* thread acquires the segment lock, immediately after acquiring the lock.
     */
    @GuardedBy("this")
    void preWriteCleanup() {
      runLockedCleanup();
    }

    void runCleanup() {
      runLockedCleanup();
    }

    void runLockedCleanup() {
      if (tryLock()) {
        try {
          maybeDrainReferenceQueues();
          readCount.set(0);
        } finally {

    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()) {