Java7新特性（四）并发 2 Lock对象处理死锁

本文主要根据《Java程序员修炼之道》整理的代码笔记片段

一个线程更新，备用线程确认更新 （Lock lock = new ReentrantLock(); boolean acquired = lock.tryLock(wait, TimeUnit.MILLISECONDS); //Java 5）

public interface ConfirmingMicroBlogNode {  void propagateUpdate(Update upd_, ConfirmingMicroBlogNode backup_);  boolean tryConfirmUpdate(ConfirmingMicroBlogNode other_, Update update_);  String getIdent();}

public class FixedDeadlockWithLockMicroBlogNode implements    ConfirmingMicroBlogNode {  private static Update getUpdate(String s) {    Update.Builder b = new Update.Builder();    b.updateText(s).author(new Author("Ben"));    return b.build();  }  private final String ident;  private final Lock lock = new ReentrantLock();  public FixedDeadlockWithLockMicroBlogNode(String ident_) {    ident = ident_;  }  @Override  public String getIdent() {    return ident;  }  @Override  public void propagateUpdate(Update upd_, ConfirmingMicroBlogNode backup_) {    boolean acquired = false;    boolean done = false;    while (!done) {      int wait = (int) (Math.random() * 10);      try {        acquired = lock.tryLock(wait, TimeUnit.MILLISECONDS);        if (acquired) {          System.out.println(ident + ": recvd: " + upd_.getUpdateText()              + " ; backup: " + backup_.getIdent());          done = backup_.tryConfirmUpdate(this, upd_);        }      } catch (InterruptedException e) {      } finally {        if (acquired)          lock.unlock();      }      if (!done)        try {          Thread.sleep(wait);        } catch (InterruptedException e) {        }    }  }  @Override  public boolean tryConfirmUpdate(ConfirmingMicroBlogNode other_, Update upd_) {    long startTime = System.currentTimeMillis();    boolean acquired = false;    try {      int wait = (int) (Math.random() * 10);      acquired = lock.tryLock(wait, TimeUnit.MILLISECONDS);      if (acquired) {        long elapsed = System.currentTimeMillis() - startTime;        System.out.println(ident + ": recvd confirm: " + upd_.getUpdateText()            + " from " + other_.getIdent() + " - took " + elapsed + " millis");        return true;      }    } catch (InterruptedException e) {    } finally {      if (acquired)        lock.unlock();    }    return false;  }  public static void main(String[] a) {    final FixedDeadlockWithLockMicroBlogNode local = new FixedDeadlockWithLockMicroBlogNode(        "localhost:8888");    final FixedDeadlockWithLockMicroBlogNode other = new FixedDeadlockWithLockMicroBlogNode(        "localhost:8988");    final Update first = getUpdate("1");    final Update second = getUpdate("2");    new Thread(new Runnable() {      public void run() {        local.propagateUpdate(first, other);      }    }).start();    new Thread(new Runnable() {      public void run() {        other.propagateUpdate(second, local);      }    }).start();  }}