C++11 std::thread

一 简介

1、头文件

2、 thread标识单个执行线程，线程允许多个函数并发执行。
在默认构造、移动、detach或join后，std::thread对象会处在不表示任何线程的状态。detach之后，执行线程可能不关联到任何thread对象。成员类 std::thread::id ，是轻量的频繁复制类，作为std::thread对象的唯一标识符工作。

二 函数

1、观察器
joinable：检查thread对象是否标识活跃的执行线程。当get_id() !=std::thread::id()返回true,所以默认构造的thread不可合并。
get_id：返回标识与*this关联的线程的std::thread::id类型值。若无关联的线程，则返回默认构造的std::thread::id。
native_handle：返回实现定义的底层线程句柄
hardware_concurrency： 静态，返回实现所支持的并发线程数。应该只把值当做提示。
2、操作
join ：阻塞当前线程，直至*this所标识的线程完成其执行。*this所标识的线程的完成同步与从join()的成功返回
detach ：从thread对象分离执行的线程，允许执行独立地持续。一旦线程退出，则释放所有分配的资源。调用detach后，*this不再占有任何线程。
swap： 互换2个thread对象的底层句柄。
3、非成员函数：
std::swap（std::thread）

三 举例

包括thread的主要函数和常见用法。

示例的头文件和全局变量、函数如下：

#include      // std::cout
#include        // std::thread
#include 
#include       // std::move
// #include     // std::swap
#include    // std::ref
#include        // vector
#include         // clock_t clock()
#include         // std::mutex
#include 

using namespace std;

void func1(int n) {
  cout << "func1" << endl;
  n += 10;
  this_thread::sleep_for(chrono::milliseconds(10));
}

void func2(int& n) {
  cout << "func2" << endl;
  n += 20;
  this_thread::sleep_for(chrono::milliseconds(10));
}

void show() {
  cout << "show hello world" << endl;
}

const int N = 1000000;
int num = 0;
void count() {
  for (int i = 0; i < N; i++) {
    num++;
  }
}

mutex m;
void count_mutex() {
  for (int i = 0; i < N; i++) {
    m.lock();
    num++;
    m.unlock();
  }
}

std::atomic_int num1 = 0;
void count_atomic_int() {
  for (int i = 0; i < N; i++) {
    num1++;
  }
}

1 thread构造及初始化

  {
    // 1 thread构造及初始化
    int n = 1;
    thread t1; // t1处在不表示任何线程的状态
    thread t2(func1, n);
    t2.join();
    cout << "after func1 n: " << n << endl;
    thread t3(func2, ref(n));
    t3.join();
    cout << "after func2 n: " << n << endl;

    // thread不可复制构造或可复制复制
    // thread t4(t3); // error
    // thread t5 = t3; // error

    thread t6(func1, n);
    thread t7(move(t6)); // thread可移动构造
    t7.join();

    std::vector vc;
    vc.push_back(thread(show)); // thread可存放在vector中
    vc[0].join();

    shared_ptr p(new thread(show)); // share_ptr和thread结合
    p->join();
  }

结果：

2 join detach

  {
    // 2 join detach
    thread t1(show);
    cout << endl;
    cout.setf(ios_base::boolalpha); // bool输出为true/false
    cout << "t1 joinable: " << t1.joinable() << endl;
    t1.join();
    cout << "t1 joinable after join: " << t1.joinable() << endl;

    thread t2(show);
    cout << endl;
    cout << "t2 joinable: " << t2.joinable() << endl;
    t2.detach();
    cout << "t2 joinable after detach: " << t2.joinable() << endl;

  }

结果：

3 hardware_concurrency

  {
    // 3 hardware_concurrency
    auto n = thread::hardware_concurrency(); // cpu核数
    cout << "thread::hardware_concurrency(): " << n << endl;
  }

结果：

4 线程安全

  {
    // 4 thread 原子变量与线程安全
    {
      clock_t start = clock();
      thread t1(count);
      thread t2(count);
      t1.join();
      t2.join();
      clock_t end = clock();
      cout << "after count num: " << num << " , use " 
      << end - start << "ms" << endl;
    }
    {
      num = 0;
      // 互斥量 方式1
      clock_t start = clock();
      thread t1(count_mutex);
      thread t2(count_mutex);
      t1.join();
      t2.join();
      clock_t end = clock();
      cout << "method1 after count_mutex num: " << num << " , use " 
      << end - start << "ms" << endl;
    }
    {
      num = 0;
      // 互斥量 方式2
      clock_t start = clock();
      thread t1(count_mutex);
      t1.join();
      thread t2(count_mutex);
      t2.join();
      clock_t end = clock();
      cout << "method2 after count_mutex num: " << num << " , use " 
      << end - start << "ms" << endl;
    }
    {
      // 原子变量 方式1
      clock_t start = clock();
      thread t1(count_atomic_int);
      thread t2(count_atomic_int);
      t1.join();
      t2.join();
      clock_t end = clock();
      cout << "method1 after count_atomic_int num1: " << num1 << " , use " 
      << end - start << "ms" << endl;
    }
    {
      num1 = 0;
      // 原子变量 方式2
      clock_t start = clock();
      thread t1(count_atomic_int);
      t1.join();
      thread t2(count_atomic_int);
      t2.join();
      clock_t end = clock();
      cout << "method2 after count_atomic_int num1: " << num1 << " , use " 
      << end - start << "ms" << endl;
    }
  }

结果：

5 lambda

  {
    // 5 lambda
    auto lam = [] {cout << "hello world" << endl; };
    thread t1(lam);
    t1.join();
    thread t2(lam);
    t2.join();
  }

6 时间等待

  {
    // 6 时间等待
    thread t1([]() {
      this_thread::sleep_for(chrono::seconds(3));
      this_thread::yield();
      cout << "u can u up" << endl;
    });
    t1.join();
  }

7 可变参数函数

  {
    // 7 可变参数
    thread t1(printf, "%s%d", "hi", 999);
    t1.join();
  }

8 线程交换

  {
    // 8 线程交换
    thread t1([] {/*cout << "thread1"; cout << endl; */});
    thread t2([] {/*cout << "thread2"; cout << endl; */});
    cout << "thread1 id: " << t1.get_id() << endl;
    cout << "thread2 id: " << t2.get_id() << endl;
    std::swap(t1, t2);
    cout << "after swap:" << endl;
    cout << "thread1 id: " << t1.get_id() << endl;
    cout << "thread2 id: " << t2.get_id() << endl;
    t1.join();
    t2.join();
  }

结果：

9 线程移动

  {
    // 9 线程移动
    thread t1([] {cout << "thread1"; cout << endl; });
    cout << "thread1 id: " << t1.get_id() << endl;
    thread t2 = move(t1);
    cout << "thread2 id: " << t2.get_id() << endl;
    t2.join();
  }

结果：

四 参考 

std::thread