如何在c ++中初始化线程局部变量？ [英] How to initialize thread local variable in c++?

问题描述

可能存在重复：

C ++ 11 thread_local in gcc - alternatives

我想用c ++ 11 thread_local 来创建和使用thread_local变量，但因为它不是但由gcc支持，我使用特定于gcc的 __ thread 。我声明变量的方式是：

$ $ $ $ $ $ $ $ $ $ $ $ $ b static __thread int64_t m_minInt;

};
__thread int64_t myClass :: m_minInt = 100;

当我编译它时，我收到一个错误，如$ /

 错误：'myClass :: minInt'是线程本地的，所以不能被动态初始化
  

如何正确做到这一点？

PS：gcc版本：4.6.3

  myClass 
 =h2_lin>解决方案

{
public：

static __thread int64_t m_minInt;
static __thread bool m_minIntInitialized;

static int64_t getMinInt（）;
};
__thread int64_t myClass :: m_minInt;
__thread bool myClass :: m_minIntInitialized;


int64_t myClass :: getMinInt（）
{
if（！m_minIntInitialized）//注意 - 这是（由于__thread）threadsafe
{
m_minIntInitialized = true;
m_minInt = 100;
}

return m_minInt;
}


m_minIntInitialized 有保证为零。

在大多数情况下（ ELF规范 a>）它被放置到.tbss节，该节已被初始化。

对于C ++ - http://en.cppreference.com/w/cpp/language/initialization

对于所有其他非本地静态和线程局部变量，将执行Zero
初始化。在实践中，将变为零初始化的变量放置在程序
图像的.bss段中，该段在磁盘上不占用空间，并且被OS
清零当加载程序。

Possible Duplicate:
C++11 thread_local in gcc - alternatives
Is there any way to fully emulate thread_local using GCC's __thread?

I wanted to use the c++11 thread_local to create and use thread_local variable but as it is not yet supported by gcc, I am using gcc specific __thread. The way I declared the variable is

myClass
{
public:

  static __thread int64_t m_minInt;

};
__thread int64_t myClass::m_minInt = 100;

When I compile it, I get an error like

error: ‘myClass::minInt’ is thread-local and so cannot be dynamically initialized

How to properly do it?

PS: gcc version: 4.6.3

解决方案

You need to use lazy initialization.

myClass
{
public:

  static __thread int64_t m_minInt;
  static __thread bool m_minIntInitialized;

  static int64_t getMinInt();
};
__thread int64_t myClass::m_minInt;
__thread bool myClass::m_minIntInitialized;


int64_t myClass::getMinInt()
{
  if (!m_minIntInitialized)  // note - this is (due to __thread) threadsafe
  {
    m_minIntInitialized = true;
    m_minInt = 100;
  }

  return m_minInt;
}

m_minIntInitialized is guaranteed to be zero.

In most cases (ELF specification) it is placed to .tbss section, which is zero-initialized.

For C++ - http://en.cppreference.com/w/cpp/language/initialization

For all other non-local static and thread-local variables, Zero initialization takes place. In practice, variables that are going to be zero-initialized are placed in the .bss segment of the program image, which occupies no space on disk, and is zeroed out by the OS when loading the program.

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