Question

在C ++ 11中，我创建了一个长期活动的帖子：

class Server
{
   public:
      void operator() () const {
         while(true)
            dosomething();
      }
      ~Server()
       {
         clean();
       }
};

// in main
Server s;
std::thread t(s);
t.detach();

我希望在系统终止时使用析构函数添加一些干净的工作。但是，如果我直接在Server中添加析构函数，系统启动时将调用clean。

怎么做？

Answer 1

在他的书（The C ++ Programming Language，Chapter 42.2.5）中，Bjarne Stroustrup不鼓励使用detach，如果你不需要，并给出了几个理由。

另见：https://stackoverflow.com/a/22804813/5717589。

在这种情况下的结果是解析器被困在线程中未被执行，cleanup()不会运行。

我写了下面的代码，看看那里发生了什么：

#include <iostream>
#include <thread>
#include <unistd.h>   // for linux usleep

using namespace std;
static bool needed;   // tells the server if we need it

class Server {
public:
    Server () : id (0){
        ++id;
        cout << "Server " << id << " started. Work status: " << work_done << endl;
    }
    Server (const Server & rhs) : id (rhs.id){
        ++id;
        cout << "Server " << id << " started by copy. Work status: " << work_done << endl;
    }
    Server (Server && rhs) : id (rhs.id) {
        ++id;
        cout << "Server " << id << " started by move. Work status: " << work_done << endl;
    }

    void operator()() {
        cout << "Hi! Doing work..." << endl;
        work_done = true;
        while (needed) {
            usleep(300000);
            cout << "sleeping... Work status: " << work_done << endl;
        }
    }
    ~Server() {
        cout << "Server " << id << " stopping. Work status: " << work_done << endl;
        if (work_done)
            cout << "Cleanup triggered by Server " << id << endl;
    }
    bool work_done {false};
    int id;
};

int main() {
    needed = true;
    Server s;
//    thread t(s);
    thread t(std::move(s));
//    t.detach();
    usleep(1000000);
    needed = false;
    t.join();
    cout << "end" << endl;
}

输出结果为：

Server 1 started. Work status: 0
Server 2 started by move. Work status: 0
Server 3 started by move. Work status: 0
Server 2 stopping. Work status: 0
Hi! Doing work...
sleeping... Work status: 1
sleeping... Work status: 1
sleeping... Work status: 1
sleeping... Work status: 1
Server 3 stopping. Work status: 1
Cleanup triggered by Server 3
end
Server 1 stopping. Work status: 0

关闭t.detach()并关闭t.join()后，结果为：

Server 1 started. Work status: 0
Server 2 started by move. Work status: 0
Server 3 started by move. Work status: 0
Server 2 stopping. Work status: 0
Hi! Doing work...
sleeping... Work status: 1
sleeping... Work status: 1
sleeping... Work status: 1
end
Server 1 stopping. Work status: 0

（令我困惑的是一些临时实例，服务器2，它同时显示移动和复制。）

如何为线程添加析构函数？

1 个答案: