Thread Pools

Spawning a new thread introduces system overhead due to OS context allocation. A Thread Pool resolves this by pre-allocating a fixed set of worker threads that pull tasks from a shared queue.

Thread Pool Architecture

Thread pools use condition variables to manage workers:

1. The main thread pushes a task into the queue and notifies a worker using notify_one().
2. An idle worker thread wakes up, locks the queue, extracts the task, unlocks the queue, and executes the task.
3. On destruction, the pool sets a stop flag, notifies all worker threads, and joins them.

Code Walkthrough

A basic implementation of a thread pool using standard C++ features.

#include <iostream>
#include <vector>
#include <queue>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <functional>
class ThreadPool {
private:
    std::vector<std::thread> m_workers;
    std::queue<std::function<void()>> m_tasks;
    std::mutex m_queueMutex;
    std::condition_variable m_cv;
    bool m_stop = false;
public:
    ThreadPool(size_t threads) {
        for (size_t i = 0; i < threads; ++i) {
            m_workers.emplace_back([this] {
                while (true) {
                    std::function<void()> task;
                    {
                        std::unique_lock<std::mutex> lock(this->m_queueMutex);
                        this->m_cv.wait(lock, [this] {
                            return this->m_stop || !this->m_tasks.empty();
                        });
if (this->m_stop && this->m_tasks.empty()) return;
task = std::move(this->m_tasks.front());
                        this->m_tasks.pop();
                    }
                    task(); // Execute task outside lock
                }
            });
        }
    }
void enqueue(std::function<void()> task) {
        {
            std::lock_guard<std::mutex> lock(m_queueMutex);
            m_tasks.push(task);
        }
        m_cv.notify_one();
    }
~ThreadPool() {
        {
            std::lock_guard<std::mutex> lock(m_queueMutex);
            m_stop = true;
        }
        m_cv.notify_all();
        for (std::thread& worker : m_workers) {
            if (worker.joinable()) worker.join();
        }
    }
};
int main() {
    ThreadPool pool(4);
    for (int i = 0; i < 8; ++i) {
        pool.enqueue([i] {
            std::cout << "Task " << i << " executed on thread: " 
                      << std::this_thread::get_id() << "\n";
        });
    }
    return 0;
}

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