Dispatch objects share functions for coordinating memory management, suspension, cancellation and con- text pointers. While all dispatch objects are retainable, not all objects support suspension, context pointers or finalizers (currently only queues and sources support these additional interfaces).

The invocation of blocks on dispatch queues or dispatch sources may be suspended or resumed with the methods DispatchObject.Suspend() and DispatchObject.Resume() respectively. The dispatch framework always checks the suspension status before executing a block, but such changes never affect a block during execution (non-preemptive). Therefore the suspension of an object is asynchronous, unless it is performed from the context of the target queue for the given object. The result of suspending or resuming an object that is not a dispatch queue or a dispatch source is undefined.

Important: suspension applies to all aspects of the dispatch object life cycle, including the finalizer function and cancellation handler. Therefore it is important to balance calls to DispatchObject.Suspend() and DispatchObject.Resume() such that the dispatch object is fully resumed when the last reference is released. The result of releasing all references to a dispatch object while in a suspended state is undefined.

Dispatch queues and sources support supplemental context pointers. The value of the context point may be retrieved and updated with the DispatchObject.Context property.

The result of getting or setting the context of an object that is not a dispatch queue or a dispatch source is undefined.