dispatch_object(3)
NAME
dispatch_object -- General manipulation of dispatch objects
SYNOPSIS
#include <dispatch/dispatch.h> void dispatch_retain(dispatch_object_t object); void dispatch_release(dispatch_object_t object); void dispatch_suspend(dispatch_object_t object); void dispatch_resume(dispatch_object_t object); void * dispatch_get_context(dispatch_object_t object); void dispatch_set_context(dispatch_object_t object, void *context); void dispatch_set_finalizer_f(dispatch_object_t object, dispatch_function_t finalizer);
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 dispatch_retain() and
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 dispatch_suspend() and
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 dispatch_suspend() and
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
dispatch_get_context() and dispatch_set_context() respectively. The
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.