table of contents
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|dispatch_object(3)||Library Functions Manual||dispatch_object(3)|
General manipulation of dispatch objects
object, void *context);
object, dispatch_function_t finalizer);
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).
Objects returned by creation functions in the dispatch framework
may be uniformly retained and released with the functions
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.
The invocation of blocks on dispatch queues or dispatch sources
may be suspended or resumed with the functions
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.
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
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 pointer may be retrieved and updated with
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.
dispatch(3), dispatch_group_create(3), dispatch_queue_create(3), dispatch_semaphore_create(3), dispatch_source_create(3)
|May 1, 2009||Darwin|