dlclose

- close a shared object

Synopsis

#include <dlfcn.h>

int dlclose(void *handle);

Description

The dlclose() function decrements the reference count of the supplied handle. This handle represents an executable object file and its dependencies, acquired from a previous call to dlopen(). A handle that is no longer referenced is processed in an attempt to unload any objects that are associated with the handle from the current process. An unreferenced handle is no longer available to dlsym().

Any finalization code within an object is executed prior to that object being unloaded. Any routines registered by an object using atexit(3C) are called prior to that object being unloaded. See NOTES.

Return Values

If the handle was successfully unreferenced, dlclose() returns 0. If the handle is invalid, or an error occurred as a result of unloading an object, dlclose() returns a non-zero value. Additional diagnostic information is available through dlerror().

Usage

The dlclose() function is one of a family of functions that give the user direct access to the dynamic linking facilities. These facilities are available to dynamically-linked processes only. See the Linker and Libraries Guide.

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

ld(1), ld.so.1(1), atexit(3C), dladdr(3C), dldump(3C), dlerror(3C), dlopen(3C), dlsym(3C), attributes(5), standards(5)

Linker and Libraries Guide

Notes

A successful invocation of dlclose() does not guarantee that the objects associated with the handle are removed from the address space of the current process. Objects can be referenced by multiple handles, or by other objects. An object is not removed from the address space of the current process until all references to that object are removed.

Once an object has been closed by dlclose(), referencing symbols contained in that object can cause undefined behavior.

As part of unloading an object, finalization code within the object is called before the dlclose() returns. This finalization is user code, and as such, can produce errors that can not be caught by dlclose(). For example, an object loaded using RTLD_LAZY that attempts to call a function that can not be located, results in process termination. Erroneous programming practices within the finalization code can also result in process termination. The runtime linkers debugging facility can offer help identifying these types of error. See the LD_DEBUG environment variable of ld.so.1(1).