Maintainer	gtk2hs-devel@lists.sourceforge.net
Stability	alpha
Portability	portable (depends on GHC)
Safe Haskell	None
Language	Haskell98

System.GIO.Async.Cancellable

Contents

Details
Types
Methods
Signals

Description

Synopsis

Details

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

Types

newtype Cancellable Source

Constructors

Cancellable (ForeignPtr Cancellable)

Instances

Eq Cancellable Source
Ord Cancellable Source
GObjectClass Cancellable Source
CancellableClass Cancellable Source

class GObjectClass o => CancellableClass o Source

Instances

CancellableClass Cancellable Source

Methods

cancellableNew :: IO Cancellable Source

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, but not in multiple concurrent operations.

cancellableIsCancelled Source

Arguments

:: Cancellable
-> IO Bool	returns `True` if cancellable is cancelled, `False` if called with `Nothing` or if item is not cancelled.

Checks if a cancellable job has been cancelled.

cancellableThrowErrorIfCancelled :: Cancellable -> IO () Source

If the cancellable is cancelled, throws a GError to notify that the operation was cancelled.

cancellableGetCurrent Source

Arguments

:: IO (Maybe Cancellable)

returns a Cancellable from the top of the stack, or Nothing if the stack is empty.

Gets the top cancellable from the stack.

cancellablePopCurrent :: Maybe Cancellable -> IO () Source

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

cancellablePushCurrent :: Maybe Cancellable -> IO () Source

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

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.

cancellableReset :: Cancellable -> IO () Source

Resets cancellable to its uncancelled state.

cancellableCancel :: Cancellable -> IO () Source

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 AsyncReadyCallback will not be invoked until the application returns to the main loop.

Signals

cancellableCancelled :: Signal Cancellable (IO ()) Source

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 signalHandlerDisconnect for that handler has already returned.

There is also a problem when cancellation happen 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.