threads_condition_variable.cpp

Condition variable synchronization primitive example

 
#include "threads/condition_variable.h"
#include "threads/thread.h"
 
#include <iostream>
#include <thread>
#include <vector>
 
int main(int argc, char** argv)
{
    std::string help = "Please enter '+' to notify one waiting thread, enter '*' to notify all waiting threads of the condition variable...";
 
    // Show help message
    std::cout << help << std::endl;
 
    int concurrency = 8;
    bool finish = false;
 
    // Condition variable sample
    CppCommon::CriticalSection cs;
    CppCommon::ConditionVariable cv;
 
    // Start some threads
    std::vector<std::thread> threads;
    for (int thread = 0; thread < concurrency; ++thread)
    {
        threads.emplace_back([&cs, &cv, &finish, thread]()
        {
            std::cout << "Thread " << thread << " initialized!" << std::endl;
 
            // Sleep for a while...
            CppCommon::Thread::SleepFor(CppCommon::Timespan::milliseconds(thread * 10));
 
            std::cout << "Thread " << thread << " waiting for the notification!" << std::endl;
 
            // Lock the critical section
            cs.Lock();
 
            // Safe check for the finish flag under the lock
            while (!finish)
            {
                // Wait for the notification
                cv.Wait(cs);
 
                std::cout << "Thread " << thread << " notified!" << std::endl;
            }
 
            // Unlock the critical section
            cs.Unlock();
 
            std::cout << "Thread " << thread << " finished!" << std::endl;
        });
    }
 
    // Perform text input
    std::string line;
    while (!finish && getline(std::cin, line))
    {
        // Lock the critical section
        cs.Lock();
 
        if (line == "+")
        {
            std::cout << "Notify one thread!" << std::endl;
            cv.NotifyOne();
        }
        else if (line == "*")
        {
            // Safe set the finish flag under the lock
            finish = true;
 
            std::cout << "Notify all threads!" << std::endl;
            cv.NotifyAll();
        }
        else
            std::cout << help << std::endl;
 
        // Unlock the critical section
        cs.Unlock();
    }
 
    // Wait for all threads
    for (auto& thread : threads)
        thread.join();
 
    return 0;
}