cds/refcounter.h

   1 //$$CDS-header$$
   2
   3 #ifndef __CDS_REFCOUNTER_H
   4 #define __CDS_REFCOUNTER_H
   5
   6 /*
   7     Refernce counting primitives
   8
   9     Editions:
  10 */
  11
  12 #include <cds/cxx11_atomic.h>
  13
  14 namespace cds {
  15
  16     /// Simple reference counter
  17     /**
  18         Thread-safe reference counter build on atomic primitives.
  19         \p T is one of integer types
  20     */
  21     template <typename T>
  22     class ref_counter
  23     {
  24         atomics::atomic<T>   m_nRefCount    ;        ///< The reference counter
  25
  26     public:
  27         typedef T   ref_counter_type  ; ///< The reference counter type
  28
  29     public:
  30         /// Construct reference counter with specified value \p initValue
  31         ref_counter( T initValue = 0 ) CDS_NOEXCEPT
  32             : m_nRefCount(initValue)
  33         {}
  34
  35         /// Get current value of reference counter.
  36         T   value() const CDS_NOEXCEPT
  37         {
  38             return m_nRefCount.load( atomics::memory_order_relaxed );
  39         }
  40
  41         /// Current value of reference counter
  42         operator T() const CDS_NOEXCEPT
  43         {
  44             return value();
  45         }
  46
  47         /// Atomic increment
  48         void    inc() CDS_NOEXCEPT
  49         {
  50             m_nRefCount.fetch_add( 1, atomics::memory_order_relaxed );
  51         }
  52
  53         /// Atomic decrement. Return \p true if reference counter is 0, otherwise \p false
  54         bool    dec() CDS_NOEXCEPT
  55         {
  56             if ( m_nRefCount.fetch_sub( 1, atomics::memory_order_relaxed ) == 1 ) {
  57                 atomics::atomic_thread_fence( atomics::memory_order_release );
  58                 return true;
  59             }
  60             return false;
  61         }
  62
  63         /// Atomic increment
  64         void operator ++() CDS_NOEXCEPT
  65         {
  66             inc();
  67         }
  68
  69         /// Atomic decrement
  70         bool operator--() CDS_NOEXCEPT
  71         {
  72             return dec();
  73         }
  74     };
  75
  76     /// Signed 32bit reference counter
  77     typedef ref_counter<int32_t>       signed_ref_counter;
  78
  79     /// Unsigned 32bit reference counter
  80     typedef ref_counter<uint32_t>      unsigned_ref_counter;
  81
  82 } // namespace cds
  83
  84 #endif    // #ifndef __CDS_REFCOUNTER_H