为什么在C ++中构造一个静态thread_local对象两次? [英] Why is a static thread_local object in C++ constructed twice?
问题描述
此代码:
#include <iostream>
#include <thread>
#include <mutex>
struct Singl{
Singl(Singl const&) = delete;
Singl(Singl&&) = delete;
inline static thread_local bool alive = true;
Singl(){
std::cout << "Singl() " << std::this_thread::get_id() << std::endl;
}
~Singl(){
std::cout << "~Singl() " << std::this_thread::get_id() << std::endl;
alive = false;
}
};
static auto& singl(){
static thread_local Singl i;
return i;
}
struct URef{
~URef(){
const bool alive = singl().alive;
std::cout << alive << std::endl;
}
};
int main() {
std::thread([](){
singl();
static thread_local URef u;
}).join();
return 0;
}
具有以下输出:
Singl() 2
Singl() 2
1
~Singl() 2
~Singl() 2
我正在使用mingw-w64 gcc7.2 POSIX线程在Windows下编译和运行.
I'm compiling and running under Windows with mingw-w64 gcc7.2 POSIX threads.
Coliru具有不同的输出: http://coliru.stacked-crooked.com/a/3da415345ea6c2ee
Coliru has a different output: http://coliru.stacked-crooked.com/a/3da415345ea6c2ee
这是什么?我的工具链/编译器出问题了,还是应该这样?为什么在同一线程上有两个thread_local对象(或构造两次?)?
What's this? Something wrong with my toolchain / compiler, or is that how it should be? Why do I have two thread_local objects (or constructed twice?) on the same thread?
推荐答案
您的编译器或工具链可能有问题.
It's probably something wrong with your compiler or toolchain.
对于Linux上的clang ++ 8和g ++ 8.2(确切地说是Devuan ASCII),线程局部变量仅构造一次.
With both clang++ 8 and g++ 8.2 on Linux (Devuan ASCII to be exact), the thread-local variable is constructed just once.
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