Signals

Name

Signals -- Signals provide a means for customization of object behaviour and are used as general purpose notification mechanism.

Synopsis


#include <gobject.h>


struct      GSignalInvocationHint;
gboolean    (*GSignalAccumulator)           (GSignalInvocationHint *ihint,
                                             GValue *return_accu,
                                             const GValue *return_value);
typedef     GSignalCMarshaller;
gboolean    (*GSignalEmissionHook)          (GSignalInvocationHint *ihint,
                                             guint n_param_values,
                                             const GValue *param_values);
enum        GSignalFlags;
enum        GSignalMatchType;
struct      GSignalQuery;
guint       g_signal_newv                   (const gchar *signal_name,
                                             GType itype,
                                             GSignalFlags signal_flags,
                                             GClosure *class_closure,
                                             GSignalAccumulator accumulator,
                                             GSignalCMarshaller c_marshaller,
                                             GType return_type,
                                             guint n_params,
                                             GType *param_types);
void        g_signal_emitv                  (const GValue *instance_and_params,
                                             guint signal_id,
                                             GQuark detail,
                                             GValue *return_value);
guint       g_signal_lookup                 (const gchar *name,
                                             GType itype);
gchar*      g_signal_name                   (guint signal_id);
void        g_signal_query                  (guint signal_id,
                                             GSignalQuery *query);
guint*      g_signal_list_ids               (GType itype,
                                             guint *n_ids);
guint       g_signal_connect_closure_by_id  (gpointer instance,
                                             guint signal_id,
                                             GQuark detail,
                                             GClosure *closure,
                                             gboolean after);
void        g_signal_handler_block          (gpointer instance,
                                             guint handler_id);
void        g_signal_handler_unblock        (gpointer instance,
                                             guint handler_id);
void        g_signal_handler_disconnect     (gpointer instance,
                                             guint handler_id);
guint       g_signal_handler_find           (gpointer instance,
                                             GSignalMatchType mask,
                                             guint signal_id,
                                             GQuark detail,
                                             GClosure *closure,
                                             gpointer func,
                                             gpointer data);
guint       g_signal_handlers_block_matched (gpointer instance,
                                             GSignalMatchType mask,
                                             guint signal_id,
                                             GQuark detail,
                                             GClosure *closure,
                                             gpointer func,
                                             gpointer data);
guint       g_signal_handlers_unblock_matched
                                            (gpointer instance,
                                             GSignalMatchType mask,
                                             guint signal_id,
                                             GQuark detail,
                                             GClosure *closure,
                                             gpointer func,
                                             gpointer data);
guint       g_signal_handlers_disconnect_matched
                                            (gpointer instance,
                                             GSignalMatchType mask,
                                             guint signal_id,
                                             GQuark detail,
                                             GClosure *closure,
                                             gpointer func,
                                             gpointer data);
gboolean    g_signal_has_handler_pending    (gpointer instance,
                                             guint signal_id,
                                             GQuark detail,
                                             gboolean may_be_blocked);
void        g_signal_stop_emission          (gpointer instance,
                                             guint signal_id,
                                             GQuark detail);
GClosure*   g_signal_type_closure_new       (GType itype,
                                             guint struct_offset);
guint       g_signal_add_emission_hook_full (guint signal_id,
                                             GClosure *closure);
void        g_signal_remove_emission_hook   (guint signal_id,
                                             guint hook_id);
gboolean    g_signal_parse_name             (const gchar *detailed_signal,
                                             GType itype,
                                             guint *signal_id_p,
                                             GQuark *detail_p,
                                             gboolean force_detail_quark);

Description

The basic concept of the signal system is that of the emission of a signal. Signals are introduced per-type and are identified through strings. Signals introduced for a parent type are availale in derived types as well, so basically they are a per-type facility that is inherited. A signal emission mainly involves invocation of a certain set of callbacks in precisely defined manner. There are two main categories of such callbacks, per-object [1] ones and user provided ones. The per-object callbacks are most often referred to as "object method handler" or "default (signal) handler", while user provided callbacks are usually just called "signal handler". The object method handler is provided at signal creation time (this most frequently happens at the end of an object class' creation), while user provided handlers are frequently connected and disconnected to/from a certain signal on certain object instances.

A signal emission consists of five stages, unless prematurely stopped:

1 - Invocation of the object method handler for G_SIGNAL_RUN_FIRST signals

2 - Invocation of normal user-provided signal handlers (after flag FALSE)

3 - Invocation of the object method handler for G_SIGNAL_RUN_LAST signals

4 - Invocation of user provided signal handlers, connected with an after flag of TRUE

5 - Invocation of the object method handler for G_SIGNAL_RUN_CLEANUP signals

The user provided signal handlers are called in the order they were connected in. All handlers may prematurely stop a signal emission, and any number of handlers may be connected, disconnected, blocked or unblocked during a signal emission. There are certain criteria for skipping user handlers in stages 2 and 4 of a signal emission. First, user handlers may be blocked, blocked handlers are omitted during callback invocation, to return from the "blocked" state, a handler has to get unblocked exactly the same amount of times it has been blocked before. Second, upon emission of a G_SIGNAL_DETAILED signal, an additional "detail" argument passed in to g_signal_emit() has to match the detail argument of the signal handler currently subject to invocation. Specification of no detail argument for signal handlers (omission of the detail part of the signal specification upon connection) serves as a wildcard and matches any detail argument passed in to emission.

Details

struct GSignalInvocationHint

struct GSignalInvocationHint
{
  guint		signal_id;
  GQuark	detail;
  GSignalFlags	run_type;
};

The GSignalInvocationHint structure is used to pass on additional information to callbacks during a signal emission.

guint signal_idThe signal id of the signal invoking the callback
GQuark detailThe detail passed on for this emission
GSignalFlags run_typeThe stage the signal emission is currently in, this field will contain one of G_SIGNAL_RUN_FIRST, G_SIGNAL_RUN_LAST or G_SIGNAL_RUN_CLEANUP.


GSignalAccumulator ()

gboolean    (*GSignalAccumulator)           (GSignalInvocationHint *ihint,
                                             GValue *return_accu,
                                             const GValue *return_value);

The signal accumulator is a special callback function that can be used to collect return values of the various callbacks that are called during a signal emission. The signal accumulator is specified at signal creation time, if it is left NULL, no accumulation of callback return values is perfomed. The return value of signal emissions is then the value returned by the last callback.

ihint :Signal invokation hint, see GSignalInvocationHint
return_accu :Accumulator to collect callback return values in, this is the return value of the current signal emission
return_value :The return value of the most recent callback function
Returns :The accumulator function returns whether the signal emission should be aborted. Returning FALSE means to abort the current emission and TRUE is returned for continuation.


GSignalCMarshaller

typedef GClosureMarshal			 GSignalCMarshaller;


GSignalEmissionHook ()

gboolean    (*GSignalEmissionHook)          (GSignalInvocationHint *ihint,
                                             guint n_param_values,
                                             const GValue *param_values);

ihint : 
n_param_values : 
param_values : 
Returns : 


enum GSignalFlags

typedef enum
{
  G_SIGNAL_RUN_FIRST	= 1 << 0,
  G_SIGNAL_RUN_LAST	= 1 << 1,
  G_SIGNAL_RUN_CLEANUP	= 1 << 2,
  G_SIGNAL_NO_RECURSE	= 1 << 3,
  G_SIGNAL_DETAILED	= 1 << 4,
  G_SIGNAL_ACTION	= 1 << 5,
  G_SIGNAL_NO_HOOKS	= 1 << 6
#define G_SIGNAL_FLAGS_MASK  0x7f
} GSignalFlags;


enum GSignalMatchType

typedef enum
{
  G_SIGNAL_MATCH_ID	   = 1 << 0,
  G_SIGNAL_MATCH_DETAIL	   = 1 << 1,
  G_SIGNAL_MATCH_CLOSURE   = 1 << 2,
  G_SIGNAL_MATCH_FUNC	   = 1 << 3,
  G_SIGNAL_MATCH_DATA	   = 1 << 4,
  G_SIGNAL_MATCH_UNBLOCKED = 1 << 5
#define G_SIGNAL_MATCH_MASK  0x3f
} GSignalMatchType;


struct GSignalQuery

struct GSignalQuery
{
  guint		signal_id;
  const gchar  *signal_name;
  GType		itype;
  GSignalFlags	signal_flags;
  GType		return_type;
  guint		n_params;
  const GType  *param_types;
};

A structure holding in-depth information for a specific signal. It is filled in by the g_signal_query() function.

guint signal_idThe signal id of the signal being querried, or 0 if the signal to be querried was unknown
const gchar *signal_nameThe signal name
GType itypeThe interface/instance type that this signal can be emitted for
GSignalFlags signal_flagsThe signal flags as passed in to @g_signal_new()
GType return_typeThe return type for user callbacks
guint n_paramsThe number of parameters that user callbacks take
const GType *param_typesThe individual parameter types for user callbacks, note that the effective callback signature is:
return_type callback (gpointer     data1,
                      [param_types param_names,]
                      gpointer     data2);


g_signal_newv ()

guint       g_signal_newv                   (const gchar *signal_name,
                                             GType itype,
                                             GSignalFlags signal_flags,
                                             GClosure *class_closure,
                                             GSignalAccumulator accumulator,
                                             GSignalCMarshaller c_marshaller,
                                             GType return_type,
                                             guint n_params,
                                             GType *param_types);

signal_name : 
itype : 
signal_flags : 
class_closure : 
accumulator : 
c_marshaller : 
return_type : 
n_params : 
param_types : 
Returns : 


g_signal_emitv ()

void        g_signal_emitv                  (const GValue *instance_and_params,
                                             guint signal_id,
                                             GQuark detail,
                                             GValue *return_value);

instance_and_params : 
signal_id : 
detail : 
return_value : 


g_signal_lookup ()

guint       g_signal_lookup                 (const gchar *name,
                                             GType itype);

name : 
itype : 
Returns : 


g_signal_name ()

gchar*      g_signal_name                   (guint signal_id);

signal_id : 
Returns : 


g_signal_query ()

void        g_signal_query                  (guint signal_id,
                                             GSignalQuery *query);

Query the signal system for in-depth information about a specific signal. This function will fill in a user-provided structure to hold signal-specific information. If an invalid dignal id is passed in, the signal_id member of the GSignalQuery is 0. All members filled into the GSignalQuery structure should be considered constant and have to be left untouched.

signal_id :The signal id of the signal to query information for
query :A user provided structure that is filled in with constant values upon success.


g_signal_list_ids ()

guint*      g_signal_list_ids               (GType itype,
                                             guint *n_ids);

List the signals by id, that a certain instance or interface type created. Further information about the signals can be aquired through g_signal_query().

itype :Instance or interface type
n_ids :Location to store the number of signal ids for itype
Returns :Newly allocated array of signal ids


g_signal_connect_closure_by_id ()

guint       g_signal_connect_closure_by_id  (gpointer instance,
                                             guint signal_id,
                                             GQuark detail,
                                             GClosure *closure,
                                             gboolean after);

instance : 
signal_id : 
detail : 
closure : 
after : 
Returns : 


g_signal_handler_block ()

void        g_signal_handler_block          (gpointer instance,
                                             guint handler_id);

g_signal_handler_block() blocks a handler of an instance so it will not be called during any signal emissions unless it is unblocked again. Thus "blocking" a signal handler means to temporarily deactive it, a signal handler has to be unblocked exactly the same amount of times it has been blocked before to become active again. The handler_id passed into g_signal_handler_block() has to be a valid signal handler id, connected to a signal of instance.

instance :The instance to block the signal handler of
handler_id :Handler id of the handler to be blocked


g_signal_handler_unblock ()

void        g_signal_handler_unblock        (gpointer instance,
                                             guint handler_id);

g_signal_handler_unblock() undoes the effect of a previous g_signal_handler_block() call. A blocked handler is skipped during signal emissions and will not be invoked, unblocking it (for exactly the amount of times it has been blocked before) reverts its "blocked" state, so the handler will be recognized by the signal system and is called upon future or currently ongoing signal emissions (since the order in which handlers are called during signal emissions is deterministic, whether the unblocked handler in question is called as part of a currently ongoing emission depends on how far that emission has proceeded yet). The handler_id passed into g_signal_handler_unblock() has to be a valid id of a signal handler that is connected to a signal of instance and is currently blocked.

instance :The instance to unblock the signal handler of
handler_id :Handler id of the handler to be unblocked


g_signal_handler_disconnect ()

void        g_signal_handler_disconnect     (gpointer instance,
                                             guint handler_id);

g_signal_handler_disconnect() disconnects a handler from an instance so it will not be called during any future or currently ongoing emissions of the signal it has been connected to. The handler_id becomes invalid and may be reused. The handler_id passed into g_signal_handler_disconnect() has to be a valid signal handler id, connected to a signal of instance.

instance :The instance to remove the signal handler from
handler_id :Handler id of the handler to be disconnected


g_signal_handler_find ()

guint       g_signal_handler_find           (gpointer instance,
                                             GSignalMatchType mask,
                                             guint signal_id,
                                             GQuark detail,
                                             GClosure *closure,
                                             gpointer func,
                                             gpointer data);

Find the first signal handler that matches certain selection criteria. The criteria mask is passed as an OR-ed combination of GSignalMatchType flags, and the criteria values are passed as arguments. The match mask has to be non-0 for successfull matches. If no handler was found, 0 is returned.

instance :The instance owning the signal handler to be found
mask :Mask indicating which of signal_id, detail, closure, func and/or data the handler has to match
signal_id :Signal the handler has to be connected to
detail :Signal detail the handler has to be connected to
closure :The closure the handler will invoke
func :The C closure callback of the handler (useless for non-C closures)
data :The closure data of the handler's closure
Returns :A valid non-0 signal handler id for a successfull match


g_signal_handlers_block_matched ()

guint       g_signal_handlers_block_matched (gpointer instance,
                                             GSignalMatchType mask,
                                             guint signal_id,
                                             GQuark detail,
                                             GClosure *closure,
                                             gpointer func,
                                             gpointer data);

This function blocks all handlers on an instance that match a certain selection criteria. The criteria mask is passed as an OR-ed combination of GSignalMatchType flags, and the criteria values are passed as arguments. Passing at least one of the G_SIGNAL_MATCH_CLOSURE, G_SIGNAL_MATCH_FUNC or G_SIGNAL_MATCH_DATA match flags is required for successfull matches. If no handlers were found, 0 is returned, the number of blocked handlers otherwise.

instance :The instance to block handlers from
mask :Mask indicating which of signal_id, detail, closure, func and/or data the handlers have to match
signal_id :Signal the handlers have to be connected to
detail :Signal detail the handlers have to be connected to
closure :The closure the handlers will invoke
func :The C closure callback of the handlers (useless for non-C closures)
data :The closure data of the handlers' closures
Returns :The amount of handlers that got blocked


g_signal_handlers_unblock_matched ()

guint       g_signal_handlers_unblock_matched
                                            (gpointer instance,
                                             GSignalMatchType mask,
                                             guint signal_id,
                                             GQuark detail,
                                             GClosure *closure,
                                             gpointer func,
                                             gpointer data);

This function unblocks all handlers on an instance that match a certain selection criteria. The criteria mask is passed as an OR-ed combination of GSignalMatchType flags, and the criteria values are passed as arguments. Passing at least one of the G_SIGNAL_MATCH_CLOSURE, G_SIGNAL_MATCH_FUNC or G_SIGNAL_MATCH_DATA match flags is required for successfull matches. If no handlers were found, 0 is returned, the number of unblocked handlers otherwise. The match criteria should not apply to any handlers that are not currently blocked.

instance :The instance to unblock handlers from
mask :Mask indicating which of signal_id, detail, closure, func and/or data the handlers have to match
signal_id :Signal the handlers have to be connected to
detail :Signal detail the handlers have to be connected to
closure :The closure the handlers will invoke
func :The C closure callback of the handlers (useless for non-C closures)
data :The closure data of the handlers' closures
Returns :The amount of handlers that got unblocked


g_signal_handlers_disconnect_matched ()

guint       g_signal_handlers_disconnect_matched
                                            (gpointer instance,
                                             GSignalMatchType mask,
                                             guint signal_id,
                                             GQuark detail,
                                             GClosure *closure,
                                             gpointer func,
                                             gpointer data);

This function disconnects all handlers on an instance that match a certain selection criteria. The criteria mask is passed as an OR-ed combination of GSignalMatchType flags, and the criteria values are passed as arguments. Passing at least one of the G_SIGNAL_MATCH_CLOSURE, G_SIGNAL_MATCH_FUNC or G_SIGNAL_MATCH_DATA match flags is required for successfull matches. If no handlers were found, 0 is returned, the number of disconnected handlers otherwise.

instance :The instance to remove handlers from
mask :Mask indicating which of signal_id, detail, closure, func and/or data the handlers have to match
signal_id :Signal the handlers have to be connected to
detail :Signal detail the handlers have to be connected to
closure :The closure the handlers will invoke
func :The C closure callback of the handlers (useless for non-C closures)
data :The closure data of the handlers' closures
Returns :The amount of handlers that got disconnected


g_signal_has_handler_pending ()

gboolean    g_signal_has_handler_pending    (gpointer instance,
                                             guint signal_id,
                                             GQuark detail,
                                             gboolean may_be_blocked);

instance : 
signal_id : 
detail : 
may_be_blocked : 
Returns : 


g_signal_stop_emission ()

void        g_signal_stop_emission          (gpointer instance,
                                             guint signal_id,
                                             GQuark detail);

instance : 
signal_id : 
detail : 


g_signal_type_closure_new ()

GClosure*   g_signal_type_closure_new       (GType itype,
                                             guint struct_offset);

itype : 
struct_offset : 
Returns : 


g_signal_add_emission_hook_full ()

guint       g_signal_add_emission_hook_full (guint signal_id,
                                             GClosure *closure);

signal_id : 
closure : 
Returns : 


g_signal_remove_emission_hook ()

void        g_signal_remove_emission_hook   (guint signal_id,
                                             guint hook_id);

signal_id : 
hook_id : 


g_signal_parse_name ()

gboolean    g_signal_parse_name             (const gchar *detailed_signal,
                                             GType itype,
                                             guint *signal_id_p,
                                             GQuark *detail_p,
                                             gboolean force_detail_quark);

Internal function to parse a signal names into its signal_id and detail quark.

detailed_signal :A string of the form "signal-name::detail"
itype :The interface/instance type taht introduced "signal-name"
signal_id_p :Location to store the signal id
detail_p :Location to stroe the detail quark
force_detail_quark :TRUE forces creation of a GQuark for the detail
Returns :Whether the signal name could successfully be parsed and signal_id_p and detail_p contain valid return values.

Notes

[1]

Although signals can deal with any kind of type, i'm referring to those types as "object types" in the following, simply because that is the context most users will encounter signals in.