Question or issue on macOS:
I have a dynamic library which I load using dlopen() and then unload using dlclose();
If I dont include any objective c code dlopen() needs one dlclose() call which is expected behavior. But when I include any objective c code to target, I have problem that I need to do two dlclose() calls to the loaded library in order to unload.
Is this something expected behavior? How can I fix it?
How to solve this problem?
I realize that you are using dlopen, not CFBundle or NSBundle. Nevertheless, the Code Loading Programming Topics manual says this:
In Cocoa applications, you should not use CFBundle routines to load and unload executable code, because CFBundle does not natively support the Objective-C runtime. NSBundle correctly loads Objective-C symbols into the runtime system, but there is no way to unload Cocoa bundles once loaded due to a runtime limitation.
and this:
Because of a limitation in the Objective-C runtime system, NSBundle cannot unload executable code.
This makes me suspect that when you load your library, it registers itself with the Objective-C runtime, and the runtime calls dlopen on the library again (or somehow increases the library’s reference count).
I searched the Objective-C runtime source code and found this:
// dylibs are not allowed to unload // ...except those with image_info and nothing else (5359412) if (result->mhdr->filetype == MH_DYLIB && _hasObjcContents(result)) { dlopen(result->os.dl_info.dli_fname, RTLD_NOLOAD); }
So yes, the Objective-C runtime is calling dlopen on your library specifically to prevent it from being unloaded. If you cheat and call dlclose twice, you should expect bad things to happen.
