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Java多线程 原子性操作类的使用

2022-03-03 00:43冬日毛毛雨 Java教程

这篇文章主要介绍了Java多线程 原子性操作类的使用,在java5以后,我们接触到了线程原子性操作,也就是在修改时我们只需要保证它的那个瞬间是安全的即可,经过相应的包装后可以再处理对象的并发修改,本文总结一下Atomic系列的类的

前言:

在java5以后,我们接触到了线程原子性操作,也就是在修改时我们只需要保证它的那个瞬间是安全的即可,经过相应的包装后可以再处理对象的并发修改,本文总结一下Atomic系列的类的使用方法,其中包含:

Java多线程 原子性操作类的使用

1. 基本类型的使用

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public class AtomicTest {
    /**
     * 常见的方法列表
     *
     * @see AtomicInteger#get()             直接返回值
     * @see AtomicInteger#getAndAdd(int)    增加指定的数据,返回变化前的数据
     * @see AtomicInteger#getAndDecrement() 减少1,返回减少前的数据
     * @see AtomicInteger#getAndIncrement() 增加1,返回增加前的数据
     * @see AtomicInteger#getAndSet(int)    设置指定的数据,返回设置前的数据
     * @see AtomicInteger#addAndGet(int)    增加指定的数据后返回增加后的数据
     * @see AtomicInteger#decrementAndGet() 减少1,返回减少后的值
     * @see AtomicInteger#incrementAndGet() 增加1,返回增加后的值
     * @see AtomicInteger#lazySet(int)      仅仅当get时才会set
     * @see AtomicInteger#compareAndSet(int, int) 尝试新增后对比,若增加成功则返回true否则返回false
     **/
 
    public static void main(String[] args) {
 
        final AtomicTicket ticket = new AtomicTicket();
        for (int i = 0; i < 3; i++) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    while (ticket.getCount() > 0) {
                        System.out.println(Thread.currentThread().getName() + " count: " + ticket.decrement());
                    }
                }
            }).start();
        }
    }
}
 
 
class AtomicTicket {
 
    public AtomicInteger count = new AtomicInteger(100);
 
    public int decrement() {
 
        return count.getAndDecrement();
    }
 
    public int getCount() {
        return count.get();
 
    }
}

Thread-0 count: 100
Thread-2 count: 98
Thread-1 count: 99
Thread-2 count: 96
Thread-0 count: 97
Thread-2 count: 94
Thread-2 count: 92
Thread-1 count: 95
中间省略...
Thread-1 count: 12
Thread-2 count: 7
Thread-0 count: 9
Thread-2 count: 5
Thread-1 count: 6
Thread-2 count: 3
Thread-0 count: 4
Thread-2 count: 1
Thread-1 count: 2

2. 数组类型的使用

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public class AtomicIntegerArrayTest {
 
    /**
     * 常见的方法列表
     * @see AtomicIntegerArray#addAndGet(int, int) 执行加法,第一个参数为数组的下标,第二个参数为增加的数量,返回增加后的结果
     * @see AtomicIntegerArray#compareAndSet(int, int, int) 对比修改,参数1:数组下标,参数2:原始值,参数3,修改目标值,修改成功返回true否则false
     * @see AtomicIntegerArray#decrementAndGet(int) 参数为数组下标,将数组对应数字减少1,返回减少后的数据
     * @see AtomicIntegerArray#incrementAndGet(int) 参数为数组下标,将数组对应数字增加1,返回增加后的数据
     *
     * @see AtomicIntegerArray#getAndAdd(int, int) 和addAndGet类似,区别是返回值是变化前的数据
     * @see AtomicIntegerArray#getAndDecrement(int) 和decrementAndGet类似,区别是返回变化前的数据
     * @see AtomicIntegerArray#getAndIncrement(int) 和incrementAndGet类似,区别是返回变化前的数据
     * @see AtomicIntegerArray#getAndSet(int, int) 将对应下标的数字设置为指定值,第二个参数为设置的值,返回是变化前的数据
     */
    private final static AtomicIntegerArray ATOMIC_INTEGER_ARRAY = new AtomicIntegerArray(new int[]{1,2,3,4,5,6,7,8,9,10});
 
    public static void main(String []args) throws InterruptedException {
        Thread []threads = new Thread[10];
        for(int i = 0 ; i < 10 ; i++) {
            final int index = i;
            threads[i] = new Thread() {
                public void run() {
                    int original =  ATOMIC_INTEGER_ARRAY.get(index);
                    int result = ATOMIC_INTEGER_ARRAY.addAndGet(index, index + 1);
                    System.out.println("currentThread:" + Thread.currentThread().getName() + " , 原始值为:" + original + ",增加后的结果为:" + result);
                }
            };
            threads[i].start();
        }
        for(Thread thread : threads) {
            thread.join();
        }
        System.out.println("=========================>\n执行已经完成,结果列表:");
        for(int i = 0 ; i < ATOMIC_INTEGER_ARRAY.length() ; i++) {
            System.out.println(ATOMIC_INTEGER_ARRAY.get(i));
        }
    }
}

currentThread:Thread-0 , 原始值为:1,增加后的结果为:2
currentThread:Thread-3 , 原始值为:4,增加后的结果为:8
currentThread:Thread-2 , 原始值为:3,增加后的结果为:6
currentThread:Thread-1 , 原始值为:2,增加后的结果为:4
currentThread:Thread-5 , 原始值为:6,增加后的结果为:12
currentThread:Thread-4 , 原始值为:5,增加后的结果为:10
currentThread:Thread-6 , 原始值为:7,增加后的结果为:14
currentThread:Thread-7 , 原始值为:8,增加后的结果为:16
currentThread:Thread-8 , 原始值为:9,增加后的结果为:18
currentThread:Thread-9 , 原始值为:10,增加后的结果为:20
=========================>

执行已经完成,结果列表:
2
4
6
8
10
12
14
16
18
20

3. 引用类型的使用

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public class AtomicReferenceTest {
 
    public static void main(String[] args) {
        People people1 =new People("Bom", 0);
        People people2 =new People("Tom",10);
 
        //先初始化一个值,如果不初始化则默认值为null
        AtomicReference<People> reference = new AtomicReference<>(people1);
        People people3 = reference.get();
        if (people3.equals(people1)) {
            System.out.println("people3:" + people3);
        } else {
            System.out.println("else:" + people3);
        }
 
        /**
         * 当前值:拿当前值和reference.get()获取到的值去比较,如果相等则true并更新值为期望值
         * 期望值:如果返回true则更新为期望值,如果返回false则不更新值
         */
        boolean b = reference.compareAndSet(null, people2);
        System.out.println("myClass.main-"+b+"--"+reference.get());
 
        boolean b1 = reference.compareAndSet(people1, people2);
        System.out.println("myClass.main-"+b1+"--"+reference.get());
 
 
        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName());
 
                People people = reference.get();
                people.setName("Tom"+Thread.currentThread().getName());
                people.setAge(people.getAge()+1);
                reference.getAndSet(people);
                System.out.println(Thread.currentThread().getName()+reference.get().toString());
            }
        }).start();
 
        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName());
 
                People people = reference.get();
                people.setName("Tom"+Thread.currentThread().getName());
                people.setAge(people.getAge()+4);
                reference.getAndSet(people);
                System.out.println(Thread.currentThread().getName()+reference.get().toString());
            }
        }).start();
 
    }
 
}
 
 class People {
    private String name;
    private int age;
 
    public People(String name, int age) {
        this.name = name;
        this.age = age;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public int getAge() {
        return age;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
 
    @Override
    public String toString() {
        return "People{" +
                "name='" + name + ''' +
                ", age=" + age +
                '}';
    }
}

4.字段类型的使用

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public class AtomicIntegerFieldUpdaterTest {
 
    /**
     * 可以直接访问对应的变量,进行修改和处理
     * 条件:要在可访问的区域内,如果是private或挎包访问default类型以及非父亲类的protected均无法访问到
     * 其次访问对象不能是static类型的变量(因为在计算属性的偏移量的时候无法计算),也不能是final类型的变量(因为根本无法修改),必须是普通的成员变量
     * <p>
     * 方法(说明上和AtomicInteger几乎一致,唯一的区别是第一个参数需要传入对象的引用)
     *
     * @see AtomicIntegerFieldUpdater#addAndGet(Object, int)
     * @see AtomicIntegerFieldUpdater#compareAndSet(Object, int, int)
     * @see AtomicIntegerFieldUpdater#decrementAndGet(Object)
     * @see AtomicIntegerFieldUpdater#incrementAndGet(Object)
     * @see AtomicIntegerFieldUpdater#getAndAdd(Object, int)
     * @see AtomicIntegerFieldUpdater#getAndDecrement(Object)
     * @see AtomicIntegerFieldUpdater#getAndIncrement(Object)
     * @see AtomicIntegerFieldUpdater#getAndSet(Object, int)
     */
    public final static AtomicIntegerFieldUpdater<A> ATOMIC_INTEGER_UPDATER = AtomicIntegerFieldUpdater.newUpdater(A.class, "intValue");
 
    public static void main(String[] args) {
        final A a = new A();
        for (int i = 0; i < 10; i++) {
 
            new Thread() {
                public void run() {
                    System.out.println(
                            Thread.currentThread().getName() + " " + ATOMIC_INTEGER_UPDATER.get(a));
                    ATOMIC_INTEGER_UPDATER.addAndGet(a, 11);
                    System.out.println(
                            Thread.currentThread().getName() + " " + ATOMIC_INTEGER_UPDATER.get(a));
                    if (ATOMIC_INTEGER_UPDATER.compareAndSet(a, ATOMIC_INTEGER_UPDATER.get(a), 120)) {
                        System.out.println(Thread.currentThread().getName() + " 对应的值做了修改!");
                    }
                    System.out.println(
                            Thread.currentThread().getName() + " " + ATOMIC_INTEGER_UPDATER.get(a));
                }
            }.start();
        }
    }
 
    static class A {
        volatile int intValue = 100;
    }
}

Thread-0 100
Thread-2 100
Thread-1 100
Thread-2 122
Thread-3 111
Thread-5 120
Thread-0 111
Thread-5 142
Thread-3 131
Thread-2 对应的值做了修改!
Thread-2 120
Thread-8 120
Thread-4 133
Thread-1 133
Thread-9 142
Thread-4 142
Thread-4 对应的值做了修改!
Thread-8 131
Thread-3 对应的值做了修改!
Thread-3 120
Thread-7 120
Thread-7 131
Thread-5 对应的值做了修改!
Thread-5 120
Thread-6 120
Thread-0 对应的值做了修改!
Thread-6 131
Thread-7 对应的值做了修改!
Thread-8 对应的值做了修改!
Thread-4 120
Thread-9 131
Thread-1 对应的值做了修改!
Thread-9 对应的值做了修改!
Thread-8 120
Thread-7 120
Thread-6 对应的值做了修改!
Thread-0 131
Thread-6 120
Thread-9 120
Thread-1 120

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原文链接:https://juejin.cn/post/7017409081920995364

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