Linux下C++多线程编程（入门实例）_linux下c++实例

于 2025-01-13 00:56:01 发布
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文章标签： c++ linux 开发语言
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本文链接：https://blog.youkuaiyun.com/2501_90222999/article/details/145103364
版权 
// 线程的运行函数
void\* say\_hello(void\* args)
{
    cout << "Hello Runoob！" << endl;
    return 0;
}
 
int main()
{
    // 定义线程的 id 变量，多个变量使用数组
    pthread_t tids[NUM_THREADS];
    for(int i = 0; i < NUM_THREADS; ++i)
    {
        //参数依次是：创建的线程id，线程参数，调用的函数，传入的函数参数
        int ret = pthread\_create(&tids[i], NULL, say_hello, NULL);
        if (ret != 0)
        {
           cout << "pthread\_create error: error\_code=" << ret << endl;
        }
    }
    //等各个线程退出后，进程才结束，否则进程强制结束了，线程可能还没反应过来；
    pthread\_exit(NULL);
}


使用 -lpthread 库编译下面的程序：

$ g++ test.cpp -lpthread -o test.o


现在，执行程序，将产生下列结果：




$ ./test.o
Hello Runoob！
Hello Runoob！
Hello Runoob！
Hello Runoob！
Hello Runoob！


以下简单的实例代码使用 pthread\_create() 函数创建了 5 个线程，并接收传入的参数。每个线程打印一个 “Hello Runoob!” 消息，并输出接收的参数，然后调用 pthread\_exit() 终止线程。


### 实例




//文件名：test.cpp
 
#include <iostream>
#include <cstdlib>
#include <pthread.h>
 
using namespace std;
 
#define NUM\_THREADS 5
 
void \*PrintHello(void \*threadid)
{  
   // 对传入的参数进行强制类型转换，由无类型指针变为整形数指针，然后再读取
   int tid = \*((int\*)threadid);
   cout << "Hello Runoob! 线程 ID, " << tid << endl;
   pthread\_exit(NULL);
}
 
int main ()
{
   pthread_t threads[NUM_THREADS];
   int indexes[NUM_THREADS];// 用数组来保存i的值
   int rc;
   int i;
   for( i=0; i < NUM_THREADS; i++ ){      
      cout << "main() : 创建线程, " << i << endl;
      indexes[i] = i; //先保存i的值
      // 传入的时候必须强制转换为void\* 类型，即无类型指针 
      rc = pthread\_create(&threads[i], NULL, 
                          PrintHello, (void \*)&(indexes[i]));
      if (rc){
         cout << "Error:无法创建线程," << rc << endl;
         exit(-1);
      }
   }
   pthread\_exit(NULL);
}


现在编译并执行程序，将产生下列结果：




$ g++ test.cpp -lpthread -o test.o
$ ./test.o
main() : 创建线程, 0
main() : 创建线程, 1
Hello Runoob! 线程 ID, 0
main() : 创建线程, Hello Runoob! 线程 ID, 21
 
main() : 创建线程, 3
Hello Runoob! 线程 ID, 2
main() : 创建线程, 4
Hello Runoob! 线程 ID, 3
Hello Runoob! 线程 ID, 4


### 向线程传递参数


这个实例演示了如何通过结构传递多个参数。您可以在线程回调中传递任意的数据类型，因为它指向 void，如下面的实例所示：


### 实例




#include <iostream>
#include <cstdlib>
#include <pthread.h>
 
using namespace std;
 
#define NUM\_THREADS 5
 
struct thread_data{
   int  thread_id;
   char \*message;
};
 
void \*PrintHello(void \*threadarg)
{
   struct thread_data \*my_data;
 
   my_data = (struct thread_data \*) threadarg;
 
   cout << "Thread ID : " << my_data->thread_id ;
   cout << " Message : " << my_data->message << endl;
 
   pthread\_exit(NULL);
}
 
int main ()
{
   pthread_t threads[NUM_THREADS];
   struct thread_data td[NUM_THREADS];
   int rc;
   int i;
 
   for( i=0; i < NUM_THREADS; i++ ){
      cout <<"main() : creating thread, " << i << endl;
      td[i].thread_id = i;
      td[i].message = (char\*)"This is message";
      rc = pthread\_create(&threads[i], NULL,
                          PrintHello, (void \*)&td[i]);
      if (rc){
         cout << "Error:unable to create thread," << rc << endl;
         exit(-1);
      }
   }
   pthread\_exit(NULL);
}


当上面的代码被编译和执行时，它会产生下列结果：




$ g++ -Wno-write-strings test.cpp -lpthread -o test.o
$ ./test.o
main() : creating thread, 0
main() : creating thread, 1
Thread ID : 0 Message : This is message
main() : creating thread, Thread ID : 21
 Message : This is message
main() : creating thread, 3
Thread ID : 2 Message : This is message
main() : creating thread, 4
Thread ID : 3 Message : This is message
Thread ID : 4 Message : This is message


### 连接和分离线程


我们可以使用以下两个函数来连接或分离线程：




pthread_join (threadid, status) 
pthread_detach (threadid) 


pthread\_join() 子程序阻碍调用程序，直到指定的 threadid 线程终止为止。当创建一个线程时，它的某个属性会定义它是否是可连接的（joinable）或可分离的（detached）。只有创建时定义为可连接的线程才可以被连接。如果线程创建时被定义为可分离的，则它永远也不能被连接。


这个实例演示了如何使用 pthread\_join() 函数来等待线程的完成。


### 实例




#include <iostream>
#include <cstdlib>
#include <pthread.h>
#include <unistd.h>
 
using namespace std;
 
#define NUM\_THREADS 5
 
void \*wait(void \*t)
{
   int i;
   long tid;
 
   tid = (long)t;
 
   sleep(1);
   cout << "Sleeping in thread " << endl;
   cout << "Thread with id : " << tid << " ...exiting " << endl;
   pthread\_exit(NULL);
}
 
int main ()
{
   int rc;
   int i;
   pthread_t threads[NUM_THREADS];
   pthread_attr_t attr;
   void \*status;
 
   // 初始化并设置线程为可连接的（joinable）
   pthread\_attr\_init(&attr);
   pthread\_attr\_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
 
   for( i=0; i < NUM_THREADS; i++ ){
      cout << "main() : creating thread, " << i << endl;
      rc = pthread\_create(&threads[i], NULL, wait, (void \*)&i );
      if (rc){
         cout << "Error:unable to create thread," << rc << endl;
         exit(-1);
      }
   }
 
   // 删除属性，并等待其他线程
   pthread\_attr\_destroy(&attr);
   for( i=0; i < NUM_THREADS; i++ ){
      rc = pthread\_join(threads[i], &status);
      if (rc){
         cout << "Error:unable to join," << rc << endl;
         exit(-1);
      }
      cout << "Main: completed thread id :" << i ;
      cout << " exiting with status :" << status << endl;
   }
 
   cout << "Main: program exiting." << endl;
   pthread\_exit(NULL);
}


当上面的代码被编译和执行时，它会产生下列结果：




main() : creating thread, 0
main() : creating thread, 1
main() : creating thread, 2
main() : creating thread, 3
main() : creating thread, 4
Sleeping in thread 
Thread with id : 4  ...exiting 
Sleeping in thread 
Thread with id : 3  ...exiting 
Sleeping in thread 
Thread with id : 2  ...exiting 
Sleeping in thread 
Thread with id : 1  ...exiting 
Sleeping in thread 
Thread with id : 0  ...exiting 
Main: completed thread id :0  exiting with status :0
Main: completed thread id :1  exiting with status :0
Main: completed thread id :2  exiting with status :0
Main: completed thread id :3  exiting with status :0
Main: completed thread id :4  exiting with status :0
Main: program exiting.


c++ 11 之后有了标准的线程库：




#include <iostream>
 
#include <thread>
 
std::thread::id main_thread_id = std::this_thread::get\_id();
 
void hello()  
{
    std::cout << "Hello Concurrent World\n";
    if (main_thread_id == std::this_thread::get\_id())
        std::cout << "This is the main thread.\n";
    else
        std::cout << "This is not the main thread.\n";
}
 
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::thread t(hello);
    std::cout << t.hardware\_concurrency() << std::endl;//可以并发执行多少个(不准确)
    std::cout << "native\_handle " << t.native\_handle() << std::endl;//可以并发执行多少个(不准确)
    t.join();
    std::thread a(hello);
    a.detach();
    std::thread threads[5];                         // 默认构造线程
 
    std::cout << "Spawning 5 threads...\n";
    for (int i = 0; i < 5; ++i)
        threads[i] = std::thread(pause_thread, i + 1);   // move-assign threads
    std::cout << "Done spawning threads. Now waiting for them to join:\n";
    for (auto &thread : threads)
        thread.join();
    std::cout << "All threads joined!\n";
}


之前一些编译器使用 C++11 的编译参数是 -std=c++11

g++ -std=c++11 test.cpp -lpthread
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