Syntax:
The /reentrancy or /reentrancy:threads option requests that the compiler generate reentrant code that supports a multithreaded application. In the visual development environment, specify the Enable Reentrancy Support or Disable Reentrancy Support in the Libraries Compiler Option Category.
If you omit /reentrancy, /reentrancy:threads, or /threads, /reentrancy:none (same as /noreentrancy) is used.
Specifying /threads sets /reentrancy:threads, since multithreaded code must be reentrant.