Confusion using threads and thread techniques - c++

Question

There's a construction zone. 100m long for cars going East/West....10m across for pedestrians crossing N/S. Here are the rules that must be followed:
neither car nor pedestrians should wait if the intersection is empty;
cars cannot go in the opposite directions simultaneously on the one-lane section;
a pedestrian cannot cross the street while there is a car in the one-lane section, but
multiple pedestrians can cross the street at the same time;
a car may enter the one lane section if there is a car there going in the same direction, however, a car is not allowed to pass another car;
a car does not wait for more than two cars going in the opposite direction;
a pedestrian has to yield to cars BUT a pedestrian should not wait for more than two cars (in either direction).
The example file being used is as follows: (Each row is a separate entity. E means "car going east" and W is west. P is for pedestrians. The first column is the number of seconds after the previous entity arrived at which now the new entity is arriving. The third column is the speed (meters per second):
Example being used:
0 E1 10
1 P1 1
4 E2 15
5 W1 10
Currently my code is printing out E1 enters.... (next line) E1 exits.... This is repeated on and on. I'm pretty confused on using threads and the techniques included so at this moment I'm stuck. What do I need to change to get this to print out the correct order at which the entities should be arriving and leaving the construction zone? All help is appreciated.
#include <iostream>
#include <vector>
#include <fstream>
#include <chrono>
#include <thread>
#include <random>
#include <ctime>
#include <mutex>
#include <string>
#include <condition_variable>
using namespace std;
class Traffic{
public:
void set_time(int a) {prevArrival = a;}
void set_name(string a) {name = a;}
void set_speed(int a) {carSpeed = a;}
int get_time() {return prevArrival;}
string get_name() {return name;}
int get_speed() {return carSpeed;}
private:
int prevArrival;
string name;
int carSpeed;
};
condition_variable_any cE, cW, ped;
mutex mtx;
int east=0; //number of cars traveling East currently in the zone
int west=0; //...traveling West...
int peds=0; //# of pedestrians crossing the street
void sleep(int secs);
void carWest(int time, string name, int speed);
void carEast(int time, string name, int speed);
void pedestrian(int time, string name, int speed);
int main(void){
srand(time(NULL));
ifstream ifs;
ofstream ofs;
string info, title, temp;
int i=0, e=0, w=0, p=0, time, speed;
Traffic crossers[50];
vector <thread> eastCars, westCars, pedestrians;
ifs.open("traffic.txt");
while (!ifs.eof()){
ifs >> time; crossers[i].set_time(time);
ifs >> title; crossers[i].set_name(title);
temp = crossers[i].get_name();
if(temp[0] == 'E' || temp[0] == 'e') {e++;}
else if(temp[0] == 'W' || temp[0] == 'w') {w++;}
else {p++;}
ifs >> speed; crossers[i].set_speed(speed);
i++;
}
ifs.close();
for (int i=0; i < e; i++) eastCars.push_back(thread(carEast, crossers[i].get_time(), crossers[i].get_name(), crossers[i].get_speed())); //creating threads
for (int i=0; i < p; i++) pedestrians.push_back(thread(pedestrian, crossers[i].get_time(), crossers[i].get_name(), crossers[i].get_speed()));
for (int i=0; i < w; i++) westCars.push_back(thread(carWest, crossers[i].get_time(), crossers[i].get_name(), crossers[i].get_speed()));
for (thread& t: eastCars) t.join(); // waiting for eastCars, westCars, and pedestrians to finish
for (thread& t: pedestrians) t.join();
for (thread& t: westCars) t.join();
}
void pedestrian(int time, string name, int speed) {
while(true){
if(name[0] == 'P' || name[0] == 'p'){
if(time == 0 || (east == 0 && west == 0 && peds == 0))
mtx.lock();
cout << name << " entering construction" << endl;
while(peds>0 || west>0 || east>0)
ped.wait(mtx);
peds++;
mtx.unlock();
sleep(10/speed);
cout << name << " exiting construction" << endl;
mtx.lock();
peds--;
ped.notify_one();
cE.notify_all();
cW.notify_all();
mtx.unlock();
}
}
}
void carWest(int time, string name, int speed) {
while(true){
if(name[0] == 'W' || name[0] == 'w'){
if(time == 0 || (east == 0 && west == 0 && peds == 0))
mtx.lock();
cout << name << " entering construction" << endl;
while(peds>0 || west>0 || east>0)
cW.wait(mtx);
west++;
mtx.unlock();
sleep(100/speed);
cout << name << " exiting construction" << endl;
mtx.lock();
west--;
cW.notify_one();
ped.notify_all();
cE.notify_all();
mtx.unlock();
}
}
}
void carEast(int time, string name, int speed) {
while(true){
if(name[0] == 'E' || name[0] == 'e'){
if(time == 0 || (east == 0 && west == 0 && peds == 0))
mtx.lock();
cout << name << " entering construction" << endl;
while(peds>0 || west>0 || east>0)
cE.wait(mtx);
east++;
mtx.unlock();
sleep(100/speed);
cout << name << " exiting construction" << endl;
mtx.lock();
east--;
cE.notify_one();
cW.notify_all();
ped.notify_all();
mtx.unlock();
}
}
}
void sleep(int secs){
this_thread::sleep_for(chrono::milliseconds(rand()%secs*1000));
}

Answer 1

Your problem is here:
for (int i=0; i < e; i++) eastCars.push_back(thread(carEast, crossers[i].get_time(), crossers[i].get_name(), crossers[i].get_speed())); //creating threads
for (int i=0; i < p; i++) pedestrians.push_back(thread(pedestrian, crossers[i].get_time(), crossers[i].get_name(), crossers[i].get_speed()));
for (int i=0; i < w; i++) westCars.push_back(thread(carWest, crossers[i].get_time(), crossers[i].get_name(), crossers[i].get_speed()));
In your small data file, you've got 2 east cars, 1 west car, and one pedestrian. So e will be 2, and p and w will be 1. crosser[0] is an east car
Now, look at those push_back loops. You're adding crossers[0] to all lists! Thus your first (and only) westCar is really an east car. But your carWest refuses to do any work except on west cars, so it does no work.
You probably want to keep completely separate lists, rather than putting everyone into a single crossers list. Either that or you can loop once over your crossers list, and examine the name to see what list/thread it goes in.