Producer and Consumer threads using Condition variable and mutex

threaded-queue.cpp

// Compile With: $ clang++ -ggdb -std=c++17  -fsanitize=address src/main.cpp -o T

#include <condition_variable>
#include <iostream>
#include <mutex>
#include <queue>
#include <sstream>
#include <thread>

int main() {

  auto do_wait = [](int s) {
    using namespace std::chrono;
    this_thread::sleep_for(seconds{s});
  };

  queue<string> message_queue;
  condition_variable mcond;
  mutex mmutex;
  // Thanks to Aram Gevorgyan for the spurious condition variable wake up issue
  // pointed out
  bool data_pushed = false;

  auto consumer = [&do_wait, &mmutex, &mcond, &message_queue,
                   &data_pushed]() -> void {
    while (true) {
      do_wait(4);
      string *m = nullptr;
      {
        unique_lock<mutex> lck{mmutex};
        mcond.wait(lck, [&]() -> bool { return data_pushed; });
        data_pushed = false;
        string **h = &m;
        *h = &message_queue.front();
        message_queue.pop();
      }
      printf("Pulled: %s in consumer thread\n", m->c_str());
    }
  };

  int counter{0};

  auto producer = [&mmutex, &message_queue, &mcond, &counter, &do_wait,
                   &data_pushed]() {
    while (true) {
      do_wait(2);
      {
        unique_lock<mutex> lck{mmutex};
        stringstream ss;
        ss << ++counter;
        message_queue.push(ss.str());
        data_pushed = true;
      }
      printf("Producer sent: %d\n", counter);
      mcond.notify_one();
    }
  };

  thread t1{consumer};
  thread t2{producer};

  t1.join();
  t2.join();
}