<dependency>
            <groupId>org.apache.dubbo</groupId>
            <artifactId>dubbo</artifactId>
            <version>3.1.0</version>
        </dependency>

	public HashedWheelTimer(
            ThreadFactory threadFactory,
            long tickDuration, TimeUnit unit, int ticksPerWheel,
            long maxPendingTimeouts) {
		// 檢查參數(shù)
        if (threadFactory == null) {
            throw new NullPointerException("threadFactory");
        }
        if (unit == null) {
            throw new NullPointerException("unit");
        }
        if (tickDuration <= 0) {
            throw new IllegalArgumentException("tickDuration must be greater than 0: " + tickDuration);
        }
        if (ticksPerWheel <= 0) {
            throw new IllegalArgumentException("ticksPerWheel must be greater than 0: " + ticksPerWheel);
        }

        // Normalize ticksPerWheel to power of two and initialize the wheel.
		// 創(chuàng)建時間輪
        wheel = createWheel(ticksPerWheel);
		
		// 位運算標識 
		// 因為一圈的長度為2的n次方，mask = 2^n-1后低位將全部是1，然后deadline& mast == deadline % wheel.length    
		// deadline = System.nanoTime() + unit.toNanos(delay) - startTime; TODO
        mask = wheel.length - 1;

        // Convert tickDuration to nanos.
		// 時間輪的基本時間跨度，轉成最小時間單位Nanos
        this.tickDuration = unit.toNanos(tickDuration);

        // Prevent overflow.
		// 時間跨度限制不能太大，計算會有問題
        if (this.tickDuration >= Long.MAX_VALUE / wheel.length) {
            throw new IllegalArgumentException(String.format(
                    "tickDuration: %d (expected: 0 < tickDuration in nanos < %d",
                    tickDuration, Long.MAX_VALUE / wheel.length));
        }
		// 創(chuàng)建時間輪工作線程
        workerThread = threadFactory.newThread(worker);

        this.maxPendingTimeouts = maxPendingTimeouts;
		// 延遲任務太多的時間，警告日志
        if (INSTANCE_COUNTER.incrementAndGet() > INSTANCE_COUNT_LIMIT &&
                WARNED_TOO_MANY_INSTANCES.compareAndSet(false, true)) {
            reportTooManyInstances();
        }
    }

    private static HashedWheelBucket[] createWheel(int ticksPerWheel) {
        if (ticksPerWheel <= 0) {
            throw new IllegalArgumentException(
                    "ticksPerWheel must be greater than 0: " + ticksPerWheel);
        }
        if (ticksPerWheel > 1073741824) {
            throw new IllegalArgumentException(
                    "ticksPerWheel may not be greater than 2^30: " + ticksPerWheel);
        }
		// 如果不是2^n 則調整為2^n
        ticksPerWheel = normalizeTicksPerWheel(ticksPerWheel);
		// 初始化時間輪槽
        HashedWheelBucket[] wheel = new HashedWheelBucket[ticksPerWheel];
        for (int i = 0; i < wheel.length; i++) {
            wheel[i] = new HashedWheelBucket();
        }
        return wheel;
    }

	public Timeout newTimeout(TimerTask task, long delay, TimeUnit unit) {
        if (task == null) {
            throw new NullPointerException("task");
        }
        if (unit == null) {
            throw new NullPointerException("unit");
        }

        long pendingTimeoutsCount = pendingTimeouts.incrementAndGet();
		// 如果任務大于最大量，則不允許繼續(xù)添加
        if (maxPendingTimeouts > 0 && pendingTimeoutsCount > maxPendingTimeouts) {
            pendingTimeouts.decrementAndGet();
            throw new RejectedExecutionException("Number of pending timeouts ("
                    + pendingTimeoutsCount + ") is greater than or equal to maximum allowed pending "
                    + "timeouts (" + maxPendingTimeouts + ")");
        }
		// 啟動時間輪工作線程
        start();

        // Add the timeout to the timeout queue which will be processed on the next tick.
        // During processing all the queued HashedWheelTimeouts will be added to the correct HashedWheelBucket.
        long deadline = System.nanoTime() + unit.toNanos(delay) - startTime;

        // Guard against overflow.
		// 如果為負數(shù)，那么說明超過了long的最大值
        if (delay > 0 && deadline < 0) {
            deadline = Long.MAX_VALUE;
        }
        HashedWheelTimeout timeout = new HashedWheelTimeout(this, task, deadline);
        timeouts.add(timeout);
        return timeout;
    }

    public void start() {
        switch (WORKER_STATE_UPDATER.get(this)) {
			// 如果是初始化 啟動實踐論
            case WORKER_STATE_INIT:
				// 保證只啟動一次，原子性
                if (WORKER_STATE_UPDATER.compareAndSet(this, WORKER_STATE_INIT, WORKER_STATE_STARTED)) {
                    workerThread.start();
                }
                break;
			// 已經啟動過了
            case WORKER_STATE_STARTED:
                break;
			// 時間輪停止了
            case WORKER_STATE_SHUTDOWN:
                throw new IllegalStateException("cannot be started once stopped");
            default:
                throw new Error("Invalid WorkerState");
        }

        // Wait until the startTime is initialized by the worker.
		// 線程啟動執(zhí)行任務是異步的，這里是等待workerThread.start()，線程已經啟動了
        while (startTime == 0) {
            try {
                startTimeInitialized.await();
            } catch (InterruptedException ignore) {
                // Ignore - it will be ready very soon.
            }
        }
    }

public void run() {
    // Initialize the startTime.
    startTime = System.nanoTime();
    if (startTime == 0) {
        // We use 0 as an indicator for the uninitialized value here, so make sure it's not 0 when initialized.
        startTime = 1;
    }

    // Notify the other threads waiting for the initialization at start().
	// 喚醒被阻塞的start()方法。
    startTimeInitialized.countDown();

    do {
		// 等下一個槽的到達時間，開始執(zhí)行上一個槽的任務 TODO 不明白這里的設計，哪位大佬知道可以指點一下
        final long deadline = waitForNextTick();
        if (deadline > 0) {
			// 計算時間輪的槽位
            int idx = (int) (tick & mask);
			// 移除取消的了task
            processCancelledTasks();
            HashedWheelBucket bucket = wheel[idx];
            // 將newTimeout()方法中加入到待處理定時任務隊列中的任務加入到指定的格子中
			transferTimeoutsToBuckets();
			// 運行目前指針指向的槽中的bucket鏈表中的任務，執(zhí)行到期的延時任務
            bucket.expireTimeouts(deadline);
            tick++;
        }
		
    } 
	// 如果Worker_State一只是started狀態(tài)，就一直循環(huán)
	while (WORKER_STATE_UPDATER.get(HashedWheelTimer.this) == WORKER_STATE_STARTED);

    // Fill the unprocessedTimeouts so we can return them from stop() method.
    for (HashedWheelBucket bucket : wheel) {
		// 清除時間輪中超時未處理的任務
        bucket.clearTimeouts(unprocessedTimeouts);
    }
    for (; ; ) {
		// 遍歷任務隊列，發(fā)現(xiàn)如果有任務被取消，則添加到unprocessedTimeouts,也就是不需要處理的隊列中。
        HashedWheelTimeout timeout = timeouts.poll();
        if (timeout == null) {
            break;
        }
        if (!timeout.isCancelled()) {
            unprocessedTimeouts.add(timeout);
        }
    }
	// 再次移除取消的了task
    processCancelledTasks();
}

	/**
     * 根據(jù)startTime和當前槽位計算目標nanoTime，
     * 等待時間到達
     *
     * @return Long.MIN_VALUE if received a shutdown request,
     * current time otherwise (with Long.MIN_VALUE changed by +1)
     */
    private long waitForNextTick() {
		// tick槽位，tickDuration表示每個時間格的跨度，所以deadline返回的是下一次時間輪指針跳動的時間
        long deadline = tickDuration * (tick + 1);

        for (; ; ) {
			// 計算當前時間距離啟動時間的時間間隔，期間休眠
            final long currentTime = System.nanoTime() - startTime;
			// 計算sleepTimeMs先加999999，應該是不足1ms的，補足1ms
            long sleepTimeMs = (deadline - currentTime + 999999) / 1000000;
			
            // sleepTimeMs小于零表示走到了下一個時間槽位置
			if (sleepTimeMs <= 0) {
                if (currentTime == Long.MIN_VALUE) {
                    return -Long.MAX_VALUE;
                } else {
                    return currentTime;
                }
            }
			// Windows 時間換算
            if (isWindows()) {
                sleepTimeMs = sleepTimeMs / 10 * 10;
            }

            try {
				// 當前時間距離下一次tick時間還有一段距離，需要sleep
                Thread.sleep(sleepTimeMs);
            } catch (InterruptedException ignored) {
                if (WORKER_STATE_UPDATER.get(HashedWheelTimer.this) == WORKER_STATE_SHUTDOWN) {
                    return Long.MIN_VALUE;
                }
            }
        }
    }

	// 將延時任務隊列中等待添加到時間輪中的延時任務轉移到時間輪的指定位置
	private void transferTimeoutsToBuckets() {
        // transfer only max. 100000 timeouts per tick to prevent a thread to stale the workerThread when it just
        // adds new timeouts in a loop.
		// 循環(huán)100000次，也就是每次轉移10w個任務
		// 為了防止這個操作銷毀太多時間，導致更多的任務時間不準，因此一次最多操作10w個
        for (int i = 0; i < 100000; i++) {
			// 從阻塞隊列中獲得具體的任務
            HashedWheelTimeout timeout = timeouts.poll();
            if (timeout == null) {
                // all processed
                break;
            }
            if (timeout.state() == HashedWheelTimeout.ST_CANCELLED) {
                // Was cancelled in the meantime.
                continue;
            }

            // 計算tick次數(shù)，deadline表示當前任務的延遲時間，tickDuration表示時間槽的間隔，兩者相除就可以計算當前任務需要tick幾次才能被執(zhí)行
			long calculated = timeout.deadline / tickDuration;
            // 計算剩余的輪數(shù), 只有 timer 走夠輪數(shù), 并且到達了 task 所在的 slot, task 才會過期.(被執(zhí)行)
			timeout.remainingRounds = (calculated - tick) / wheel.length;

            // Ensure we don't schedule for past.
			// 如果任務在timeouts隊列里面放久了, 以至于已經過了執(zhí)行時間, 這個時候就使用當前tick, 也就是放到當前bucket, 此方法調用完后就會被執(zhí)行
            final long ticks = Math.max(calculated, tick);
            // 算出任務應該插入的 wheel 的 slot, stopIndex = tick 次數(shù) & mask, mask = wheel.length - 1
			int stopIndex = (int) (ticks & mask);

            // 把timeout任務插入到指定的bucket鏈中。
			HashedWheelBucket bucket = wheel[stopIndex];
            bucket.addTimeout(timeout);
        }
    }

	void expireTimeouts(long deadline) {
		// 雙向鏈表
        HashedWheelTimeout timeout = head;

        // process all timeouts
        // 遍歷當前時間槽中的所有任務
		while (timeout != null) {
            HashedWheelTimeout next = timeout.next;
			// 如果當前任務要被執(zhí)行，那么remainingRounds應該小于或者等于0
            if (timeout.remainingRounds <= 0) {
				// 從bucket鏈表中移除當前timeout，并返回鏈表中下一個timeout
                next = remove(timeout);
				// 如果timeout的時間小于當前的時間，那么就調用expire執(zhí)行task
                if (timeout.deadline <= deadline) {
                    timeout.expire();
                } else {
                    // The timeout was placed into a wrong slot. This should never happen.
                    // 不可能發(fā)生的情況，就是說round已經為0了，deadline卻 > 當前槽的deadline
					throw new IllegalStateException(String.format(
                            "timeout.deadline (%d) > deadline (%d)", timeout.deadline, deadline));
                }
            } else if (timeout.isCancelled()) {
                next = remove(timeout);
            } else {
				// 因為當前的槽位已經過了，說明已經走了一圈了，把輪數(shù)減一
                timeout.remainingRounds--;
            }
			// 把指針放置到下一個timeout
            timeout = next;
        }
    }