man/dispatch_object.3

   1 .\" Copyright (c) 2008-2010 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. Suspending an object causes it
  73 to be retained and resuming an object causes it to be released. Therefore it is
  74 important to balance calls to
  75 .Fn dispatch_suspend
  76 and
  77 .Fn dispatch_resume
  78 such that the dispatch object is fully resumed when the last reference is
  79 released. The result of releasing all references to a dispatch object while in
  80 a suspended state is undefined.
  81 .Sh CONTEXT POINTERS
  82 Dispatch queues and sources support supplemental context pointers. The value of
  83 the context pointer may be retrieved and updated with
  84 .Fn dispatch_get_context
  85 and
  86 .Fn dispatch_set_context
  87 respectively.
  88 The
  89 .Fn dispatch_set_finalizer_f
  90 specifies an optional per-object finalizer function that is invoked
  91 asynchronously if the context pointer is not NULL when the last
  92 reference to the object is released.
  93 This gives the
  94 application an opportunity to free the context data associated with the object.
  95 The finalizer will be run on the object's target queue.
  96 .Pp
  97 The result of getting or setting the context of an object that is not a
  98 dispatch queue or a dispatch source is undefined.
  99 .Sh SEE ALSO
 100 .Xr dispatch 3 ,
 101 .Xr dispatch_group_create 3 ,
 102 .Xr dispatch_queue_create 3 ,
 103 .Xr dispatch_semaphore_create 3 ,
 104 .Xr dispatch_source_create 3 ,
 105 .Xr dispatch_set_target_queue 3