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.