void preWriteCleanup(long now) {
      runLockedCleanup(now);
    }

    /** Performs routine cleanup following a write. */
    void postWriteCleanup() {
      runUnlockedCleanup();
    }

    void cleanUp() {
      long now = map.ticker.read();
      runLockedCleanup(now);
      runUnlockedCleanup();
    }

    void runLockedCleanup(long now) {
      if (tryLock()) {