Class Socket

Whenever the source_property is changed the target_property is updated using the same value. For instance:

  g_object_bind_property (action, "active", widget, "sensitive", 0);

Will result in the "sensitive" property of the widget #GObject instance to be updated with the same value of the "active" property of the action #GObject instance.

If flags contains %G_BINDING_BIDIRECTIONAL then the binding will be mutual: if target_property on target changes then the source_property on source will be updated as well.

The binding will automatically be removed when either the source or the target instances are finalized. To remove the binding without affecting the source and the target you can just call g_object_unref() on the returned #GBinding instance.

Removing the binding by calling g_object_unref() on it must only be done if the binding, source and target are only used from a single thread and it is clear that both source and target outlive the binding. Especially it is not safe to rely on this if the binding, source or target can be finalized from different threads. Keep another reference to the binding and use g_binding_unbind() instead to be on the safe side.

A #GObject can have multiple bindings.

This function is the language bindings friendly version of g_object_bind_property_full(), using #GClosures instead of function pointers.

The callback on the source is of the #GDatagramBasedSourceFunc type.

It is meaningless to specify %G_IO_ERR or %G_IO_HUP in condition; these conditions will always be reported in the callback if they are true.

If non-%NULL, cancellable can be used to cancel the source, which will cause the source to trigger, reporting the current condition (which is likely 0 unless cancellation happened at the same time as a condition change). You can check for this in the callback using g_cancellable_is_cancelled().

This is necessary for accessors that modify multiple properties to prevent premature notification while the object is still being modified.

The value can be:

• an empty #GValue initialized by %G_VALUE_INIT, which will be automatically initialized with the expected type of the property (since GLib 2.60)
• a #GValue initialized with the expected type of the property
• a #GValue initialized with a type to which the expected type of the property can be transformed

In general, a copy is made of the property contents and the caller is responsible for freeing the memory by calling g_value_unset().

Note that g_object_get_property() is really intended for language bindings, g_object_get() is much more convenient for C programming.

This method is intended for language bindings. If writing in C, g_initable_new() should typically be used instead.

The object must be initialized before any real use after initial construction, either with this function or g_async_initable_init_async().

Implementations may also support cancellation. If cancellable is not %NULL, then initialization can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error %G_IO_ERROR_CANCELLED will be returned. If cancellable is not %NULL and the object doesn't support cancellable initialization the error %G_IO_ERROR_NOT_SUPPORTED will be returned.

If the object is not initialized, or initialization returns with an error, then all operations on the object except g_object_ref() and g_object_unref() are considered to be invalid, and have undefined behaviour. See the [introduction][ginitable] for more details.

Callers should not assume that a class which implements #GInitable can be initialized multiple times, unless the class explicitly documents itself as supporting this. Generally, a class’ implementation of init() can assume (and assert) that it will only be called once. Previously, this documentation recommended all #GInitable implementations should be idempotent; that recommendation was relaxed in GLib 2.54.

If a class explicitly supports being initialized multiple times, it is recommended that the method is idempotent: multiple calls with the same arguments should return the same results. Only the first call initializes the object; further calls return the result of the first call.

One reason why a class might need to support idempotent initialization is if it is designed to be used via the singleton pattern, with a #GObjectClass.constructor that sometimes returns an existing instance. In this pattern, a caller would expect to be able to call g_initable_init() on the result of g_object_new(), regardless of whether it is in fact a new instance.

When possible, eg. when signaling a property change from within the class that registered the property, you should use g_object_notify_by_pspec() instead.

Note that emission of the notify signal may be blocked with g_object_freeze_notify(). In this case, the signal emissions are queued and will be emitted (in reverse order) when g_object_thaw_notify() is called.

This function omits the property name lookup, hence it is faster than g_object_notify().

One way to avoid using g_object_notify() from within the class that registered the properties, and using g_object_notify_by_pspec() instead, is to store the GParamSpec used with g_object_class_install_property() inside a static array, e.g.:

  enum
  {
    PROP_0,
    PROP_FOO,
    PROP_LAST
  };

  static GParamSpec *properties[PROP_LAST];

  static void
  my_object_class_init (MyObjectClass *klass)
  {
    properties[PROP_FOO] = g_param_spec_int ("foo", "Foo", "The foo",
                                             0, 100,
                                             50,
                                             G_PARAM_READWRITE);
    g_object_class_install_property (gobject_class,
                                     PROP_FOO,
                                     properties[PROP_FOO]);
  }

and then notify a change on the "foo" property with:

  g_object_notify_by_pspec (self, properties[PROP_FOO]);

Since GLib 2.56, if GLIB_VERSION_MAX_ALLOWED is 2.56 or greater, the type of object will be propagated to the return type (using the GCC typeof() extension), so any casting the caller needs to do on the return type must be explicit.

In other words, if the object is floating, then this call "assumes ownership" of the floating reference, converting it to a normal reference by clearing the floating flag while leaving the reference count unchanged. If the object is not floating, then this call adds a new normal reference increasing the reference count by one.

Since GLib 2.56, the type of object will be propagated to the return type under the same conditions as for g_object_ref().

This function should only be called from object system implementations.

If the object already had an association with that name, the old association will be destroyed.

Internally, the key is converted to a #GQuark using g_quark_from_string(). This means a copy of key is kept permanently (even after object has been finalized) — so it is recommended to only use a small, bounded set of values for key in your program, to avoid the #GQuark storage growing unbounded.

void
object_add_to_user_list (GObject     *object,
                         const gchar *new_string)
{
  // the quark, naming the object data
  GQuark quark_string_list = g_quark_from_static_string ("my-string-list");
  // retrieve the old string list
  GList *list = g_object_steal_qdata (object, quark_string_list);

  // prepend new string
  list = g_list_prepend (list, g_strdup (new_string));
  // this changed 'list', so we need to set it again
  g_object_set_qdata_full (object, quark_string_list, list, free_string_list);
}
static void
free_string_list (gpointer data)
{
  GList *node, *list = data;

  for (node = list; node; node = node->next)
    g_free (node->data);
  g_list_free (list);
}

Using g_object_get_qdata() in the above example, instead of g_object_steal_qdata() would have left the destroy function set, and thus the partial string list would have been freed upon g_object_set_qdata_full().

Duplicate notifications for each property are squashed so that at most one #GObject::notify signal is emitted for each property, in the reverse order in which they have been queued.

It is an error to call this function when the freeze count is zero.

If the pointer to the #GObject may be reused in future (for example, if it is an instance variable of another object), it is recommended to clear the pointer to %NULL rather than retain a dangling pointer to a potentially invalid #GObject instance. Use g_clear_object() for this.

%G_IO_IN will be set in the return value if data is available to read with g_datagram_based_receive_messages(), or if the connection is closed remotely (EOS); and if the datagram_based has not been closed locally using some implementation-specific method (such as g_socket_close() or g_socket_shutdown() with shutdown_read set, if it’s a #GSocket).

If the connection is shut down or closed (by calling g_socket_close() or g_socket_shutdown() with shutdown_read set, if it’s a #GSocket, for example), all calls to this function will return %G_IO_ERROR_CLOSED.

%G_IO_OUT will be set if it is expected that at least one byte can be sent using g_datagram_based_send_messages() without blocking. It will not be set if the datagram_based has been closed locally.

%G_IO_HUP will be set if the connection has been closed locally.

%G_IO_ERR will be set if there was an asynchronous error in transmitting data previously enqueued using g_datagram_based_send_messages().

Note that on Windows, it is possible for an operation to return %G_IO_ERROR_WOULD_BLOCK even immediately after g_datagram_based_condition_check() has claimed that the #GDatagramBased is ready for writing. Rather than calling g_datagram_based_condition_check() and then writing to the #GDatagramBased if it succeeds, it is generally better to simply try writing right away, and try again later if the initial attempt returns %G_IO_ERROR_WOULD_BLOCK.

It is meaningless to specify %G_IO_ERR or %G_IO_HUP in condition; these conditions will always be set in the output if they are true. Apart from these flags, the output is guaranteed to be masked by condition.

This call never blocks.

If cancellable is cancelled before the condition is met, or if timeout is reached before the condition is met, then %FALSE is returned and error is set appropriately (%G_IO_ERROR_CANCELLED or %G_IO_ERROR_TIMED_OUT).

The callback on the source is of the #GDatagramBasedSourceFunc type.

It is meaningless to specify %G_IO_ERR or %G_IO_HUP in condition; these conditions will always be reported in the callback if they are true.

If non-%NULL, cancellable can be used to cancel the source, which will cause the source to trigger, reporting the current condition (which is likely 0 unless cancellation happened at the same time as a condition change). You can check for this in the callback using g_cancellable_is_cancelled().

This method is intended for language bindings. If writing in C, g_initable_new() should typically be used instead.

The object must be initialized before any real use after initial construction, either with this function or g_async_initable_init_async().

Implementations may also support cancellation. If cancellable is not %NULL, then initialization can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error %G_IO_ERROR_CANCELLED will be returned. If cancellable is not %NULL and the object doesn't support cancellable initialization the error %G_IO_ERROR_NOT_SUPPORTED will be returned.

If the object is not initialized, or initialization returns with an error, then all operations on the object except g_object_ref() and g_object_unref() are considered to be invalid, and have undefined behaviour. See the [introduction][ginitable] for more details.

Callers should not assume that a class which implements #GInitable can be initialized multiple times, unless the class explicitly documents itself as supporting this. Generally, a class’ implementation of init() can assume (and assert) that it will only be called once. Previously, this documentation recommended all #GInitable implementations should be idempotent; that recommendation was relaxed in GLib 2.54.

If a class explicitly supports being initialized multiple times, it is recommended that the method is idempotent: multiple calls with the same arguments should return the same results. Only the first call initializes the object; further calls return the result of the first call.

One reason why a class might need to support idempotent initialization is if it is designed to be used via the singleton pattern, with a #GObjectClass.constructor that sometimes returns an existing instance. In this pattern, a caller would expect to be able to call g_initable_init() on the result of g_object_new(), regardless of whether it is in fact a new instance.

When possible, eg. when signaling a property change from within the class that registered the property, you should use g_object_notify_by_pspec() instead.

Note that emission of the notify signal may be blocked with g_object_freeze_notify(). In this case, the signal emissions are queued and will be emitted (in reverse order) when g_object_thaw_notify() is called.

messages must point to an array of #GInputMessage structs and num_messages must be the length of this array. Each #GInputMessage contains a pointer to an array of #GInputVector structs describing the buffers that the data received in each message will be written to.

flags modify how all messages are received. The commonly available arguments for this are available in the #GSocketMsgFlags enum, but the values there are the same as the system values, and the flags are passed in as-is, so you can pass in system-specific flags too. These flags affect the overall receive operation. Flags affecting individual messages are returned in #GInputMessage.flags.

The other members of #GInputMessage are treated as described in its documentation.

If timeout is negative the call will block until num_messages have been received, the connection is closed remotely (EOS), cancellable is cancelled, or an error occurs.

If timeout is 0 the call will return up to num_messages without blocking, or %G_IO_ERROR_WOULD_BLOCK if no messages are queued in the operating system to be received.

If timeout is positive the call will block on the same conditions as if timeout were negative. If the timeout is reached before any messages are received, %G_IO_ERROR_TIMED_OUT is returned, otherwise it will return the number of messages received before timing out. (Note: This is effectively the behaviour of MSG_WAITFORONE with recvmmsg().)

To be notified when messages are available, wait for the %G_IO_IN condition. Note though that you may still receive %G_IO_ERROR_WOULD_BLOCK from g_datagram_based_receive_messages() even if you were previously notified of a %G_IO_IN condition.

If the remote peer closes the connection, any messages queued in the underlying receive buffer will be returned, and subsequent calls to g_datagram_based_receive_messages() will return 0 (with no error set).

If the connection is shut down or closed (by calling g_socket_close() or g_socket_shutdown() with shutdown_read set, if it’s a #GSocket, for example), all calls to this function will return %G_IO_ERROR_CLOSED.

On error -1 is returned and error is set accordingly. An error will only be returned if zero messages could be received; otherwise the number of messages successfully received before the error will be returned. If cancellable is cancelled, %G_IO_ERROR_CANCELLED is returned as with any other error.

messages must point to an array of #GOutputMessage structs and num_messages must be the length of this array. Each #GOutputMessage contains an address to send the data to, and a pointer to an array of #GOutputVector structs to describe the buffers that the data to be sent for each message will be gathered from.

flags modify how the message is sent. The commonly available arguments for this are available in the #GSocketMsgFlags enum, but the values there are the same as the system values, and the flags are passed in as-is, so you can pass in system-specific flags too.

The other members of #GOutputMessage are treated as described in its documentation.

If timeout is negative the call will block until num_messages have been sent, cancellable is cancelled, or an error occurs.

If timeout is 0 the call will send up to num_messages without blocking, or will return %G_IO_ERROR_WOULD_BLOCK if there is no space to send messages.

If timeout is positive the call will block on the same conditions as if timeout were negative. If the timeout is reached before any messages are sent, %G_IO_ERROR_TIMED_OUT is returned, otherwise it will return the number of messages sent before timing out.

To be notified when messages can be sent, wait for the %G_IO_OUT condition. Note though that you may still receive %G_IO_ERROR_WOULD_BLOCK from g_datagram_based_send_messages() even if you were previously notified of a %G_IO_OUT condition. (On Windows in particular, this is very common due to the way the underlying APIs work.)

If the connection is shut down or closed (by calling g_socket_close() or g_socket_shutdown() with shutdown_write set, if it’s a #GSocket, for example), all calls to this function will return %G_IO_ERROR_CLOSED.

On error -1 is returned and error is set accordingly. An error will only be returned if zero messages could be sent; otherwise the number of messages successfully sent before the error will be returned. If cancellable is cancelled, %G_IO_ERROR_CANCELLED is returned as with any other error.