4.2.7. __declspec(thread)
The __declspec(thread) attribute asserts that variables are thread‑local and have thread storage duration, so that the linker arranges for the storage to be allocated automatically when a thread is created.
Note
The keyword __thread is supported as a synonym for __declspec(thread).
File‑scope thread‑local variables cannot be dynamically initialized.
__declspec(thread) int i;
__thread int j; // same as __decspec(thread) int j;