C++随机uniform_int_distribution在所有线程中返回相同的值

C++ random uniform_int_distribution return same values in all threads

本文关键字：返回 线程 uniform 随机 int distribution C++      更新时间：2023-10-16

我有以下代码，我需要在给定的时间间隔内有一个随机数。似乎按照我需要的方式工作。

std::default_random_engine eng;
std::uniform_int_distribution<int> dist(3, 7);
int timeout = dist(eng);

但是后来我在不同的线程中运行它并在循环中重复。

std::default_random_engine defRandEng(std::this_thread::get_id());
std::uniform_int_distribution<int> dist(3, 7);
int timeout; // if I put timeout = dist(defRandEng); here it's all the same
while (true)
{
timeout = dist(defRandEng);
std::cout<<"Thread "<<std::this_thread::get_id()<<" timeout = "<<timeout<<std::endl;
std::this_thread::sleep_for(std::chrono::seconds(timeout));
}

但是对于所有线程中的每次迭代，值都是相同的

Thread 139779167999744 timeout = 6
Thread 139779134428928 timeout = 6
Thread 139779067287296 timeout = 6
Thread 139779117643520 timeout = 6
Thread 139779100858112 timeout = 6
Thread 139779084072704 timeout = 6
Thread 139779151214336 timeout = 6
Thread 139779050501888 timeout = 6
Thread 139779033716480 timeout = 6

下一页

Thread 139779167999744 timeout = 4
Thread 139779151214336 timeout = 4
Thread 139779134428928 timeout = 4
Thread 139779117643520 timeout = 4
Thread 139779100858112 timeout = 4
Thread 139779084072704 timeout = 4
Thread 139779067287296 timeout = 4
Thread 139779050501888 timeout = 4
Thread 139779033716480 timeout = 4

您需要根据随机引擎的一些自然随机值提供种子。以下示例采用自您的代码片段，适用于 3 个线程：

std::mutex lock;
void sample_time_out()
{
std::stringstream ss;
ss << std::this_thread::get_id();
uint64_t thread_id = std::stoull(ss.str());
std::default_random_engine eng(thread_id);
std::uniform_int_distribution<int> dis(3, 7);

for (int i = 0; i < 3; i++)
{
auto timeout = dis(eng);
std::this_thread::sleep_for(std::chrono::seconds(timeout));
{
std::unique_lock<std::mutex> lock1(lock);
std::cout << "Thread " << std::this_thread::get_id() << " timeout = " << timeout << std::endl;
}
}
}
int main()
{
std::thread t1(sample_time_out);
std::thread t2(sample_time_out);
std::thread t3(sample_time_out);
t1.join();
t2.join();
t3.join();
return 0;
}

我第一次运行的输出是：

Thread 31420 timeout = 3
Thread 18616 timeout = 6
Thread 31556 timeout = 7
Thread 31420 timeout = 4
Thread 18616 timeout = 7
Thread 31420 timeout = 6
Thread 31556 timeout = 7
Thread 18616 timeout = 4
Thread 31556 timeout = 7
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