84 lines
2.5 KiB
C++
84 lines
2.5 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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class ThreadPool {
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private:
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vector<thread> workers;
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queue<function<void()>> tasks;
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mutex mtx;
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condition_variable cv;
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bool stop = false;
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public:
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ThreadPool(int num_threads) {
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while (num_threads-- > 0) {
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workers.emplace_back([this] {
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while (true) {
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function<void()> task;
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{
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unique_lock<mutex> lock(mtx);
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cv.wait(lock,
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[this] { return stop || !tasks.empty(); });
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if (stop && tasks.empty()) return;
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task = std::move(tasks.front());
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tasks.pop();
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}
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task();
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}
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});
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}
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}
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template <typename F, typename... Args>
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future<typename result_of<F(Args...)>::type> enqueue(F&& f,
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Args&&... args) {
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if (stop) throw std::runtime_error("enqueue on stopped ThreadPool");
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using return_type = typename std::result_of<F(Args...)>::type;
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// this is not calling the return type its a func with no args and
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// returning return type value as in int(int) this is int()
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auto task = make_shared<packaged_task<return_type()>>(
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bind(forward<F>(f), forward<Args>(args)...));
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future<return_type> fut = task->get_future();
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// since its a share pointer so the task lives as long as future lives
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// you could not make it shared but then pool might die with future
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// being invalid now the desctructor isn't called now unless the future
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// also goes out of scope
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{
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unique_lock<mutex> lock(mtx);
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tasks.emplace([task] { (*task)(); });
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}
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cv.notify_one();
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return fut;
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}
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~ThreadPool() {
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{
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unique_lock<mutex> lock(mtx);
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stop = true;
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}
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cv.notify_all();
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for (auto& worker : workers) worker.join();
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}
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};
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int main() {
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ThreadPool pool(4);
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auto taskFunction = [](int a, int& b, std::string&& c) {
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std::cout << "Task executed with: " << a << ", " << b << ", " << c
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<< std::endl;
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b *= 2; // Modify the lvalue reference
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return a + b;
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};
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int lval = 10;
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auto future = pool.enqueue(taskFunction, 5, ref(lval), "hello");
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cout << "result: " << future.get() << endl;
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} |