Subj : Re: Improving read-write lock
To   : comp.programming.threads
From : Alexander Terekhov
Date : Wed Feb 16 2005 04:18 pm


Rob wrote:
[...]
> Maybe something like this already exists and has been implemented.

Here's sorta charade for you.

void read_write(rw_mutex & m, which_t w) {
  sharable_lock<rw_mutex, true> read_lock(m);
  // May need access to many releated which_t's 
  if (compute_expensive_result(w)) {
    // Upgrade (blocks upcoming readers while pending)
    scoped_lock<rw_mutex> write_lock(upgrade(read_lock)); 
    if (read_lock.atomic_upgrade()) {
      modify_state(w);
      if (write_lock.upgrade_pending())
        register_change(w);
    }
    else if (!computation_invalidated(w) || // check registry
             compute_expensive_result(w)) {
      modify_state(w);
      write_lock.upgrade_pending() ?
        register_change(w) : clear_registry();
    }
    else if (!write_lock.upgrade_pending()) {
      clear_registry();
    }
  }
}

Now, what do you think? ;-)

regards,
alexander.

.