mpmc-queue/mpmc-queue.h

   1 template <typename t_element, size_t t_size>
   2 struct mpmc_boundq_1_alt
   3 {
   4 private:
   5
   6         // elements should generally be cache-line-size padded :
   7         nonatomic<t_element>  m_array[t_size];
   8
   9         // rdwr counts the reads & writes that have started
  10         atomic<unsigned int>    m_rdwr;
  11         // "read" and "written" count the number completed
  12         atomic<unsigned int>    m_read;
  13         atomic<unsigned int>    m_written;
  14
  15 public:
  16
  17         mpmc_boundq_1_alt() : m_rdwr(0), m_read(0), m_written(0)
  18         {
  19         }
  20
  21         //-----------------------------------------------------
  22
  23         nonatomic<t_element> * read_fetch() {
  24                 unsigned int rdwr = m_rdwr($).load(mo_acquire);
  25                 unsigned int rd,wr;
  26                 for(;;) {
  27                         rd = (rdwr>>16) & 0xFFFF;
  28                         wr = rdwr & 0xFFFF;
  29
  30                         if ( wr == rd ) // empty
  31                                 return false;
  32
  33                         if ( m_rdwr($).compare_exchange_weak(rdwr,rdwr+(1<<16),mo_acq_rel) )
  34                                 break;
  35                 }
  36
  37                 // (*1)
  38                 rl::backoff bo;
  39                 while ( (m_written($).load(mo_acquire) & 0xFFFF) != wr ) {
  40                         bo.yield($);
  41                 }
  42
  43                 nonatomic<t_element> * p = & ( m_array[ rd % t_size ] );
  44
  45                 return p;
  46         }
  47
  48         void read_consume() {
  49                 m_read($).fetch_add(1,mo_release);
  50         }
  51
  52         //-----------------------------------------------------
  53
  54         nonatomic<t_element> * write_prepare() {
  55                 unsigned int rdwr = m_rdwr($).load(mo_acquire);
  56                 unsigned int rd,wr;
  57                 for(;;) {
  58                         rd = (rdwr>>16) & 0xFFFF;
  59                         wr = rdwr & 0xFFFF;
  60
  61                         if ( wr == ((rd + t_size)&0xFFFF) ) // full
  62                                 return NULL;
  63
  64                         if ( m_rdwr($).compare_exchange_weak(rdwr,(rd<<16) | ((wr+1)&0xFFFF),mo_acq_rel) )
  65                                 break;
  66                 }
  67
  68                 // (*1)
  69                 rl::backoff bo;
  70                 while ( (m_read($).load(mo_acquire) & 0xFFFF) != rd ) {
  71                         bo.yield($);
  72                 }
  73
  74                 nonatomic<t_element> * p = & ( m_array[ wr % t_size ] );
  75
  76                 return p;
  77         }
  78
  79         void write_publish()
  80         {
  81                 m_written($).fetch_add(1,mo_release);
  82         }
  83
  84         //-----------------------------------------------------
  85
  86
  87 };