Cancellable
Superclasses: Object
- Constructors:
Cancellable(**properties)
new() -> Gio.Cancellable
Constructors
- class Cancellable
- classmethod new() Cancellable
Creates a new
Cancellable
object.Applications that want to start one or more operations that should be cancellable should create a
Cancellable
and pass it to the operations.One
Cancellable
can be used in multiple consecutive operations or in multiple concurrent operations.
Methods
- class Cancellable
- cancel() None
Will set
cancellable
to cancelled, and will emit theCancellable
::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
isNone
, 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
AsyncReadyCallback
will not be invoked until the application returns to the main loop.
- connect(callback: Callable[[...], None], *data: Any) int
Convenience function to connect to the
Cancellable
::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 ifcancellable
is already cancelled, or whencancellable
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
Cancellable
::cancelled for details on how to use this.Since GLib 2.40, the lock protecting
cancellable
is not held whencallback
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.cancel()
.Added in version 2.22.
- Parameters:
callback – The
Callback
to connect.data – Data to pass to
callback
.
- disconnect(handler_id: int) None
Disconnects a handler from a cancellable instance similar to
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 aCancellable
::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
::cancelled for details on how to use this.If
cancellable
isNone
orhandler_id
is0
this function does nothing.Added in version 2.22.
- Parameters:
handler_id – Handler id of the handler to be disconnected, or
0
.
- get_current() Cancellable | None
Gets the top cancellable from the stack.
- get_fd() int
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
reset()
.After a successful return from this function, you should use
release_fd()
to free up resources allocated for the returned file descriptor.See also
make_pollfd()
.
- make_pollfd(pollfd: PollFD) bool
Creates a
PollFD
corresponding tocancellable
; this can be passed topoll()
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 userelease_fd()
to free up resources allocated for thepollfd
. After aFalse
return, do not callrelease_fd()
.If this function returns
False
, either nocancellable
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 thecancellable
.You are not supposed to read from the fd yourself, just check for readable status. Reading to unset the readable status is done with
reset()
.Added in version 2.22.
- Parameters:
pollfd – a pointer to a
PollFD
- pop_current() None
Pops
cancellable
off the cancellable stack (verifying thatcancellable
is on the top of the stack).
- push_current() None
Pushes
cancellable
onto the cancellable stack. The current cancellable can then be received usingget_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.
- release_fd() None
Releases a resources previously allocated by
get_fd()
ormake_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, thecancellable
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 manyCancellable
are used at the same time.Added in version 2.22.
- reset() None
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.
- set_error_if_cancelled() bool
If the
cancellable
is cancelled, sets the error to notify that the operation was cancelled.
- source_new() Source
Creates a source that triggers if
cancellable
is cancelled and calls its callback of typeGCancellableSourceFunc
. This is primarily useful for attaching to another (non-cancellable) source withadd_child_source()
to add cancellability to it.For convenience, you can call this with a
None
Cancellable
, in which case the source will never trigger.The new
Source
will hold a reference to theCancellable
.Added in version 2.28.