interface/wx/recguard.h

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