|
|
|
GLib Reference Manual | |
|---|---|---|---|---|
Dynamic Loading of ModulesDynamic Loading of Modules — portable method for dynamically loading 'plug-ins'. |
#include <gmodule.h>
GModule;
gboolean g_module_supported (void);
gchar* g_module_build_path (const gchar *directory,
const gchar *module_name);
GModule* g_module_open (const gchar *file_name,
GModuleFlags flags);
enum GModuleFlags;
gboolean g_module_symbol (GModule *module,
const gchar *symbol_name,
gpointer *symbol);
const gchar* g_module_name (GModule *module);
void g_module_make_resident (GModule *module);
gboolean g_module_close (GModule *module);
const gchar* g_module_error (void);
const gchar* (*GModuleCheckInit) (GModule *module);
void (*GModuleUnload) (GModule *module);
#define G_MODULE_SUFFIX
#define G_MODULE_EXPORT
#define G_MODULE_IMPORT
These functions provide a portable way to dynamically load object files
(commonly known as 'plug-ins').
The current implementation supports all systems that provide
an implementation of dlopen() (e.g. Linux/Sun), as well as HP-UX via its
shl_load() mechanism, and Windows platforms via DLLs.
A program which wants to use these functions must be linked to the libraries output by the command pkg-config --libs gmodule-2.0.
To use them you must first determine whether dynamic loading
is supported on the platform by calling g_module_supported().
If it is, you can open a module with g_module_open(),
find the module's symbols (e.g. function names) with g_module_symbol(),
and later close the module with g_module_close().
g_module_name() will return the file name of a currently opened module.
If any of the above functions fail, the error status can be found with
g_module_error().
The GModule implementation features reference counting for opened modules, and supports hook functions within a module which are called when the module is loaded and unloaded (see GModuleCheckInit and GModuleUnload).
If your module introduces static data to common subsystems in the running
program, e.g. through calling g_quark_from_static_string ("my-module-stuff"),
it must ensure that it is never unloaded, by calling g_module_make_resident().
Example 13. Calling a function defined in a GModule
/* the function signature for 'say_hello' */
typedef void (* SayHelloFunc) (const char *message);
gboolean
just_say_hello (const char *filename, GError **error)
{
SayHelloFunc say_hello;
GModule *module;
module = g_module_open (filename, G_MODULE_BIND_LAZY);
if (!module)
{
g_set_error (error, FOO_ERROR, FOO_ERROR_BLAH,
"%s", g_module_error ());
return FALSE;
}
if (!g_module_symbol (module, "say_hello", (gpointer *)&say_hello))
{
g_set_error (error, SAY_ERROR, SAY_ERROR_OPEN,
"%s: %s", filename, g_module_error ());
if (!g_module_close (module))
g_warning ("%s: %s", filename, g_module_error ());
return FALSE;
}
if (say_hello == NULL)
{
g_set_error (error, SAY_ERROR, SAY_ERROR_OPEN, "symbol say_hello is NULL");
if (!g_module_close (module))
g_warning ("%s: %s", filename, g_module_error ());
return FALSE;
}
if (say_hello == NULL)
{
g_set_error (error, SAY_ERROR, SAY_ERROR_OPEN, "symbol say_hello is NULL");
if (!g_module_close (module))
g_warning ("%s: %s", filename, g_module_error ());
return FALSE;
}
/* call our function in the module */
say_hello ("Hello world!");
if (!g_module_close (module))
g_warning ("%s: %s", filename, g_module_error ());
return TRUE;
}
typedef struct _GModule GModule;
The GModule struct is an opaque data structure to represent a Dynamically-Loaded Module. It should only be accessed via the following functions.
gboolean g_module_supported (void);
Checks if modules are supported on the current platform.
| Returns : |
TRUE if modules are supported.
|
gchar* g_module_build_path (const gchar *directory, const gchar *module_name);
A portable way to build the filename of a module. The platform-specific prefix and suffix are added to the filename, if needed, and the result is added to the directory, using the correct separator character.
The directory should specify the directory where the module can be found.
It can be NULL or an empty string to indicate that the module is in a standard
platform-specific directory, though this is not recommended since the
wrong module may be found.
For example, calling g_module_build_path() on a Linux system with a directory
of /lib and a module_name of "mylibrary" will return
/lib/libmylibrary.so. On a Windows system, using
\Windows as the directory it will return
\Windows\mylibrary.dll.
directory : |
the directory where the module is. This can be NULL or the empty
string to indicate that the standard platform-specific directories will be
used, though that is not recommended.
|
module_name : |
the name of the module. |
| Returns : | the complete path of the module, including the standard library prefix and suffix. This should be freed when no longer needed. |
GModule* g_module_open (const gchar *file_name, GModuleFlags flags);
Opens a module. If the module has already been opened, its reference count is incremented.
First of all g_module_open() tries to open file_name as a module. If
that fails and file_name has the ".la"-suffix (and is a libtool archive)
it tries to open the corresponding module. If that fails and it doesn't
have the proper module suffix for the platform (G_MODULE_SUFFIX), this
suffix will be appended and the corresponding module will be opended. If
that fails and file_name doesn't have the ".la"-suffix, this suffix is
appended and g_module_open() tries to open the corresponding module. If
eventually that fails as well, NULL is returned.
file_name : |
the name of the file containing the module, or NULL to obtain
a GModule representing the main program itself.
|
flags : |
the flags used for opening the module. This can be the logical OR of any of the GModuleFlags. |
| Returns : | a GModule on success, or NULL on failure.
|
typedef enum
{
G_MODULE_BIND_LAZY = 1 << 0,
G_MODULE_BIND_LOCAL = 1 << 1,
G_MODULE_BIND_MASK = 0x03
} GModuleFlags;
Flags passed to g_module_open(). Note that these flags are
not supported on all platforms.
gboolean g_module_symbol (GModule *module, const gchar *symbol_name, gpointer *symbol);
Gets a symbol pointer from a module.
Note that a valid symbol can be NULL.
Note that a valid symbol can be NULL.
const gchar* g_module_name (GModule *module);
Gets the filename from a GModule.
module : |
a GModule. |
| Returns : | the filename of the module, or "main" if the module is the main program itself. |
void g_module_make_resident (GModule *module);
Ensures that a module will never be unloaded.
Any future g_module_close() calls on the module will be ignored.
module : |
a GModule to make permanently resident. |
const gchar* g_module_error (void);
Gets a string describing the last module error.
| Returns : | a string describing the last module error. |
const gchar* (*GModuleCheckInit) (GModule *module);
Specifies the type of the module initialization function.
If a module contains a function named g_module_check_init() it is called
automatically when the module is loaded. It is passed the GModule structure
and should return NULL on success or a string describing the initialization
error.
void (*GModuleUnload) (GModule *module);
Specifies the type of the module function called when it is unloaded.
If a module contains a function named g_module_unload() it is called
automatically when the module is unloaded.
It is passed the GModule structure.
module : |
the GModule about to be unloaded. |
#define G_MODULE_SUFFIX "so"
Expands to the proper shared library suffix for the current platform without the leading dot. For the most Unices and Linux this is "so", for some HP-UX versions this is "sl" and for Windows this is "dll".