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Java基础之线程新特性条件变量
条件变量都实现了java.util.concurrent.locks.Condition接口，条件变量的实例化是通过一个Lock对象上调用newCondition()方法来获取的，这样，条件就和一个锁对象绑定起来了。因此，Java中的条件变量只能和锁配合使用，来控制并发程序访问竞争资源的安全。条件变量的出现是为了更精细控制线程等待与唤醒，在Java5之前，线程的等待与唤醒依靠的是Object对象的wait()和notify()/notifyAll()方法，这样的处理不够精细
package unit_fifteen;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;/** * Java线程：条件变量 * */ public class Test { public static void main(String[] args) { //创建并发访问的账户 MyCount myCount = new MyCount("95599200901215522", 10000); //创建一个线程池 ExecutorService pool = Executors.newFixedThreadPool(2); Thread t1 = new SaveThread("张三", myCount, 2000); Thread t2 = new SaveThread("李四", myCount, 3600); Thread t3 = new DrawThread("王五", myCount, 2700); Thread t4 = new SaveThread("老张", myCount, 600); Thread t5 = new DrawThread("老牛", myCount, 1300); Thread t6 = new DrawThread("胖子", myCount, 800); //执行各个线程 pool.execute(t1); pool.execute(t2); pool.execute(t3); pool.execute(t4); pool.execute(t5); pool.execute(t6); //关闭线程池 pool.shutdown(); } } /** * 存款线程类 */ class SaveThread extends Thread { private String name; //操作人 private MyCount myCount; //账户 private int x; //存款金额 SaveThread(String name, MyCount myCount, int x) { this.name = name; this.myCount = myCount; this.x = x; } public void run() { myCount.saving(x, name); } } /** * 取款线程类 */ class DrawThread extends Thread { private String name; //操作人 private MyCount myCount; //账户 private int x; //存款金额 DrawThread(String name, MyCount myCount, int x) { this.name = name; this.myCount = myCount; this.x = x; } public void run() { myCount.drawing(x, name); } } /** * 普通银行账户，不可透支 */ class MyCount { private String oid; //账号 private int cash; //账户余额 private Lock lock =new ReentrantLock(); //账户锁 private Condition _save = lock.newCondition(); //存款条件 private Condition _draw = lock.newCondition(); //取款条件 MyCount(String oid, int cash) { this.oid = oid; this.cash = cash; } /** * 存款 * * @param x 操作金额 * @param name 操作人 */ public void saving(int x, String name) { lock.lock(); //获取锁 if (x > 0) { cash += x; //存款 System.out.println(name + "存款" + x +"，当前余额为" + cash); } _draw.signalAll(); //唤醒所有等待线程。 lock.unlock(); //释放锁 } /** * 取款 * * @param x 操作金额 * @param name 操作人 */ public void drawing(int x, String name) { lock.lock(); //获取锁 try { if (cash - x < 0) { _draw.await(); //阻塞取款操作 } else { cash -= x; //取款 System.out.println(name + "取款" + x +"，当前余额为" + cash); } _save.signalAll(); //唤醒所有存款操作 } catch (InterruptedException e) { e.printStackTrace(); } finally { lock.unlock(); //释放锁 } } }
假如我们不用锁和条件变量，如何实现此功能呢？下面是实现代码：
package unit_fifteen;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** * Java线程：不用条件变量* */ public class Test { public static void main(String[] args) { //创建并发访问的账户 MyCount myCount = new MyCount("95599200901215522", 10000); //创建一个线程池 ExecutorService pool = Executors.newFixedThreadPool(2); Thread t1 = new SaveThread("张三", myCount, 2000); Thread t2 = new SaveThread("李四", myCount, 3600); Thread t3 = new DrawThread("王五", myCount, 2700); Thread t4 = new SaveThread("老张", myCount, 600); Thread t5 = new DrawThread("老牛", myCount, 1300); Thread t6 = new DrawThread("胖子", myCount, 800); //执行各个线程 pool.execute(t1); pool.execute(t2); pool.execute(t3); pool.execute(t4); pool.execute(t5); pool.execute(t6); //关闭线程池 pool.shutdown(); } } /** * 存款线程类 */ class SaveThread extends Thread { private String name; //操作人 private MyCount myCount; //账户 private int x; //存款金额 SaveThread(String name, MyCount myCount, int x) { this.name = name; this.myCount = myCount; this.x = x; } public void run() { myCount.saving(x, name); } } /** * 取款线程类 */ class DrawThread extends Thread { private String name; //操作人 private MyCount myCount; //账户 private int x; //存款金额 DrawThread(String name, MyCount myCount, int x) { this.name = name; this.myCount = myCount; this.x = x; } public void run() { myCount.drawing(x, name); } } /** * 普通银行账户，不可透支 */ class MyCount { private String oid; //账号 private int cash; //账户余额 MyCount(String oid, int cash) { this.oid = oid; this.cash = cash; } /** * 存款 * * @param x 操作金额 * @param name 操作人 */ public synchronized void saving(int x, String name) { if (x > 0) { cash += x; //存款 System.out.println(name + "存款" + x +"，当前余额为" + cash); } notifyAll(); //唤醒所有等待线程。 } /** * 取款 * * @param x 操作金额 * @param name 操作人 */ public synchronized void drawing(int x, String name) { if (cash - x < 0) { try { wait(); } catch (InterruptedException e1) { e1.printStackTrace(); } } else { cash -= x; //取款 System.out.println(name + "取款" + x +"，当前余额为" + cash); } notifyAll(); //唤醒所有存款操作 } }
结合先前同步代码知识，举一反三，将此例改为同步代码块来实现，代码如下：
package unit_fifteen;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** * Java线程：改为同步代码块* */ public class Test { public static void main(String[] args) { //创建并发访问的账户 MyCount myCount = new MyCount("95599200901215522", 10000); //创建一个线程池 ExecutorService pool = Executors.newFixedThreadPool(2); Thread t1 = new SaveThread("张三", myCount, 2000); Thread t2 = new SaveThread("李四", myCount, 3600); Thread t3 = new DrawThread("王五", myCount, 2700); Thread t4 = new SaveThread("老张", myCount, 600); Thread t5 = new DrawThread("老牛", myCount, 1300); Thread t6 = new DrawThread("胖子", myCount, 800); //执行各个线程 pool.execute(t1); pool.execute(t2); pool.execute(t3); pool.execute(t4); pool.execute(t5); pool.execute(t6); //关闭线程池 pool.shutdown(); } } /** * 存款线程类 */ class SaveThread extends Thread { private String name; //操作人 private MyCount myCount; //账户 private int x; //存款金额 SaveThread(String name, MyCount myCount, int x) { this.name = name; this.myCount = myCount; this.x = x; } public void run() { myCount.saving(x, name); } } /** * 取款线程类 */ class DrawThread extends Thread { private String name; //操作人 private MyCount myCount; //账户 private int x; //存款金额 DrawThread(String name, MyCount myCount, int x) { this.name = name; this.myCount = myCount; this.x = x; } public void run() { myCount.drawing(x, name); } } /** * 普通银行账户，不可透支 */ class MyCount { private String oid; //账号 private int cash; //账户余额 MyCount(String oid, int cash) { this.oid = oid; this.cash = cash; } /** * 存款 * * @param x 操作金额 * @param name 操作人 */ public void saving(int x, String name) { if (x > 0) { synchronized (this) { cash += x; //存款 System.out.println(name + "存款" + x +"，当前余额为" + cash); notifyAll(); //唤醒所有等待线程。 } } } /** * 取款 * * @param x 操作金额 * @param name 操作人 */ public synchronized void drawing(int x, String name) { synchronized (this) { if (cash - x < 0) { try { wait(); } catch (InterruptedException e1) { e1.printStackTrace(); } } else { cash -= x; //取款 System.out.println(name + "取款" + x +"，当前余额为" + cash); } } notifyAll(); //唤醒所有存款操作 } }
Java基础之线程新特性条件变量
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