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93 lines
2.7 KiB
Markdown
93 lines
2.7 KiB
Markdown
Title: Dynamic Loading of Modules
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## Dynamic Loading of Modules
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These functions provide a portable way to dynamically load object files
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(commonly known as 'plug-ins'). The current implementation supports all
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systems that provide an implementation of `dlopen()` (e.g. Linux/Sun), as
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well as Windows platforms via DLLs.
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A program which wants to use these functions must be linked to the libraries
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output by the command:
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pkg-config --libs gmodule-2.0
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To use them you must first determine whether dynamic loading is supported on
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the platform by calling [`func@GModule.Module.supported`]. If it is, you can
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open a module with [`func@GModule.Module.open`], find the module's symbols
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(e.g. function names) with [`method@GModule.Module.symbol`], and later close
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the module with [`method@GModule.Module.close`].
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[`method@GModule.Module.name`] will return the file name of a currently
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opened module.
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If any of the above functions fail, the error status can be found with
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[`func@GModule.Module.error`].
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The `GModule` implementation features reference counting for opened modules,
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and supports hook functions within a module which are called when the module
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is loaded and unloaded (see [callback@GModule.ModuleCheckInit] and
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[callback@GModule.ModuleUnload]).
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If your module introduces static data to common subsystems in the running
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program, e.g. through calling API like:
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```c
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static GQuark my_module_quark =
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g_quark_from_static_string ("my-module-stuff");
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```
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it must ensure that it is never unloaded, by calling
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[`method@GModule.Module.make_resident`].
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### Calling a function defined in a GModule
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```c
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// the function signature for 'say_hello'
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typedef void (* SayHelloFunc) (const char *message);
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gboolean
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just_say_hello (const char *filename, GError **error)
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{
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SayHelloFunc say_hello;
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GModule *module;
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module = g_module_open (filename, G_MODULE_BIND_LAZY);
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if (module == NULL)
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{
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g_set_error (error, FOO_ERROR, FOO_ERROR_BLAH,
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"%s", g_module_error ());
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return FALSE;
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}
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if (!g_module_symbol (module, "say_hello", (gpointer *)&say_hello))
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{
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g_set_error (error, SAY_ERROR, SAY_ERROR_OPEN,
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"%s: %s", filename, g_module_error ());
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if (!g_module_close (module))
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g_warning ("%s: %s", filename, g_module_error ());
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return FALSE;
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}
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if (say_hello == NULL)
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{
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g_set_error (error, SAY_ERROR, SAY_ERROR_OPEN,
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"symbol say_hello is NULL");
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if (!g_module_close (module))
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g_warning ("%s: %s", filename, g_module_error ());
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return FALSE;
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}
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// call our function in the module
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say_hello ("Hello world!");
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if (!g_module_close (module))
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g_warning ("%s: %s", filename, g_module_error ());
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return TRUE;
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}
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```
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