[apple/libdispatch.git] / man / dispatch_object.3

.\" Copyright (c) 2008-2009 Apple Inc. All rights reserved.
.Dd May 1, 2009
.Dt dispatch_object 3
.Os Darwin
.Sh NAME
.Nm dispatch_object
.Nd General manipulation of dispatch objects
.Sh SYNOPSIS
.Fd #include <dispatch/dispatch.h>
.Ft void
.Fo dispatch_retain
.Fa "dispatch_object_t object"
.Fc
.Ft void
.Fo dispatch_release
.Fa "dispatch_object_t object"
.Fc
.Ft void
.Fo dispatch_suspend
.Fa "dispatch_object_t object"
.Fc
.Ft void
.Fo dispatch_resume
.Fa "dispatch_object_t object"
.Fc
.Ft "void *"
.Fo dispatch_get_context
.Fa "dispatch_object_t object"
.Fc
.Ft void
.Fo dispatch_set_context
.Fa "dispatch_object_t object"
.Fa "void *context"
.Fc
.Ft void
.Fo dispatch_set_finalizer_f
.Fa "dispatch_object_t object"
.Fa "dispatch_function_t finalizer"
.Fc
.Sh 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).
.Sh MEMORY MANGEMENT
Objects returned by creation functions in the dispatch framework may be
uniformly retained and released with the functions
.Fn dispatch_retain
and
.Fn dispatch_release
respectively.
.Pp
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.
.Sh SUSPENSION
The invocation of blocks on dispatch queues or dispatch sources may be suspended
or resumed with the functions
.Fn dispatch_suspend
and
.Fn 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.
.Pp
.Em 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
.Fn dispatch_suspend
and
.Fn 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.
.Sh CONTEXT POINTERS
Dispatch queues and sources support supplemental context pointers. The value of
the context point may be retrieved and updated with
.Fn dispatch_get_context
and
.Fn dispatch_set_context
respectively.
The
.Fn dispatch_set_finalizer_f
specifies an optional per-object finalizer function to that is invoked
asynchronously when the last reference to the object is released. This gives the
application an opportunity to free the context data associated with the object.
.Pp
The result of getting or setting the context of an object that is not a
dispatch queue or a dispatch source is undefined.
.Sh SEE ALSO
.Xr dispatch_group_create 3 ,
.Xr dispatch_queue_create 3 ,
.Xr dispatch_semaphore_create 3 ,
.Xr dispatch_source_create 3
Commit	Line	Data
0ab74447 A	1	.\" Copyright (c) 2008-2009 Apple Inc. All rights reserved.
	2	.Dd May 1, 2009
	3	.Dt dispatch_object 3
	4	.Os Darwin
	5	.Sh NAME
	6	.Nm dispatch_object
	7	.Nd General manipulation of dispatch objects
	8	.Sh SYNOPSIS
	9	.Fd #include <dispatch/dispatch.h>
	10	.Ft void
	11	.Fo dispatch_retain
	12	.Fa "dispatch_object_t object"
	13	.Fc
	14	.Ft void
	15	.Fo dispatch_release
	16	.Fa "dispatch_object_t object"
	17	.Fc
	18	.Ft void
	19	.Fo dispatch_suspend
	20	.Fa "dispatch_object_t object"
	21	.Fc
	22	.Ft void
	23	.Fo dispatch_resume
	24	.Fa "dispatch_object_t object"
	25	.Fc
	26	.Ft "void *"
	27	.Fo dispatch_get_context
	28	.Fa "dispatch_object_t object"
	29	.Fc
	30	.Ft void
	31	.Fo dispatch_set_context
	32	.Fa "dispatch_object_t object"
	33	.Fa "void *context"
	34	.Fc
	35	.Ft void
	36	.Fo dispatch_set_finalizer_f
	37	.Fa "dispatch_object_t object"
	38	.Fa "dispatch_function_t finalizer"
	39	.Fc
	40	.Sh DESCRIPTION
	41	Dispatch objects share functions for coordinating memory management, suspension,
	42	cancellation and context pointers. While all dispatch objects are retainable,
	43	not all objects support suspension, context pointers or finalizers (currently
	44	only queues and sources support these additional interfaces).
	45	.Sh MEMORY MANGEMENT
	46	Objects returned by creation functions in the dispatch framework may be
	47	uniformly retained and released with the functions
	48	.Fn dispatch_retain
	49	and
	50	.Fn dispatch_release
	51	respectively.
	52	.Pp
	53	The dispatch framework does not guarantee that any given client has the last or
	54	only reference to a given object. Objects may be retained internally by the
	55	system.
	56	.Sh SUSPENSION
	57	The invocation of blocks on dispatch queues or dispatch sources may be suspended
	58	or resumed with the functions
	59	.Fn dispatch_suspend
	60	and
	61	.Fn dispatch_resume
	62	respectively.
	63	The dispatch framework always checks the suspension status before executing a
	64	block, but such changes never affect a block during execution (non-preemptive).
65	Therefore the suspension of an object is asynchronous, unless it is performed
66	from the context of the target queue for the given object.
67	The result of suspending or resuming an object that is not a dispatch queue or
68	a dispatch source is undefined.
69	.Pp
70	.Em Important :
71	suspension applies to all aspects of the dispatch object life cycle, including
72	the finalizer function and cancellation handler. Therefore it is important to
73	balance calls to
74	.Fn dispatch_suspend
75	and
76	.Fn dispatch_resume
77	such that the dispatch object is fully resumed when the last reference is
78	released. The result of releasing all references to a dispatch object while in
79	a suspended state is undefined.
80	.Sh CONTEXT POINTERS
81	Dispatch queues and sources support supplemental context pointers. The value of
82	the context point may be retrieved and updated with
83	.Fn dispatch_get_context
84	and
85	.Fn dispatch_set_context
86	respectively.
87	The
88	.Fn dispatch_set_finalizer_f
89	specifies an optional per-object finalizer function to that is invoked
90	asynchronously when the last reference to the object is released. This gives the
91	application an opportunity to free the context data associated with the object.
92	.Pp
93	The result of getting or setting the context of an object that is not a
94	dispatch queue or a dispatch source is undefined.
95	.Sh SEE ALSO
96	.Xr dispatch_group_create 3 ,
97	.Xr dispatch_queue_create 3 ,
98	.Xr dispatch_semaphore_create 3 ,
99	.Xr dispatch_source_create 3