wait(restroomcount);
cout <<"A Man has entered the Restroom"<<endl;
cout <<"People in the Restroom:" << restroom++ <<endl<<endl;
signal(restroomcount);
Menwaiting--;
//signal(mutex);
Delay();
//wait(mutex);
wait(restroomcount);
cout << "A man has exited the Restroom"<<endl;
cout <<"People in the Restroom:" << restroom-- <<endl<<endl;
signal(restroomcount);
signal(mutex);
signal(max_capacity);
if(Womenwaiting > Menwaiting){
signal(woman);
}
else{
signal(man);
}
//signal(max_capacity);
//signal(woman);
//}
}
void main()
{
initialsem(woman,1);
initialsem(man,1);
initialsem(max_capacity,4);
initialsem(mutex,1);
initialsem(restroomcount,1);
cobegin
{
Woman(); Woman(); Woman(); Woman(); Woman(); Man(); Man(); Man(); Man(); Man();
}
}
This generates the following output:
A Man has entered the Restroom
People in the Restroom:1A man has exited the Restroom
People in the Restroom:0A Man has entered the Restroom
People in the Restroom:1A man has exited the Restroom
People in the Restroom:0A Woman has entered Restroom
People in the Restroom:1A woman has exited Restroom
People in the Restroom:0A Woman has entered Restroom
People in the Restroom:1A woman has exited Restroom
People in the Restroom:0
And so on, forever.
Answer
I think you have too many semaphores. Your man/woman semaphores are gating to 1 person at a time. Consider using some state variables protected by mutexes (current sex of bathroom, number of people in bathroom) rather than so many different semaphores.
Do you maintain a line ordering or can people skip based on the current restroom sex? For instance, if you have woman,woman,woman,man,woman, is the 4th woman allowed to skip the man and go into the restroom, or do the 3 women exit, then the man enters/exits, then the woman can enter? This is an easier problem than allowing a skip.