// synchronized - 固定密碼鎖
public synchronized void oldMethod() {
    // 自動(dòng)上鎖和解鎖
    // 但無法中斷、無法超時(shí)、無法嘗試獲取
}
// Lock - 智能電子鎖  
public void newMethod() {
    Lock lock = new ReentrantLock();
    lock.lock();  // 手動(dòng)開鎖
    try {
        // 臨界區(qū)代碼
    } finally {
        lock.unlock();  // 手動(dòng)關(guān)鎖
    }
}

/**
 * AQS同步狀態(tài)管理示例
 */
public class AQSCoreConcept {
    // state字段的三種典型用法：
    // 1. 互斥鎖：state = 0(未鎖定) 或 1(已鎖定)
    // 2. 重入鎖：state = 重入次數(shù)  
    // 3. 讀寫鎖：高16位 = 讀鎖計(jì)數(shù)，低16位 = 寫鎖計(jì)數(shù)
    private volatile int state;
    // 三個(gè)核心的state操作方法：
    protected final int getState() { return state; }
    protected final void setState(int newState) { state = newState; }
    protected final boolean compareAndSetState(int expect, int update) {
        // CAS原子操作，保證線程安全
        return unsafe.compareAndSwapInt(this, stateOffset, expect, update);
    }
}

/**
 * AQS同步隊(duì)列結(jié)構(gòu)演示
 */
public class SyncQueueDemo {
    /**
     * 同步隊(duì)列節(jié)點(diǎn)結(jié)構(gòu)（雙向鏈表）：
     * 
     * head (虛擬節(jié)點(diǎn)) ? [prev|thread|next|waitStatus] ? [prev|thread|next|waitStatus] ? tail
     * 
     * waitStatus狀態(tài)說明：
     * - CANCELLED(1)：線程已取消
     * - SIGNAL(-1)：后繼線程需要被喚醒  
     * - CONDITION(-2)：線程在Condition隊(duì)列中
     * - PROPAGATE(-3)：共享模式下傳播喚醒
     */
    // 獨(dú)占模式獲取鎖的典型流程
    public void acquireDemo() {
        Lock lock = new ReentrantLock();
        // 底層調(diào)用AQS的acquire方法
        lock.lock();  // -> sync.acquire(1);
        /**
         * acquire方法執(zhí)行流程：
         * 1. tryAcquire()嘗試直接獲取鎖
         * 2. 失敗 → addWaiter()加入同步隊(duì)列隊(duì)尾
         * 3. acquireQueued()在隊(duì)列中自旋等待
         * 4. 被前驅(qū)節(jié)點(diǎn)喚醒后重新嘗試獲取鎖
         */
    }
}

/**
 * TwinsLock - 同一時(shí)刻最多允許兩個(gè)線程訪問的共享鎖
 * 設(shè)計(jì)思路：將AQS的state作為許可證計(jì)數(shù)器
 */
public class TwinsLock implements Lock {
    private final Sync sync = new Sync(2);
    private static final class Sync extends AbstractQueuedSynchronizer {
        Sync(int count) {
            if (count <= 0) throw new IllegalArgumentException("計(jì)數(shù)必須大于0");
            setState(count);  // 初始化許可證數(shù)量
        }
        /**
         * 共享模式獲取鎖
         * @return 負(fù)數(shù)：獲取失敗；0：獲取成功但無剩余；正數(shù)：獲取成功且有剩余
         */
        @Override
        public int tryAcquireShared(int reduceCount) {
            for (;;) {  // 自旋避免CAS失敗
                int current = getState();
                int newCount = current - reduceCount;
                // 如果新計(jì)數(shù)<0（無許可證）或CAS設(shè)置成功，返回結(jié)果
                if (newCount < 0 || compareAndSetState(current, newCount)) {
                    return newCount;
                }
            }
        }
        /**
         * 共享模式釋放鎖
         */
        @Override
        public boolean tryReleaseShared(int returnCount) {
            for (;;) {
                int current = getState();
                int newCount = current + returnCount;
                if (compareAndSetState(current, newCount)) {
                    return true;
                }
            }
        }
    }
    @Override
    public void lock() {
        sync.acquireShared(1);  // 獲取1個(gè)許可證
    }
    @Override
    public void unlock() {
        sync.releaseShared(1);  // 釋放1個(gè)許可證
    }
    // 其他Lock方法實(shí)現(xiàn)...
}
/**
 * 測(cè)試TwinsLock
 */
public class TwinsLockTest {
    @Test
    public void testTwinsLock() {
        final Lock lock = new TwinsLock();
        // 啟動(dòng)10個(gè)線程，但同一時(shí)刻只有2個(gè)能獲取鎖
        for (int i = 0; i < 10; i++) {
            Thread worker = new Thread(() -> {
                lock.lock();
                try {
                    System.out.println(Thread.currentThread().getName() + " 獲取鎖");
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                } finally {
                    lock.unlock();
                }
            });
            worker.start();
        }
    }
}

/**
 * 重入鎖的重入特性演示
 */
public class ReentrantDemo {
    private final ReentrantLock lock = new ReentrantLock();
    public void outer() {
        lock.lock();
        try {
            System.out.println("外層方法獲取鎖，重入計(jì)數(shù): " + getHoldCount());
            inner();  // 重入：同一個(gè)線程再次獲取同一把鎖
        } finally {
            lock.unlock();
        }
    }
    public void inner() {
        lock.lock();  // 這里不會(huì)阻塞，因?yàn)橐呀?jīng)是鎖的持有者
        try {
            System.out.println("內(nèi)層方法獲取鎖，重入計(jì)數(shù): " + getHoldCount());
        } finally {
            lock.unlock();
        }
    }
    private int getHoldCount() {
        // 返回當(dāng)前線程持有該鎖的次數(shù)
        return lock.getHoldCount();
    }
}

/**
 * 公平性對(duì)比測(cè)試
 */
public class FairVsUnfairTest {
    private static Lock fairLock = new ReentrantLock(true);      // 公平鎖
    private static Lock unfairLock = new ReentrantLock(false);   // 非公平鎖
    @Test
    public void comparePerformance() {
        // 測(cè)試結(jié)果通常顯示：
        // - 公平鎖：保證順序，但性能較低
        // - 非公平鎖：可能饑餓，但吞吐量高
        testLock("公平鎖", fairLock);
        testLock("非公平鎖", unfairLock);
    }
    private void testLock(String type, Lock lock) {
        long start = System.currentTimeMillis();
        // 多個(gè)線程競(jìng)爭(zhēng)鎖...
        long duration = System.currentTimeMillis() - start;
        System.out.println(type + " 耗時(shí): " + duration + "ms");
    }
}

/**
 * 重入鎖核心實(shí)現(xiàn)解析
 */
public class ReentrantLockCore {
    /**
     * 非公平鎖獲取邏輯
     */
    final boolean nonfairTryAcquire(int acquires) {
        final Thread current = Thread.currentThread();
        int c = getState();
        if (c == 0) {  // 鎖空閑
            if (compareAndSetState(0, acquires)) {
                setExclusiveOwnerThread(current);
                return true;
            }
        } else if (current == getExclusiveOwnerThread()) {  // 重入
            int nextc = c + acquires;
            if (nextc < 0) throw new Error("超過最大鎖計(jì)數(shù)");
            setState(nextc);  // 增加重入計(jì)數(shù)
            return true;
        }
        return false;
    }
    /**
     * 釋放鎖邏輯
     */
    protected final boolean tryRelease(int releases) {
        int c = getState() - releases;
        if (Thread.currentThread() != getExclusiveOwnerThread())
            throw new IllegalMonitorStateException();
        boolean free = false;
        if (c == 0) {  // 完全釋放
            free = true;
            setExclusiveOwnerThread(null);
        }
        setState(c);
        return free;
    }
}

/**
 * 基于讀寫鎖的緩存實(shí)現(xiàn)
 */
public class ReadWriteCache<K, V> {
    private final Map<K, V> cache = new HashMap<>();
    private final ReadWriteLock rwLock = new ReentrantReadWriteLock();
    private final Lock readLock = rwLock.readLock();
    private final Lock writeLock = rwLock.writeLock();
    /**
     * 讀操作：共享鎖，允許多個(gè)線程同時(shí)讀
     */
    public V get(K key) {
        readLock.lock();
        try {
            String value = cache.get(key);
            // 模擬配置讀取的耗時(shí)操作
            simulateProcess(1);
            return value;
        } finally {
            readLock.unlock();
        }
    }
    /**
     * 批量獲取配置 - 讀鎖支持并發(fā)
     */
    public Map<String, String> getConfigs(Set<String> keys) {
        readLock.lock();
        try {
            Map<String, String> result = new HashMap<>();
            for (String key : keys) {
                result.put(key, cache.get(key));
            }
            simulateProcess(keys.size());
            return result;
        } finally {
            readLock.unlock();
        }
    }
    /**
     * 更新配置 - 低頻操作，使用寫鎖
     */
    public void updateConfig(String key, String value) {
        writeLock.lock();
        try {
            // 模擬配置更新的耗時(shí)操作
            simulateProcess(10);
            cache.put(key, value);
            System.out.println("配置更新: " + key + " = " + value);
        } finally {
            writeLock.unlock();
        }
    }
    private void simulateProcess(int milliseconds) {
        try {
            Thread.sleep(milliseconds);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }
}

/**
 * 讀寫鎖狀態(tài)設(shè)計(jì)的精妙之處
 */
public class ReadWriteStateDesign {
    /**
     * 32位state字段的劃分：
     * 
     * ┌─────────────────┬─────────────────┐
     * │     高16位      │     低16位      │
     * │     讀狀態(tài)      │     寫狀態(tài)      │
     * │   (讀鎖計(jì)數(shù))    │  (寫鎖重入數(shù))   │
     * └─────────────────┴─────────────────┘
     */
    // 獲取寫狀態(tài)（低16位）
    static int exclusiveCount(int c) { 
        return c & 0x0000FFFF; 
    }
    // 獲取讀狀態(tài)（高16位）
    static int sharedCount(int c) { 
        return c >>> 16; 
    }
    // 讀鎖計(jì)數(shù)+1
    int newReadState = currentState + (1 << 16);  // 即 + 0x00010000
    // 寫鎖計(jì)數(shù)+1  
    int newWriteState = currentState + 1;
}

/**
 * 鎖降級(jí)示例：寫鎖 → 讀鎖
 * 目的：保證數(shù)據(jù)的可見性
 */
public class LockDemotionExample {
    private final ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
    private final Lock readLock = rwLock.readLock();
    private final Lock writeLock = rwLock.writeLock();
    private volatile boolean update = false;
    private Object data;
    public void processData() {
        readLock.lock();
        if (!update) {
            // 數(shù)據(jù)需要更新，必須先釋放讀鎖
            readLock.unlock();
            // 獲取寫鎖
            writeLock.lock();
            try {
                // 雙重檢查
                if (!update) {
                    // 準(zhǔn)備數(shù)據(jù)...
                    data = fetchData();
                    update = true;
                }
                // 關(guān)鍵步驟：在釋放寫鎖前獲取讀鎖
                readLock.lock();  // 鎖降級(jí)開始
            } finally {
                writeLock.unlock();  // 鎖降級(jí)完成，現(xiàn)在持有讀鎖
            }
        }
        try {
            // 使用數(shù)據(jù)（仍在讀鎖保護(hù)下）
            useData(data);
        } finally {
            readLock.unlock();
        }
    }
    // 不支持鎖升級(jí)！可能產(chǎn)生死鎖
    public void invalidLockUpgrade() {
        readLock.lock();
        try {
            // 危險(xiǎn)操作：嘗試在持有讀鎖時(shí)獲取寫鎖
            // 如果其他線程也持有讀鎖，會(huì)產(chǎn)生死鎖
            writeLock.lock();  // 可能永遠(yuǎn)阻塞！
            try {
                // 修改數(shù)據(jù)...
            } finally {
                writeLock.unlock();
            }
        } finally {
            readLock.unlock();
        }
    }
    private Object fetchData() { return null; }
    private void useData(Object data) {}
}

/**
 * LockSupport基礎(chǔ)使用
 */
public class LockSupportBasic {
    public static void main(String[] args) throws InterruptedException {
        Thread worker = new Thread(() -> {
            System.out.println("工作線程開始執(zhí)行");
            System.out.println("工作線程即將被阻塞");
            // 阻塞當(dāng)前線程（停車）
            LockSupport.park();
            System.out.println("工作線程被喚醒，繼續(xù)執(zhí)行");
        });
        worker.start();
        Thread.sleep(2000);  // 主線程等待2秒
        System.out.println("主線程準(zhǔn)備喚醒工作線程");
        // 喚醒指定線程（開車）
        LockSupport.unpark(worker);
        System.out.println("主線程已發(fā)送喚醒信號(hào)");
    }
}

/**
 * LockSupport的許可機(jī)制演示
 * 每個(gè)線程有一個(gè)許可（最多為1）：
 * - unpark：添加一個(gè)許可
 * - park：消耗一個(gè)許可，沒有許可就阻塞
 */
public class PermitMechanism {
    public static void main(String[] args) {
        Thread thread = new Thread(() -> {
            System.out.println("子線程開始");
            try {
                Thread.sleep(1000);  // 確保主線程先調(diào)用unpark
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
            System.out.println("子線程調(diào)用park");
            // 這里不會(huì)阻塞，因?yàn)橹骶€程已經(jīng)給了許可
            LockSupport.park();
            System.out.println("子線程第一次park完成");
            // 這次會(huì)阻塞，因?yàn)樵S可已經(jīng)被消耗
            LockSupport.park(); 
            System.out.println("子線程第二次park完成");
        });
        thread.start();
        // 立即給子線程許可（先發(fā)）
        System.out.println("主線程調(diào)用unpark");
        LockSupport.unpark(thread);
        // 等待后再次喚醒
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
        System.out.println("主線程再次調(diào)用unpark");
        LockSupport.unpark(thread);
    }
}

/**
 * Blocker的作用：在線程dump中標(biāo)識(shí)等待目標(biāo)
 */
public class BlockerDemo {
    public static void main(String[] args) throws InterruptedException {
        Object blocker = new Object();  // 阻塞對(duì)象
        Thread withBlocker = new Thread(() -> {
            System.out.println("帶Blocker的線程開始阻塞");
            // 推薦：使用帶blocker的park方法
            LockSupport.park(blocker);  
            System.out.println("帶Blocker的線程被喚醒");
        }, "WithBlocker-Thread");
        Thread withoutBlocker = new Thread(() -> {
            System.out.println("無Blocker的線程開始阻塞");
            // 不推薦：無blocker的park方法
            LockSupport.park();  
            System.out.println("無Blocker的線程被喚醒");
        }, "WithoutBlocker-Thread");
        withBlocker.start();
        withoutBlocker.start();
        Thread.sleep(1000);
        // 在實(shí)際環(huán)境中使用jstack查看線程dump，區(qū)別明顯：
        // 有Blocker: "parking to wait for <0x00000000d5e8a6c0> (a java.lang.Object)"
        // 無Blocker: 只顯示在LockSupport.park處等待
        LockSupport.unpark(withBlocker);
        LockSupport.unpark(withoutBlocker);
        withBlocker.join();
        withoutBlocker.join();
    }
}

/**
 * 有界阻塞隊(duì)列 - Condition的經(jīng)典應(yīng)用
 * 功能：
 * - 隊(duì)列空時(shí)，消費(fèi)者等待
 * - 隊(duì)列滿時(shí)，生產(chǎn)者等待
 */
public class BoundedBlockingQueue<T> {
    private final Object[] items;
    private int addIndex, removeIndex, count;
    private final Lock lock = new ReentrantLock();
    private final Condition notEmpty = lock.newCondition();  // 非空條件
    private final Condition notFull = lock.newCondition();   // 非滿條件
    public BoundedBlockingQueue(int capacity) {
        if (capacity <= 0) throw new IllegalArgumentException();
        items = new Object[capacity];
    }
    /**
     * 生產(chǎn)方法：隊(duì)列滿時(shí)阻塞
     */
    public void put(T item) throws InterruptedException {
        lock.lock();
        try {
            // 使用while防止虛假喚醒
            while (count == items.length) {
                System.out.println("隊(duì)列已滿，生產(chǎn)者等待...");
                notFull.await();  // 在notFull條件上等待
            }
            // 生產(chǎn)元素
            items[addIndex] = item;
            if (++addIndex == items.length) addIndex = 0;
            count++;
            System.out.println("生產(chǎn): " + item + ", 當(dāng)前數(shù)量: " + count);
            // 通知可能等待的消費(fèi)者
            notEmpty.signal();
        } finally {
            lock.unlock();
        }
    }
    /**
     * 消費(fèi)方法：隊(duì)列空時(shí)阻塞
     */
    @SuppressWarnings("unchecked")
    public T take() throws InterruptedException {
        lock.lock();
        try {
            // 使用while防止虛假喚醒
            while (count == 0) {
                System.out.println("隊(duì)列為空，消費(fèi)者等待...");
                notEmpty.await();  // 在notEmpty條件上等待
            }
            // 消費(fèi)元素
            T item = (T) items[removeIndex];
            if (++removeIndex == items.length) removeIndex = 0;
            count--;
            System.out.println("消費(fèi): " + item + ", 當(dāng)前數(shù)量: " + count);
            // 通知可能等待的生產(chǎn)者
            notFull.signal();
            return item;
        } finally {
            lock.unlock();
        }
    }
}

/**
 * Condition內(nèi)部工作機(jī)制解析
 */
public class ConditionInternalMechanism {
    /**
     * Condition內(nèi)部有兩個(gè)重要隊(duì)列：
     * 
     * 1. 等待隊(duì)列（Condition隊(duì)列）：?jiǎn)蜗蜴湵?
     *    firstWaiter → [thread|nextWaiter] → [thread|nextWaiter] → lastWaiter
     *    
     * 2. 同步隊(duì)列（AQS隊(duì)列）：雙向鏈表  
     *    head ? [prev|thread|next] ? [prev|thread|next] ? tail
     * 
     * await過程：同步隊(duì)列 → 等待隊(duì)列
     * signal過程：等待隊(duì)列 → 同步隊(duì)列
     */
    /**
     * await方法核心流程：
     */
    public final void await() throws InterruptedException {
        // 1. 創(chuàng)建節(jié)點(diǎn)加入Condition等待隊(duì)列
        Node node = addConditionWaiter();
        // 2. 完全釋放鎖（保存重入狀態(tài)）
        int savedState = fullyRelease(node);
        // 3. 阻塞直到被signal或中斷
        while (!isOnSyncQueue(node)) {
            LockSupport.park(this);
            if (checkInterruptWhileWaiting(node) != 0) break;
        }
        // 4. 被喚醒后重新競(jìng)爭(zhēng)鎖
        if (acquireQueued(node, savedState)) {
            // 處理中斷...
        }
    }
    /**
     * signal方法核心流程：
     */
    public final void signal() {
        // 1. 必須持有鎖才能調(diào)用
        if (!isHeldExclusively())
            throw new IllegalMonitorStateException();
        // 2. 轉(zhuǎn)移等待隊(duì)列的第一個(gè)節(jié)點(diǎn)到同步隊(duì)列
        Node first = firstWaiter;
        if (first != null)
            doSignal(first);
    }
}

/**
 * 演示兩個(gè)隊(duì)列如何協(xié)作工作
 */
public class TwoQueuesCollaboration {
    private final ReentrantLock lock = new ReentrantLock();
    private final Condition condition = lock.newCondition();
    public void demonstrate() throws InterruptedException {
        Thread waiter = new Thread(() -> {
            lock.lock();
            try {
                System.out.println("Waiter: 獲取鎖，準(zhǔn)備await");
                // 此時(shí)：
                // - Waiter在同步隊(duì)列中（持有鎖）
                // - 等待隊(duì)列為空
                condition.await();  // 關(guān)鍵操作！
                // await內(nèi)部完成：
                // 1. Waiter節(jié)點(diǎn)從同步隊(duì)列移到等待隊(duì)列
                // 2. 釋放鎖
                // 3. 阻塞等待
                System.out.println("Waiter: 被喚醒，重新獲得鎖");
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            } finally {
                lock.unlock();
            }
        });
        Thread signaler = new Thread(() -> {
            lock.lock();
            try {
                System.out.println("Signaler: 獲取鎖，調(diào)用signal");
                // 此時(shí)：
                // - Signaler在同步隊(duì)列中（持有鎖）  
                // - Waiter在等待隊(duì)列中
                condition.signal();  // 關(guān)鍵操作！
                // signal內(nèi)部完成：
                // 1. Waiter節(jié)點(diǎn)從等待隊(duì)列移到同步隊(duì)列
                // 2. 喚醒Waiter線程
                System.out.println("Signaler: signal完成");
            } finally {
                lock.unlock();  // 釋放鎖，Waiter有機(jī)會(huì)競(jìng)爭(zhēng)鎖
            }
        });
        waiter.start();
        Thread.sleep(100);  // 確保waiter先執(zhí)行
        signaler.start();
        waiter.join();
        signaler.join();
    }
}

/**
 * 正確的鎖釋放方式
 */
public class CorrectLockUsage {
    private final Lock lock = new ReentrantLock();
    // ? 正確做法
    public void correctMethod() {
        lock.lock();
        try {
            // 業(yè)務(wù)邏輯
            doBusiness();
        } finally {
            lock.unlock();  // 確保鎖被釋放
        }
    }
    // ? 錯(cuò)誤做法
    public void wrongMethod() {
        lock.lock();
        doBusiness();
        lock.unlock();  // 如果doBusiness拋出異常，鎖不會(huì)被釋放！
    }
    private void doBusiness() {
        // 可能拋出異常的業(yè)務(wù)邏輯
        if (Math.random() > 0.5) {
            throw new RuntimeException("業(yè)務(wù)異常");
        }
    }
}

/**
 * 死鎖預(yù)防示例
 */
public class DeadlockPrevention {
    private final Lock lockA = new ReentrantLock();
    private final Lock lockB = new ReentrantLock();
    // ? 容易導(dǎo)致死鎖的做法
    public void potentialDeadlock() {
        lockA.lock();
        try {
            // 一些操作...
            lockB.lock();  // 如果另一個(gè)線程以相反順序獲取鎖，可能死鎖
            try {
                // 更多操作...
            } finally {
                lockB.unlock();
            }
        } finally {
            lockA.unlock();
        }
    }
    // ? 使用tryLock避免死鎖
    public void safeMethod() {
        while (true) {
            if (lockA.tryLock()) {
                try {
                    if (lockB.tryLock()) {
                        try {
                            // 成功獲取兩個(gè)鎖，執(zhí)行業(yè)務(wù)
                            doBusiness();
                            return;  // 成功完成，退出循環(huán)
                        } finally {
                            lockB.unlock();
                        }
                    }
                } finally {
                    lockA.unlock();
                }
            }
            // 獲取鎖失敗，短暫休息后重試
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                break;
            }
        }
    }
    // ? 使用固定的鎖獲取順序
    public void fixedOrderMethod(Object resource1, Object resource2) {
        // 通過hash值確定固定的獲取順序
        int hash1 = System.identityHashCode(resource1);
        int hash2 = System.identityHashCode(resource2);
        if (hash1 < hash2) {
            lockA.lock();
            lockB.lock();
        } else {
            lockB.lock();
            lockA.lock();
        }
        try {
            doBusiness();
        } finally {
            lockA.unlock();
            lockB.unlock();
        }
    }
    private void doBusiness() {}
}

/**
 * 基于ReentrantLock的簡(jiǎn)單數(shù)據(jù)庫(kù)連接池
 * 特性：支持超時(shí)獲取、中斷響應(yīng)、連接驗(yàn)證
 */
public class DatabaseConnectionPool {
    private final LinkedList<Connection> pool = new LinkedList<>();
    private final ReentrantLock lock = new ReentrantLock(true);  // 公平鎖
    private final Condition notEmpty = lock.newCondition();
    private final int maxSize;
    private final long maxWaitTime;
    public DatabaseConnectionPool(int maxSize, long maxWaitMillis) {
        this.maxSize = maxSize;
        this.maxWaitTime = maxWaitMillis;
        initializePool();
    }
    /**
     * 獲取連接 - 支持超時(shí)和中斷
     */
    public Connection getConnection() throws InterruptedException, TimeoutException {
        lock.lock();
        try {
            long endTime = System.currentTimeMillis() + maxWaitTime;
            while (pool.isEmpty()) {
                long remainingTime = endTime - System.currentTimeMillis();
                if (remainingTime <= 0) {
                    throw new TimeoutException("獲取連接超時(shí)");
                }
                // 等待連接可用，支持超時(shí)
                if (!notEmpty.await(remainingTime, TimeUnit.MILLISECONDS)) {
                    throw new TimeoutException("獲取連接超時(shí)");
                }
            }
            // 獲取并驗(yàn)證連接
            Connection conn = pool.removeFirst();
            if (!isConnectionValid(conn)) {
                conn = createNewConnection();
            }
            return conn;
        } finally {
            lock.unlock();
        }
    }
    /**
     * 歸還連接
     */
    public void returnConnection(Connection conn) {
        if (conn == null) return;
        lock.lock();
        try {
            if (pool.size() < maxSize && isConnectionValid(conn)) {
                pool.addLast(conn);
                notEmpty.signal();  // 通知等待的線程
            } else {
                // 連接池已滿或連接無效，關(guān)閉連接
                closeConnection(conn);
            }
        } finally {
            lock.unlock();
        }
    }
    /**
     * 嘗試獲取連接（非阻塞）
     */
    public Connection tryGetConnection() {
        if (lock.tryLock()) {
            try {
                if (!pool.isEmpty()) {
                    Connection conn = pool.removeFirst();
                    if (isConnectionValid(conn)) {
                        return conn;
                    }
                }
            } finally {
                lock.unlock();
            }
        }
        return null;
    }
    private boolean isConnectionValid(Connection conn) {
        // 連接有效性檢查邏輯
        try {
            return conn != null && !conn.isClosed() && conn.isValid(2);
        } catch (SQLException e) {
            return false;
        }
    }
    private Connection createNewConnection() {
        // 創(chuàng)建新連接的邏輯
        return null; // 簡(jiǎn)化實(shí)現(xiàn)
    }
    private void closeConnection(Connection conn) {
        // 關(guān)閉連接的邏輯
    }
    private void initializePool() {
        // 初始化連接池
        for (int i = 0; i < maxSize / 2; i++) {
            pool.add(createNewConnection());
        }
    }
}

/**
 * 基于讀寫鎖的配置中心
 * 特性：高頻讀取，低頻更新，保證數(shù)據(jù)一致性
 */
public class ConfigurationCenter {
    private final Map<String, String> configs = new HashMap<>();
    private final ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
    private final Lock readLock = rwLock.readLock();
    private final Lock writeLock = rwLock.writeLock();
    /**
     * 獲取配置 - 高頻操作，使用讀鎖
     */
    public String getConfig(String key) {
        readLock.lock();
        try {
            String value = configs.get(key);
            // 模擬配置讀取的耗時(shí)操作
            simulateProcess(1);
            return value;
        } finally {
            readLock.unlock();
        }
    }
    /**
     * 批量獲取配置 - 讀鎖支持并發(fā)
     */
    public Map<String, String> getConfigs(Set<String> keys) {
        readLock.lock();
        try {
            Map<String, String> result = new HashMap<>();
            for (String key : keys) {
                result.put(key, configs.get(key));
            }
            simulateProcess(keys.size());
            return result;
        } finally {
            readLock.unlock();
        }
    }
    /**
     * 更新配置 - 低頻操作，使用寫鎖
     */
    public void updateConfig(String key, String value) {
        writeLock.lock();
        try {
            // 模擬配置更新的耗時(shí)操作
            simulateProcess(10);
            configs.put(key, value);
            System.out.println("配置更新: " + key + " = " + value);
        } finally {
            writeLock.unlock();
        }
    }
    /**
     * 批量更新配置 - 寫鎖保證原子性
     */
    public void updateConfigs(Map<String, String> newConfigs) {
        writeLock.lock();
        try {
            simulateProcess(newConfigs.size() * 5);
            configs.putAll(newConfigs);
            System.out.println("批量更新配置: " + newConfigs.size() + " 項(xiàng)");
        } finally {
            writeLock.unlock();
        }
    }
    /**
     * 熱更新配置 - 使用鎖降級(jí)保證數(shù)據(jù)一致性
     */
    public void hotUpdateConfig(String key, String value) {
        // 先獲取寫鎖進(jìn)行更新
        writeLock.lock();
        try {
            // 更新配置
            configs.put(key, value);
            System.out.println("熱更新配置: " + key + " = " + value);
            // 鎖降級(jí)：在釋放寫鎖前獲取讀鎖
            readLock.lock();
        } finally {
            writeLock.unlock();  // 鎖降級(jí)完成
        }
        try {
            // 在讀鎖保護(hù)下進(jìn)行后續(xù)操作（如通知觀察者、記錄日志等）
            notifyConfigChange(key, value);
            logConfigChange(key, value);
        } finally {
            readLock.unlock();
        }
    }
    private void notifyConfigChange(String key, String value) {
        // 通知配置變更觀察者
        simulateProcess(2);
    }
    private void logConfigChange(String key, String value) {
        // 記錄配置變更日志
        simulateProcess(1);
    }
    private void simulateProcess(int milliseconds) {
        try {
            Thread.sleep(milliseconds);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }
}

/**
 * 基于Condition的任務(wù)調(diào)度器
 * 特性：支持任務(wù)等待、超時(shí)控制、優(yōu)雅關(guān)閉
 */
public class TaskScheduler {
    private final PriorityBlockingQueue<Task> taskQueue = new PriorityBlockingQueue<>();
    private final ReentrantLock lock = new ReentrantLock();
    private final Condition taskAvailable = lock.newCondition();
    private final Condition schedulerStopped = lock.newCondition();
    private volatile boolean running = true;
    private final Thread workerThread;
    public TaskScheduler() {
        this.workerThread = new Thread(this::processTasks, "TaskScheduler-Worker");
        this.workerThread.start();
    }
    /**
     * 提交任務(wù) - 支持超時(shí)
     */
    public boolean submitTask(Task task, long timeout, TimeUnit unit) 
            throws InterruptedException {
        lock.lock();
        try {
            long deadline = System.nanoTime() + unit.toNanos(timeout);
            // 等待直到有空間或超時(shí)
            while (taskQueue.size() >= 1000) {  // 隊(duì)列容量限制
                long remaining = deadline - System.nanoTime();
                if (remaining <= 0) {
                    return false;  // 超時(shí)
                }
                if (!taskAvailable.await(remaining, TimeUnit.NANOSECONDS)) {
                    return false;  // 超時(shí)
                }
            }
            taskQueue.offer(task);
            taskAvailable.signal();  // 通知工作線程
            return true;
        } finally {
            lock.unlock();
        }
    }
    /**
     * 立即提交任務(wù)（非阻塞）
     */
    public boolean submitTaskNow(Task task) {
        lock.lock();
        try {
            if (taskQueue.size() >= 1000) {
                return false;  // 隊(duì)列已滿
            }
            taskQueue.offer(task);
            taskAvailable.signal();
            return true;
        } finally {
            lock.unlock();
        }
    }
    /**
     * 優(yōu)雅關(guān)閉 - 等待所有任務(wù)完成
     */
    public void shutdown() throws InterruptedException {
        lock.lock();
        try {
            running = false;
            taskAvailable.signalAll();  // 喚醒工作線程
            // 等待任務(wù)隊(duì)列清空
            while (!taskQueue.isEmpty()) {
                schedulerStopped.await(1, TimeUnit.SECONDS);
            }
        } finally {
            lock.unlock();
        }
        workerThread.join();
    }
    /**
     * 立即關(guān)閉
     */
    public void shutdownNow() {
        lock.lock();
        try {
            running = false;
            taskQueue.clear();
            taskAvailable.signalAll();
        } finally {
            lock.unlock();
        }
    }
    private void processTasks() {
        while (running || !taskQueue.isEmpty()) {
            try {
                Task task = taskQueue.poll(1, TimeUnit.SECONDS);
                if (task != null) {
                    executeTask(task);
                }
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                break;
            }
        }
        // 通知關(guān)閉完成
        lock.lock();
        try {
            schedulerStopped.signalAll();
        } finally {
            lock.unlock();
        }
    }
    private void executeTask(Task task) {
        try {
            task.execute();
        } catch (Exception e) {
            System.err.println("任務(wù)執(zhí)行失敗: " + e.getMessage());
        }
    }
    public static class Task implements Comparable<Task> {
        private final Runnable runnable;
        private final long scheduledTime;
        private final int priority;
        public Task(Runnable runnable, long delay, TimeUnit unit, int priority) {
            this.runnable = runnable;
            this.scheduledTime = System.nanoTime() + unit.toNanos(delay);
            this.priority = priority;
        }
        public void execute() {
            runnable.run();
        }
        @Override
        public int compareTo(Task other) {
            int timeCompare = Long.compare(this.scheduledTime, other.scheduledTime);
            if (timeCompare != 0) {
                return timeCompare;
            }
            return Integer.compare(other.priority, this.priority);  // 優(yōu)先級(jí)高的在前
        }
    }
}

/**
 * 基于LockSupport的自定義閉鎖
 * 特性：一次性屏障，支持超時(shí)和中斷
 */
public class SimpleCountDownLatch {
    private volatile int count;
    private final Queue<Thread> waiters = new ConcurrentLinkedQueue<>();
    public SimpleCountDownLatch(int count) {
        if (count < 0) throw new IllegalArgumentException("計(jì)數(shù)不能為負(fù)");
        this.count = count;
    }
    /**
     * 等待閉鎖打開
     */
    public void await() throws InterruptedException {
        if (Thread.interrupted()) {
            throw new InterruptedException();
        }
        if (count <= 0) {
            return;  // 已經(jīng)打開
        }
        // 使用LockSupport阻塞
        Thread current = Thread.currentThread();
        waiters.offer(current);
        // 雙重檢查避免錯(cuò)過信號(hào)
        if (count > 0) {
            LockSupport.park(this);
        }
        // 檢查是否被中斷喚醒
        if (Thread.interrupted()) {
            throw new InterruptedException();
        }
    }
    /**
     * 超時(shí)等待
     */
    public boolean await(long timeout, TimeUnit unit) throws InterruptedException {
        if (Thread.interrupted()) {
            throw new InterruptedException();
        }
        if (count <= 0) {
            return true;
        }
        long deadline = System.nanoTime() + unit.toNanos(timeout);
        Thread current = Thread.currentThread();
        waiters.offer(current);
        try {
            while (count > 0) {
                long remaining = deadline - System.nanoTime();
                if (remaining <= 0) {
                    return false;  // 超時(shí)
                }
                LockSupport.parkNanos(this, remaining);
                if (Thread.interrupted()) {
                    throw new InterruptedException();
                }
            }
            return true;
        } finally {
            waiters.remove(current);
        }
    }
    /**
     * 計(jì)數(shù)減1
     */
    public void countDown() {
        if (count <= 0) {
            return;  // 已經(jīng)打開
        }
        if (--count == 0) {
            // 喚醒所有等待線程
            Thread waiter;
            while ((waiter = waiters.poll()) != null) {
                LockSupport.unpark(waiter);
            }
        }
    }
    /**
     * 獲取當(dāng)前計(jì)數(shù)
     */
    public int getCount() {
        return count;
    }
}

/**
 * 鎖性能優(yōu)化實(shí)踐
 */
public class LockPerformanceOptimization {
    private final ReentrantLock lock = new ReentrantLock();
    private int counter = 0;
    private long lastLogTime = System.currentTimeMillis();
    // ? 鎖粒度太粗
    public void coarseGrainedLock() {
        lock.lock();
        try {
            // 包含非臨界區(qū)操作
            loadFromDatabase();  // 耗時(shí)IO操作
            counter++;           // 真正的臨界區(qū)
            saveToDatabase();    // 耗時(shí)IO操作
        } finally {
            lock.unlock();
        }
    }
    // ? 鎖粒度細(xì)化
    public void fineGrainedLock() {
        // 在鎖外執(zhí)行IO操作
        loadFromDatabase();
        lock.lock();
        try {
            counter++;  // 只保護(hù)真正的臨界區(qū)
        } finally {
            lock.unlock();
        }
        saveToDatabase();  // 在鎖外執(zhí)行IO操作
    }
    // ? 使用原子變量替代鎖
    private final AtomicInteger atomicCounter = new AtomicInteger(0);
    public void atomicOperation() {
        atomicCounter.incrementAndGet();  // 無鎖操作，性能更高
    }
    // ? 讀寫分離
    private final ReadWriteLock rwLock = new ReentrantReadWriteLock();
    private final Lock readLock = rwLock.readLock();
    private final Lock writeLock = rwLock.writeLock();
    private volatile boolean initialized = false;
    public void lazyInit() {
        if (!initialized) {
            writeLock.lock();
            try {
                // 雙重檢查
                if (!initialized) {
                    performInitialization();
                    initialized = true;
                }
            } finally {
                writeLock.unlock();
            }
        }
        // 后續(xù)讀操作使用讀鎖
        readLock.lock();
        try {
            useInitializedResource();
        } finally {
            readLock.unlock();
        }
    }
    private void loadFromDatabase() {
        // 模擬數(shù)據(jù)庫(kù)加載
    }
    private void saveToDatabase() {
        // 模擬數(shù)據(jù)庫(kù)保存
    }
    private void performInitialization() {
        // 初始化操作
    }
    private void useInitializedResource() {
        // 使用初始化后的資源
    }
}

/**
 * 并發(fā)編程常見陷阱及解決方案
 */
public class ConcurrentPitfalls {
    // 陷阱1：在鎖內(nèi)調(diào)用外部方法（可能發(fā)生死鎖）
    public void trap1() {
        ReentrantLock lock = new ReentrantLock();
        lock.lock();
        try {
            externalMethod();  // 危險(xiǎn)！可能獲取其他鎖
        } finally {
            lock.unlock();
        }
    }
    // 解決方案：減少鎖內(nèi)代碼，只包含必要的臨界區(qū)操作
    public void solution1() {
        ReentrantLock lock = new ReentrantLock();
        // 在鎖外準(zhǔn)備數(shù)據(jù)
        Object data = prepareData();
        lock.lock();
        try {
            // 只執(zhí)行必須同步的操作
            updateSharedState(data);
        } finally {
            lock.unlock();
        }
    }
    // 陷阱2：忘記在finally中釋放鎖
    public void trap2() {
        ReentrantLock lock = new ReentrantLock();
        lock.lock();
        if (someCondition()) {
            return;  // 忘記釋放鎖！
        }
        lock.unlock();
    }
    // 解決方案：使用try-finally模板
    public void solution2() {
        ReentrantLock lock = new ReentrantLock();
        lock.lock();
        try {
            if (someCondition()) {
                return;
            }
            // 其他操作
        } finally {
            lock.unlock();  // 確保釋放
        }
    }
    // 陷阱3：在Condition.await()中使用if而不是while
    public void trap3() throws InterruptedException {
        ReentrantLock lock = new ReentrantLock();
        Condition condition = lock.newCondition();
        boolean conditionMet = false;
        lock.lock();
        try {
            if (!conditionMet) {  // 錯(cuò)誤！應(yīng)該用while
                condition.await();
            }
            // 可能被虛假喚醒，條件仍未滿足
        } finally {
            lock.unlock();
        }
    }
    // 解決方案：總是使用while循環(huán)檢查條件
    public void solution3() throws InterruptedException {
        ReentrantLock lock = new ReentrantLock();
        Condition condition = lock.newCondition();
        boolean conditionMet = false;
        lock.lock();
        try {
            while (!conditionMet) {  // 正確！防止虛假喚醒
                condition.await();
            }
            // 條件確定滿足
        } finally {
            lock.unlock();
        }
    }
    private boolean someCondition() {
        return Math.random() > 0.5;
    }
    private Object prepareData() {
        return new Object();
    }
    private void updateSharedState(Object data) {
        // 更新共享狀態(tài)
    }
    private void externalMethod() {
        // 可能獲取其他鎖的外部方法
    }
}

/**
 * 鎖監(jiān)控和診斷工具
 */
public class LockMonitor {
    /**
     * 監(jiān)控鎖競(jìng)爭(zhēng)情況
     */
    public static void monitorLockContention(ReentrantLock lock, String lockName) {
        new Thread(() -> {
            while (true) {
                try {
                    Thread.sleep(5000);  // 每5秒檢查一次
                    System.out.printf("鎖[%s]監(jiān)控: %n", lockName);
                    System.out.printf("  - 等待隊(duì)列長(zhǎng)度: %d%n", lock.getQueueLength());
                    System.out.printf("  - 是否有等待線程: %b%n", lock.hasQueuedThreads());
                    System.out.printf("  - 是否被當(dāng)前線程持有: %b%n", lock.isHeldByCurrentThread());
                    System.out.printf("  - 重入次數(shù): %d%n", lock.getHoldCount());
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                    break;
                }
            }
        }, "LockMonitor-" + lockName).start();
    }
    /**
     * 死鎖檢測(cè)
     */
    public static void detectDeadlock() {
        ThreadMXBean threadMXBean = ManagementFactory.getThreadMXBean();
        long[] threadIds = threadMXBean.findDeadlockedThreads();
        if (threadIds != null) {
            System.err.println("檢測(cè)到死鎖！");
            ThreadInfo[] threadInfos = threadMXBean.getThreadInfo(threadIds);
            for (ThreadInfo threadInfo : threadInfos) {
                System.err.println("死鎖線程: " + threadInfo.getThreadName());
                System.err.println("阻塞對(duì)象: " + threadInfo.getLockName());
                System.err.println("阻塞者: " + threadInfo.getLockOwnerName());
            }
        }
    }
    /**
     * 鎖性能統(tǒng)計(jì)
     */
    public static class LockStats {
        private final ReentrantLock lock;
        private long lockAcquireCount = 0;
        private long totalWaitTime = 0;
        private long maxWaitTime = 0;
        public LockStats(ReentrantLock lock) {
            this.lock = lock;
        }
        public void recordLockAcquire(long waitTime) {
            lockAcquireCount++;
            totalWaitTime += waitTime;
            maxWaitTime = Math.max(maxWaitTime, waitTime);
        }
        public void printStats() {
            System.out.printf("鎖統(tǒng)計(jì): %n");
            System.out.printf("  - 獲取次數(shù): %d%n", lockAcquireCount);
            System.out.printf("  - 平均等待時(shí)間: %.2fms%n", 
                lockAcquireCount > 0 ? (double)totalWaitTime / lockAcquireCount : 0);
            System.out.printf("  - 最大等待時(shí)間: %dms%n", maxWaitTime);
            System.out.printf("  - 當(dāng)前等待線程: %d%n", lock.getQueueLength());
        }
    }
}