include/library/triplebuffer.hpp

   1 #ifndef _library_triplebuffer__hpp__included__
   2 #define _library_triplebuffer__hpp__included__
   3
   4 #include <stdexcept>
   5 #include "threads.hpp"
   6
   7 namespace triplebuffer
   8 {
   9 /**
  10  * Triple-buffering logic.
  11  */
  12 class logic
  13 {
  14 public:
  15 /**
  16  * Create a new triple buffer.
  17  */
  18         logic() throw();
  19 /**
  20  * Get read pointer and increment read count by 1.
  21  *
  22  * Return value: Read pointer (0-2).
  23  *
  24  * Note: If read count is zero, last complete buffer is returned. Otherwise the same buffer as last call is returned.
  25  */
  26         unsigned get_read() throw();
  27 /**
  28  * Put read pointer and decrement read count by 1.
  29  *
  30  * Throws std::logic_error: If read count is 0.
  31  */
  32         void put_read() throw(std::logic_error);
  33 /**
  34  * Get write pointer and increment write count by 1.
  35  *
  36  * Return value: Write pointer (0-2).
  37  *
  38  * Note: If write count is nonzero before call, the returned buffer is the same as last time.
  39  */
  40         unsigned get_write() throw();
  41 /**
  42  * Put write pointer and decrement write count by 1. If write count hits 0, the buffer is marked as last complete
  43  * buffer.
  44  *
  45  * Throws std::logic_error: If write count is 0.
  46  */
  47         void put_write() throw(std::logic_error);
  48 /**
  49  * Call specified function synchronously for last written buffer.
  50  *
  51  * The buffer number is passed to specified function.
  52  */
  53         void read_last_write_synchronous(std::function<void(unsigned)> fn) throw();
  54 private:
  55         threads::lock lock;
  56         unsigned last_complete;         //Number of last completed buffer
  57         unsigned current_read;          //Number of current read buffer (only valid if count_read > 0).
  58         unsigned current_write;         //Number of current write buffer (only valid if count_write > 0).
  59         unsigned count_read;            //Number of readers.
  60         unsigned count_write;           //Number of writers.
  61 };
  62
  63 /**
  64  * Triple buffer with objects.
  65  */
  66 template<typename T>
  67 class triplebuffer
  68 {
  69 public:
  70 /**
  71  * Create a new triple buffer.
  72  *
  73  * Parameter A: Object #1.
  74  * Parameter B: Object #2.
  75  * Parameter C: Object #3.
  76  */
  77         triplebuffer(T& A, T& B, T& C) throw()
  78         {
  79                 objs[0] = &A;
  80                 objs[1] = &B;
  81                 objs[2] = &C;
  82         }
  83 /**
  84  * Get read pointer and increment read count by 1.
  85  *
  86  * Return value: Read pointer.
  87  *
  88  * Note: If read count is zero, last complete buffer is returned. Otherwise the same buffer as last call is returned.
  89  */
  90         T& get_read() throw() { return *objs[l.get_read()]; }
  91 /**
  92  * Put read pointer and decrement read count by 1.
  93  *
  94  * Throws std::logic_error: If read count is 0.
  95  */
  96         void put_read() throw(std::logic_error) { l.put_read(); }
  97 /**
  98  * Get write pointer and increment write count by 1.
  99  *
 100  * Return value: Write pointer.
 101  *
 102  * Note: If write count is nonzero before call, the returned buffer is the same as last time.
 103  */
 104         T& get_write() throw() { return *objs[l.get_write()]; }
 105 /**
 106  * Put write pointer and decrement write count by 1. If write count hits 0, the buffer is marked as last complete
 107  * buffer.
 108  *
 109  * Throws std::logic_error: If write count is 0.
 110  */
 111         void put_write() throw(std::logic_error) { l.put_write(); }
 112 /**
 113  * Call specified function synchronously for last written buffer.
 114  *
 115  * The buffer itself is passed to the function.
 116  */
 117         void read_last_write_synchronous(std::function<void(T&)> fn) throw()
 118         {
 119                 l.read_last_write_synchronous([this,fn](unsigned x){ fn(*objs[x]); });
 120         }
 121 private:
 122         T* objs[3];
 123         logic l;
 124 };
 125 }
 126
 127 #endif