Multithreading usually means that threads share the address space and so can (inadvertently) stomp on each other's "errno". (Hence making it Thread-Local Storag

Multithreading usually means that threads share the address space and so can (inadvertently) stomp on each other's "errno". (Hence making it Thread-Local Storage to solve that issue. Doesn't solve the reentrancy issue, though.) If multithreading were pervasive nobody in their right mind would choose to use a global variable for error status codes.