glibmm: Gio::Cancellable Class Reference

Allows actions to be cancelled. More...

#include </home/kjell/checkout/gnome/glibmm/gio/giomm/cancellable.h>

Inheritance diagram for Gio::Cancellable:

Public Types

using SlotCancelledCallback = sigc::slot< void()>
 
- Public Types inherited from Glib::Object
using DestroyNotify = void(*)(gpointer data)
 
- Public Types inherited from sigc::trackable
typedef internal::func_destroy_notify func_destroy_notify
 
- Public Types inherited from sigc::notifiable
typedef internal::func_destroy_notify func_destroy_notify
 

Public Member Functions

 Cancellable (Cancellable&& src) noexcept
 
Cancellableoperator= (Cancellable&& src) noexcept
 
 ~Cancellable () noexcept override
 
GCancellable* gobj ()
 Provides access to the underlying C GObject. More...

 
const GCancellable* gobj () const
 Provides access to the underlying C GObject. More...

 
GCancellable* gobj_copy ()
 Provides access to the underlying C instance. The caller is responsible for unrefing it. Use when directly setting fields in structs. More...

 
bool is_cancelled () const
 Checks if a cancellable job has been cancelled. More...

 
int get_fd () const
 Gets the file descriptor for a cancellable job. More...

 
bool make_pollfd (GPollFD* pollfd)
 Creates a PollFD corresponding to cancellable; this can be passed to Glib::poll() and used to poll for cancellation. More...

 
void release_fd ()
 Releases a resources previously allocated by g_cancellable_get_fd() or g_cancellable_make_pollfd(). More...

 
void cancel ()
 Will set cancellable to cancelled, and will emit the Cancellable::signal_cancelled() signal. More...

 
void push_current ()
 Pushes cancellable onto the cancellable stack. More...

 
void pop_current ()
 Pops cancellable off the cancellable stack (verifying that cancellable is on the top of the stack). More...

 
void reset ()
 Resets cancellable to its uncancelled state. More...

 
gulong connect (const SlotCancelledCallback& slot)
 Convenience function to connect to the Cancellable::signal_cancelled() signal. More...

 
void disconnect (gulong handler_id)
 Disconnects a handler from a cancellable instance similar to Glib::signal_handler_disconnect(). More...

 
Glib::SignalProxy< void()> signal_cancelled ()
 
- Public Member Functions inherited from Glib::Object
 Object (const Object&)=delete
 
Objectoperator= (const Object&)=delete
 
 Object (Object&& src) noexcept
 
Objectoperator= (Object&& src) noexcept
 
void* get_data (const QueryQuark& key)
 
void set_data (const Quark& key, void* data)
 
void set_data (const Quark& key, void* data, DestroyNotify notify)
 
void remove_data (const QueryQuark& quark)
 
void* steal_data (const QueryQuark& quark)
 
- Public Member Functions inherited from Glib::ObjectBase
 ObjectBase (const ObjectBase&)=delete
 
ObjectBaseoperator= (const ObjectBase&)=delete
 
void set_property_value (const Glib::ustring& property_name, const Glib::ValueBase& value)
 You probably want to use a specific property_*() accessor method instead. More...

 
void get_property_value (const Glib::ustring& property_name, Glib::ValueBase& value) const
 You probably want to use a specific property_*() accessor method instead. More...

 
template<class PropertyType >
void set_property (const Glib::ustring& property_name, const PropertyType& value)
 You probably want to use a specific property_*() accessor method instead. More...

 
template<class PropertyType >
void get_property (const Glib::ustring& property_name, PropertyType& value) const
 You probably want to use a specific property_*() accessor method instead. More...

 
template<class PropertyType >
PropertyType get_property (const Glib::ustring& property_name) const
 You probably want to use a specific property_*() accessor method instead. More...

 
sigc::connection connect_property_changed (const Glib::ustring& property_name, const sigc::slot< void()>& slot)
 You can use the signal_changed() signal of the property proxy instead. More...

 
sigc::connection connect_property_changed (const Glib::ustring& property_name, sigc::slot< void()>&& slot)
 You can use the signal_changed() signal of the property proxy instead. More...

 
void freeze_notify ()
 Increases the freeze count on object. More...

 
void thaw_notify ()
 Reverts the effect of a previous call to freeze_notify(). More...

 
virtual void reference () const
 Increment the reference count for this object. More...

 
virtual void unreference () const
 Decrement the reference count for this object. More...

 
GObject* gobj ()
 Provides access to the underlying C GObject. More...

 
const GObject* gobj () const
 Provides access to the underlying C GObject. More...

 
GObject* gobj_copy () const
 Give a ref-ed copy to someone. Use for direct struct access. More...

 
- Public Member Functions inherited from sigc::trackable
 trackable () noexcept
 
 trackable (const trackable &src) noexcept
 
 trackable (trackable &&src) noexcept
 
 ~trackable ()
 
void add_destroy_notify_callback (notifiable *data, func_destroy_notify func) const
 
void notify_callbacks ()
 
trackableoperator= (const trackable &src)
 
trackableoperator= (trackable &&src) noexcept
 
void remove_destroy_notify_callback (notifiable *data) const
 

Static Public Member Functions

static GType get_type ()
 Get the GType for this class, for use with the underlying GObject type system. More...

 
static Glib::RefPtr< Cancellablecreate ()
 
static Glib::RefPtr< Cancellableget_current ()
 Gets the top cancellable from the stack. More...

 

Protected Member Functions

 Cancellable ()
 
virtual void on_cancelled ()
 This is a default handler for the signal signal_cancelled(). More...

 
- Protected Member Functions inherited from Glib::Object
 Object ()
 
 Object (const Glib::ConstructParams& construct_params)
 
 Object (GObject* castitem)
 
 ~Object () noexcept override
 
- Protected Member Functions inherited from Glib::ObjectBase
 ObjectBase ()
 This default constructor is called implicitly from the constructor of user-derived classes, even if, for instance, Gtk::Button calls a different ObjectBase constructor. More...

 
 ObjectBase (const char* custom_type_name)
 A derived constructor always overrides this choice. More...

 
 ObjectBase (const std::type_info& custom_type_info)
 This constructor is a special feature to allow creation of derived types on the fly, without having to use g_object_new() manually. More...

 
 ObjectBase (ObjectBase&& src) noexcept
 
ObjectBaseoperator= (ObjectBase&& src) noexcept
 
virtual ~ObjectBase () noexcept=0
 
void initialize (GObject* castitem)
 
void initialize_move (GObject* castitem, Glib::ObjectBase* previous_wrapper)
 

Related Functions

(Note that these are not member functions.)

Glib::RefPtr< Gio::Cancellablewrap (GCancellable* object, bool take_copy=false)
 A Glib::wrap() method for this object. More...

 

Detailed Description

Allows actions to be cancelled.

Cancellable is a thread-safe operation cancellation stack used throughout GIO to allow for cancellation of synchronous and asynchronous operations.

Since glibmm 2.16:

Member Typedef Documentation

using Gio::Cancellable::SlotCancelledCallback = sigc::slot<void()>

Constructor & Destructor Documentation

Gio::Cancellable::Cancellable ( Cancellable&&  src)
noexcept
Gio::Cancellable::~Cancellable ( )
overridenoexcept
Gio::Cancellable::Cancellable ( )
protected

Member Function Documentation

void Gio::Cancellable::cancel ( )

Will set cancellable to cancelled, and will emit the Cancellable::signal_cancelled() signal.

(However, see the warning about race conditions in the documentation for that signal if you are planning to connect to it.)

This function is thread-safe. In other words, you can safely call it from a thread other than the one running the operation that was passed the cancellable.

If cancellable is nullptr, this function returns immediately for convenience.

The convention within GIO is that cancelling an asynchronous operation causes it to complete asynchronously. That is, if you cancel the operation from the same thread in which it is running, then the operation's SlotAsyncReady will not be invoked until the application returns to the main loop.

gulong Gio::Cancellable::connect ( const SlotCancelledCallback slot)

Convenience function to connect to the Cancellable::signal_cancelled() signal.

Also handles the race condition that may happen if the cancellable is cancelled right before connecting.

slot is called at most once, either directly at the time of the connect if cancellable is already cancelled, or when cancellable is cancelled in some thread.

See Cancellable::signal_cancelled() for details on how to use this.

Since glibmm 2.22:
Parameters
slotThe slot to connect.
Returns
The id of the signal handler or 0 if cancellable has already been cancelled.
static Glib::RefPtr<Cancellable> Gio::Cancellable::create ( )
static
void Gio::Cancellable::disconnect ( gulong  handler_id)

Disconnects a handler from a cancellable instance similar to Glib::signal_handler_disconnect().

Additionally, in the event that a signal handler is currently running, this call will block until the handler has finished. Calling this function from a Cancellable::signal_cancelled() signal handler will therefore result in a deadlock.

This avoids a race condition where a thread cancels at the same time as the cancellable operation is finished and the signal handler is removed. See Cancellable::signal_cancelled() for details on how to use this.

If cancellable is nullptr or handler_id is 0 this function does nothing.

Since glibmm 2.22:
Parameters
handler_idHandler id of the handler to be disconnected, or 0.
static Glib::RefPtr<Cancellable> Gio::Cancellable::get_current ( )
static

Gets the top cancellable from the stack.

Returns
A Cancellable from the top of the stack, or nullptr if the stack is empty.
int Gio::Cancellable::get_fd ( ) const

Gets the file descriptor for a cancellable job.

This can be used to implement cancellable operations on Unix systems. The returned fd will turn readable when cancellable is cancelled.

You are not supposed to read from the fd yourself, just check for readable status. Reading to unset the readable status is done with g_cancellable_reset().

After a successful return from this function, you should use g_cancellable_release_fd() to free up resources allocated for the returned file descriptor.

See also g_cancellable_make_pollfd().

Returns
A valid file descriptor. -1 if the file descriptor is not supported, or on errors.
static GType Gio::Cancellable::get_type ( )
static

Get the GType for this class, for use with the underlying GObject type system.

GCancellable* Gio::Cancellable::gobj ( )
inline

Provides access to the underlying C GObject.

const GCancellable* Gio::Cancellable::gobj ( ) const
inline

Provides access to the underlying C GObject.

GCancellable* Gio::Cancellable::gobj_copy ( )

Provides access to the underlying C instance. The caller is responsible for unrefing it. Use when directly setting fields in structs.

bool Gio::Cancellable::is_cancelled ( ) const

Checks if a cancellable job has been cancelled.

Returns
true if cancellable is cancelled, false if called with nullptr or if item is not cancelled.
bool Gio::Cancellable::make_pollfd ( GPollFD *  pollfd)

Creates a PollFD corresponding to cancellable; this can be passed to Glib::poll() and used to poll for cancellation.

This is useful both for unix systems without a native poll and for portability to windows.

When this function returns true, you should use g_cancellable_release_fd() to free up resources allocated for the pollfd. After a false return, do not call g_cancellable_release_fd().

If this function returns false, either no cancellable was given or resource limits prevent this function from allocating the necessary structures for polling. (On Linux, you will likely have reached the maximum number of file descriptors.) The suggested way to handle these cases is to ignore the cancellable.

You are not supposed to read from the fd yourself, just check for readable status. Reading to unset the readable status is done with g_cancellable_reset().

Since glibmm 2.22:
Parameters
pollfdA pointer to a PollFD.
Returns
true if pollfd was successfully initialized, false on failure to prepare the cancellable.
virtual void Gio::Cancellable::on_cancelled ( )
protectedvirtual

This is a default handler for the signal signal_cancelled().

Cancellable& Gio::Cancellable::operator= ( Cancellable&&  src)
noexcept
void Gio::Cancellable::pop_current ( )

Pops cancellable off the cancellable stack (verifying that cancellable is on the top of the stack).

void Gio::Cancellable::push_current ( )

Pushes cancellable onto the cancellable stack.

The current cancellable can then be received using g_cancellable_get_current().

This is useful when implementing cancellable operations in code that does not allow you to pass down the cancellable object.

This is typically called automatically by e.g. File operations, so you rarely have to call this yourself.

void Gio::Cancellable::release_fd ( )

Releases a resources previously allocated by g_cancellable_get_fd() or g_cancellable_make_pollfd().

For compatibility reasons with older releases, calling this function is not strictly required, the resources will be automatically freed when the cancellable is finalized. However, the cancellable will block scarce file descriptors until it is finalized if this function is not called. This can cause the application to run out of file descriptors when many Cancellables are used at the same time.

Since glibmm 2.22:
void Gio::Cancellable::reset ( )

Resets cancellable to its uncancelled state.

If cancellable is currently in use by any cancellable operation then the behavior of this function is undefined.

Note that it is generally not a good idea to reuse an existing cancellable for more operations after it has been cancelled once, as this function might tempt you to do. The recommended practice is to drop the reference to a cancellable after cancelling it, and let it die with the outstanding async operations. You should create a fresh cancellable for further async operations.

Glib::SignalProxy<void()> Gio::Cancellable::signal_cancelled ( )
Slot Prototype:
void on_my_cancelled()

Flags: Run Last

Emitted when the operation has been cancelled.

Can be used by implementations of cancellable operations. If the operation is cancelled from another thread, the signal will be emitted in the thread that cancelled the operation, not the thread that is running the operation.

Note that disconnecting from this signal (or any signal) in a multi-threaded program is prone to race conditions. For instance it is possible that a signal handler may be invoked even after a call to Glib::signal_handler_disconnect() for that handler has already returned.

There is also a problem when cancellation happens right before connecting to the signal. If this happens the signal will unexpectedly not be emitted, and checking before connecting to the signal leaves a race condition where this is still happening.

In order to make it safe and easy to connect handlers there are two helper functions: g_cancellable_connect() and g_cancellable_disconnect() which protect against problems like this.

An example of how to us this:

[C example ellipted]

Note that the cancelled signal is emitted in the thread that the user cancelled from, which may be the main thread. So, the cancellable signal should not do something that can block.

Friends And Related Function Documentation

Glib::RefPtr< Gio::Cancellable > wrap ( GCancellable *  object,
bool  take_copy = false 
)
related

A Glib::wrap() method for this object.

Parameters
objectThe C instance.
take_copyFalse if the result should take ownership of the C instance. True if it should take a new copy or ref.
Returns
A C++ instance that wraps this C instance.