Thread--lock,lockInterruptibly,tryLock,tryLock(long timeout, TimeUnit unit)

 

参考：http://www.dewen.net.cn/q/9077

　　　http://coolxing.iteye.com/blog/1236909

lock,tryLock,lockInterruptibly

分别对应无限制锁，定时锁（通过while可以作为轮询锁），可中断锁。

Lock接口的 线程请求锁的 几个方法：

lock(), 拿不到lock就不罢休，不然线程就一直block。 比较无赖的做法。
tryLock()，马上返回，拿到lock就返回true，不然返回false。 比较潇洒的做法。
带时间限制的tryLock()，拿不到lock，就等一段时间，超时返回false。比较聪明的做法。

下面的lockInterruptibly()就稍微难理解一些。

先说说线程的打扰机制，每个线程都有一个 打扰 标志。这里分两种情况，
1. 线程在sleep或wait,join， 此时如果别的进程调用此进程的 interrupt（）方法，此线程会被唤醒并被要求处理InterruptedException；(thread在做IO操作时也可能有类似行为，见java thread api)
2. 此线程在运行中， 则不会收到提醒。但是 此线程的 “打扰标志”会被设置， 可以通过isInterrupted()查看并作出处理。

lockInterruptibly()和上面的第一种情况是一样的， 线程在请求lock并被阻塞时，如果被interrupt，则“此线程会被唤醒并被要求处理InterruptedException”。

E.G.  lock() & lockInterruptibly()

--lock()

package lockInterruptibly;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class MyService {

    public ReentrantLock lock = new ReentrantLock();
    private Condition condition = lock.newCondition();

    public void waitMethod() {
        try {
            lock.lock();
            // lock.lockInterruptibly();
            System.out.println("lock begin " + Thread.currentThread().getName());
            for (int i = 0; i < 100000000; i++) {
                String newString = new String();
                Math.random();
                // System.out.println(i + " ");
            }
            System.out.println("lock end " + Thread.currentThread().getName());
        } finally {
            if (lock.isHeldByCurrentThread()) {
                lock.unlock();
            }
        }
    }

}

package lockInterruptibly;

public class Run {

    public static void main(String[] args) {
        try {
            final MyService service = new MyService();
            Runnable runnable = new Runnable() {

                @Override
                public void run() {
                    // TODO Auto-generated method stub
                    service.waitMethod();
                }
            };
            Thread a = new Thread(runnable);
            a.setName("A");
            a.start();
            Thread b = new Thread(runnable);
            b.setName("B");
            b.start();
            Thread.sleep(500);
            b.interrupt();
            System.out.println("main end");
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

正如lock()拿不到锁誓不罢休，线程b并未响应interrupt，一直在等待着锁。

 

--lockInterruptibly()

package lockInterruptibly;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class MyService {

    public ReentrantLock lock = new ReentrantLock();
    private Condition condition = lock.newCondition();

    public void waitMethod() {
        try {
//            lock.lock();
            lock.lockInterruptibly();
            System.out.println("lock begin " + Thread.currentThread().getName());
            for (int i = 0; i < 100000000; i++) {
                String newString = new String();
                Math.random();
                // System.out.println(i + " ");
            }
            System.out.println("lock end " + Thread.currentThread().getName());
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            if (lock.isHeldByCurrentThread()) {
                lock.unlock();
            }
        }
    }

}

package lockInterruptibly;

public class Run {

    public static void main(String[] args) {
        try {
            final MyService service = new MyService();
            Runnable runnable = new Runnable() {

                @Override
                public void run() {
                    // TODO Auto-generated method stub
                    service.waitMethod();
                }
            };
            Thread a = new Thread(runnable);
            a.setName("A");
            a.start();
            Thread b = new Thread(runnable);
            b.setName("B");
            b.start();
            Thread.sleep(500);
            b.interrupt();
            System.out.println("main end");
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

 

线程b并没有拿到锁，此时调用interrupt方法，则线程b被唤醒并被要求处理InterruptedException，即抛出了InterruptedException

当然，线程b也并不会执行了

但是当线程b拿到锁执行时才调用interrupt，这时候线程b并不会中断

 

tryLock() & tryLock(long, TimeUnit)

|--void lock(): 执行此方法时, 如果锁处于空闲状态, 当前线程将获取到锁. 相反, 如果锁已经被其他线程持有, 将禁用当前线程, 直到当前线程获取到锁.

|--boolean tryLock(): 如果锁可用, 则获取锁, 并立即返回true, 否则返回false. 该方法和lock()的区别在于, tryLock()只是"试图"获取锁, 如果锁不可用, 不会导致当前线程被禁用, 当前线程仍然继续往下执行代码. 而lock()方法则是一定要获取到锁, 如果锁不可用, 就一直等待, 在未获得锁之前,当前线程并不继续向下执行. 通常采用如下的代码形式调用tryLock()方法:

|--boolean tryLock(long timeout, TimeUnit unit):如果锁定在给定等待时间内没有被另一个线程保持，且当前线程未被中断，则获取该锁定。

通常采用如下的代码形式调用tryLock()方法:

   Lock lock = new ReentrantLock();
      if (lock.tryLock()) {
          try {
              // manipulate protected state
          } finally {
              lock.unlock();
          }
      } else {
          // perform alternative actions
      }

此用法可确保如果获取了锁, 则会释放锁; 如果未获取锁, 则不会试图将其释放.

 

--tryLock()

package tryLock.copy.copy;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;

/**
 * boolean tryLock(long timeout, TimeUnit unit) 如果锁定在给定等待时间内没有被另一个线程保
 * 持，且当前线程未被中断，则获取该锁定
 * 
 * @author MicroCat
 *
 */
public class MyService {

    public ReentrantLock lock = new ReentrantLock();

    public void waitMethod() {
        if (lock.tryLock()) {
            try {
                System.out.println(Thread.currentThread().getName() + " 获得锁");
                for (int i = 0; i < 10000; i++) {
                    if (i % 100 == 0) {
                        System.out.println(Thread.currentThread().getName() + " " + i);
                    }
                }
            } finally {
                lock.unlock();
            }
        } else {
            System.out.println(Thread.currentThread().getName() + " 没有获得锁");
        }
    }

}

package tryLock.copy.copy;

public class Run {

    public static void main(String[] args) throws InterruptedException {
        final MyService service = new MyService();
        Runnable runnable = new Runnable() {

            @Override
            public void run() {
                service.waitMethod();
            }
        };
        Thread a = new Thread(runnable);
        a.setName("A");
        a.start();
        Thread b = new Thread(runnable);
        b.setName("B");
        b.start();
    }

}

线程b没有获得锁，a线程执行完也没有继续执行

 

--tryLock(long, TimeUnit)

package tryLock.copy.copy.copy;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;

/**
 * boolean tryLock(long timeout, TimeUnit unit) 如果锁定在给定等待时间内没有被另一个线程保
 * 持，且当前线程未被中断，则获取该锁定
 * 
 * @author MicroCat
 *
 */
public class MyService {

    public ReentrantLock lock = new ReentrantLock();

    public void waitMethod() {
        try {
            if (lock.tryLock(3, TimeUnit.SECONDS)) {
                try {
                    System.out.println(Thread.currentThread().getName() + " 获得锁");
                    for (int i = 0; i < 10000; i++) {
                        if (i % 100 == 0) {
                            System.out.println(Thread.currentThread().getName() + " " + i);
                        }
                    }
                } finally {
                    lock.unlock();
                }
            } else {
                System.out.println(Thread.currentThread().getName() + " 没有获得锁");
            }
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

package tryLock.copy.copy.copy;

public class Run {

    public static void main(String[] args) throws InterruptedException {
        final MyService service = new MyService();
        Runnable runnable = new Runnable() {

            @Override
            public void run() {
                service.waitMethod();
            }
        };
        Thread a = new Thread(runnable);
        a.setName("A");
        a.start();
        Thread b = new Thread(runnable);
        b.setName("B");
        b.start();
    }

}

在给定时间内各线程都有拿到锁，所以线程a,b都有执行