GObject.Closure¶

record (struct)

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 responsibility of the marshaller to convert the arguments for the invocation from [GValues]Value into a suitable form, perform the callback on the converted arguments, and transform the return value back into a Value.

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 Value and native C types. The GObject library provides the CClosure type for this purpose. Bindings for other languages need marshallers which convert between [GValues]Value and suitable representations in the runtime of the language in order to use functions written in that language as callbacks. Use Closure.set_marshal to set the marshaller on such a custom closure implementation.

Within GObject, closures play an important role in the implementation of signals. When a signal is registered, the c_marshaller argument to 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][glib-genmarshal] utility. Closures can be explicitly connected to signals with 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 Closure 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.
Closure.invalidate and invalidation notifiers allow callbacks to be automatically removed when the objects they point to go away.

Constructors¶

new_object¶

@classmethod
def new_object(cls, sizeof_closure: int, object: Object) -> Closure

A variant of Closure.new_simple which stores object in the data field of the closure and calls Object.watch_closure on object and the created closure. This function is mainly useful when implementing new types of closures.

Parameters:

sizeof_closure — the size of the structure to allocate, must be at least sizeof (GClosure)
object — a Object pointer to store in the data field of the newly allocated Closure

new_simple¶

@classmethod
def new_simple(cls, sizeof_closure: int, data: int | None = ...) -> Closure

Allocates a struct of the given size and initializes the initial part as a Closure.

This function is mainly useful when implementing new types of closures:

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;
}

Parameters:

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 Closure

Methods¶

invalidate¶

def invalidate(self) -> None

Sets a flag on the closure to indicate that its calling environment has become invalid, and thus causes any future invocations of 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 Closure.invalidate, make sure that you've previously called Closure.ref.

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

invoke¶

def invoke(self, param_values: list[Value], invocation_hint: int | None = ...) -> Value

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

Parameters:

param_values — an array of GValues holding the arguments on which to invoke the callback of closure
invocation_hint — a context-dependent invocation hint

ref¶

def ref(self) -> Closure

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

sink¶

def sink(self) -> None

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.

This function 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, Closure.sink does nothing.

The reason for the existence of the floating state is to prevent cumbersome code sequences like:

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

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

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

Generally, this function is used together with Closure.ref. An example of storing a closure for later notification looks like:

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 Closure.sink may decrement the reference count of a closure (if it hasn't been called on closure yet) just like Closure.unref, Closure.ref should be called prior to this function.

unref¶

def unref(self) -> None

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.

Properties¶

ref_count¶

ref_count: int  # read/write

meta_marshal_nouse¶

meta_marshal_nouse: int  # read/write

n_guards¶

n_guards: int  # read/write

n_fnotifiers¶

n_fnotifiers: int  # read/write

n_inotifiers¶

n_inotifiers: int  # read/write

in_inotify¶

in_inotify: int  # read/write

floating¶

floating: int  # read/write

derivative_flag¶

derivative_flag: int  # read/write

in_marshal¶

in_marshal: int  # read/write

is_invalid¶

is_invalid: int  # read/write

marshal¶

marshal: Any  # read/write

data¶

data: int  # read/write

notifiers¶

notifiers: ClosureNotifyData  # read/write