Description

glib-genmarshal is a small utility that generates C code marshallers for callback functions of the GClosure mechanism in the GObject sublibrary of GLib. The marshaller functions have a standard signature, they get passed in the invoking closure, an array of value structures holding the callback function parameters and a value structure for the return value of the callback. The marshaller is then responsible to call the respective C code function of the closure with all the parameters on the stack and to collect its return value.

glib-genmarshal takes a list of marshallers to generate as input. The marshaller list is either read from files passed as additional arguments on the command line; or from standard input, by using - as the input file.

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Options

Using glib-genmarshal with Meson

Meson supports generating closure marshallers using glib-genmarshal out of the box in its "gnome" module.

In your meson.build file you will typically call the gnome.genmarshal() method with the source list of marshallers to generate:

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gnome = import('gnome')
marshal_files = gnome.genmarshal('marshal',
  sources: 'marshal.list',
  internal: true,
)

The marshal_files variable will contain an array of two elements in the following order:

You should use the returned objects to provide a dependency on every other build target that references the source or header file; for instance, if you are using the source to build a library:

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mainlib = library('project',
  sources: project_sources + marshal_files,
  ...
)

Additionally, if you are including the generated header file inside a build target that depends on the library you just built, you must ensure that the internal dependency includes the generated header as a required source file:

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mainlib_dep = declare_dependency(sources: marshal_files[1], link_with: mainlib)

You should not include the generated source file as well, otherwise it will be built separately for every target that depends on it, causing build failures. To know more about why all this is required, please refer to the corresponding Meson FAQ entry.

For more information on how to use the method, see the Meson documentation for gnome.genmarshal().

Using glib-genmarshal with Autotools

In order to use glib-genmarshal in your project when using Autotools as the build system, you will first need to modify your configure.ac file to ensure you find the appropriate command using pkg-config, similarly as to how you discover the compiler and linker flags for GLib.

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PKG_PROG_PKG_CONFIG([0.28])

PKG_CHECK_VAR([GLIB_GENMARSHAL], [glib-2.0], [glib_genmarshal])

In your Makefile.am file you will typically need very simple rules to generate the C files needed for the build.

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marshal.h: marshal.list
        $(AM_V_GEN)$(GLIB_GENMARSHAL) \
                --header \
                --output=$@ \
                $<

marshal.c: marshal.list marshal.h
        $(AM_V_GEN)$(GLIB_GENMARSHAL) \
                --include-header=marshal.h \
                --body \
                --output=$@ \
                $<

BUILT_SOURCES += marshal.h marshal.c
CLEANFILES += marshal.h marshal.c
EXTRA_DIST += marshal.list

In the example above, the first rule generates the header file and depends on a marshal.list file in order to regenerate the result in case the marshallers list is updated. The second rule generates the source file for the same marshal.list, and includes the file generated by the header rule.

Example

To generate marshallers for the following callback functions:

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void   foo (gpointer data1,
            gpointer data2);
void   bar (gpointer data1,
            gint     param1,
            gpointer data2);
gfloat baz (gpointer data1,
            gboolean param1,
            guchar   param2,
            gpointer data2);

The marshaller.list file has to look like this:

VOID:VOID
VOID:INT
FLOAT:BOOLEAN,UCHAR

and you call glib-genmarshal like this:

glib-genmarshal --header marshaller.list > marshaller.h
glib-genmarshal --body marshaller.list > marshaller.c

The generated marshallers have the arguments encoded in their function name. For this particular list, they are

g_cclosure_user_marshal_VOID__VOID(...),
g_cclosure_user_marshal_VOID__INT(...),
g_cclosure_user_marshal_FLOAT__BOOLEAN_UCHAR(...).

They can be used directly for GClosures or be passed in as the GSignalCMarshaller c_marshaller; argument upon creation of signals:

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GClosure *cc_foo, *cc_bar, *cc_baz;

cc_foo = g_cclosure_new (NULL, foo, NULL);
g_closure_set_marshal (cc_foo, g_cclosure_user_marshal_VOID__VOID);
cc_bar = g_cclosure_new (NULL, bar, NULL);
g_closure_set_marshal (cc_bar, g_cclosure_user_marshal_VOID__INT);
cc_baz = g_cclosure_new (NULL, baz, NULL);
g_closure_set_marshal (cc_baz, g_cclosure_user_marshal_FLOAT__BOOLEAN_UCHAR);

See also

glib-mkenums(1)