DLCLOSE(3C) Standard C Library Functions DLCLOSE(3C)

NAME

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(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO

ld(1), ld.so.1(1), atexit(3C), dladdr(3C), dldump(3C), dlerror(3C),
dlopen(3C), dlsym(3C), attributes(7), standards(7)


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).

March 1, 2004 DLCLOSE(3C)