Threads

Threads — Functions for using GDK in multi-threaded programs

Includes

#include <gdk/gdk.h>

Description

For thread safety, GDK relies on the thread primitives in GLib, and on the thread-safe GLib main loop.

GLib is completely thread safe (all global data is automatically locked), but individual data structure instances are not automatically locked for performance reasons. So e.g. you must coordinate accesses to the same GHashTable from multiple threads.

GTK+, however, is not thread safe. You should only use GTK+ and GDK from the thread gtk_init() and gtk_main() were called on. This is usually referred to as the “main thread”.

Signals on GTK+ and GDK types, as well as non-signal callbacks, are emitted in the main thread.

You can schedule work in the main thread safely from other threads by using gdk_threads_add_idle() and gdk_threads_add_timeout():

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static void
worker_thread (void)
{
  ExpensiveData *expensive_data = do_expensive_computation ();

  gdk_threads_add_idle (got_value, expensive_data);
}

static gboolean
got_value (gpointer user_data)
{
  ExpensiveData *expensive_data = user_data;

  my_app->expensive_data = expensive_data;
  gtk_button_set_sensitive (my_app->button, TRUE);
  gtk_button_set_label (my_app->button, expensive_data->result_label);

  return G_SOURCE_REMOVE;
}

You should use gdk_threads_add_idle() and gdk_threads_add_timeout() instead of g_idle_add() and g_timeout_add() since libraries not under your control might be using the deprecated GDK locking mechanism. If you are sure that none of the code in your application and libraries use the deprecated gdk_threads_enter() or gdk_threads_leave() methods, then you can safely use g_idle_add() and g_timeout_add().

For more information on this "worker thread" pattern, you should also look at GTask, which gives you high-level tools to perform expensive tasks from worker threads, and will handle thread management for you.

Functions

GDK_THREADS_ENTER

#define GDK_THREADS_ENTER() gdk_threads_enter()

GDK_THREADS_ENTER has been deprecated since version 3.6 and should not be used in newly-written code.

Use g_main_context_invoke(), g_idle_add() and related functions if you need to schedule GTK+ calls from other threads.

This macro marks the beginning of a critical section in which GDK and GTK+ functions can be called safely and without causing race conditions. Only one thread at a time can be in such a critial section. The macro expands to a no-op if G_THREADS_ENABLED has not been defined. Typically gdk_threads_enter() should be used instead of this macro.


GDK_THREADS_LEAVE

#define GDK_THREADS_LEAVE() gdk_threads_leave()

GDK_THREADS_LEAVE has been deprecated since version 3.6 and should not be used in newly-written code.

Deprecated in 3.6.

This macro marks the end of a critical section begun with GDK_THREADS_ENTER.


gdk_threads_init ()

void
gdk_threads_init (void);

gdk_threads_init has been deprecated since version 3.6 and should not be used in newly-written code.

All GDK and GTK+ calls should be made from the main thread

Initializes GDK so that it can be used from multiple threads in conjunction with gdk_threads_enter() and gdk_threads_leave().

This call must be made before any use of the main loop from GTK+; to be safe, call it before gtk_init().


gdk_threads_enter ()

void
gdk_threads_enter (void);

gdk_threads_enter has been deprecated since version 3.6 and should not be used in newly-written code.

All GDK and GTK+ calls should be made from the main thread

This function marks the beginning of a critical section in which GDK and GTK+ functions can be called safely and without causing race conditions. Only one thread at a time can be in such a critial section.


gdk_threads_leave ()

void
gdk_threads_leave (void);

gdk_threads_leave has been deprecated since version 3.6 and should not be used in newly-written code.

All GDK and GTK+ calls should be made from the main thread

Leaves a critical region begun with gdk_threads_enter().


gdk_threads_set_lock_functions ()

void
gdk_threads_set_lock_functions (GCallback enter_fn,
                                GCallback leave_fn);

gdk_threads_set_lock_functions has been deprecated since version 3.6 and should not be used in newly-written code.

All GDK and GTK+ calls should be made from the main thread

Allows the application to replace the standard method that GDK uses to protect its data structures. Normally, GDK creates a single GMutex that is locked by gdk_threads_enter(), and released by gdk_threads_leave(); using this function an application provides, instead, a function enter_fn that is called by gdk_threads_enter() and a function leave_fn that is called by gdk_threads_leave().

The functions must provide at least same locking functionality as the default implementation, but can also do extra application specific processing.

As an example, consider an application that has its own recursive lock that when held, holds the GTK+ lock as well. When GTK+ unlocks the GTK+ lock when entering a recursive main loop, the application must temporarily release its lock as well.

Most threaded GTK+ apps won’t need to use this method.

This method must be called before gdk_threads_init(), and cannot be called multiple times.

[skip]

Parameters

enter_fn

function called to guard GDK

 

leave_fn

function called to release the guard

 

Since: 2.4


gdk_threads_add_idle ()

guint
gdk_threads_add_idle (GSourceFunc function,
                      gpointer data);

A wrapper for the common usage of gdk_threads_add_idle_full() assigning the default priority, G_PRIORITY_DEFAULT_IDLE.

See gdk_threads_add_idle_full().

[skip]

Parameters

function

function to call

 

data

data to pass to function

 

Returns

the ID (greater than 0) of the event source.

Since: 2.12


gdk_threads_add_idle_full ()

guint
gdk_threads_add_idle_full (gint priority,
                           GSourceFunc function,
                           gpointer data,
                           GDestroyNotify notify);

Adds a function to be called whenever there are no higher priority events pending. If the function returns FALSE it is automatically removed from the list of event sources and will not be called again.

This variant of g_idle_add_full() calls function with the GDK lock held. It can be thought of a MT-safe version for GTK+ widgets for the following use case, where you have to worry about idle_callback() running in thread A and accessing self after it has been finalized in thread B:

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static gboolean
idle_callback (gpointer data)
{
   // gdk_threads_enter(); would be needed for g_idle_add()

   SomeWidget *self = data;
   // do stuff with self

   self->idle_id = 0;

   // gdk_threads_leave(); would be needed for g_idle_add()
   return FALSE;
}

static void
some_widget_do_stuff_later (SomeWidget *self)
{
   self->idle_id = gdk_threads_add_idle (idle_callback, self)
   // using g_idle_add() here would require thread protection in the callback
}

static void
some_widget_finalize (GObject *object)
{
   SomeWidget *self = SOME_WIDGET (object);
   if (self->idle_id)
     g_source_remove (self->idle_id);
   G_OBJECT_CLASS (parent_class)->finalize (object);
}

[rename-to gdk_threads_add_idle]

Parameters

priority

the priority of the idle source. Typically this will be in the range between G_PRIORITY_DEFAULT_IDLE and G_PRIORITY_HIGH_IDLE

 

function

function to call

 

data

data to pass to function

 

notify

function to call when the idle is removed, or NULL.

[allow-none]

Returns

the ID (greater than 0) of the event source.

Since: 2.12


gdk_threads_add_timeout ()

guint
gdk_threads_add_timeout (guint interval,
                         GSourceFunc function,
                         gpointer data);

A wrapper for the common usage of gdk_threads_add_timeout_full() assigning the default priority, G_PRIORITY_DEFAULT.

See gdk_threads_add_timeout_full().

[skip]

Parameters

interval

the time between calls to the function, in milliseconds (1/1000ths of a second)

 

function

function to call

 

data

data to pass to function

 

Returns

the ID (greater than 0) of the event source.

Since: 2.12


gdk_threads_add_timeout_full ()

guint
gdk_threads_add_timeout_full (gint priority,
                              guint interval,
                              GSourceFunc function,
                              gpointer data,
                              GDestroyNotify notify);

Sets a function to be called at regular intervals holding the GDK lock, with the given priority. The function is called repeatedly until it returns FALSE, at which point the timeout is automatically destroyed and the function will not be called again. The notify function is called when the timeout is destroyed. The first call to the function will be at the end of the first interval .

Note that timeout functions may be delayed, due to the processing of other event sources. Thus they should not be relied on for precise timing. After each call to the timeout function, the time of the next timeout is recalculated based on the current time and the given interval (it does not try to “catch up” time lost in delays).

This variant of g_timeout_add_full() can be thought of a MT-safe version for GTK+ widgets for the following use case:

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static gboolean timeout_callback (gpointer data)
{
   SomeWidget *self = data;
   
   // do stuff with self
   
   self->timeout_id = 0;
   
   return G_SOURCE_REMOVE;
}
 
static void some_widget_do_stuff_later (SomeWidget *self)
{
   self->timeout_id = g_timeout_add (timeout_callback, self)
}
 
static void some_widget_finalize (GObject *object)
{
   SomeWidget *self = SOME_WIDGET (object);
   
   if (self->timeout_id)
     g_source_remove (self->timeout_id);
   
   G_OBJECT_CLASS (parent_class)->finalize (object);
}

[rename-to gdk_threads_add_timeout]

Parameters

priority

the priority of the timeout source. Typically this will be in the range between G_PRIORITY_DEFAULT_IDLE and G_PRIORITY_HIGH_IDLE.

 

interval

the time between calls to the function, in milliseconds (1/1000ths of a second)

 

function

function to call

 

data

data to pass to function

 

notify

function to call when the timeout is removed, or NULL.

[allow-none]

Returns

the ID (greater than 0) of the event source.

Since: 2.12


gdk_threads_add_timeout_seconds ()

guint
gdk_threads_add_timeout_seconds (guint interval,
                                 GSourceFunc function,
                                 gpointer data);

A wrapper for the common usage of gdk_threads_add_timeout_seconds_full() assigning the default priority, G_PRIORITY_DEFAULT.

For details, see gdk_threads_add_timeout_full().

[skip]

Parameters

interval

the time between calls to the function, in seconds

 

function

function to call

 

data

data to pass to function

 

Returns

the ID (greater than 0) of the event source.

Since: 2.14


gdk_threads_add_timeout_seconds_full ()

guint
gdk_threads_add_timeout_seconds_full (gint priority,
                                      guint interval,
                                      GSourceFunc function,
                                      gpointer data,
                                      GDestroyNotify notify);

A variant of gdk_threads_add_timeout_full() with second-granularity. See g_timeout_add_seconds_full() for a discussion of why it is a good idea to use this function if you don’t need finer granularity.

[rename-to gdk_threads_add_timeout_seconds]

Parameters

priority

the priority of the timeout source. Typically this will be in the range between G_PRIORITY_DEFAULT_IDLE and G_PRIORITY_HIGH_IDLE.

 

interval

the time between calls to the function, in seconds

 

function

function to call

 

data

data to pass to function

 

notify

function to call when the timeout is removed, or NULL.

[allow-none]

Returns

the ID (greater than 0) of the event source.

Since: 2.14

Types and Values