Not thread-safe about dlfcn-win32

[TimothyGu]

@wm4 said:

For some reason, library handles are cached (why?), using a global linked list.

They are cached only when RTLD_GLOBAL is specified in dlopen, as POSIX mandates:

Any object loaded by dlopen() that requires relocations against global symbols can reference [...] any objects that were loaded in any dlopen() invocation and which specified the RTLD_GLOBAL flag.

This makes the exported functions unsafe to use in a multithreaded setting.

We never said this project is thread-safe. In fact, in dlfcn.c we specifically said that:

/* Note:
 * MSDN says these functions are not thread-safe. We make no efforts to have
 * any kind of thread safety.
 */

(Can't seem to find the MSDN page right now but I swear I saw somewhere that they are not thread-safe)

Also, POSIX doesn't say that the functions have to be thread safe anyway.