mpmc-queue/note.txt

   1 #1 Why this data structure is non-SC (but it's SC at abstraction).
   2
   3 The underlying pattern of the non-SCness are as the following:
   4
   5 T1                              T2
   6 x = 1;                  y = 1;
   7 r1 = y;                 r2 = x;
   8
   9 Suppose there are two identical threads, both having a writer followed by a
  10 reader, as follows:
  11
  12 T1                                                      T2
  13 m_written.CAS;                          m_rdwr.CAS;
  14
  15 m_rdwr.CAS;                                     m_written.CAS; // In write_publish()
  16
  17 m_written.load; // a            m_rdwr.load; // The first in the read_fetch() // b
  18
  19 a & b can both read old value and it's non-SC. However, the later loads and CAS
  20 in the loops will finally fix this problem.