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

Gets the top cancellable from the stack.

Creates a new T object.

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

One T can be used in multiple consecutive operations or in multiple concurrent operations.

Will set cancellable to cancelled, and will emit the "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.

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 Gtk.Gio.GAsyncReadyCallback will not be invoked until the application returns to the main loop.

Convenience function to connect to the "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 "cancelled" for details on how to use this.

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 "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 "cancelled" for details on how to use this.

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

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 ReleaseFd to free up resources allocated for the returned file descriptor.

See also MakePollfd.

Checks if a cancellable job has been cancelled.

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 ReleaseFd to free up resources allocated for the pollfd. After a FALSE return, do not call ReleaseFd.

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 Reset.

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

Pushes cancellable onto the cancellable stack. The current cancellable can then be received using GetCurrent.

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. Gtk.Gio.GFile.T operations, so you rarely have to call this yourself.

Releases a resources previously allocated by GetFd or MakePollfd.

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.

Resets cancellable to its uncancelled state.

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

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