HP-UX Linker and Libraries User's Guide

TOTAL SYMBOLS: 9
[/usr/lib/libc.1]
Imports:
_res_rmutex STORAGE
errno STORAGE
_regrpc_rmutex STORAGE
_yellowup_rmutex STORAGE
_FPU_MODEL STORAGE
_environ_rmutex STORAGE
_iop_rmutex STORAGE
_rpcnls_rmutex STORAGE
_switch_rmutex STORAGE
_mem_rmutex STORAGE
_dir_rmutex STORAGE
The shl_unload Routine
The shl_unload routine unloads or frees up space for a shared library.
Syntax
int shl_unload(shl_t handle)
Parameters
handle The handle of the shared library you wish to unload. The handle value is obtained from
a previous call to shl_load, shl_findsym, or shl_get.
Return Value
If successful, shl_unloadreturns 0. Otherwise, shl_unload returns -1 and sets errno to an
appropriate value: EINVAL Indicates the specified handle is invalid. ETXTBSY Indicates the
specified shared library is currently in use and hence cannot be unloaded. Read more
information.ENOENT Indicates the specified handle cannot be found.
Description
To unload a shared library, use the shl_unload function. One reason to do this is to free up the
private copy of shared library data and swap space allocated when the library was loaded with
shl_load. (This is done automatically when a process exits.)
Another reason for doing this occurs if a program needs to replace a shared library. For example,
suppose you implement some sort of shell or interpreter, and you want to load and execute user
“"programs"” which are actually shared libraries. So you load one program, look up its entry
point, and call it. Now you want to run a different program. If you do not unload the old one, its
symbol definitions may get in the way of the new library. So you must unload it before loading
the new library.
Note that if shared library initializers are declared for a shared library, they are called when the
shared library is explicitly unloaded. For details, see “Initializers for Shared Libraries” (page 138).
If unloading a C++ library, use thecxxshl_unload routine. This ensures that destructors of
nonlocal static objects are executed when the library is unloaded. The syntax of cxxshl_unload
is the same as that of shl_unload.
Usage
When a library is unloaded, existing linkages to symbols in an unloaded library are not invalidated.
Therefore, the programmer must ensure that the program does not reference symbols in an unloaded
library as undefined behavior can result. In general, this routine is recommended only for
experienced programmers.
182 Shared Library Management Routines