Question

I read that there was a new keyword in C++: it’s __thread from what I’ve read.

All I know is that it’s a keyword to be used like the static keyword but I know nothing else. Does this keyword just mean that, for instance, if a variable were declared like so:

__thread int foo;

then anything to do with that variable will be executed with a new thread?

Answer 1

It’s thread_local, not __thread. It’s used to define variables which has storage duration of the thread.

thread_local is a new storage duration specifier added in C++0x. There are other storage duration : static, automatic and dynamic.

From this link:

thread local storage duration (C++11 feature). The variable is allocated when the thread begins and deallocated when the thread ends. Each thread has its own instance of the variable. Only variables declared thread_local have this storage duration.

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I think the introduction of this keyword was made possible by introducing a standardized memory model in C++0x:

• C++11 introduced a standardized memory model. What does it mean? And how is it going to affect C++ programming?