* Each thread, on thread attach in DllMain(), allocates its thread-local
* data and uses this index with TlsSetValue() to store it.
* It can then subsequently be retrieved with TlsGetValue().
* Each thread, on thread attach in DllMain(), allocates its thread-local
* data and uses this index with TlsSetValue() to store it.
* It can then subsequently be retrieved with TlsGetValue().