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使用Runnable實現(xiàn)數(shù)據(jù)共享

 更新時間：2018年07月18日 10:32:22   作者：NewUser2771894007  
這篇文章主要為大家詳細(xì)介紹了如何使用Runnable實現(xiàn)數(shù)據(jù)共享，具有一定的參考價值，感興趣的小伙伴們可以參考一下

使用Runnable實現(xiàn)數(shù)據(jù)共享，供大家參考，具體內(nèi)容如下

先上代碼：

public class TestThread {
  private static final Logger logger = LoggerFactory.getLogger(TestThread.class);

  private final class MyRunnable implements Runnable {
    private int i;
    public MyRunnable() {
      this.i = 10;
    }
    public void run() {
      while(i > 0) {
        synchronized (this) {
          if (i > 0) {
            i--;
            logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i);
          }
        }
      }
    }
  }

  @Test
  public void testRunable() throws InterruptedException{
    MyRunnable myRunnable = new MyRunnable();
    Thread th1 = new Thread(myRunnable);
    Thread th2 = new Thread(myRunnable);
    th1.start();
    th2.start();
    th1.join();
    th2.join();
  }
}

樓上的代碼很簡單，模擬一個售票系統(tǒng)。通過兩個Thread對象開啟兩條線程同時運行一個MyRunnable實例。

幾個注意點：

1. 沒有加上synchronised關(guān)鍵詞的話，即

public void run() {
      while(i > 0) {
        if (i > 0) {
          i--;
          logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i);
        }
      }
    }

系統(tǒng)的運行結(jié)果：

Thread-1 buy one ticket, 8 left. 
Thread-2 buy one ticket, 8 left. 
Thread-2 buy one ticket, 6 left. 
Thread-1 buy one ticket, 6 left. 
Thread-2 buy one ticket, 5 left. 
Thread-1 buy one ticket, 4 left. 
Thread-2 buy one ticket, 3 left. 
Thread-1 buy one ticket, 2 left. 
Thread-2 buy one ticket, 1 left. 
Thread-1 buy one ticket, 0 left.

可以看到，缺少同步的程序輸出明顯有問題。

2. 在進入同步代碼塊之后，還需要對i的值再進行一次判斷，即，如果不加if判斷：

public void run() {
      while(i > 0) {
        synchronized (this) {
          i--;
          logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i);

        }
      }
    }

程序的運行結(jié)果為：

Thread-2 buy one ticket, 9 left. 
Thread-2 buy one ticket, 8 left. 
Thread-2 buy one ticket, 7 left. 
Thread-2 buy one ticket, 6 left. 
Thread-2 buy one ticket, 5 left. 
Thread-2 buy one ticket, 4 left. 
Thread-2 buy one ticket, 3 left. 
Thread-2 buy one ticket, 2 left. 
Thread-2 buy one ticket, 1 left. 
Thread-2 buy one ticket, 0 left. 
Thread-1 buy one ticket, -1 left.

可以看出，出現(xiàn)了“多賣”的現(xiàn)象， 所以需要在進入同步代碼塊中再進行一次if判斷。

總結(jié)

synchronised用于互斥訪問共享變量， 并在同步代碼塊中使用if判斷更新共享變量。

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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