Method PrepareRead

library/cpp/threading/chunk_queue/queue.h:313–340

        }

        TEntry* PrepareRead(size_t& index) {
            TEntry* entry = nullptr;
            ui64 tag = Max();

            for (size_t i = 0; i < Concurrency; ++i) {
                TEntry* e = Queues[i].PrepareRead();
                if (e && e->Tag < tag) {
                    index = i;
                    entry = e;
                    tag = e->Tag;
                }
            }

            if (entry) {
                // need second pass to catch updates within already scanned range
                size_t candidate = index;
                for (size_t i = 0; i < candidate; ++i) {
                    TEntry* e = Queues[i].PrepareRead();
                    if (e && e->Tag < tag) {
                        index = i;
                        entry = e;
                        tag = e->Tag;
                    }
                }
            }

            return entry;
        }
    };

    ////////////////////////////////////////////////////////////////////////////////