6 Basics [basic]

6.7 Memory and objects [basic.memobj]

6.7.5 Storage duration [basic.stc] Thread storage duration [basic.stc.thread]

All variables declared with the thread_­local keyword have thread storage duration.
The storage for these entities lasts for the duration of the thread in which they are created.
There is a distinct object or reference per thread, and use of the declared name refers to the entity associated with the current thread.
[Note 1:
A variable with thread storage duration is initialized as specified in [basic.start.static], [basic.start.dynamic], and [stmt.dcl] and, if constructed, is destroyed on thread exit ([basic.start.term]).
— end note]