C++: dlclose doesn't unload the shared library

c++ shared dlopen
Ben picture Ben · Jan 9, 2012 · Viewed 7.3k times · Source

I have a shared library loaded using dlopen (with the flags RTLD_NOW | RTLD_GLOBAL ). If this library is using functions from the main program, then it does not unload. So I end up with the same code for this shared lib, even if I unloaded (using dlclose), changed, compiled, (re)load it.

My goal is actually to reload the same library after making changes to it, so that I do not have to relaunch the whole program to test out my code.

I am using g++ 4.2.3, on Linux Ubuntu 10.04.

(edit)

solved:

"loaded library uses a symbol due to the RTLD_GLOBAL". Indeed, I had symbols of another .a embedded when linking that were probably called back and preventing my library to close... I think it's possible to verify that a lib unloaded using dlopen(...,RTLD_NOLOAD) to check out the library has unloaded correctly.

Answer

cateof picture cateof · Jan 9, 2012

The function dlclose() decrements the reference count on the dynamic library handle. If the reference count drops to zero and no other loaded libraries use symbols in it, then the dynamic library is unloaded.

Also the RTLD_NODELETE (upon dlopen) makes dlclose not to unload the library.

Since you have not used RTLD_NODELETE, most probable is that a loaded library uses a symbol due to the RTLD_GLOBAL.

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