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)