dlclose (3p) - Linux Manuals

dlclose: close a dlopen object

PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

dlclose - close a dlopen object

SYNOPSIS

#include <dlfcn.h>

int dlclose(void *handle);

DESCRIPTION

The dlclose() function shall inform the system that the object referenced by a handle returned from a previous dlopen() invocation is no longer needed by the application.

The use of dlclose() reflects a statement of intent on the part of the process, but does not create any requirement upon the implementation, such as removal of the code or symbols referenced by handle. Once an object has been closed using dlclose() an application should assume that its symbols are no longer available to dlsym(). All objects loaded automatically as a result of invoking dlopen() on the referenced object shall also be closed if this is the last reference to it.

Although a dlclose() operation is not required to remove structures from an address space, neither is an implementation prohibited from doing so. The only restriction on such a removal is that no object shall be removed to which references have been relocated, until or unless all such references are removed. For instance, an object that had been loaded with a dlopen() operation specifying the RTLD_GLOBAL flag might provide a target for dynamic relocations performed in the processing of other objects-in such environments, an application may assume that no relocation, once made, shall be undone or remade unless the object requiring the relocation has itself been removed.

RETURN VALUE

If the referenced object was successfully closed, dlclose() shall return 0. If the object could not be closed, or if handle does not refer to an open object, dlclose() shall return a non-zero value. More detailed diagnostic information shall be available through dlerror().

ERRORS

No errors are defined.

The following sections are informative.

EXAMPLES

The following example illustrates use of dlopen() and dlclose():

...
/* Open a dynamic library and then close it ... */


#include <dlfcn.h>
void *mylib;
int eret;


mylib = dlopen("mylib.so", RTLD_LOCAL | RTLD_LAZY);
...
eret = dlclose(mylib);
...

APPLICATION USAGE

A conforming application should employ a handle returned from a dlopen() invocation only within a given scope bracketed by the dlopen() and dlclose() operations. Implementations are free to use reference counting or other techniques such that multiple calls to dlopen() referencing the same object may return the same object for handle. Implementations are also free to reuse a handle. For these reasons, the value of a handle must be treated as an opaque object by the application, used only in calls to dlsym() and dlclose().

RATIONALE

None.

FUTURE DIRECTIONS

None.

COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .