来自不同进程的线程可以具有相同的 id 吗？答案

【问题标题】：Can threads from different processes have the same id?来自不同进程的线程可以具有相同的 id 吗？
【发布时间】：2019-04-01 11:03:27
【问题描述】：

我正在编写一个程序，我想在其中为每个进程创建多个进程和多个线程。简而言之，我的程序创建了多个进程，每个进程创建了多个线程。

这是一个简短的sn-p代码：

void NormalityComponent::newThread(int thread_id){
    std::cout << "New Thread [" << thread_id +1 << "] created in Component [" << name_component << "] with id " << std::this_thread::get_id() << std::endl;
    timeSimulation();
    std::cout << "Thread [" << thread_id +1 << "] in [" << name_component << "] with id " << std::this_thread::get_id() << " ends its simulation" << std::endl;
}

void NormalityComponent::timeSimulation(){
    for (int i = 0; i < time_factor * TEMPORAL_PARAMETER; i++);    
}

void NormalityComponent::startAnalysisMode3(){
    //creation of a new process to simulate the Normality Component Analysis and a thread for each Instance.

            pid_t pid = fork();
            if (pid == 0){
                  //Child Process
                  std::cout << "New Normality Component ["<< name_component <<"] created with id " << getpid() << std::endl;
                  //Creation of instances
                    for(int i = 0; i < number_instances;i++){
                        v_threads.push_back(std::thread(&NormalityComponent::newThread,this, i));
                        std::this_thread::sleep_for (std::chrono::milliseconds(100));
                    }

                    std::for_each(v_threads.begin(), v_threads.end(), std::mem_fn(&std::thread::join));

                    kill(getpid(), SIGTERM); //it ends the process when the threads finish. 
            }
}

这是输出的片段：

New Thread [1] created in Component [Velocity] with id 140236340983552
New Thread [1] created in Component [FaceRecognition] with id 140236340983552
New Thread [1] created in Component [Trajectories] with id 140236340983552
New Thread [2] created in Component [Velocity] with id 140236332590848
New Thread [2] created in Component [Trajectories] with id 140236332590848
New Thread [2] created in Component [FaceRecognition] with id 140236332590848

来自不同进程的线程可以有相同的id吗？奇怪，每个线程的标识符应该是唯一的吧？

【问题讨论】：

当然他们可以在不同的进程中拥有相同的 id，你为什么认为他们不能呢？ “奇怪，每个线程的标识符应该是唯一的吧？”不，这个假设是错误的，你从哪里得到的？
在单个进程内存空间中是唯一的，我不明白为什么您可以在其他情况下确定这种唯一性。
不同程序如何知道彼此创建的线程的 ID，它们需要这些 ID 才能保持唯一性？
我知道每个进程都在内存中保留了它的空间，并且一个进程的线程共享该空间。但令我特别震惊的是，每个进程的第一个线程具有相同的标识符。对于那些以二阶和三阶创造的人来说也是如此。也许这可能发生在来自同一个父亲的进程中。

标签： c++ multithreading process

【解决方案1】：

这些线程 ID 看起来更像地址。 this_thread::get_id() 返回的值不必与系统“线程 id”相同。它主要用于提供字符串比较/工作作为关联容器中线程的关键。您可能想尝试致电gettid 或GetCurrentThreadId。注意在windows上“直到线程终止，线程标识符在整个系统中唯一标识线程。”所以来自不同进程的线程不能有相同的id。在其他平台上的行为可能会有所不同。

【讨论】：

你所说的系统明确地识别每个线程对我来说听起来更合乎逻辑。我在 gnu/linux 中运行代码。无论如何，我会尝试你的建议。谢谢;)

【解决方案2】：

您可能想尝试调用 gettid 或 GetCurrentThreadId

@VTT，gettid() 为我工作。

void NormalityComponent::newThread(int thread_id){
pid_t tid = (pid_t) syscall (SYS_gettid);

std::cout << "New Thread [" << thread_id +1 << "] created in Component [" << name_component << "] with id " << tid << std::endl;
timeSimulation();
std::cout << "Thread [" << thread_id +1 << "] in [" << name_component << "] with id " << tid << " ends its simulation" << std::endl;

}

此解决方案为每个线程提供唯一标识符。输出示例如下：

New Normality Component [Trajectories] created with id 5118
New Normality Component [Velocity] created with id 5119
New Thread [1] created in Component [Trajectories] with id 5121
New Normality Component [FaceRecognition] created with id 5120
New Thread [1] created in Component [Velocity] with id 5122
New Thread [1] created in Component [FaceRecognition] with id 5123
New Thread [2] created in Component [Trajectories] with id 5124
New Thread [2] created in Component [Velocity] with id 5125
New Thread [2] created in Component [FaceRecognition] with id 5126
Thread [1] in [Velocity] with id 5122 ends its simulation
New Thread [3] created in Component [Trajectories] with id 5127
New Thread [3] created in Component [FaceRecognition] with id 5128
New Thread [4] created in Component [FaceRecognition] with id 5129

无论如何，我想了解为什么 this_thread::get_id() 不返回线程 ID。如果您查看 c++ 文档，您将看到函数描述如何表明它返回线程标识符。

【讨论】：