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
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.