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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, sus-
     pension, 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 inter-
     nally 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. There-
     fore 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				Darwin

NAME | SYNOPSIS | DESCRIPTION | MEMORY MANGEMENT | SUSPENSION | CONTEXT POINTERS | SEE ALSO

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