C++11threadget_id(3)

2016-02-24

字数统计: 1.1k字 | 阅读时长≈ 5分

原文地址：http://www.cplusplus.com/reference/thread/thread/get\_id/

public member function

std::thread::get_id

id get_id() const noexcept;

Get thread id

Returns the thread id.

返回线程ID

If the thread object is joinable, the function returns a value that uniquely identifies the thread.

如果线程对象是joinable的，那么将会返回一个独一无二的线程标识。（这里我试了几个例子，还是搞不太明白，还是先保留该问题。看最后一个的例子）

例子：

#include
#include
using namespace std;
void show(int n){
cout<<”show1:get_id() is “<<this_thread::get_id()<<”,Now n is “<<n<<endl;
}
void show2(int n){

cout<<”show2:get_id() is “<<this_thread::get_id()<<”,Now n is “<<n<<endl;
}
int main()
{
cout<<”main starts”<<endl;
cout<<”mainThread is “<<this_thread::get_id()<<endl;
thread t2(show,10);
cout<<”t2 is “<<t2.get_id()<<endl;
t2.join();
cout<<”after t2.join(),t2 is “<<t2.get_id()<<endl;

thread t3(show2,99);
cout<<”t3 is “<<t3.get_id()<<endl;
t3.detach();
cout<<”after t3.detach(),t3 is “<<t3.get_id()<<endl;

cout<<”main complete!”<<endl;

}

运行及GDB调试截图：

可以看到，两个子线程都在main还没结束的时候就已经exited了！并且第一个子线程在第二个子线程还没有构造的时候就已经exited了。

这里的返回值都是一样，换个更好点的例子：

#include
#include
#include
using namespace std;
//delay(n) 延时n秒
void delay(double sec)
{
time_t start_time, cur_time; // 变量声明
time(&start_time);
do {
time(&cur_time);
}while((cur_time - start_time) < sec );
};
void show(int n){
cout<<”show1:get_id() is “<<this_thread::get_id()<<”,Now n is “<<n<<endl;
delay(3);
cout<<”show1 complete!”<<endl;
}
void show2(int n){

cout<<”show2:get_id() is “<<this_thread::get_id()<<”,Now n is “<<n<<endl;
delay(3);
cout<<”show2 complete!”<<endl;
}
int main()
{
cout<<”main starts”<<endl;
cout<<”mainThread is “<<this_thread::get_id()<<endl;

thread t3(show2,99);
cout<<”t3 is “<<t3.get_id()<<endl;
t3.detach();
cout<<”after t3.detach(),t3 is “<<t3.get_id()<<endl;

thread t2(show,10);
cout<<”t2 is “<<t2.get_id()<<endl;
t2.join();
cout<<”after t2.join(),t2 is “<<t2.get_id()<<endl;

cout<<”main complete!”<<endl;

}

运行截图：

可以看到show1和t1的ID是一样的，show2和t3的ID是一样的。（这里显示的有点混乱）

If the thread object is not joinable, the function returns a default-constructed object of member type thread::id.
如果线程对象不是joinable,那么将会返回默认构造时的ID。

Parameters

none

Return value

An object of member type thread::id that uniquely identifies the thread (if joinable), or default-constructed (if not joinable)

返回一个线程id标识。

Example

// thread::get_id / this_thread::get_id
#include <iostream>       // std::cout
#include <thread>         // std::thread, std::thread::id, std::this_thread::get_id
#include <chrono>         // std::chrono::seconds
 
std::thread::id main_thread_id = std::this_thread::get_id();

void is_main_thread() {
  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";
}

int main() 
{
  is_main_thread();
  std::thread th (is_main_thread);
  th.join();
}

Edit & Run

Output:

This is the main thread.
This is not the main thread.

根据example修改的例子：

#include
#include
#include
using namespace std;
std::thread::id main_thread_id = std::this_thread::get_id();
void show(int n){
cout<<endl<<”main_thread_id=”<<main_thread_id<<endl;
cout<<”thi_thread::get_id=”<<this_thread::get_id()<<endl;
cout<<”SHOW complete!”<<endl;
}
int main()
{
cout<<endl<<”Main main_thread_id=”<<main_thread_id<<endl;
cout<<”Main this_thread::get_id= “<<this_thread::get_id()<<endl;

show(888);

thread t3(show,99);
cout<<”t3 is “<<t3.get_id()<<endl;
t3.detach();

thread t2(show,10);
cout<<”t2 is “<<t2.get_id()<<endl;
t2.join();

}

结果：

令我疑惑的是在开头那个全局设置