Question

我正在尝试多线程银行转帐问题。但是，我遇到了正确同步线程的问题。在线程在账户之间进行转账之后，它会定期进行测试，以确保没有获得任何资金或完全损失。

当一个线程进入测试方法时，它应该设置一个标志，阻止任何其他线程进入tranfer方法，然后等待当前正在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，我甚至不肯定我已设置标志并正确等待。其次，如何让进入测试方法的线程等待已经执行传输的所有其他线程完成当前传输。

谢谢

Answer 1

我认为你应该使用volatile来装饰标志，以确保它在不同的线程中被更改时会受到影响。

Java多线程银行转账，同步问题

1 个答案: