Closure

class Closure(*args, **kwargs)

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 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 GCClosure type for this purpose. Bindings for other languages need marshallers which convert between Value and suitable representations in the runtime of the language in order to use functions written in that language as callbacks. Use 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.

• invalidate() and invalidation notifiers allow callbacks to be automatically removed when the objects they point to go away.

Constructors

class Closure

classmethod new_object(sizeof_closure: int, object: Object) → Callable[[...], Any]

A variant of new_simple() which stores object in the data field of the closure and calls 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

classmethod new_simple(sizeof_closure: int, data: None) → Callable[[...], Any]

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

class Closure

invalidate() → None

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

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

invoke(param_values: Sequence[Any], invocation_hint: None) → Any

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

Parameters:

• param_values – an array of Value holding the arguments on which to invoke the callback of closure

• invocation_hint – a context-dependent invocation hint

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

Fields

class Closure

data

derivative_flag

floating

in_inotify

in_marshal

Indicates whether the closure is currently being invoked with invoke()

is_invalid

Indicates whether the closure has been invalidated by invalidate()

marshal

meta_marshal_nouse

n_fnotifiers

n_guards

n_inotifiers

notifiers

ref_count