How to avoid deadlock with concurrency and multi-threading in Java functions?

Deadlock problems in multi-threaded environments can be prevented by defining a fixed lock order and acquiring locks in order. Set a timeout mechanism to give up waiting when the lock cannot be obtained within the specified time. Use deadlock detection algorithm to detect thread deadlock status and take recovery measures. In practical cases, the resource management system defines a global lock order for all resources and forces threads to acquire the required locks in order to avoid deadlocks.

Java function concurrency and multi-thread deadlock prevention

Concurrency and deadlock

In a multi-threaded environment, a deadlock occurs when two or more threads wait for other threads to release locks at the same time. For example:

public class DeadlockExample {
    private final Object lock1 = new Object();
    private final Object lock2 = new Object();

    public void method1() {
        synchronized (lock1) {
            // 获取 lock1
            synchronized (lock2) {
                // 获取 lock2
            }
        }
    }

    public void method2() {
        synchronized (lock2) {
            // 获取 lock2
            synchronized (lock1) {
                // 获取 lock1
            }
        }
    }
}

In this case, thread 1 will wait for thread 2 to release lock2, and thread 2 will wait for thread 1 to release lock1, resulting in a deadlock.

Deadlock prevention

In order to avoid deadlock, the following measures can be taken:

• Lock sequence: is All objects define a fixed lock order and always acquire locks in that order.
• Timeout mechanism: Set a timeout on the lock acquisition operation. If the lock cannot be obtained within the specified time, give up waiting.
• Deadlock detection and recovery: Use a deadlock detection algorithm, such as periodically checking whether a thread is in a deadlock state, and taking appropriate measures to recover.

Practical Case: Resource Management

Consider a resource management system in which multiple threads access shared resources at the same time. To prevent deadlocks, the following strategy can be implemented:

1. Define a global lock order for all resources, such as sorting by resource name.
2. Before acquiring a resource, a thread must acquire all required locks in order. For example:

public class ResourceManager {
    private final Map<String, Object> resources = new HashMap<>();
    private final Object lock = new Object();
    
    public void allocateResource(String resource) {
        synchronized (lock) {
            resources.get(resource);
        }
    }

    public void releaseResource(String resource) {
        synchronized (lock) {
            resources.remove(resource);
        }
    }
}

By following a fixed lock order, deadlocks on resource acquisition and release operations can be avoided.

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