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Java在高并發(fā)場景下實現(xiàn)點贊計數(shù)器

更新時間：2023年06月28日 16:01:57 作者：SSPo

點贊計數(shù)器的本質(zhì)就是對某個變量在高并發(fā)情況下的修改，這篇文章主要為大家介紹了Java實現(xiàn)點贊計數(shù)器的示例代碼，感興趣的小伙伴可以了解一下

1. Synchronized 關(guān)鍵字

package concurrent;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.LongAccumulator;
import java.util.concurrent.atomic.LongAdder;
class ClickResource{
    int number = 0;
    public synchronized void clickBySynchronized(){number++;}
}
// 100個線程, 每個線程點贊 100萬 次, 求準確率和效率
public class AccumulatorCompareDemo {
    public static final int _1w = 10000;
    public static final int threadNumber = 100;
    public static void main(String[] args) throws InterruptedException {
        ClickResource clickResource = new ClickResource();
        long startTime  = System.currentTimeMillis();
        CountDownLatch countDownLatch1 = new CountDownLatch(threadNumber);
        for (int i = 0; i < threadNumber; i++) {
            new Thread(()->{
                try {
                    for (int j = 0; j < 100*_1w; j++) {
                        clickResource.clickBySynchronized();
                    }
                }finally {
                    countDownLatch1.countDown();
                }
            },String.valueOf(i)).start();
        }
        countDownLatch1.await();
        long endTime  = System.currentTimeMillis();
        System.out.println("所用時間="+(endTime-startTime)+"ms"+"    最終點贊次數(shù)="+clickResource.number);
    }
}
// synchronized       悲觀鎖
// 所用時間=2258ms    最終點贊次數(shù)=100000000

2. 使用 AtomicLong 原子類

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.LongAccumulator;
import java.util.concurrent.atomic.LongAdder;
class ClickResource{
    int number = 0;
    AtomicLong atomicLong = new AtomicLong(0);
    public void clickByAtomicLong(){atomicLong.getAndIncrement();}
}
// 100個線程, 每個線程點贊 100萬 次, 求準確率和效率
public class AccumulatorCompareDemo {
    public static final int _1w = 10000;
    public static final int threadNumber = 100;
    public static void main(String[] args) throws InterruptedException {
        ClickResource clickResource = new ClickResource();
        long startTime  = System.currentTimeMillis();
        CountDownLatch countDownLatch = new CountDownLatch(threadNumber);
        for (int i = 0; i < threadNumber; i++) {
            new Thread(()->{
                try {
                    for (int j = 0; j < 100*_1w; j++) {
                        clickResource.clickByAtomicLong();
                    }
                }finally {
                    countDownLatch.countDown();
                }
            },String.valueOf(i)).start();
        }
        countDownLatch.await();
        long endTime  = System.currentTimeMillis();
        System.out.println("所用時間="+(endTime-startTime)+"ms"+"    最終點贊次數(shù)="+clickResource.atomicLong);
    }
}
// CAS - 輕量級鎖 - 調(diào)用 Unsafe 類的 cas 方法 - 底層操作系統(tǒng)原子指令 
// 所用時間=1177ms    最終點贊次數(shù)=100000000

3.使用 LongAdder 類

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.LongAccumulator;
import java.util.concurrent.atomic.LongAdder;
class ClickResource{
    int number = 0;
    LongAdder longAdder = new LongAdder();
    public void clickByLongAdder(){longAdder.increment();}
}
// 100個線程, 每個線程點贊 100萬 次, 求準確率和效率
public class AccumulatorCompareDemo {
    public static final int _1w = 10000;
    public static final int threadNumber = 100;
    public static void main(String[] args) throws InterruptedException {
        ClickResource clickResource = new ClickResource();
        long startTime  = System.currentTimeMillis();
        CountDownLatch countDownLatch = new CountDownLatch(threadNumber);
        CountDownLatch countDownLatch2 = new CountDownLatch(threadNumber);
        CountDownLatch countDownLatch3 = new CountDownLatch(threadNumber);
        CountDownLatch countDownLatch4 = new CountDownLatch(threadNumber);
        for (int i = 0; i < threadNumber; i++) {
            new Thread(()->{
                try {
                    for (int j = 0; j < 100*_1w; j++) {
                        clickResource.clickByLongAdder();
                    }
                }finally {
                    countDownLatch.countDown();
                }
            },String.valueOf(i)).start();
        }
        countDownLatch.await();
        long endTime  = System.currentTimeMillis();
        System.out.println("所用時間="+(endTime-startTime)+"ms"+"    最終點贊次數(shù)="+clickResource.longAdder);
    }
}
//所用時間=141ms    最終點贊次數(shù)=100000000

4. 使用 LongAccumulator 類

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.LongAccumulator;
import java.util.concurrent.atomic.LongAdder;
class ClickResource{
    int number = 0;
    LongAccumulator longAccumulator = new LongAccumulator((x,y)->x+y,0);
    public void clickByLongAccumulator(){longAccumulator.accumulate(1);}
}
// 100個線程, 每個線程點贊 100萬 次, 求準確率和效率
public class AccumulatorCompareDemo {
    public static final int _1w = 10000;
    public static final int threadNumber = 100;
    public static void main(String[] args) throws InterruptedException {
        ClickResource clickResource = new ClickResource();
        long startTime  = System.currentTimeMillis();
        CountDownLatch countDownLatch = new CountDownLatch(threadNumber);
        for (int i = 0; i < threadNumber; i++) {
            new Thread(()->{
                try {
                    for (int j = 0; j < 100*_1w; j++) {
                        clickResource.clickByLongAccumulator();
                    }
                }finally {
                    countDownLatch.countDown();
                }
            },String.valueOf(i)).start();
        }
        countDownLatch.await();
        long endTime  = System.currentTimeMillis();
        System.out.println("所用時間="+(endTime-startTime)+"ms"+"    最終點贊次數(shù)="+clickResource.longAccumulator);
    }
}
// 所用時間=150ms    最終點贊次數(shù)=100000000

LongAccumulator 和 LongAdder 底層調(diào)用的方法相同，主要區(qū)別是，LongAdder只能初始為0，且只能做加法操作，LongAccumulator 能初始成任何數(shù)

需要注意的是：

LongAdder 和 LongAccumulator 并不保證最終獲取的數(shù)據(jù)是完全準確無誤的，也許會有少許偏差，但在高并發(fā)的點贊場景下犧牲少量的數(shù)據(jù)精確性來保證高性能是完全能接受的

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