interface/recguard.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        recguard.h
   3 // Purpose:     interface of wxRecursionGuardFlag
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10     @class wxRecursionGuardFlag
  11     @wxheader{recguard.h}
  12
  13     This is a completely opaque class which exists only to be used with
  14     wxRecursionGuard, please see the example in that class' documentation.
  15
  16     @remarks
  17
  18     wxRecursionGuardFlag object must be declared @c static or the recursion
  19     would never be detected.
  20
  21     @library{wxbase}
  22     @category{misc}
  23 */
  24 class wxRecursionGuardFlag
  25 {
  26 public:
  27
  28 };
  29
  30
  31
  32 /**
  33     @class wxRecursionGuard
  34     @wxheader{recguard.h}
  35
  36     wxRecursionGuard is a very simple class which can be used to prevent reentrancy
  37     problems in a function. It is not thread-safe and so should be used only in
  38     single-threaded programs or in combination with some thread synchronization
  39     mechanisms.
  40
  41     wxRecursionGuard is always used together with the
  42     wxRecursionGuardFlag like in this example:
  43
  44     @code
  45     void Foo()
  46     {
  47         static wxRecursionGuardFlag s_flag;
  48         wxRecursionGuard guard(s_flag);
  49         if ( guard.IsInside() )
  50         {
  51             // don't allow reentrancy
  52             return;
  53         }
  54
  55         ...
  56     }
  57     @endcode
  58
  59     As you can see, wxRecursionGuard simply tests the flag value and sets it to
  60     @true if it hadn't been already set.
  61     IsInside() allows testing the old flag
  62     value. The advantage of using this class compared to directly manipulating the
  63     flag is that the flag is always reset in the wxRecursionGuard destructor and so
  64     you don't risk to forget to do it even if the function returns in an unexpected
  65     way (for example because an exception has been thrown).
  66
  67     @library{wxbase}
  68     @category{misc}
  69 */
  70 class wxRecursionGuard
  71 {
  72 public:
  73     /**
  74         A wxRecursionGuard object must always be initialized with a @c static
  75         wxRecursionGuardFlag. The constructor saves the
  76         value of the flag to be able to return the correct value from
  77         IsInside().
  78     */
  79     wxRecursionGuard(wxRecursionGuardFlag& flag);
  80
  81     /**
  82         The destructor resets the flag value so that the function can be entered again
  83         the next time.
  84
  85         @note This is not virtual, so this class is not meant to be derived
  86               from (besides, there is absolutely no reason to do it anyhow).
  87     */
  88     ~wxRecursionGuard();
  89
  90     /**
  91         Returns @true if we're already inside the code block "protected" by this
  92         wxRecursionGuard (i.e. between this line and the end of current scope).
  93         Usually the function using wxRecursionGuard takes some specific actions
  94         in such case (may be simply returning) to prevent reentrant calls to itself.
  95
  96         If this method returns @false, it is safe to continue.
  97     */
  98     bool IsInside() const;
  99 };
 100