线程同步问题（更新变量总和）

Question

当我想使用 synchronized 关键字或锁进行更新时，它在 sum 变量为 int 时有效，但在它是 Integer 对象时无效。代码看起来像这样 -public class TestSynchronized {  private  Integer sum = new Integer(0);  public static void main(String[] args) {    TestSynchronized test = new TestSynchronized();    System.out.println("The sum is :" + test.sum);  }  public TestSynchronized() {    ExecutorService executor = Executors.newFixedThreadPool(1000);    for (int i = 0; i <=2000; i++) {      executor.execute(new SumTask());    }    executor.shutdown();    while(!executor.isTerminated()) {    }  }  class SumTask implements Runnable {    Lock lock = new ReentrantLock();    public void run() {    lock.lock();      int value = sum.intValue() + 1;      sum = new Integer(value);        lock.unlock(); // Release the lock      }  }}

Answer 1

问题是您已将locks每个SumTask对象分开。这些对象应该共享locks。

lock在TestSynchronized()方法中创建一次对象。这应该由所有new SumTask(lock)对象共享。

所以你的SumTask班级看起来像：

class SumTask implements Runnable {

    Lock lock;

    public SumTask(Lock commonLock) {

        this.lock = commonLock;

    }

    public void run() {

        lock.lock();

        int value = sum.intValue() + 1;

        sum = new Integer(value);

        lock.unlock(); // Release the lock

    }

}

并且不要忘记commonLock在TestSynchronized()方法中创建一个对象：

  Lock lock = new ReentrantLock();

  executor.execute(new SumTask(commonLock));