我参考的是这篇文章： https://www.cnkirito.moe/java-ConcurrentHashMap-CAS/ 网上论述这个的文章实在是不多。
我的测试代码如下：
public class test2 { private final static Map<String, Table> map = new ConcurrentHashMap<>(); private static final String KEY = "key";
public static void increase1(String key) {
Table oldTable = map.get(key);
int value = oldTable.getI();
oldTable.setI(value + 1);
map.put(key, oldTable);
}
public static void increase2(String key) {
Table oldTable;
Table newTable = new Table(0);
while(true) {
oldTable = map.get(KEY);
newTable.setI(oldTable.getI() + 1);
if(map.replace(KEY, oldTable, newTable)) break;
}
}
public static int getTableValue(String key) {
return map.get(key).getI();
}
public static void main(String[] args) {
map.put(KEY, new Table(0));
ExecutorService executor = Executors.newFixedThreadPool(10);
int callTime = 1000;
CountDownLatch countDownLatch = new CountDownLatch(callTime);
for(int i=0; i<callTime; i++) {
executor.execute(new Runnable() {
@Override
public void run() {
increase2(KEY);
countDownLatch.countDown();
}
});
}
try {
countDownLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
executor.shutdown();
System.out.println("调用次数：" + getTableValue(KEY));
}
}
class Table { private int i;
public Table(int i) {
this.i = i;
}
public int getI() {
return i;
}
public void setI(int i) {
this.i = i;
}
}
测试结果：使用 increase1 的话，调用次数是不停变动的，存在并发错误。而用 increase2 的话，恒定都是 1000.
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