What are the different implementation strategies for Java function thread safety?

The implementation strategies for Java function thread safety include: 1. Synchronized methods, allowing only one thread to execute; 2. Using synchronized code blocks, declaring the lock object as a critical section, and only the thread that obtains the lock object can execute the code; 3. . Use thread-safe collections and data structures provided by the Java concurrency library; 4. Create immutable objects that are inherently thread-safe. These strategies ensure data consistency and program correctness in a multi-threaded environment.

Different implementation strategies to ensure thread safety of Java functions

In a multi-threaded environment, thread safety is crucial to prevent data races and program mistake. For the thread safety of Java functions, there are different implementation strategies as follows:

1. Synchronous method

The synchronized method only allows one thread to execute at the same time, thereby achieving thread safety.

public class SafeCounter {
    private int count = 0;

    public synchronized int increment() {
        return ++count;
    }
}

2. Use the synchronized code block

synchronized (lockObject) { ... } statement to declare the lock object as a critical section. Within a critical section, only the thread that acquires the lock object can execute code.

public class SafeCounter {
    private int count = 0;
    private final Object lock = new Object();

    public void increment() {
        synchronized (lock) {
            count++;
        }
    }
}

3. Use the Java concurrency library

java.util.concurrent package provides thread-safe collections and data structures, such as ConcurrentHashMap and AtomicInteger.

import java.util.concurrent.ConcurrentHashMap;

public class SafeCounter {
    private ConcurrentHashMap<String, Integer> counts = new ConcurrentHashMap<>();

    public int increment(String key) {
        return counts.computeIfAbsent(key, k -> 0) + 1;
    }
}

4. Immutable objects

Immutable objects cannot be modified after they are created, so they are inherently thread-safe.

public final class ImmutableCounter {
    private final int count;

    public ImmutableCounter(int count) {
        this.count = count;
    }

    public int getCount() {
        return count;
    }
}

Practical Case

Suppose we have a multi-threaded application in which multiple threads need to update a shared counter. By applying these thread-safety strategies, we can create a thread-safe counter implementation:

public class Main {
    public static void main(String[] args) {
        // 使用不同策略创建线程安全的计数器
        SafeCounter counter1 = new SafeCounter();
        SafeCounter counter2 = new SafeCounter();
        SafeCounter counter3 = new SafeCounter();

        // 创建多个线程并发地更新计数器
        Thread[] threads = new Thread[10];
        for (int i = 0; i < threads.length; i++) {
            threads[i] = new Thread(() -> {
                for (int j = 0; j < 1000; j++) {
                    counter1.increment();
                    counter2.increment();
                    counter3.increment();
                }
            });
        }

        // 启动线程并等待它们完成
        for (Thread thread : threads) {
            thread.start();
        }

        // 线程安全策略确保所有线程完成时，计数器包含正确的计数
        System.out.println("Counter1: " + counter1.increment());
        System.out.println("Counter2: " + counter2.increment());
        System.out.println("Counter3: " + counter3.increment());
    }
}

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