NAME
ggGetScope, ggFromScope, ggDelScope, ggNewScope - Portable code module
loading facilities
SYNOPSIS
#include <ggi/gg.h>
gg_scope ggGetScope(const char *location);
void ggDelScope(gg_scope scope);
void *ggFromScope(gg_scope, const char *symbol);
typedef void *(*ggfunc_scope_get)(void * handle, const char * symbol);
typedef void (*ggfunc_scope_del)(void * handle);
gg_scope ggNewScope(const char * location, void * handle,
ggfunc_scope_get get, ggfunc_scope_del del)
DESCRIPTION
LibGG abstracts dynamic code loading (and emulates dynamic code loading
for statically linked embedded binaries) through a simple API which
represents the very lowest level required of any loadable module
system. The actual underlying mechanisms used in various operating
systems to load additional code into an application on demand vary
drastically, however, minus OS-specific frills, they can all be mapped
to the above three LibGG API functions.
ggGetScope finds a loadable collection of symbols known by its location
through whatever system is available on the operating system. Those
symbols were once supposed to be code from modules, but the scope
abstraction does not impose this restriction. The scopes can have
different implementations and are not restricted to dynamic libraries.
They could also be used as an interface to a attribute/value
configuration system.
Note that when a scope happens to be dynamic library, the symbols are
loaded into the address space of the caller, but libgg does not
guarantee that the imported symbols will be seen by other modules.
ggDelScope unloads the symbol collection represented by the handle
scope, which must have been previously loaded with ggGetScope (scope
should be a return value from a previous call to ggGetScope.)
Reference counts are kept to ensure that redundantly loaded symbol
collections are not discarded until their last owner releases them.
Calling ggDelScope on a handle too many times, or on an invalid handle,
may produce undefined results. Accessing symbols after the collections
they were contained in are unloaded will produce undesirable and
undefined results.
ggFromScope searches the symbol collection represented by the handle
scope, which has been loaded with ggGetScope (and not yet unloaded with
ggDelScope, of course) for a symbol named symbol, so that the
application may use the item associated with the symbol. The parameter
scope should be a return value from a previous call to ggDelScope. As
ggFromScope may have no way of knowing what the symbol represents, the
application must take the responsibility for assigning the item a
correct C type.
ggNewScope allows to register a custom scope to libgg. The primary
purpose is to allow libraries to provide builtin modules that are
accessible through the same interface as dynamic ones. location is the
string at which the scope can be retreived. handle is a opaque pointer
provided by the caller that will be passed to the callbacks. get is a
function that take an opaque handle, a symbol name, and that must
return the requested symbol address, or NULL if not found. del is a
function that will take the provided handler, and that must cleanup
everything before the scope is removed from the scope registry. This
scheme allows to implement all kind of scopes in a very flexible way.
Note that ggNewScope will take a reference on the scope.
RETURN VALUE
On success, ggGetScope returns an opaque pointer to a handle
representing a newly loaded symbol collection (which must be retained
in order to use or free the collection.) These pointers are not
guaranteed to be unique. On failure, ggGetScope returns NULL.
ggFromScope returns the address of the item that the named symbol
represents, if it has been loaded into the caller’s address space.
Otherwise it returns NULL. Note that the value associated to a symbol
really depends on the scope itself and the caller must know what is
behind it. So a NULL value does not necessarily means failure. It could
be a valid value for a specific scope.
ggNewScope returns an opaque pointer to a handle representing the
custom scope. On failure, ggNewScope returns NULL.