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我正在尝试多线程银行转账问题。但是，我在正确同步线程方面遇到问题。在线程执行帐户之间的转移后，它会定期进行测试以确保完全没有钱获得或损失。

当一个线程进入测试方法时，它应该设置一个标志，以防止任何其他线程进入传输方法，然后等待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，我什至不肯定我已经设置了标志并正确等待。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完成当前传输。

谢谢

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1 回答 1

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我认为您应该使用 volatile 来装饰标志，以确保它在不同线程中更改时受到影响。

于 2012-10-02T02:41:37.923 回答