Java多线程银行转账、同步问题

Question

我正在尝试多线程银行转账问题。但是，我在正确同步线程时遇到问题。线程在帐户之间执行转账后会定期进行测试，以确保没有获得或损失金钱。

当线程进入测试方法时，它应该设置一个标志来阻止任何其他线程进入传输方法，然后等待，直到当前执行传输的所有线程结束。

public void transfer(int from, int to, int amount) {        
    //finish running all threads' current transactions before test

    accounts[from].waitForAvailableFunds(amount);
    if (!open) return;    

    //checks to see if any thread is currently testing
    //if so, wait
    while(flag) {
        try {
            wait();
        } catch (InterruptedException e) { /*ignore*/ }
    }

    //do not execute these two statements when a thread
    //is performing a test
    if (accounts[from].withdraw(amount)) {
        accounts[to].deposit(amount);

    }  

    if (shouldTest() && !flag)   test();

}

//only one thread can perform a test at any given moment
public synchronized void test() {        

    //when test starts set a flag telling threads to
    //not begin any new transfers
    flag = true;

    //wait for all threads currently performing transfers
    //to finish current transfer before continuing


    int sum = 0;
    for (int i = 0; i < accounts.length; i++) {
        System.out.printf("%s %s%n", 
                Thread.currentThread().toString(),accounts[i].toString());
        sum += accounts[i].getBalance();
    }
    System.out.println(Thread.currentThread().toString() + 
            " Sum: " + sum);
    if (sum != numAccounts * initialBalance) {
        System.out.println(Thread.currentThread().toString() + 
                " Money was gained or lost");
        System.exit(1);
    } else {
        System.out.println(Thread.currentThread().toString() + 
                " The bank is in balance");
    }

    //reset flag and notify threads test is complete.
    flag = false;
    notifyAll();
}

首先，我什至不确定我是否已正确设置标志并等待。其次，如何让进入测试方法的线程等待所有其他已经在执行传输的线程来完成当前的传输。

谢谢

Answer 1

我认为你应该使用 volatile 来装饰该标志，以确保它在不同线程中更改时受到影响。