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C++17标准实现线程池ThreadPool短小精悍实用性强

近期使用httplib，研究了httplib的源代码，里面的线程池TreadPool用C++17标准实现，短小精悍实用性强，把std::mutex、condition_variable、function、thread和lambda函数体有机结合使用，用极少的代码实现了安全可靠的线程池ThreadPool，推荐给大家共同提高。

线程池代码：

        //基类，线程常用任务

        class TaskQueue {

        public:

        TaskQueue() = default;

        virtual ~TaskQueue() = default;
        
 virtual bool enqueue(std::function<void()> fn) = 0;

        virtual void shutdown() = 0;
        
 virtual void on_idle() {}

          };
        
class ThreadPool final : public TaskQueue {

          public:

          explicit ThreadPool(size_t n, size_t mqr = 0)

          : shutdown_(false), max_queued_requests_(mqr) {

          while (n) {

          threads_.emplace_back(worker(*this));//初始化线程，worker结构体对象的默认函数是线程函数

          n--;

          }

          }
        
 ThreadPool(const ThreadPool &) = delete;

          ~ThreadPool() override = default;
        
 bool enqueue(std::function<void()> fn) override {

          {

          std::unique_lock<std::mutex> lock(mutex_);

          if (max_queued_requests_ > 0 && jobs_.size() >= max_queued_requests_) {

          return false;

          }

          jobs_.push_back(std::move(fn));//添加队列

          }
        
 cond_.notify_one();//通知消息

          return true;

          }
        
 void shutdown() override {

          // Stop all worker threads...

          {

          std::unique_lock<std::mutex> lock(mutex_);

          shutdown_ = true;

          }
        
 cond_.notify_all();//关闭时通知所有
        
 // Join...

          for (auto &t : threads_) {

          t.join();

          }

          }
        
private:

          struct worker {

          explicit worker(ThreadPool &pool) : pool_(pool) {}
        
 void operator()() {

          for (;;) {

          std::function<void()> fn;

          {

          std::unique_lock<std::mutex> lock(pool_.mutex_);//保证线程互斥，资源安全

          //等待信号

          pool_.cond_.wait(

          lock, [&] { return !pool_.jobs_.empty() || pool_.shutdown_; });

          //不满足条件退出

          if (pool_.shutdown_ && pool_.jobs_.empty()) { break; }
        
 fn = pool_.jobs_.front();

          pool_.jobs_.pop_front();

          }
        
 assert(true == static_cast<bool>(fn));

          fn();

          }
        
#if defined(CPPHTTPLIB_OPENSSL_SUPPORT) && !defined(OPENSSL_IS_BORINGSSL)

          OPENSSL_thread_stop();

          #endif

          }
        
 ThreadPool &pool_;

          };

          friend struct worker;
        
 std::vector<std::thread> threads_;

          std::list<std::function<void()>> jobs_;
        
 bool shutdown_;

          size_t max_queued_requests_ = 0;
        
 std::condition_variable cond_;

          std::mutex mutex_;

          };

调用代码：

 //this,sock是引导区给lambda函数体的参数

if (!task_queue->enqueue(

[this, sock]() { process_and_close_socket(sock); })) {

detail::shutdown_socket(sock);

detail::close_socket(sock);

}