## GCancellable

GCancellable — Thread-safe Operation Cancellation Stack

## Synopsis

    #include <gio/gio.h>

                        GCancellable;
    GCancellable *      g_cancellable_new                   (void);
    gboolean            g_cancellable_is_cancelled          (GCancellable *cancellable);
    gboolean            g_cancellable_set_error_if_cancelled
                                                            (GCancellable *cancellable,
                                                             GError **error);
    int                 g_cancellable_get_fd                (GCancellable *cancellable);
    GCancellable *      g_cancellable_get_current           (void);
    void                g_cancellable_pop_current           (GCancellable *cancellable);
    void                g_cancellable_push_current          (GCancellable *cancellable);
    void                g_cancellable_reset                 (GCancellable *cancellable);
    void                g_cancellable_cancel                (GCancellable *cancellable);

## Object Hierarchy

      GObject
       +----GCancellable

## Signals

      "cancelled"                                      : Run Last

## Description

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

## Details

### GCancellable

    typedef struct _GCancellable GCancellable;

Allows actions to be cancelled.

### g_cancellable_new ()

    GCancellable *      g_cancellable_new                   (void);

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, but not in multiple concurrent operations.

Returns : | a GCancellable.

### g_cancellable_is_cancelled ()

    gboolean            g_cancellable_is_cancelled          (GCancellable *cancellable);

Checks if a cancellable job has been cancelled.

`cancellable` : | a GCancellable or NULL.
Returns : | `TRUE` if `cancellable` is cancelled, FALSE if called with `NULL` or if item is not cancelled.

### g_cancellable_set_error_if_cancelled ()

    gboolean            g_cancellable_set_error_if_cancelled
                                                            (GCancellable *cancellable,
                                                             GError **error);

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

`cancellable` : | a GCancellable object.
`error` : | GError to append error state to.
Returns : | `TRUE` if `cancellable` was cancelled, `FALSE` if it was not.

### g_cancellable_get_fd ()

    int                 g_cancellable_get_fd                (GCancellable *cancellable);

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.

`cancellable` : | a GCancellable.
Returns : | A valid file descriptor. `-1` if the file descriptor is not supported, or on errors.

### g_cancellable_get_current ()

    GCancellable *      g_cancellable_get_current           (void);

Gets the top cancellable from the stack.

Returns : | a GCancellable from the top of the stack, or `NULL` if the stack is empty.

### g_cancellable_pop_current ()

    void                g_cancellable_pop_current           (GCancellable *cancellable);

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

`cancellable` : | optional GCancellable object, `NULL` to ignore.

### g_cancellable_push_current ()

    void                g_cancellable_push_current          (GCancellable *cancellable);

Pushes `cancellable` onto the cancellable stack. The current cancllable can then be recieved 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.

`cancellable` : | optional GCancellable object, `NULL` to ignore.

### g_cancellable_reset ()

    void                g_cancellable_reset                 (GCancellable *cancellable);

Resets `cancellable` to its uncancelled state.

`cancellable` : | a GCancellable object.

### g_cancellable_cancel ()

    void                g_cancellable_cancel                (GCancellable *cancellable);

Will set `cancellable` to cancelled, and will emit the CANCELLED signal.

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

`cancellable` : | a GCancellable object.

## Signal Details

### The `"cancelled"` signal

    void                user_function                      (GCancellable *cancellable,
                                                            gpointer      user_data)        : Run Last

Emitted when the operation has been cancelled from another thread.

Can be used by implementations of cancellable operations. This will be emitted in the thread that tried to cancel the operation, not the thread the is running the operation.

`cancellable` : | a GCancellable.
`user_data` : | user data set when the signal handler was connected.