SYNOPSIS

Fd #include <dispatch/dispatch.h> Ft void Fo dispatch_retain Fa dispatch_object_t object Fc Ft void Fo dispatch_release Fa dispatch_object_t object Fc Ft void Fo dispatch_suspend Fa dispatch_object_t object Fc Ft void Fo dispatch_resume Fa dispatch_object_t object Fc Ft void * Fo dispatch_get_context Fa dispatch_object_t object Fc Ft void Fo dispatch_set_context Fa dispatch_object_t object Fa void *context Fc Ft void Fo dispatch_set_finalizer_f Fa dispatch_object_t object Fa dispatch_function_t finalizer Fc

DESCRIPTION

Dispatch objects share functions for coordinating memory management, suspension, cancellation and context 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).

MEMORY MANGEMENT

Objects returned by creation functions in the dispatch framework may be uniformly retained and released with the functions Fn dispatch_retain and Fn dispatch_release respectively.

The dispatch framework does not guarantee that any given client has the last or only reference to a given object. Objects may be retained internally by the system.

SUSPENSION

The invocation of blocks on dispatch queues or dispatch sources may be suspended or resumed with the functions Fn dispatch_suspend and Fn dispatch_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 Fn dispatch_suspend and Fn dispatch_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.

CONTEXT POINTERS

Dispatch queues and sources support supplemental context pointers. The value of the context pointer may be retrieved and updated with Fn dispatch_get_context and Fn dispatch_set_context respectively. The Fn dispatch_set_finalizer_f specifies an optional per-object finalizer function that is invoked asynchronously if the context pointer is not NULL when the last reference to the object is released. This gives the application an opportunity to free the context data associated with the object.

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