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dispatch_object(3)                      BSD Library Functions Manual                      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 con-text context
     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).

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 point 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 to that is invoked asyn-chronously asynchronously
     chronously 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.

SEE ALSO
     dispatch_group_create(3), dispatch_queue_create(3), dispatch_semaphore_create(3),
     dispatch_source_create(3)

Darwin                                           May 1, 2009                                          Darwin