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)
