线程安全性（一）原子性基于锁的实现 - synchronized修饰静态方法

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本文通过示例解释了在Java中如何使用synchronized关键字修饰静态方法来实现线程安全。当两个不同对象的不同线程尝试访问同一类的静态同步方法时，这些方法会按顺序执行，确保了操作的原子性。

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synchronized修饰静态方法示例

synchronized修饰静态方法，其作用对象是这个类的所有对象；
2个不同的对象在不同的线程中访问静态方法，按顺序一个一个线程的执行，不会多个线程同时执行；

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

@Slf4j
public class SynchronizedStaticMethod {

    public synchronized static void test(int j) {
        for (int i = 0; i < 10; i++) {
            log.info("synchronized static method object {} - {}", j, i);
        }
    }

    public static void main(String[] args) {
        SynchronizedStaticMethod example1 = new SynchronizedStaticMethod();
        SynchronizedStaticMethod example2 = new SynchronizedStaticMethod();
        ExecutorService service = Executors.newCachedThreadPool();
        service.execute(() -> {
            example1.test(1);
        });
        service.execute(() -> {
            example2.test(2);
        });
    }

}

输出：

两个线程排队执行；

18:05:02.200 [pool-1-thread-1] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 1 - 0
18:05:02.205 [pool-1-thread-1] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 1 - 1
18:05:02.205 [pool-1-thread-1] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 1 - 2
18:05:02.205 [pool-1-thread-1] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 1 - 3
18:05:02.205 [pool-1-thread-1] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 1 - 4
18:05:02.205 [pool-1-thread-1] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 1 - 5
18:05:02.205 [pool-1-thread-1] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 1 - 6
18:05:02.205 [pool-1-thread-1] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 1 - 7
18:05:02.205 [pool-1-thread-1] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 1 - 8

18:05:02.206 [pool-1-thread-1] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 1 - 9
18:05:02.206 [pool-1-thread-2] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 2 - 0
18:05:02.206 [pool-1-thread-2] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 2 - 1
18:05:02.206 [pool-1-thread-2] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 2 - 2
18:05:02.206 [pool-1-thread-2] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 2 - 3
18:05:02.206 [pool-1-thread-2] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 2 - 4
18:05:02.206 [pool-1-thread-2] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 2 - 5
18:05:02.206 [pool-1-thread-2] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 2 - 6
18:05:02.206 [pool-1-thread-2] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 2 - 7
18:05:02.206 [pool-1-thread-2] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 2 - 8
18:05:02.206 [pool-1-thread-2] INFO com.example.concurrency.example.sync.SynchronizedStaticMethod - synchronized static method object 2 - 9