C++多線程：thread類建立線程的多種方式

文章目錄

描述
函數成員簡介
總結

描述

頭檔案 <thread>
聲明方式： std::thread <obj>
簡介

線程在構造關聯的線程對象時立即開始執行，從提供給作為構造函數參數的頂層函數開始。如果頂層函數抛出異常，則調用
std::terminate 。正如我們之前幾篇說過的thread可以通過 std::async 和 std::promise 類對修改共享變量，并将傳回值傳遞給調用方。如果共享變量在該過程中需要進行同步，則就需要我們說過的 std::mutex 和 std::condition_variable
。

std::thread 不支援拷貝構造和指派，如果需要将目前t1 對象指派給t2對象，需要通過移動指派 std::move ，即将t1的位址以及内容全部指派給t2對象才行。

函數成員簡介

構造函數（建立線程的多種方式）

a. 類對象的拷貝建立線程

b. 類對象的引用建立線程

c. 移動複制
std::move
對象建立線程

d. 臨時建立的對象建立線程

e. 函數名建立線程

f. lamda函數建立線程

g. 類對象的拷貝的成員函數建立線程

h. 類對象的位址的成員函數建立線程

#include <iostream>
#include <utility>
#include <thread>
#include <chrono>
 
void f1(int n)
{
    for (int i = 0; i < 5; ++i) {
        std::cout << "Thread 1 executing\n";
        ++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));
    }
}
 
class foo
{
public:
    void bar()
    {
        for (int i = 0; i < 5; ++i) {
            std::cout << "Thread 3 executing\n";
            ++n;
            std::this_thread::sleep_for(std::chrono::milliseconds(10));
        }
    }
    int n = 0;
};
 
class baz
{
public:
    void operator()(int n)
    {
        for (int i = 0; i < 5; ++i) {
            std::cout << "Thread 4 executing\n";
            ++n;
            std::this_thread::sleep_for(std::chrono::milliseconds(10));
        }
    }
    int n = 0;
};
 
int main()
{
    int n = 0;
    foo f;
    baz b;
    std::thread t1; // t1 is not a thread
    std::thread t2(f1, n + 1); // 普通函數名建立線程，傳遞函數參數為值
    std::thread t3(f2, std::ref(n)); // 普通函數名建立線程，傳遞函數參數為引用
    std::thread t4(std::move(t3)); // 類對象的移動指派，使用std::move
    std::thread t5(&foo::bar, &f); // 類對象的拷貝的位址的成員函數
    std::thread t6(b,6); // 類對象建立線程，預設執行operator ()函數
    std::thread t7([](int x){return x*x;},6);//lamda函數建立子線程
    std::thread t8(std::ref(b),6);//類對象的引用建立
    std::thread t9(baz(),6);//臨時對象建立
    
    t2.join();
    t4.join();
    t5.join();
    t6.join();
    t7.join();
    t8.join();
    t9.join();
    std::cout << "Final value of n is " << n << '\n';
    std::cout << "Final value of foo::n is " << f.n << '\n';
}

輸出如下,由于輸出為線程間交叉執行，輸出會有點亂:

Thread 2 executing
Thread 4 executing
Thread 1 executing
Thread 3 executing
Thread 4 executing
Thread 4 executing
Thread 2 executing
Thread 1 executing
Thread 3 executing
Thread 4 executing
Thread 4 executing
Thread 4 executing
Thread 2 executing
Thread 1 executing
Thread 4 executing
Thread 3 executing
Thread 4 executing
Thread 4 executing
Thread 2 executing
Thread 4 executing
Thread 4 executing
Thread 1 executing
Thread 3 executing
Thread 4 executing
Thread 2 executing
Thread 4 executing
Thread 4 executing
Thread 3 executing
Thread 4 executing
Thread 1 executing
Final value of n is 5
Final value of foo::n is 5

std::thread::joinable
檢查 thread 對象是否辨別活躍的執行線程,是傳回true,否則傳回false

如下代碼

#include <iostream>
#include <thread>
#include <chrono>
 
void foo()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
int main()
{
    //剛建立好的線程對象是不活躍的
    std::thread t;
    std::cout << "before starting, joinable: " << std::boolalpha << t.joinable()
              << '\n';
    //建立線程并執行代碼，但未合并，則它是活躍的
    t = std::thread(foo);
    std::cout << "after starting, joinable: " << t.joinable() 
              << '\n';
 
    //線程合并之後變為不活躍的
    t.join();
    std::cout << "after joining, joinable: " << t.joinable() 
              << '\n';
}

輸出如下:

before starting, joinable: false
after starting, joinable: true
after joining, joinable: false

std::thread::join
阻塞線程成員，直到線程函數代碼執行完畢傳回

代碼如下:

#include <iostream>
#include <thread>
#include <chrono>
 
void foo()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
void bar()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
int main()
{
    std::cout << "starting first helper...\n";
    std::thread helper1(foo);
 
    std::cout << "starting second helper...\n";
    std::thread helper2(bar);
 
    std::cout << "waiting for helpers to finish..." << std::endl;
    helper1.join();
    helper2.join();
 
    std::cout << "done!\n";
}

輸出如下:

starting first helper...
starting second helper...
waiting for helpers to finish...
done!

std::thread::detach
從 thread 對象分離執行的線程，允許執行獨立地執行線程

一旦線程退出，則釋放所有配置設定的資源。

如下代碼：

#include <iostream>
#include <chrono>
#include <thread>
 
void independentThread() 
{
    std::cout << "Starting concurrent thread.\n";
    std::this_thread::sleep_for(std::chrono::seconds(2));
    std::cout << "Exiting concurrent thread.\n";
}
 
void threadCaller() 
{
    std::cout << "Starting thread caller.\n";
    std::thread t(independentThread);
    //這裡調用detach,則線程t将獨立執行，是以目前線程的輸出會早于t線程的輸出
    t.detach();
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::cout << "Exiting thread caller.\n";
}
 
int main() 
{
    threadCaller();
    std::this_thread::sleep_for(std::chrono::seconds(5));
}

輸出如下：

Starting thread caller.
Starting concurrent thread.
Exiting thread caller.
Exiting concurrent thread.

std::thread::swap
交換兩個線程的對象的檔案句柄

代碼如下：

#include <iostream>
#include <thread>
#include <chrono>
 
void foo()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
void bar()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
int main()
{
    std::thread t1(foo);
    std::thread t2(bar);
 
    std::cout << "thread 1 id: " << t1.get_id() << std::endl;
    std::cout << "thread 2 id: " << t2.get_id() << std::endl;
 
    使用boost的swap和thread類封裝的swap函數效果類似，都會交換線程的檔案句柄
    std::swap(t1, t2);
 
    std::cout << "after std::swap(t1, t2):" << std::endl;
    std::cout << "thread 1 id: " << t1.get_id() << std::endl;
    std::cout << "thread 2 id: " << t2.get_id() << std::endl;
 
    t1.swap(t2);
 
    std::cout << "after t1.swap(t2):" << std::endl;
    std::cout << "thread 1 id: " << t1.get_id() << std::endl;
    std::cout << "thread 2 id: " << t2.get_id() << std::endl;
 
    t1.join();
    t2.join();
}

輸出如下：

thread 1 id: 0x70000f1e9000
thread 2 id: 0x70000f26c000
after std::swap(t1, t2):
thread 1 id: 0x70000f26c000
thread 2 id: 0x70000f1e9000
after t1.swap(t2):
thread 1 id: 0x70000f1e9000
thread 2 id: 0x70000f26c000

C++多線程：thread類建立線程的多種方式

文章目錄

描述

函數成員簡介

總結

繼續閱讀

HDU 5344 MZL's xor

UVA 590 Always on the run

FZU 1978 Repair the brackets

UVA 10344- 23 out of 5

ZOJ 3935 2016

POJ 2115 C Looooops

HDU 5381 The sum of gcd

ZOJ 1104 Leaps Tall Buildings

ZOJ 3700 Ever Dream

HDU 2821 Pusher

ZOJ 1199 Point of Intersection

UVA 1401 Remember the Word

UVA 620 Cellular Structure

ZOJ 2748 Free Kick

CSU 1567 Reverse Rot

UVA 519 Puzzle (II)