Practical suggestions for synchronizing threads in Java include: prioritizing synchronous code blocks over methods; considering ReentrantLock to improve flexibility; avoid deadlocks; and rational use of volatile and atomic classes. 1. When using synchronized keywords, synchronized code blocks are preferred to reduce lock granularity; 2. ReentrantLock provides enhanced functions such as tryLock and timeout mechanism, but locks must be released in finally; 3. Avoid deadlocks can be achieved by unifying the lock order, setting timeouts, reducing the lock range and avoiding nested locks; 4. volatile is suitable for lightweight scenarios that ensure the visibility of variables, and atomic classes such as AtomicInteger can optimize lock-free counting operations.

In a multi-threaded environment, the synchronization mechanism is the key to ensuring data consistency and program stability . Java provides a variety of ways to implement thread synchronization, but if used improperly, it can lead to deadlocks, race conditions, or performance issues. Here are some practical suggestions for synchronizing threads in Java.

Use synchronized keywords to control access

synchronized is the most basic synchronization mechanism in Java and can be used in methods or code blocks. It ensures that only one thread executes protected code at the same time.

• Synchronization method : It is suitable for situations where the entire method needs to be locked.
• Synchronous code block : more flexible, only locking the parts that need to be synchronized to reduce the lock granularity.

 public class Counter {
    private int count = 0;

    public void increment() {
        synchronized (this) {
            count ;
        }
    }
}

It is recommended to use synchronous code blocks instead of synchronizing the entire method, especially if there are operations in the method that do not involve shared resources.

Consider using ReentrantLock to increase flexibility

Starting in Java 5, ReentrantLock has become an alternative to synchronized , providing more features such as trying to acquire locks, timeout mechanisms, and fair locks.

 import java.util.concurrent.locks.ReentrantLock;

public class Counter {
    private final ReentrantLock lock = new ReentrantLock();
    private int count = 0;

    public void increment() {
        lock.lock();
        try {
            count ;
        } finally {
            lock.unlock();
        }
    }
}

Several advantages:

• Supports attempts to acquire locks without blocking
• Can interrupt thread waiting for lock
• More fine-grained control (such as read and write locks)

Note: When using ReentrantLock, be sure to release the lock in the finally block, otherwise a deadlock may be triggered.

Basic strategies to avoid deadlocks

Deadlock is a phenomenon in which multiple threads wait for each other to hold the locks held by the other party, causing the program to stagnate. To avoid deadlocks, you can start from the following aspects:

• Unified locking order : All threads apply for resources in the same order
• Set the timeout mechanism : use tryLock(timeout) instead of unconditional waiting
• Minimize the scope of lock
• Avoid nested locks

A common error scenario is that thread A holds lock 1 and requests lock 2, while thread B holds lock 2 and requests lock 1. Deadlock may occur at this time.

If business logic allows, try to avoid cross-dependence between multiple locks.

Optimize lightweight concurrency with volatile and atomic classes

For some simple status flags or counter operations, consider using atomic classes such as volatile or AtomicInteger .

• volatile ensures the visibility of variables and is suitable for scenarios where more reads, less writes, and less reads
• AtomicInteger provides thread-safe self-incremental operation without locking

 private volatile boolean running = true;

public void stop() {
    running = false;
}

Don't expect volatile to solve all concurrency problems, it does not guarantee the atomicity of composite operations.

Basically that's it. Thread synchronization seems simple, but it is easy to make mistakes in practical applications. The key is to select the appropriate synchronization mechanism based on the specific scenario and keep the code clear and easy to maintain.

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