thread

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thread

std::thread构造

(1). 默认构造函数，创建一个空的 thread 执行对象。
(2). 初始化构造函数，创建一个 thread对象，该 thread对象可被 joinable，新产生的线程会调用 fn 函数，该函数的参数由 args 给出。
(3). 拷贝构造函数(被禁用)，意味着 thread 不可被拷贝构造。
(4). move 构造函数，move 构造函数，调用成功之后 x 不代表任何 thread 执行对象。
注意：可被 joinable 的 thread 对象必须在他们销毁之前被主线程 join 或者将其设置为 detached.

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#include <iostream>
#include <utility>
#include <thread>
#include <chrono>
#include <functional>
#include <atomic>
 
void f1(int n)
{
    for (int i = 0; i < 5; ++i) {
        std::cout << "Thread " << n << " executing\n";
        std::this_thread::sleep_for(std::chrono::milliseconds(10));
    }
}
 
void f2(int& n)
{
    for (int i = 0; i < 5; ++i) {
        std::cout << "Thread 2 executing\n";
        ++n;
        std::this_thread::sleep_for(std::chrono::milliseconds(10));
    }
}
 
int main()
{
    int n = 0;
    std::thread t1; // t1 is not a thread
    std::thread t2(f1, n + 1); // pass by value
    std::thread t3(f2, std::ref(n)); // pass by reference
    std::thread t4(std::move(t3)); // t4 is now running f2(). t3 is no longer a thread
    t2.join();
    t4.join();
    std::cout << "Final value of n is " << n << '\n';
}

std::thread赋值操作：

(1). move 赋值操作，如果当前对象不可 joinable，需要传递一个右值引用(rhs)给 move 赋值操作；如果当前对象可被 joinable，则 terminate() 报错。
(2). 拷贝赋值操作被禁用，thread 对象不可被拷贝

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#include <stdio.h>
#include <stdlib.h>

#include <chrono>    // std::chrono::seconds
#include <iostream>  // std::cout
#include <thread>    // std::thread, std::this_thread::sleep_for

void thread_task(int n) {
    std::this_thread::sleep_for(std::chrono::seconds(n));
    std::cout << "hello thread "
        << std::this_thread::get_id()
        << " paused " << n << " seconds" << std::endl;
}

/*
 * ===  FUNCTION  =========================================================
 *         Name:  main
 *  Description:  program entry routine.
 * ========================================================================
 */
int main(int argc, const char *argv[])
{
    std::thread threads[5];
    std::cout << "Spawning 5 threads...\n";
    for (int i = 0; i < 5; i++) {
        threads[i] = std::thread(thread_task, i + 1);
    }
    std::cout << "Done spawning threads! Now wait for them to join\n";
    for (auto& t: threads) {
        t.join();
    }
    std::cout << "All threads joined.\n";

    return EXIT_SUCCESS;
}

其他成员函数

  1. get_id()

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    atd::thread::id main_thread_id = std::this_thread::get_id();

  2. joinable()

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    std::thread foo;
    std::thread bar(mythread);

    std::cout << "Joinable after construction:\n" << std::boolalpha;
    std::cout << "foo: " << foo.joinable() << '\n';//false
    std::cout << "bar: " << bar.joinable() << '\n';//true

    if (foo.joinable()) foo.join();
    if (bar.joinable()) bar.join();

    std::cout << "Joinable after joining:\n" << std::boolalpha;
    std::cout << "foo: " << foo.joinable() << '\n';//false
    std::cout << "bar: " << bar.joinable() << '\n';//false

  3. join() //等待线程完成其执行

  4. detach() //允许线程独立执行

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    #include <iostream>       // std::cout
    #include <thread>         // std::thread, std::this_thread::sleep_for
    #include <chrono>         // std::chrono::seconds
     
    void pause_thread(int n) 
    {
      std::this_thread::sleep_for (std::chrono::seconds(n));
      std::cout << "pause of " << n << " seconds ended\n";
    }
     
    int main() 
    {
      std::cout << "Spawning and detaching 3 threads...\n";
      std::thread (pause_thread,1).detach();
      std::thread (pause_thread,2).detach();
      std::thread (pause_thread,3).detach();
      std::cout << "Done spawning threads.\n";

      std::cout << "(the main thread will now pause for 5 seconds)\n";
      // give the detached threads time to finish (but not guaranteed!):
      pause_thread(5);
      return 0;
    }

  5. swap() //Swaps the state of the object with that of x.

  6. native_handle()
    std::thread::native_handle_type nht = std::thread::native_handle();