Local variables in C++ and thread safety

Question

Are automatic variables (that are defined in functions, lambdas, blocks) in C++11 thread local? Is the following code correct:

auto f1 = [
 SomeClass1 obj1;
 double z = obj1.f2(y);
 return cos(z);
}

// Some function which creates several threads which call f1.
calculate_parallel(f1);

Answer 1

This should be okay, provided that sin, cos are indeed the global functions and that SomeClass1 does not touch global state in a non-thread-safe way. You might want to use [] instead of [&], though.

Answer 2

"thread local" has a specific meaning and refers to objects declared thread_local, which have "thread storage duration", which means storage for the variables lasts as long as the thread is running.

Automatic variables have "automatic storage duration" instead, which means they are on the stack of the calling thread and their storage only lasts until exit from the block in which they are created.