The standard libraries on Windows don't involve libc. The Windows APIs look rather different, and in general are much more friendly to multi-threading. POSIX on

The standard libraries on Windows don't involve libc. The Windows APIs look rather different, and in general are much more friendly to multi-threading. POSIX on the other hand tends to assume that the program is in control of everything happening inside of it, which is an incorrect assumption due to libraries. In this particular case, the Windows APIs have neither getaddrinfo() nor getenv(); and the closest equivalent GetEnvironmentVariableW is perfectly thread-safe. Microsoft additionally has a C runtime (msvcrt) providing functions like getenv(), but this is much less fundamental than it is on other system. Every program is supposed to ship its own copy of the C runtime, it's not officially part of Windows! And it's perfectly possible for multiple different copies of the C runtime to be loaded into the same Windows process. And since *environ is a variable defined by the C runtime, there's a different copy for each C runtime...