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使用 condition_variable::wait(unique_lock<mutex>&lck, Predicate pred) 时，必须保证条件变量通过notify唤醒的同时，wait 的第二个参数 Predicate 返回 true 了才可以往下走。必须两个条件同时满足，如果notify的时候Predicate返回时false一样的唤不醒线程。
#include <iostream>
#include <future>
#include <chrono>
#include <string>
#include<functional>
#include <queue>using Task = std::function<void()>;
class ThreaPool
{
public:void start() {running_ = true;}bool is_running(){return running_;}void stop() {std::cout << "stop..." << std::endl;running_ = false;std::unique_lock<std::mutex> lk(qmutext_);tasks_.push([]() { std::cout << "hello pool end " << std::endl; });cond_.notify_all();}void push_task(Task task) {if (!running_){return;}std::unique_lock<std::mutex> lk(qmutext_);tasks_.push(task);cond_.notify_one();}ThreaPool(int count){for (int i = 0; i < count; i++){pool_.emplace_back([this]() {while (true){Task task;{std::unique_lock<std::mutex> lk(qmutext_);std::cout << "wait 1" << std::endl;cond_.wait(lk, [this] {return !running_ || !tasks_.empty(); });std::cout << "wait 2" << std::endl;if (!tasks_.empty()){task = std::move(tasks_.front());tasks_.pop();}}if (task){task();}if (!this->is_running()){std::cout << "stoped 1" << std::endl;std::unique_lock<std::mutex> lk(qmutext_);if (tasks_.empty()) {std::cout << "stoped 2" << std::endl;return;}}}});}}~ThreaPool() {for (std::thread& worker : pool_) {worker.join();}};private:std::vector<std::thread> pool_;std::mutex qmutext_;std::condition_variable cond_;std::queue< Task > tasks_;std::atomic_bool running_{ true };
};int main()
{ThreaPool pool(5);std::this_thread::sleep_for(std::chrono::seconds(1));pool.push_task([]() { std::cout << "hello pool 1 \n" << std::endl; });pool.push_task([]() { std::cout << "hello pool 2 \n" << std::endl; });pool.push_task([]() { std::cout << "hello pool 3 \n" << std::endl; });pool.push_task([]() { std::cout << "hello pool 4 \n" << std::endl; });pool.push_task([]() { std::cout << "hello pool 5 \n" << std::endl; });pool.push_task([]() { std::cout << "hello pool 6 \n" << std::endl; });pool.push_task([]() { std::cout << "hello pool 7 \n" << std::endl; });pool.push_task([]() { std::cout << "hello pool 8 \n" << std::endl; });pool.push_task([]() { std::cout << "hello pool 9 \n" << std::endl; });std::this_thread::sleep_for(std::chrono::seconds(1));pool.stop();return 0;
}