Java 多线程锁无法正常工作

Question

整个程序是：

import java.util.concurrent.*;
import java.util.concurrent.locks.*;

public class AccountWithConditionsUser {
    private static Account account = new Account();
    public static void main(String[] args) {
        System.out.println("Thread 1\t\tThread 2\t\tBalance");
        ExecutorService executor = Executors.newFixedThreadPool(2);
        executor.execute(new DepositTask());
        executor.execute(new WithdrawTask());
        executor.shutdown();
        while(!executor.isShutdown()) {
        }
    }
    public static class DepositTask implements Runnable{
        public void run() {
            try {
                while(true) {
                    account.deposit((int)(Math.random()* 10)+ 1);
                    Thread.sleep(1000);
                }
            }
            catch(InterruptedException ex) {
                ex.printStackTrace();
            }
        }
    }
    
    public static class WithdrawTask implements Runnable{
        public void run() {
            while(true) {
                account.withdraw((int)(Math.random() * 10) + 1);
            }
        }
    }
    
    private static class Account{
        private static Lock lock = new ReentrantLock(true);
        private static Condition newDeposit = lock.newCondition();
        
        private int balance = 0;
        public int getBalance() {
            return balance;
        }
        
        public void withdraw(int amount) {
            lock.lock();
            System.out.println("->Withdraw Obtained Lock");
            try {
                while(balance < amount) {
                    System.out.println("\t\t\tWait for deposit");
                    newDeposit.await();
                }
                balance-=amount;
                System.out.println("\t\t\tWithdraw "+ amount + "\t\t" + getBalance());
            }
            catch(Exception e) {
                e.printStackTrace();
            }
            finally {
                System.out.println("->Withdraw Released Lock");
                lock.unlock();
                
            }
            
        }
        
        public void deposit(int amount) {
            lock.lock();
            System.out.println("->Deposit Obtained Lock");
            try {
                balance+=amount;
                System.out.println("Deposit "+ amount + "\t\t\t\t\t" + getBalance());
                newDeposit.signalAll();
            }
            catch(Exception e) {
                e.printStackTrace();
            }
            finally {
                System.out.println("->Deposit Released Lock");
                lock.unlock();
            }
        }
    }
}

我得到的这段代码输出的示例部分是：

......

......

撤销已释放的锁

撤销获得的锁

等待存款

存款获得锁

存款 9 13

存款释放锁

退出 9 4

撤销已释放的锁

.....

.....

这里的问题是窗口获得锁后存款线程如何获得锁。不是说一旦获得了锁，其他线程就无法获得！还是因为信号方法？谁能解释一下这个输出是怎么来的？ 在此先感谢:)

Answer 1

Withdraw 获得锁后，它会检查是否有足够的余额。如果没有，那么它调用newdeposit.await，这将释放锁，以便其他等待同一个锁的线程可以进入。这似乎是发生了什么：Withdraw 进入那个 if 块，开始等待， Deposit 线程进来并存了一笔金额并唤醒了Withdraw，因此它可以继续更新金额。一旦收到通知，await 将锁定并返回，因此Withdraw 会继续执行并获得锁定。