class Gio::Cancellable

Overview

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

Defined in:

auto/gio-2.0/cancellable.cr

Constructors

Class Method Summary

Instance Method Summary

Instance methods inherited from class GObject::Object

bind_property(source_property : String, target : GObject::Object, target_property : String, flags : GObject::BindingFlags) : GObject::Binding bind_property, bind_property_full(source_property : String, target : GObject::Object, target_property : String, flags : GObject::BindingFlags, transform_to : GObject::Closure, transform_from : GObject::Closure) : GObject::Binding bind_property_full, data(key : String) : Pointer(Void)? data, finalize finalize, freeze_notify : Nil freeze_notify, getv(names : Enumerable(String), values : Enumerable(_)) : Nil getv, notify(property_name : String) : Nil notify, notify_by_pspec(pspec : GObject::ParamSpec) : Nil notify_by_pspec, notify_signal notify_signal, property(property_name : String, value : _) : Nil property, qdata(quark : UInt32) : Pointer(Void)? qdata, ref_count ref_count, run_dispose : Nil run_dispose, set_data(key : String, data : Pointer(Void)?) : Nil set_data, set_property(property_name : String, value : _) : Nil set_property, steal_data(key : String) : Pointer(Void)? steal_data, steal_qdata(quark : UInt32) : Pointer(Void)? steal_qdata, thaw_notify : Nil thaw_notify, to_unsafe : Pointer(Void) to_unsafe, watch_closure(closure : GObject::Closure) : Nil watch_closure

Constructor methods inherited from class GObject::Object

cast(obj : GObject::Object) : self cast, cast?(obj : GObject::Object) : self? cast?, new new, newv(object_type : UInt64, parameters : Enumerable(GObject::Parameter)) : self newv

Class methods inherited from class GObject::Object

compat_control(what : UInt64, data : Pointer(Void)?) : UInt64 compat_control, g_type : UInt64 g_type, interface_find_property(g_iface : GObject::TypeInterface, property_name : String) : GObject::ParamSpec interface_find_property, interface_list_properties(g_iface : GObject::TypeInterface) : Enumerable(GObject::ParamSpec) interface_list_properties

Constructor Detail

def self.new #

Creates a new #GCancellable object.

Applications that want to start one or more operations that should be cancellable should create a #GCancellable and pass it to the operations.

One #GCancellable can be used in multiple consecutive operations or in multiple concurrent operations.


Class Method Detail

def self.current : Gio::Cancellable? #

Gets the top cancellable from the stack.


def self.g_type : UInt64 #

Returns the type id (GType) registered in GLib type system.


Instance Method Detail

def cancel : Nil #

Will set @cancellable to cancelled, and will emit the #GCancellable::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 %NULL, 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 #GAsyncReadyCallback will not be invoked until the application returns to the main loop.


def cancelled_signal #

def connect(callback : GObject::Callback) : UInt64 #

Convenience function to connect to the #GCancellable::cancelled signal. Also handles the race condition that may happen if the cancellable is cancelled right before connecting.

@callback 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.

@data_destroy_func will be called when the handler is disconnected, or immediately if the cancellable is already cancelled.

See #GCancellable::cancelled for details on how to use this.

Since GLib 2.40, the lock protecting @cancellable is not held when @callback is invoked. This lifts a restriction in place for earlier GLib versions which now makes it easier to write cleanup code that unconditionally invokes e.g. g_cancellable_cancel().


def disconnect(handler_id : UInt64) : Nil #

Disconnects a handler from a cancellable instance similar to g_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 #GCancellable::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 #GCancellable::cancelled for details on how to use this.

If @cancellable is %NULL or @handler_id is 0 this function does nothing.


def fd : Int32 #

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().


def is_cancelled : Bool #

Checks if a cancellable job has been cancelled.


def make_pollfd(pollfd : GLib::PollFD) : Bool #

Creates a #GPollFD corresponding to @cancellable; this can be passed to g_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().


def pop_current : Nil #

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


def push_current : Nil #

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. #GFile operations, so you rarely have to call this yourself.


def release_fd : Nil #

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 #GCancellables are used at the same time.


def reset : Nil #

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.


def set_error_if_cancelled : Bool #

If the @cancellable is cancelled, sets the error to notify that the operation was cancelled.


def source_new : GLib::Source #

Creates a source that triggers if @cancellable is cancelled and calls its callback of type #GCancellableSourceFunc. This is primarily useful for attaching to another (non-cancellable) source with g_source_add_child_source() to add cancellability to it.

For convenience, you can call this with a %NULL #GCancellable, in which case the source will never trigger.

The new #GSource will hold a reference to the #GCancellable.