Open System Services Library Calls Reference Manual (G06.29+, H06.08+, J06.03+)

dlclose(3) OSS Library Calls Reference Manual
NAME
dlclose - Invalidates a dynamic-link library handle and unloads any dynamically loaded library
LIBRARY
G-series native Guardian processes: $SYSTEM.SYSnn.ZRLDSRL
G-series native OSS processes: /G/system/sysnn/zrldsrl
H-series and J-series native Guardian processes: $SYSTEM.ZDLLnnn.ZRLDDLL
H-series and J-series OSS processes: /G/system/zdllnnn/zrlddll
SYNOPSIS
#include <dlfcn.h>
int dlclose (
dlHandle dlopen_handle );
PARAMETERS
dlopen_handle Specifies a currently valid library handle previously returned by a call to the
dlopen( ) function
DESCRIPTION
The dlclose( ) function invalidates the library handle designated by the dlopen_handle value. It
unloads any libraries that are no longer required.
In the simplest case, dlclose( ) unloads any library loaded by the dlopen( ) invocation that
returned the destroyed library handle. When there are linkages between libraries loaded by
separate dlopen( ) calls, a library loaded by one call might be required by a library loaded by
another call, and might be unloaded by a subsequent call to dlclose( ) specifying another library
handle.
dlclose( ) does not unload the main program or libraries that were loaded with the main program.
When dlclose( ) invalidates a library handle, it decrements the usage count for the library loaded
by the dlopen( ) invocation that returned the destroyed handle, and for any libraries that library
required. dlclose() unloads any dynamically loaded libraries that have become unused.
Once a library has been unloaded by dlclose(), referencing addresses where the library text and
data were loaded results in undefined behavior.
NOTES
The rld dynamic loader is an unprivileged interface; it cannot be invoked from a program or
DLL that is licensed or has callable functions, or from a program with a priv entry point. Process
creation fails if such a file refers to dlopen( ), dlsym( ), dlclose( ), dlerror( ),ordlresultcode( ).
Depending upon the circumstances, process-creation error/detail value combinations of 77,11 or
78,7 can result.
EXAMPLES
Suppose that library A requires library C (because C is specified on the libList of A). Suppose
that library B also requires library C. Consider the following program:
hA = dlopen("A", ...); // loads A and C; links A to C.
hB = dlopen("B", ...); // loads B; links B to already-loaded C
if (perverse) { // close in order of opening
dlclose(hA); // unloads A but not C
dlclose(hB); // unloads B and C
}
else { // close in inverse order of opening
dlclose(hB); // unloads B
dlclose(hA); // unloads A and C
}
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