脚踏实地

/**
 * Creates an instance of {@code ReentrantLock}.
 * This is equivalent to using {@code ReentrantLock(false)}.
 */
public ReentrantLock() {
    sync = new NonfairSync();
}

/**
 * Creates an instance of {@code ReentrantLock} with the
 * given fairness policy.
 *
 * @param fair {@code true} if this lock should use a fair ordering policy
 */
public ReentrantLock(boolean fair) {
    sync = fair ? new FairSync() : new NonfairSync();
}

public class ReentrantExample {
    public synchronized void outerMethod() {
        System.out.println("Outer method");
        innerMethod();
    }

    public synchronized void innerMethod() {
        System.out.println("Inner method");
    }

    public static void main(String[] args) {
        ReentrantExample example = new ReentrantExample();
        example.outerMethod();
    }
}

public class ReentrantLockExample {
    private final ReentrantLock lock = new ReentrantLock();

    public void outerMethod() {
        lock.lock();
        try {
            System.out.println("Outer method");
            innerMethod();
        } finally {
            lock.unlock();
        }
    }

    public void innerMethod() {
        lock.lock();
        try {
            System.out.println("Inner method");
        } finally {
            lock.unlock();
        }
    }

    public static void main(String[] args) {
        ReentrantLockExample example = new ReentrantLockExample();
        example.outerMethod();
    }
}

public class SharedLockExample {
    private final ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
    private final ReentrantReadWriteLock.ReadLock readLock = rwLock.readLock();
    private final ReentrantReadWriteLock.WriteLock writeLock = rwLock.writeLock();

    public void readMethod() {
        readLock.lock();
        try {
            System.out.println(Thread.currentThread().getName() + " acquired the read lock");
            // Read-only critical section
        } finally {
            readLock.unlock();
            System.out.println(Thread.currentThread().getName() + " released the read lock");
        }
    }

    public void writeMethod() {
        writeLock.lock();
        try {
            System.out.println(Thread.currentThread().getName() + " acquired the write lock");
            // Write critical section
        } finally {
            writeLock.unlock();
            System.out.println(Thread.currentThread().getName() + " released the write lock");
        }
    }

    public static void main(String[] args) {
        SharedLockExample example = new SharedLockExample();
        Runnable readTask = () -> {
            for (int i = 0; i < 3; i++) {
                example.readMethod();
            }
        };

        Runnable writeTask = () -> {
            for (int i = 0; i < 3; i++) {
                example.writeMethod();
            }
        };

        Thread t1 = new Thread(readTask);
        Thread t2 = new Thread(readTask);
        Thread t3 = new Thread(writeTask);
        t1.start();
        t2.start();
        t3.start();
    }
}

public class SynchronizedExample {
    private int count = 0;

    public synchronized void increment() {
        count++;
    }

    public synchronized int getCount() {
        return count;
    }

    public static void main(String[] args) {
        SynchronizedExample example = new SynchronizedExample();
        example.increment();
        System.out.println("Count: " + example.getCount());
    }
}

public class CASExample {
    private final AtomicInteger count = new AtomicInteger(0);

    public void increment() {
        while (true) {
            int existingValue = count.get();
            int newValue = existingValue + 1;
            if (count.compareAndSet(existingValue, newValue)) {
                break;
            }
        }
    }

    public int getCount() {
        return count.get();
    }

    public static void main(String[] args) {
        CASExample example = new CASExample();
        example.increment();
        System.out.println("Count: " + example.getCount());
    }
}

public class SpinLock {
    private volatile boolean locked = false;

    public void lock() {
        // 自旋等待获取锁
        while (locked);
        // 获取到锁后，将 locked 设置为 true
        locked = true;
    }

    public void unlock() {
        // 释放锁
        locked = false;
    }

    public static void main(String[] args) {
        SpinLock spinLock = new SpinLock();

        // 线程1
        new Thread(() -> {
            spinLock.lock();
            try {
                System.out.println("Thread 1 in critical section");
                Thread.sleep(1000); // 模拟临界区代码执行
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                spinLock.unlock();
            }
        }).start();

        // 线程2
        new Thread(() -> {
            spinLock.lock();
            try {
                System.out.println("Thread 2 in critical section");
                Thread.sleep(1000); // 模拟临界区代码执行
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                spinLock.unlock();
            }
        }).start();
    }
}

public class AdaptiveSpinLock {
    private static final int MIN_SPIN_COUNT = 10;
    private static final int MAX_SPIN_COUNT = 1000;
    private AtomicBoolean locked = new AtomicBoolean(false);
    private int spinCount = MIN_SPIN_COUNT; // 初始自旋等待次数设定为最小值

    public void lock() {
        int spins = spinCount; // 获取当前自旋次数
        while (!locked.compareAndSet(false, true)) {
            if (spins < MAX_SPIN_COUNT) {
                spins++; // 自旋次数递增
            }
            // 在真实场景中，可能需要添加短暂的延时，避免过多占用CPU资源
            for (int i = 0; i < spins; i++) {
                Thread.onSpinWait(); // 在Java 9及以上版本中，可以使用Thread.onSpinWait()来优化自旋等待
            }
        }
        spinCount = spins; // 更新自旋次数
    }

    public void unlock() {
        locked.set(false);
    }

    public static void main(String[] args) {
        AdaptiveSpinLock spinLock = new AdaptiveSpinLock();

        // 线程1
        new Thread(() -> {
            spinLock.lock();
            try {
                System.out.println("Thread 1 in critical section");
                Thread.sleep(1000); // 模拟临界区代码执行
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                spinLock.unlock();
            }
        }).start();

        // 线程2
        new Thread(() -> {
            spinLock.lock();
            try {
                System.out.println("Thread 2 in critical section");
                Thread.sleep(1000); // 模拟临界区代码执行
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                spinLock.unlock();
            }
        }).start();
    }
}

public class SynchronizedExample {
    private static final Object lock = new Object();

    public static void main(String[] args) throws InterruptedException {
        Thread thread1 = new Thread(() -> {
            synchronized (lock) {
                System.out.println(Thread.currentThread().getName() + " acquired the lock");
                try {
                    Thread.sleep(5000); // 模拟线程持有锁的操作
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "Thread-1");

        Thread thread2 = new Thread(() -> {
            synchronized (lock) {
                System.out.println(Thread.currentThread().getName() + " acquired the lock");
            }
        }, "Thread-2");

        thread1.start();
        Thread.sleep(1000); // 让Thread-1先获取锁
        thread2.start();

        // 等待线程执行完成
        thread1.join();
        thread2.join();
    }
}

public class LockExample {
    private static final Lock lock = new ReentrantLock();

    public static void main(String[] args) throws InterruptedException {
        Thread thread1 = new Thread(() -> {
            lock.lock();
            try {
                System.out.println(Thread.currentThread().getName() + " acquired the lock");
                Thread.sleep(5000); // 模拟线程持有锁的操作
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }, "Thread-1");

        Thread thread2 = new Thread(() -> {
            try {
                if (lock.tryLock()) { // 可中断地尝试获取锁
                    try {
                        System.out.println(Thread.currentThread().getName() + " acquired the lock");
                    } finally {
                        lock.unlock();
                    }
                } else {
                    System.out.println(Thread.currentThread().getName() + " unable to acquire the lock");
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }, "Thread-2");

        thread1.start();
        Thread.sleep(1000); // 让Thread-1先获取锁
        thread2.start();

        // 等待线程执行完成
        thread1.join();
        thread2.join();
    }
}

public class SynchronizedMutexExample {
    private static int counter = 0;
    private static final Object lock = new Object();

    public static void main(String[] args) throws InterruptedException {
        Runnable task = () -> {
            synchronized (lock) {
                for (int i = 0; i < 10000; i++) {
                    counter++;
                }
            }
        };

        Thread thread1 = new Thread(task);
        Thread thread2 = new Thread(task);

        thread1.start();
        thread2.start();

        thread1.join();
        thread2.join();

        System.out.println("Counter: " + counter);
    }
}

 public class MainTest {
 
     public static void main(String[] args) {
          String lockA = "lockA";
          String lockB = "lockB";
         new Thread(new ThreadHolderLock(lockA,lockB),"线程AAA").start();
         new Thread(new ThreadHolderLock(lockB,lockA),"线程BBB").start();
     }
 }
 
 class ThreadHolderLock implements Runnable{
 
     private String lockA;
     private String lockB;
 
     public ThreadHolderLock(String lockA, String lockB){
         this.lockA = lockA;
         this.lockB = lockB;
     }
 
     @Override
     public void run() {
         synchronized (lockA){
             System.out.println(Thread.currentThread().getName() + "\t 持有锁 "+ lockA+", 尝试获得"+ lockB);
 
             try {
                 Thread.sleep(1000);
             } catch (InterruptedException e) {
                 e.printStackTrace();
             }
 
             synchronized (lockB){
                 System.out.println(Thread.currentThread().getName() + "\t 持有锁 "+ lockB+", 尝试获得"+ lockA);
             }
         }
     }
 }

class Resource {
    private final int id;

    public Resource(int id) {
        this.id = id;
    }

    public int getId() {
        return id;
    }
}

class Process extends Thread {
    private final int id;
    private final Resource[] resources;

    public Process(int id, Resource[] resources) {
        this.id = id;
        this.resources = resources;
    }

    @Override
    public void run() {
        try {
            acquireResources();
            // 模拟处理
            Thread.sleep((int) (Math.random() * 1000));
            releaseResources();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private void acquireResources() throws InterruptedException {
        for (Resource resource : resources) {
            synchronized (resource) {
                System.out.println("Process " + id + " acquired Resource " + resource.getId());
            }
        }
    }

    private void releaseResources() {
        for (Resource resource : resources) {
            synchronized (resource) {
                System.out.println("Process " + id + " released Resource " + resource.getId());
            }
        }
    }
}

public class ResourceOrderingExample {
    public static void main(String[] args) {
        Resource resource1 = new Resource(1);
        Resource resource2 = new Resource(2);
        Resource resource3 = new Resource(3);

        Process process1 = new Process(1, new Resource[]{resource1, resource2});
        Process process2 = new Process(2, new Resource[]{resource2, resource3});
        Process process3 = new Process(3, new Resource[]{resource3, resource1});

        process1.start();
        process2.start();
        process3.start();
    }
}

class Banker {
    private int[] available;  // 系统可用资源
    private int[][] maximum;  // 每个进程的最大资源需求
    private int[][] allocation; // 每个进程当前已分配的资源
    private int[][] need;      // 每个进程剩余的资源需求

    public Banker(int[] available, int[][] maximum) {
        this.available = available;
        this.maximum = maximum;
        int numProcesses = maximum.length;
        int numResources = available.length;
        allocation = new int[numProcesses][numResources];
        need = new int[numProcesses][numResources];
        for (int i = 0; i < numProcesses; i++) {
            for (int j = 0; j < numResources; j++) {
                need[i][j] = maximum[i][j]; // 初始时，Need等于Maximum
            }
        }
    }

    // 请求资源的方法
    public synchronized boolean requestResources(int processId, int[] request) {
        if (!isRequestValid(processId, request)) {
            return false; // 请求不合法，拒绝请求
        }

        // 试探性分配
        for (int i = 0; i < available.length; i++) {
            available[i] -= request[i];
            allocation[processId][i] += request[i];
            need[processId][i] -= request[i];
        }

        // 安全性检查
        boolean safe = isSafeState();

        if (!safe) {
            // 如果不安全，恢复试探性分配前的状态
            for (int i = 0; i < available.length; i++) {
                available[i] += request[i];
                allocation[processId][i] -= request[i];
                need[processId][i] += request[i];
            }
        }

        return safe;
    }

    private boolean isRequestValid(int processId, int[] request) {
        for (int i = 0; i < request.length; i++) {
            if (request[i] > need[processId][i] || request[i] > available[i]) {
                return false; // 请求超出需求或可用资源
            }
        }
        return true;
    }

    private boolean isSafeState() {
        int[] work = available.clone();
        boolean[] finish = new boolean[allocation.length];

        while (true) {
            boolean found = false;
            for (int i = 0; i < allocation.length; i++) {
                if (!finish[i]) {
                    boolean canProceed = true;
                    for (int j = 0; j < work.length; j++) {
                        if (need[i][j] > work[j]) {
                            canProceed = false;
                            break;
                        }
                    }
                    if (canProceed) {
                        for (int j = 0; j < work.length; j++) {
                            work[j] += allocation[i][j];
                        }
                        finish[i] = true;
                        found = true;
                    }
                }
            }
            if (!found) {
                break;
            }
        }

        for (boolean f : finish) {
            if (!f) {
                return false; // 存在未完成的进程，系统不安全
            }
        }
        return true; // 所有进程都完成，系统安全
    }
}

public class BankerExample {
    public static void main(String[] args) {
        int[] available = {3, 3, 2};
        int[][] maximum = {
            {7, 5, 3},
            {3, 2, 2},
            {9, 0, 2},
            {2, 2, 2},
            {4, 3, 3}
        };

        Banker banker = new Banker(available, maximum);

        int[] request1 = {1, 0, 2};
        boolean granted1 = banker.requestResources(1, request1);
        System.out.println("Request 1 granted: " + granted1);

        int[] request2 = {3, 3, 0};
        boolean granted2 = banker.requestResources(4, request2);
        System.out.println("Request 2 granted: " + granted2);

        int[] request3 = {2, 0, 0};
        boolean granted3 = banker.requestResources(0, request3);
        System.out.println("Request 3 granted: " + granted3);
    }
}

class Process extends Thread {
    private final int id;
    private final Lock lock1;
    private final Lock lock2;

    public Process(int id, Lock lock1, Lock lock2) {
        this.id = id;
        this.lock1 = lock1;
        this.lock2 = lock2;
    }

    @Override
    public void run() {
        try {
            while (true) {
                if (lock1.tryLock(50, TimeUnit.MILLISECONDS)) {
                    try {
                        if (lock2.tryLock(50, TimeUnit.MILLISECONDS)) {
                            try {
                                System.out.println("Process " + id + " acquired both locks");
                                // 模拟处理
                                Thread.sleep((int) (Math.random() * 1000));
                                return;
                            } finally {
                                lock2.unlock();
                            }
                        }
                    } finally {
                        lock1.unlock();
                    }
                }
                // 等待一段时间再重试
                Thread.sleep((int) (Math.random() * 50));
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class TryLockExample {
    public static void main(String[] args) {
        Lock lock1 = new ReentrantLock();
        Lock lock2 = new ReentrantLock();

        Process process1 = new Process(1, lock1, lock2);
        Process process2 = new Process(2, lock2, lock1);

        process1.start();
        process2.start();
    }
}