When exactly is a thread_local variable declared at global scope initialized?

Question

For example:

#include <thread> thread_local int n = 1; void f() { ++n; // is n initialized here for each thread or prior to entering f()? } int main() { std::thread ta(f); std::thread tb(f); ta.join(); tb.join(); }

It's still not entirely clear from here when is n initialized.

It does look confusing a bit. What's local is the storage for n for each thread. But the scope of n (i.e. its visibility in code) is global. — Leo Heinsaar
– Leo Heinsaar, Commented Feb 19, 2016 at 16:04
The initialization itself takes place as the answers (here and in the linked question) describe: before its use. When exactly? Not specified by the standard. — Leo Heinsaar
– Leo Heinsaar, Commented Feb 19, 2016 at 16:10

SergeyA · Accepted Answer · 2016-02-19 14:58:12Z

Simple enough, and all according to specification. n is going to be initialized whenever the new thread is run - before you enter any thread-specific functions.

To be exact, it is going to be initialized three times.

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