docs/random/wtay/rwlocks

   1 ***********************************************
   2
   3 typedef struct {
   4   int pre_count;
   5   int post_count;
   6   Mutex *lock;
   7 } RWLock;
   8
   9
  10 reader:
  11
  12   retry:
  13     post = atomic_get (lock->post_count);
  14
  15     ... do read ...
  16
  17     if (atomic_get (lock->pre_count) != post) {
  18       /* wait for writer to finish then retry */
  19       lock (lock->mutex);
  20       unlock (lock->mutex);
  21       goto retry;
  22     }
  23
  24
  25 writer:
  26
  27    lock (lock->mutex);
  28    atomic_inc (lock->pre_count);
  29
  30    ... update ...
  31
  32    atomic_inc (lock->post_count);
  33    unlock (lock->mutex);