Java并發庫提供了很多原子類來支持并發訪問的數據安全性，除了常用的

AtomicInteger、AtomicBoolean、AtomicLong 外還有

AtomicReference 用以支持對象的原子操作：AtomicReference<V> 可以封裝引用一個V實例， 通過

public final boolean compareAndSet(V expect, V update)

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可以支持并發訪問，set的時候進行對比判斷，如果當前值和操作之前一樣則返回false，否則表示數據沒有 變化，例如下面的代碼
使用 AtomicReference 實現了并發計數：

package test; import java.util.concurrent.CountDownLatch; import java.util.concurrent.atomic.AtomicReference; public class TS { public static void main(String[] args) throws InterruptedException { dfasd111(); } private static AtomicReference<Integer> ar = new AtomicReference<Integer>(0); public static void dfasd111() throws InterruptedException { int t = 100; final int c = 100; final CountDownLatch latch = new CountDownLatch(t); for (int i = 0; i < t; i++) { new Thread(new Runnable() { @Override public void run() { for (int i = 0; i < c; i++) { while (true) { Integer temp = ar.get(); if (ar.compareAndSet(temp, temp + 1)) { break; } } } latch.countDown(); } }).start(); } latch.await(); System.out.println(ar.get()); //10000000 } public final void test() { System.out.println(this.getClass()); } }

一、原子量實現的計數器

import java.util.HashSet; import java.util.Set; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.atomic.AtomicInteger; public class AtomicCounter { private AtomicInteger value = new AtomicInteger(); public int getValue() { return value.get(); } public int increase() { return value.incrementAndGet();// 內部使用死循環for(;;)調用compareAndSet(current, next) // return value.getAndIncrement(); } public int increase(int i) { return value.addAndGet(i);// 內部使用死循環for(;;)調用compareAndSet(current, next) // return value.getAndAdd(i); } public int decrease() { return value.decrementAndGet();// 內部使用死循環for(;;)調用compareAndSet(current, next) // return value.getAndDecrement(); } public int decrease(int i) { return value.addAndGet(-i);// 內部使用死循環for(;;)調用compareAndSet(current, next) // return value.addAndGet(-i); } public static void main(String[] args) { final AtomicCounter counter = new AtomicCounter(); ExecutorService service = Executors.newCachedThreadPool(); for (int i = 0; i < 10; i++) { service.execute(new Runnable() { @Override public void run() { System.out.println(counter.increase()); } }); } service.shutdown(); } }

二、原子量實現的銀行取款

import java.util.Random; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.atomic.AtomicLong; public class Account { private AtomicLong balance; public Account(long money) { balance = new AtomicLong(money); System.out.println("Total Money:" + balance); } public void deposit(long money) { balance.addAndGet(money); } public void withdraw(long money) { for (; ; ) {//保證即時同一時間有人也在取款也可以再次嘗試取款，如果不需要并發嘗試取款，可以去掉這句 long oldValue = balance.get(); if (oldValue < money) { System.out.println(Thread.currentThread().getName() + " 余額不足！ 余額：" + balance); break; } try {Thread.sleep(new Random().nextInt(1000));} catch (Exception e) { }// 模擬取款時間 if (balance.compareAndSet(oldValue, oldValue - money)) { System.out.println(Thread.currentThread().getName() + " 取款 " + money + " 成功！ 余額：" + balance); break; } System.out.println(Thread.currentThread().getName() + " 遇到并發，再次嘗試取款！"); } } public static void main(String[] args) { final Account account = new Account(1000); ExecutorService pool = Executors.newCachedThreadPool(); int i = 0; while (i++ < 13) { pool.execute(new Runnable() { @Override public void run() { account.withdraw(100); } }); } pool.shutdown(); } }

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轉載于:https://my.oschina.net/vshcxl/blog/843787

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