Method modify_atomic_state

be/src/util/cache/lirs-cache.cc:241–256

Since compare and swap can fail when there are concurrent modifications, this wraps some of the boilerplate compare and swap retry logic. This performs the provided lambda in a loop until the compare and swap succeeds. The lambda is required to mutate the AtomicState argument passed to it. This returns a structure containing the old atomic value and new atomic value.

  // The lambda is required to mutate the AtomicState argument passed to it.
  // This returns a structure containing the old atomic value and new atomic value.
  AtomicStateTransition modify_atomic_state(const std::function<void(AtomicState&)>& fn) {
    AtomicState old_atomic_state = atomic_state_.load();
    AtomicState new_atomic_state = old_atomic_state;
    while (true) {
      new_atomic_state = old_atomic_state;
      // fn mutates new_atomic_state and must change something
      fn(new_atomic_state);
      DCHECK(old_atomic_state.ref_count != new_atomic_state.ref_count ||
             old_atomic_state.state != new_atomic_state.state ||
             old_atomic_state.residency != new_atomic_state.residency);
      if (atomic_state_.compare_exchange_weak(old_atomic_state, new_atomic_state)) {
        break;
      }
    }
    return AtomicStateTransition(old_atomic_state, new_atomic_state);
  }

  LIRSState state() const {
    return atomic_state_.load().state;