Closures

## Closures Closures — Functions as first-class objects |

## Synopsis

    #include <glib-object.h>

    #define             G_CLOSURE_NEEDS_MARSHAL             (closure)
    #define             G_CLOSURE_N_NOTIFIERS               (cl)
    #define             G_CCLOSURE_SWAP_DATA                (cclosure)
    #define             G_CALLBACK                          (f)
    void                (*GCallback)                        (void);
    struct              GClosure;
    #define             G_TYPE_CLOSURE
    struct              GCClosure;
    void                (*GClosureMarshal)                  (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                (*GClosureNotify)                   (gpointer data,
                                                             GClosure *closure);
    GClosure *          g_cclosure_new                      (GCallback callback_func,
                                                             gpointer user_data,
                                                             GClosureNotify destroy_data);
    GClosure *          g_cclosure_new_swap                 (GCallback callback_func,
                                                             gpointer user_data,
                                                             GClosureNotify destroy_data);
    GClosure *          g_cclosure_new_object               (GCallback callback_func,
                                                             GObject *object);
    GClosure *          g_cclosure_new_object_swap          (GCallback callback_func,
                                                             GObject *object);
    void                g_cclosure_marshal_generic          (GClosure *closure,
                                                             GValue *return_gvalue,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    GClosure *          g_closure_new_object                (guint sizeof_closure,
                                                             GObject *object);
    GClosure *          g_closure_ref                       (GClosure *closure);
    void                g_closure_sink                      (GClosure *closure);
    void                g_closure_unref                     (GClosure *closure);
    void                g_closure_invoke                    (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint);
    void                g_closure_invalidate                (GClosure *closure);
    void                g_closure_add_finalize_notifier     (GClosure *closure,
                                                             gpointer notify_data,
                                                             GClosureNotify notify_func);
    void                g_closure_add_invalidate_notifier   (GClosure *closure,
                                                             gpointer notify_data,
                                                             GClosureNotify notify_func);
    void                g_closure_remove_finalize_notifier  (GClosure *closure,
                                                             gpointer notify_data,
                                                             GClosureNotify notify_func);
    void                g_closure_remove_invalidate_notifier
                                                            (GClosure *closure,
                                                             gpointer notify_data,
                                                             GClosureNotify notify_func);
    GClosure *          g_closure_new_simple                (guint sizeof_closure,
                                                             gpointer data);
    void                g_closure_set_marshal               (GClosure *closure,
                                                             GClosureMarshal marshal);
    void                g_closure_add_marshal_guards        (GClosure *closure,
                                                             gpointer pre_marshal_data,
                                                             GClosureNotify pre_marshal_notify,
                                                             gpointer post_marshal_data,
                                                             GClosureNotify post_marshal_notify);
    void                g_closure_set_meta_marshal          (GClosure *closure,
                                                             gpointer marshal_data,
                                                             GClosureMarshal meta_marshal);
    void                g_source_set_closure                (GSource *source,
                                                             GClosure *closure);
    void                g_source_set_dummy_callback         (GSource *source);

    void                g_cclosure_marshal_VOID__VOID       (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__BOOLEAN    (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__CHAR       (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__UCHAR      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__INT        (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__UINT       (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__LONG       (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__ULONG      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__ENUM       (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__FLAGS      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__FLOAT      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__DOUBLE     (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__STRING     (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__PARAM      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__BOXED      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__POINTER    (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__OBJECT     (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__VARIANT    (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_STRING__OBJECT_POINTER
                                                            (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_VOID__UINT_POINTER
                                                            (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    void                g_cclosure_marshal_BOOLEAN__FLAGS   (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    #define             g_cclosure_marshal_BOOL__FLAGS
    void                g_cclosure_marshal_BOOLEAN__BOXED_BOXED
                                                            (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);
    #define             g_cclosure_marshal_BOOL__BOXED_BOXED

## Description

A GClosure represents a callback supplied by the programmer. It will generally comprise a function of some kind and a marshaller used to call it. It is the reponsibility of the marshaller to convert the arguments for the invocation from GValues into a suitable form, perform the callback on the converted arguments, and transform the return value back into a GValue.

In the case of C programs, a closure usually just holds a pointer to a function and maybe a data argument, and the marshaller converts between GValue and native C types. The GObject library provides the GCClosure type for this purpose. Bindings for other languages need marshallers which convert between GValues and suitable representations in the runtime of the language in order to use functions written in that languages as callbacks.

Within GObject, closures play an important role in the implementation of signals. When a signal is registered, the `c_marshaller` argument to `g_signal_new()` specifies the default C marshaller for any closure which is connected to this signal. GObject provides a number of C marshallers for this purpose, see the g_cclosure_marshal_*() functions. Additional C marshallers can be generated with the glib-genmarshal utility. Closures can be explicitly connected to signals with `g_signal_connect_closure()`, but it usually more convenient to let GObject create a closure automatically by using one of the g_signal_connect_*() functions which take a callback function/user data pair.

Using closures has a number of important advantages over a simple callback function/data pointer combination:

- Closures allow the callee to get the types of the callback parameters, which means that language bindings don't have to write individual glue for each callback type.

- The reference counting of GClosure makes it easy to handle reentrancy right; if a callback is removed while it is being invoked, the closure and its parameters won't be freed until the invocation finishes.

- `g_closure_invalidate()` and invalidation notifiers allow callbacks to be automatically removed when the objects they point to go away.

## Details

### G_CLOSURE_NEEDS_MARSHAL()

    #define G_CLOSURE_NEEDS_MARSHAL(closure) (((GClosure*) (closure))->marshal == NULL)

Check if the closure still needs a marshaller. See `g_closure_set_marshal()`.

`closure` : | a GClosure
Returns : | `TRUE` if a GClosureMarshal marshaller has not yet been set on `closure`.

### G_CLOSURE_N_NOTIFIERS()

    #define             G_CLOSURE_N_NOTIFIERS(cl)

Get the total number of notifiers connected with the closure `cl`. The count includes the meta marshaller, the finalize and invalidate notifiers and the marshal guards. Note that each guard counts as two notifiers. See `g_closure_set_meta_marshal()`, `g_closure_add_finalize_notifier()`, `g_closure_add_invalidate_notifier()` and `g_closure_add_marshal_guards()`.

`cl` : | a GClosure
Returns : | number of notifiers

### G_CCLOSURE_SWAP_DATA()

    #define G_CCLOSURE_SWAP_DATA(cclosure)	 (((GClosure*) (cclosure))->derivative_flag)

Checks whether the user data of the GCClosure should be passed as the first parameter to the callback. See `g_cclosure_new_swap()`.

`cclosure` : | a GCClosure
Returns : | `TRUE` if data has to be swapped.

### G_CALLBACK()

    #define G_CALLBACK(f)			 ((GCallback) (f))

Cast a function pointer to a GCallback.

`f` : | a function pointer.

### GCallback ()

    void                (*GCallback)                        (void);

The type used for callback functions in structure definitions and function signatures. This doesn't mean that all callback functions must take no parameters and return void. The required signature of a callback function is determined by the context in which is used (e.g. the signal to which it is connected). Use `G_CALLBACK()` to cast the callback function to a GCallback.

### struct GClosure

    struct GClosure {
      volatile       	guint	 in_marshal : 1;
      volatile       	guint	 is_invalid : 1;
    };

A GClosure represents a callback supplied by the programmer.

volatile guint `in_marshal` : 1; | Indicates whether the closure is currently being invoked with `g_closure_invoke()`
volatile guint `is_invalid` : 1; | Indicates whether the closure has been invalidated by `g_closure_invalidate()`

### G_TYPE_CLOSURE

    #define G_TYPE_CLOSURE (g_closure_get_type ())

The GType for GClosure.

### struct GCClosure

    struct GCClosure {
      GClosure closure;
      gpointer callback;
    };

A GCClosure is a specialization of GClosure for C function callbacks.

GClosure `closure`; | the GClosure
gpointer `callback`; | the callback function

### GClosureMarshal ()

    void                (*GClosureMarshal)                  (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

The type used for marshaller functions.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | a GValue to store the return value. May be `NULL` if the callback of `closure` doesn't return a value. [allow-none]
`n_param_values` : | the length of the `param_values` array
`param_values` : | an array of GValues holding the arguments on which to invoke the callback of `closure`. [array length=n_param_values]
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`. [allow-none]
`marshal_data` : | additional data specified when registering the marshaller, see `g_closure_set_marshal()` and `g_closure_set_meta_marshal()`. [allow-none]

### GClosureNotify ()

    void                (*GClosureNotify)                   (gpointer data,
                                                             GClosure *closure);

The type used for the various notification callbacks which can be registered on closures.

`data` : | data specified when registering the notification callback
`closure` : | the GClosure on which the notification is emitted

### g_cclosure_new ()

    GClosure *          g_cclosure_new                      (GCallback callback_func,
                                                             gpointer user_data,
                                                             GClosureNotify destroy_data);

Creates a new closure which invokes `callback_func` with `user_data` as the last parameter.

`callback_func` : | the function to invoke
`user_data` : | user data to pass to `callback_func`
`destroy_data` : | destroy notify to be called when `user_data` is no longer used
Returns : | a new GCClosure

### g_cclosure_new_swap ()

    GClosure *          g_cclosure_new_swap                 (GCallback callback_func,
                                                             gpointer user_data,
                                                             GClosureNotify destroy_data);

Creates a new closure which invokes `callback_func` with `user_data` as the first parameter.

`callback_func` : | the function to invoke
`user_data` : | user data to pass to `callback_func`
`destroy_data` : | destroy notify to be called when `user_data` is no longer used
Returns : | a new GCClosure. [transfer full]

### g_cclosure_new_object ()

    GClosure *          g_cclosure_new_object               (GCallback callback_func,
                                                             GObject *object);

A variant of `g_cclosure_new()` which uses `object` as `user_data` and calls `g_object_watch_closure()` on `object` and the created closure. This function is useful when you have a callback closely associated with a GObject, and want the callback to no longer run after the object is is freed.

`callback_func` : | the function to invoke
`object` : | a GObject pointer to pass to `callback_func`
Returns : | a new GCClosure

### g_cclosure_new_object_swap ()

    GClosure *          g_cclosure_new_object_swap          (GCallback callback_func,
                                                             GObject *object);

A variant of `g_cclosure_new_swap()` which uses `object` as `user_data` and calls `g_object_watch_closure()` on `object` and the created closure. This function is useful when you have a callback closely associated with a GObject, and want the callback to no longer run after the object is is freed.

`callback_func` : | the function to invoke
`object` : | a GObject pointer to pass to `callback_func`
Returns : | a new GCClosure

### g_cclosure_marshal_generic ()

    void                g_cclosure_marshal_generic          (GClosure *closure,
                                                             GValue *return_gvalue,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A generic marshaller function implemented via libffi.

`closure` : | A GClosure.
`return_gvalue` : | A GValue to store the return value. May be `NULL` if the callback of closure doesn't return a value.
`n_param_values` : | The length of the `param_values` array.
`param_values` : | An array of GValues holding the arguments on which to invoke the callback of closure.
`invocation_hint` : | The invocation hint given as the last argument to `g_closure_invoke()`.
`marshal_data` : | Additional data specified when registering the marshaller, see `g_closure_set_marshal()` and `g_closure_set_meta_marshal()`

Since 2.30

### g_closure_new_object ()

    GClosure *          g_closure_new_object                (guint sizeof_closure,
                                                             GObject *object);

A variant of `g_closure_new_simple()` which stores `object` in the `data` field of the closure and calls `g_object_watch_closure()` on `object` and the created closure. This function is mainly useful when implementing new types of closures.

`sizeof_closure` : | the size of the structure to allocate, must be at least `sizeof (GClosure)`
`object` : | a GObject pointer to store in the `data` field of the newly allocated GClosure
Returns : | a newly allocated GClosure. [transfer full]

### g_closure_ref ()

    GClosure *          g_closure_ref                       (GClosure *closure);

Increments the reference count on a closure to force it staying alive while the caller holds a pointer to it.

`closure` : | GClosure to increment the reference count on
Returns : | The `closure` passed in, for convenience. [transfer none]

### g_closure_sink ()

    void                g_closure_sink                      (GClosure *closure);

Takes over the initial ownership of a closure. Each closure is initially created in a floating state, which means that the initial reference count is not owned by any caller. `g_closure_sink()` checks to see if the object is still floating, and if so, unsets the floating state and decreases the reference count. If the closure is not floating, `g_closure_sink()` does nothing. The reason for the existence of the floating state is to prevent cumbersome code sequences like:

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    closure = g_cclosure_new (cb_func, cb_data);
    g_source_set_closure (source, closure);
    g_closure_unref (closure); // XXX GObject doesn't really need this

Because `g_source_set_closure()` (and similar functions) take ownership of the initial reference count, if it is unowned, we instead can write:

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    g_source_set_closure (source, g_cclosure_new (cb_func, cb_data));

Generally, this function is used together with `g_closure_ref()`. Ane example of storing a closure for later notification looks like:

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    static GClosure *notify_closure = NULL;
    void
    foo_notify_set_closure (GClosure *closure)
    {
      if (notify_closure)
        g_closure_unref (notify_closure);
      notify_closure = closure;
      if (notify_closure)
        {
          g_closure_ref (notify_closure);
          g_closure_sink (notify_closure);
        }
    }

Because `g_closure_sink()` may decrement the reference count of a closure (if it hasn't been called on `closure` yet) just like `g_closure_unref()`, `g_closure_ref()` should be called prior to this function.

`closure` : | GClosure to decrement the initial reference count on, if it's still being held

### g_closure_unref ()

    void                g_closure_unref                     (GClosure *closure);

Decrements the reference count of a closure after it was previously incremented by the same caller. If no other callers are using the closure, then the closure will be destroyed and freed.

`closure` : | GClosure to decrement the reference count on

### g_closure_invoke ()

    void                g_closure_invoke                    (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint);

Invokes the closure, i.e. executes the callback represented by the `closure`.

`closure` : | a GClosure
`return_value` : | a GValue to store the return value. May be `NULL` if the callback of `closure` doesn't return a value. [allow-none]
`n_param_values` : | the length of the `param_values` array
`param_values` : | an array of GValues holding the arguments on which to invoke the callback of `closure`. [array length=n_param_values]
`invocation_hint` : | a context-dependent invocation hint. [allow-none]

### g_closure_invalidate ()

    void                g_closure_invalidate                (GClosure *closure);

Sets a flag on the closure to indicate that its calling environment has become invalid, and thus causes any future invocations of `g_closure_invoke()` on this `closure` to be ignored. Also, invalidation notifiers installed on the closure will be called at this point. Note that unless you are holding a reference to the closure yourself, the invalidation notifiers may unref the closure and cause it to be destroyed, so if you need to access the closure after calling `g_closure_invalidate()`, make sure that you've previously called `g_closure_ref()`.

Note that `g_closure_invalidate()` will also be called when the reference count of a closure drops to zero (unless it has already been invalidated before).

`closure` : | GClosure to invalidate

### g_closure_add_finalize_notifier ()

    void                g_closure_add_finalize_notifier     (GClosure *closure,
                                                             gpointer notify_data,
                                                             GClosureNotify notify_func);

Registers a finalization notifier which will be called when the reference count of `closure` goes down to 0. Multiple finalization notifiers on a single closure are invoked in unspecified order. If a single call to `g_closure_unref()` results in the closure being both invalidated and finalized, then the invalidate notifiers will be run before the finalize notifiers.

`closure` : | a GClosure
`notify_data` : | data to pass to `notify_func`
`notify_func` : | the callback function to register

### g_closure_add_invalidate_notifier ()

    void                g_closure_add_invalidate_notifier   (GClosure *closure,
                                                             gpointer notify_data,
                                                             GClosureNotify notify_func);

Registers an invalidation notifier which will be called when the `closure` is invalidated with `g_closure_invalidate()`. Invalidation notifiers are invoked before finalization notifiers, in an unspecified order.

`closure` : | a GClosure
`notify_data` : | data to pass to `notify_func`
`notify_func` : | the callback function to register

### g_closure_remove_finalize_notifier ()

    void                g_closure_remove_finalize_notifier  (GClosure *closure,
                                                             gpointer notify_data,
                                                             GClosureNotify notify_func);

Removes a finalization notifier.

Notice that notifiers are automatically removed after they are run.

`closure` : | a GClosure
`notify_data` : | data which was passed to `g_closure_add_finalize_notifier()` when registering `notify_func`
`notify_func` : | the callback function to remove

### g_closure_remove_invalidate_notifier ()

    void                g_closure_remove_invalidate_notifier
                                                            (GClosure *closure,
                                                             gpointer notify_data,
                                                             GClosureNotify notify_func);

Removes an invalidation notifier.

Notice that notifiers are automatically removed after they are run.

`closure` : | a GClosure
`notify_data` : | data which was passed to `g_closure_add_invalidate_notifier()` when registering `notify_func`
`notify_func` : | the callback function to remove

### g_closure_new_simple ()

    GClosure *          g_closure_new_simple                (guint sizeof_closure,
                                                             gpointer data);

Allocates a struct of the given size and initializes the initial part as a GClosure. This function is mainly useful when implementing new types of closures.

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    typedef struct _MyClosure MyClosure;
    struct _MyClosure
    {
      GClosure closure;
      // extra data goes here
    };

    static void
    my_closure_finalize (gpointer  notify_data,
                         GClosure *closure)
    {
      MyClosure *my_closure = (MyClosure *)closure;

      // free extra data here
    }

    MyClosure *my_closure_new (gpointer data)
    {
      GClosure *closure;
      MyClosure *my_closure;

      closure = g_closure_new_simple (sizeof (MyClosure), data);
      my_closure = (MyClosure *) closure;

      // initialize extra data here

      g_closure_add_finalize_notifier (closure, notify_data,
                                       my_closure_finalize);
      return my_closure;
    }

`sizeof_closure` : | the size of the structure to allocate, must be at least `sizeof (GClosure)`
`data` : | data to store in the `data` field of the newly allocated GClosure
Returns : | a newly allocated GClosure. [transfer full]

### g_closure_set_marshal ()

    void                g_closure_set_marshal               (GClosure *closure,
                                                             GClosureMarshal marshal);

Sets the marshaller of `closure`. The `marshal_data` of `marshal` provides a way for a meta marshaller to provide additional information to the marshaller. (See `g_closure_set_meta_marshal()`.) For GObject's C predefined marshallers (the g_cclosure_marshal_*() functions), what it provides is a callback function to use instead of `closure->callback`.

`closure` : | a GClosure
`marshal` : | a GClosureMarshal function

### g_closure_add_marshal_guards ()

    void                g_closure_add_marshal_guards        (GClosure *closure,
                                                             gpointer pre_marshal_data,
                                                             GClosureNotify pre_marshal_notify,
                                                             gpointer post_marshal_data,
                                                             GClosureNotify post_marshal_notify);

Adds a pair of notifiers which get invoked before and after the closure callback, respectively. This is typically used to protect the extra arguments for the duration of the callback. See `g_object_watch_closure()` for an example of marshal guards.

`closure` : | a GClosure
`pre_marshal_data` : | data to pass to `pre_marshal_notify`
`pre_marshal_notify` : | a function to call before the closure callback
`post_marshal_data` : | data to pass to `post_marshal_notify`
`post_marshal_notify` : | a function to call after the closure callback

### g_closure_set_meta_marshal ()

    void                g_closure_set_meta_marshal          (GClosure *closure,
                                                             gpointer marshal_data,
                                                             GClosureMarshal meta_marshal);

Sets the meta marshaller of `closure`. A meta marshaller wraps `closure->marshal` and modifies the way it is called in some fashion. The most common use of this facility is for C callbacks. The same marshallers (generated by glib-genmarshal) are used everywhere, but the way that we get the callback function differs. In most cases we want to use `closure->callback`, but in other cases we want to use some different technique to retrieve the callback function.

For example, class closures for signals (see `g_signal_type_cclosure_new()`) retrieve the callback function from a fixed offset in the class structure. The meta marshaller retrieves the right callback and passes it to the marshaller as the `marshal_data` argument.

`closure` : | a GClosure
`marshal_data` : | context-dependent data to pass to `meta_marshal`
`meta_marshal` : | a GClosureMarshal function

### g_source_set_closure ()

    void                g_source_set_closure                (GSource *source,
                                                             GClosure *closure);

Set the callback for a source as a GClosure.

If the source is not one of the standard GLib types, the `closure_callback` and `closure_marshal` fields of the GSourceFuncs structure must have been filled in with pointers to appropriate functions.

`source` : | the source
`closure` : | a GClosure

### g_source_set_dummy_callback ()

    void                g_source_set_dummy_callback         (GSource *source);

Sets a dummy callback for `source`. The callback will do nothing, and if the source expects a gboolean return value, it will return `TRUE`. (If the source expects any other type of return value, it will return a 0/`NULL` value; whatever `g_value_init()` initializes a GValue to for that type.)

If the source is not one of the standard GLib types, the `closure_callback` and `closure_marshal` fields of the GSourceFuncs structure must have been filled in with pointers to appropriate functions.

`source` : | the source

### g_cclosure_marshal_VOID__VOID ()

    void                g_cclosure_marshal_VOID__VOID       (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 1
`param_values` : | a GValue array holding only the instance
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__BOOLEAN ()

    void                g_cclosure_marshal_VOID__BOOLEAN    (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, gboolean arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the gboolean parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__CHAR ()

    void                g_cclosure_marshal_VOID__CHAR       (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, gchar arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the gchar parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__UCHAR ()

    void                g_cclosure_marshal_VOID__UCHAR      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, guchar arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the guchar parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__INT ()

    void                g_cclosure_marshal_VOID__INT        (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, gint arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the gint parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__UINT ()

    void                g_cclosure_marshal_VOID__UINT       (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, guint arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the guint parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__LONG ()

    void                g_cclosure_marshal_VOID__LONG       (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, glong arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the glong parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__ULONG ()

    void                g_cclosure_marshal_VOID__ULONG      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, gulong arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the gulong parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__ENUM ()

    void                g_cclosure_marshal_VOID__ENUM       (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, gint arg1, gpointer user_data)` where the gint parameter denotes an enumeration type..

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the enumeration parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__FLAGS ()

    void                g_cclosure_marshal_VOID__FLAGS      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, gint arg1, gpointer user_data)` where the gint parameter denotes a flags type.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the flags parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__FLOAT ()

    void                g_cclosure_marshal_VOID__FLOAT      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, gfloat arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the gfloat parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__DOUBLE ()

    void                g_cclosure_marshal_VOID__DOUBLE     (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, gdouble arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the gdouble parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__STRING ()

    void                g_cclosure_marshal_VOID__STRING     (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, const gchar *arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the gchar* parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__PARAM ()

    void                g_cclosure_marshal_VOID__PARAM      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, GParamSpec *arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the GParamSpec* parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__BOXED ()

    void                g_cclosure_marshal_VOID__BOXED      (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, GBoxed *arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the GBoxed* parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__POINTER ()

    void                g_cclosure_marshal_VOID__POINTER    (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, gpointer arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the gpointer parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__OBJECT ()

    void                g_cclosure_marshal_VOID__OBJECT     (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, GObject *arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the GObject* parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__VARIANT ()

    void                g_cclosure_marshal_VOID__VARIANT    (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, GVariant *arg1, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 2
`param_values` : | a GValue array holding the instance and the GVariant* parameter
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

Since 2.26

### g_cclosure_marshal_STRING__OBJECT_POINTER ()

    void                g_cclosure_marshal_STRING__OBJECT_POINTER
                                                            (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `gchar* (*callback) (gpointer instance, GObject *arg1, gpointer arg2, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | a GValue, which can store the returned string
`n_param_values` : | 3
`param_values` : | a GValue array holding instance, arg1 and arg2
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_VOID__UINT_POINTER ()

    void                g_cclosure_marshal_VOID__UINT_POINTER
                                                            (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `void (*callback) (gpointer instance, guint arg1, gpointer arg2, gpointer user_data)`.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | ignored
`n_param_values` : | 3
`param_values` : | a GValue array holding instance, arg1 and arg2
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_BOOLEAN__FLAGS ()

    void                g_cclosure_marshal_BOOLEAN__FLAGS   (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

A marshaller for a GCClosure with a callback of type `gboolean (*callback) (gpointer instance, gint arg1, gpointer user_data)` where the gint parameter denotes a flags type.

`closure` : | the GClosure to which the marshaller belongs
`return_value` : | a GValue which can store the returned gboolean
`n_param_values` : | 2
`param_values` : | a GValue array holding instance and arg1
`invocation_hint` : | the invocation hint given as the last argument to `g_closure_invoke()`
`marshal_data` : | additional data specified when registering the marshaller

### g_cclosure_marshal_BOOL__FLAGS

    #define             g_cclosure_marshal_BOOL__FLAGS

Another name for `g_cclosure_marshal_BOOLEAN__FLAGS()`.

### g_cclosure_marshal_BOOLEAN__BOXED_BOXED ()

    void                g_cclosure_marshal_BOOLEAN__BOXED_BOXED
                                                            (GClosure *closure,
                                                             GValue *return_value,
                                                             guint n_param_values,
                                                             const GValue *param_values,
                                                             gpointer invocation_hint,
                                                             gpointer marshal_data);

### g_cclosure_marshal_BOOL__BOXED_BOXED

    #define             g_cclosure_marshal_BOOL__BOXED_BOXED