How to deal with deadlock problems in Java concurrent programming?

In Java concurrent programming, deadlock problems can be dealt with by avoiding and breaking them. Methods to avoid deadlock include resource ordering, deadlock detection and recovery mechanisms, and avoiding circular waiting; methods to break deadlock include thread interruption, lock degradation, and thread priority adjustment. In practical cases, deadlock can be avoided by defining an account object and using the synchronized keyword, ensuring that two threads acquire locks in the same order.

Deadlock handling in Java concurrent programming

Deadlock is a common error in concurrent programming, which can lead to Threads wait for each other, bringing the entire system to a standstill. In Java, the deadlock problem can be dealt with in the following ways:

1. Avoiding deadlock

The easiest way to avoid deadlock is to ensure that threads do not wait for each other Lock. This can be achieved through the following techniques:

• Resource ordering: Acquire resources in a certain order, ensuring that all threads obtain these resources in the same order.
• Use deadlock detection and recovery mechanism: Use specific algorithms (such as timeout mechanism) to detect deadlock and automatically recover.
• Avoid circular waiting: Ensure that the thread does not enter the circular waiting state, that is, the same thread repeatedly tries to acquire the same lock.

2. Breaking the deadlock

If a deadlock has occurred, you can break it through the following methods:

• Thread interruption: Interrupt the thread trapped in deadlock and let it release the lock.
• Lock downgrade: Downgrade locks held by deadlocked threads to lower-level locks, allowing other threads to acquire them.
• Thread priority adjustment: Adjust the priority of the deadlock thread to make it more likely to release the lock.

Practical case:

Suppose we have a banking system with multiple accounts and threads performing transfer operations. If two threads try to transfer money to each other from two different accounts at the same time, a deadlock can occur.

We can avoid this deadlock by:

// 定义账户对象
class Account {
    private final Object lock = new Object();
    private int balance;

    public void transfer(Account other, int amount) {
        synchronized (this.lock) {
            synchronized (other.lock) {
                // 执行转账操作
            }
        }
    }
}

Use the synchronized keyword to ensure that both threads acquire locks in the same order, thus avoiding deadlock.

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