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Java模擬死鎖發(fā)生之演繹哲學(xué)家進(jìn)餐問(wèn)題案例詳解

更新時(shí)間：2019年10月23日 09:09:21 作者：cakincqm

這篇文章主要介紹了Java模擬死鎖發(fā)生之演繹哲學(xué)家進(jìn)餐問(wèn)題,結(jié)合具體演繹哲學(xué)家進(jìn)餐問(wèn)題的案例形式詳細(xì)分析了死鎖機(jī)制與原理,需要的朋友可以參考下

本文實(shí)例講述了Java模擬死鎖發(fā)生之演繹哲學(xué)家進(jìn)餐問(wèn)題。分享給大家供大家參考，具體如下：

一點(diǎn)睛

常見(jiàn)的死鎖形式：當(dāng)線程1已經(jīng)占據(jù)資源R1，并持有資源R1上的鎖，而且還在等待資源R2的鎖；而線程2已經(jīng)占據(jù)資源R2，并且持有資源R2上的鎖，卻正在等待資源R1上的鎖。如果兩個(gè)線程不釋放自己占據(jù)的資源鎖，而且還申請(qǐng)對(duì)方資源上的鎖，申請(qǐng)不到時(shí)只能等待，而且它們只能永遠(yuǎn)的等待下去。

二實(shí)戰(zhàn)

1 代碼

public class DeadLockDemo
{
  /** knife鎖 */
  private static String knife = "餐刀"; //臨界資源
  /** fork鎖 */
  private static String fork = "叉子"; //臨界資源
  public static void main(String[] args)
  {
    DaemonThread daemonTh = new DaemonThread();
    Thread newDaemon = new Thread(daemonTh);
    newDaemon.setDaemon(true);
    newDaemon.start();
    new DeadLockDemo().deadLock();
  }
  private void deadLock()
  {
    Thread t1 = new Thread(new Runnable() {
      @Override
      public void run()
      {
        synchronized (knife) {
          System.out.println(Thread.currentThread().getName() + "拿起了" + knife + ", 等待" + fork + "......");
          try {
            Thread.sleep(2000);
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
          synchronized (fork) {
            System.out.println(Thread.currentThread().getName() + "又拿起了" + fork + "，吃飯中...");
          }
        }
      }
    });
    Thread t2 = new Thread(new Runnable() {
      @Override
      public void run() {
        synchronized (fork) {
          System.out.println(Thread.currentThread().getName() + "拿起了" + fork + ", 等待" + knife + "......");
          synchronized (knife) {
            System.out.println(Thread.currentThread().getName() + "又拿起了" + knife + "，吃飯中...");
          }
        }
      }
    });
    t1.start();
    t2.start();
  }
}
class DaemonThread implements Runnable
{
  @Override
  public void run()
  {
    while(true)
    {
      try {
        Thread.sleep(1000);
      }catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("守護(hù)線程：程序仍在運(yùn)行中...");
    }
  }
}

2 運(yùn)行

Thread-1拿起了餐刀, 等待叉子......
Thread-2拿起了叉子, 等待餐刀......
守護(hù)線程：程序仍在運(yùn)行中...
守護(hù)線程：程序仍在運(yùn)行中...
守護(hù)線程：程序仍在運(yùn)行中...
守護(hù)線程：程序仍在運(yùn)行中...
守護(hù)線程：程序仍在運(yùn)行中...

三預(yù)防死鎖

1 解決方法

如果規(guī)定線程A和B都必須先拿刀，再拿叉，就不會(huì)發(fā)生死鎖。

2 代碼

public class DeadLockDemo
{
  /** knife鎖 */
  private static String knife = "餐刀"; //臨界資源
  /** fork鎖 */
  private static String fork = "叉子"; //臨界資源
  public static void main(String[] args)
  {
    DaemonThread daemonTh = new DaemonThread();
    Thread newDaemon = new Thread(daemonTh);
    newDaemon.setDaemon(true);
    newDaemon.start();
    new DeadLockDemo().deadLock();
  }
  private void deadLock()
  {
    Thread t1 = new Thread(new Runnable() {
      @Override
      public void run()
      {
        synchronized (knife) {
          System.out.println(Thread.currentThread().getName() + "拿起了" + knife + ", 等待" + fork + "......");
          try {
            Thread.sleep(2000);
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
          synchronized (fork) {
            System.out.println(Thread.currentThread().getName() + "又拿起了" + fork + "，吃飯中...");
          }
        }
      }
    });
    Thread t2 = new Thread(new Runnable() {
      @Override
      public void run() {
        synchronized (knife) {
          System.out.println(Thread.currentThread().getName() + "拿起了" + knife + ", 等待" + fork + "......");
          synchronized (fork) {
            System.out.println(Thread.currentThread().getName() + "又拿起了" + fork + "，吃飯中...");
          }
        }
      }
    });
    t1.start();
    t2.start();
  }
}
class DaemonThread implements Runnable
{
  @Override
  public void run()
  {
    while(true)
    {
      try {
        Thread.sleep(1000);
      }catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("守護(hù)線程：程序仍在運(yùn)行中...");
    }
  }
}

3 運(yùn)行