Bakery Algorithm for Process Synchronization

Process i wants to enter:

  1. choosing[i] = true         // "I'm picking a number"
  2. number[i] = 1 + max(all numbers)   // Take the next ticket
  3. choosing[i] = false        // "Done picking"
       |
       v
  For each other process j:
       |
       +-- Wait until choosing[j] == false
       |   (Don't compare while they're still picking)
       |
       +-- Wait until:
           number[j] == 0              // j is not interested
           OR number[j] > number[i]    // j has a higher ticket
           OR (number[j] == number[i] AND j > i)  // Same ticket, but j has higher ID
       |
       v
  Enter Critical Section
       |
       v
  number[i] = 0                 // Discard the ticket

#include <iostream>
#include <thread>
#include <vector>
#include <algorithm>
#include <atomic>
using namespace std;

const int NUM_PROCESSES = 5;
atomic<bool> choosing[NUM_PROCESSES];
atomic<int> number[NUM_PROCESSES];

void bakery_process(int i) {
    for (int iter = 0; iter < 5; iter++) {
        // Doorway: Pick a ticket number
        choosing[i] = true;
        number[i] = 1 + *max_element(number, number + NUM_PROCESSES);
        choosing[i] = false;

        // Wait for all other processes
        for (int j = 0; j < NUM_PROCESSES; j++) {
            while (choosing[j]);           // Wait if they're picking
            while (number[j] != 0 &&       // Wait if they have a ticket AND
                  (number[j] < number[i] || // their number is smaller, OR
                  (number[j] == number[i] && j < i)));  // same number but lower ID
        }

        // --- Critical Section ---
        cout << "Process " << i << " is in its critical section." << endl;

        // --- Exit Section ---
        number[i] = 0;                     // Discard the ticket
        cout << "Process " << i << " is in its remainder section." << endl;
    }
}

int main() {
    vector<thread> processes;
    for (int i = 0; i < NUM_PROCESSES; i++) {
        choosing[i] = false;
        number[i] = 0;
    }
    for (int i = 0; i < NUM_PROCESSES; i++) {
        processes.push_back(thread(bakery_process, i));
    }
    for (auto &process : processes) {
        process.join();
    }
    return 0;
}

Process 0 is in its critical section.
Process 0 is in its remainder section.
Process 1 is in its critical section.
Process 1 is in its remainder section.
...