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.

SEE ALSO

       dispatch(3),    dispatch_group_create(3),     dispatch_queue_create(3),     dispatch_semaphore_create(3),
       dispatch_source_create(3)

Darwin                                             May 1, 2009                                dispatch_object(3)