Java线程-线程池-条件变量

条件变量是Java5线程当中很重要的一个概念，顾名思义，条件变量就是条件当中的一种变量，这里的条件没有实际意义，仅仅是个标记而已。
条件变量都实现了java.util.concurrent.locks.Condition接口，条件对象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，Java当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的控制线程的等待和唤醒，Java5之前，线程的等待与唤醒靠的是Object对象的wait()、notify和notifyAll()方法，这样的处理不够精细。
在Java5当中，一个锁可以有多个条件，每个条件上可以有多个线程等待，通过调用await()方法，可以使线程在该条件下进行等待。当调用了signalAll()，又可以唤醒该条件下等待的线程。
条件变量比较抽象，它不是自然语言当中的条件概念，它是控制程序的一种有效手段。
代码如下：

public class Main {public static void main(String args[]){//创建并发访问的账户MyCount myCount=new MyCount("370911199212233321",10000);//创建一个线程池ExecutorService executorService= Executors.newFixedThreadPool(2);//创建六个线程Thread thread1=new SaveMoneyThread("张三",myCount,1000);Thread thread2=new DrawMoneyThread("王五",myCount,5000);Thread thread3=new SaveMoneyThread("赵六",myCount,2000);Thread thread4=new SaveMoneyThread("李四",myCount,1000);Thread thread5=new DrawMoneyThread("吴京",myCount,8000);Thread thread6=new SaveMoneyThread("狗子",myCount,7000);Thread thread7=new DrawMoneyThread("王二麻子",myCount,9000);//执行各个线程executorService.execute(thread1);executorService.execute(thread2);executorService.execute(thread3);executorService.execute(thread4);executorService.execute(thread5);executorService.execute(thread6);executorService.execute(thread7);//关闭线程池executorService.shutdown();}}class MyCount {private String oid;                                 //账号private int cash;                                   //账户余额private Lock lock=new ReentrantLock();              //锁private Condition saveCondition=lock.newCondition();//存款条件private Condition drawCondition=lock.newCondition();//取款条件MyCount(String oid,int cash){this.oid=oid;this.cash=cash;}/***  存款* @param x 存款金额* @param name 存款人*/public void saveMoney(int x,String name){lock.lock();if(x>0){this.cash+=x;//存款System.out.println(name+"存款"+x+","+"当前余额为"+this.cash);}//唤醒取款的等待线程this.drawCondition.signalAll();//释放锁lock.unlock();}/*** 取款* @param x 取款金额* @param name 取款人*/public void drawMoney(int x,String name){try {lock.lock();if(x-this.cash>0){drawCondition.await();}else {this.cash-=x;System.out.println(name+"取款"+x+",当前余额为"+this.cash);}//唤醒所有的存款条件saveCondition.signalAll();} catch (InterruptedException e) {e.printStackTrace();}finally {//释放锁lock.unlock();}}
}class DrawMoneyThread extends Thread {private String name;    //操作人private MyCount myCount;//账户private int x;          //取款金额DrawMoneyThread(String name,MyCount myCount,int x){this.name=name;this.myCount=myCount;this.x=x;}/*** 取款*/@Overridepublic void run() {this.myCount.drawMoney(this.x,this.name);}
}class SaveMoneyThread extends Thread {private String name;    //操作人private MyCount myCount;//账户private int x;          //存款金额SaveMoneyThread(String name,MyCount myCount,int x){this.name=name;this.myCount=myCount;this.x=x;}/*** 存款*/@Overridepublic void run() {this.myCount.saveMoney(this.x,this.name);}
}

如果不用Condition来实现，用synchronized来实现，代码如下：

public class Main {public static void main(String args[]){//创建并发访问的账户MyCount myCount=new MyCount("370911199212233321",10000);//创建一个线程池ExecutorService executorService= Executors.newFixedThreadPool(2);//创建六个线程Thread thread1=new SaveMoneyThread("张三",myCount,1000);Thread thread2=new DrawMoneyThread("王五",myCount,5000);Thread thread3=new SaveMoneyThread("赵六",myCount,2000);Thread thread4=new SaveMoneyThread("李四",myCount,1000);Thread thread5=new DrawMoneyThread("吴京",myCount,8000);Thread thread6=new SaveMoneyThread("狗子",myCount,7000);Thread thread7=new DrawMoneyThread("王二麻子",myCount,9000);//执行各个线程executorService.execute(thread1);executorService.execute(thread2);executorService.execute(thread3);executorService.execute(thread4);executorService.execute(thread5);executorService.execute(thread6);executorService.execute(thread7);//关闭线程池executorService.shutdown();}}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 存款金额* @param name 存款人*/public synchronized void saveMoney(int x,String name){if(x>0){this.cash+=x;//存款System.out.println(name+"存款"+x+","+"当前余额为"+this.cash);}//唤醒取款的等待线程notifyAll();}/*** 取款* @param x 取款金额* @param name 取款人*/public synchronized void drawMoney(int x,String name){try {if(x-this.cash>0){wait();}else {this.cash-=x;System.out.println(name+"取款"+x+",当前余额为"+this.cash);}} catch (InterruptedException e) {e.printStackTrace();}notifyAll();}
}class DrawMoneyThread extends Thread {private String name;    //操作人private MyCount myCount;//账户private int x;          //取款金额DrawMoneyThread(String name,MyCount myCount,int x){this.name=name;this.myCount=myCount;this.x=x;}/*** 取款*/@Overridepublic void run() {this.myCount.drawMoney(this.x,this.name);}
}class SaveMoneyThread extends Thread {private String name;    //操作人private MyCount myCount;//账户private int x;          //存款金额SaveMoneyThread(String name,MyCount myCount,int x){this.name=name;this.myCount=myCount;this.x=x;}/*** 存款*/@Overridepublic void run() {this.myCount.saveMoney(this.x,this.name);}
}

用同步代码块来实现：

public class Main {public static void main(String args[]){//创建并发访问的账户MyCount myCount=new MyCount("370911199212233321",10000);//创建一个线程池ExecutorService executorService= Executors.newFixedThreadPool(2);//创建六个线程Thread thread1=new SaveMoneyThread("张三",myCount,1000);Thread thread2=new DrawMoneyThread("王五",myCount,5000);Thread thread3=new SaveMoneyThread("赵六",myCount,2000);Thread thread4=new SaveMoneyThread("李四",myCount,1000);Thread thread5=new DrawMoneyThread("吴京",myCount,8000);Thread thread6=new SaveMoneyThread("狗子",myCount,7000);Thread thread7=new DrawMoneyThread("王二麻子",myCount,9000);//执行各个线程executorService.execute(thread1);executorService.execute(thread2);executorService.execute(thread3);executorService.execute(thread4);executorService.execute(thread5);executorService.execute(thread6);executorService.execute(thread7);//关闭线程池executorService.shutdown();}}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 存款金额* @param name 存款人*/public void saveMoney(int x,String name){if(x>0){synchronized (this){this.cash+=x;//存款System.out.println(name+"存款"+x+","+"当前余额为"+this.cash);//唤醒取款的等待线程notifyAll();}}}/*** 取款* @param x 取款金额* @param name 取款人*/public void drawMoney(int x,String name){synchronized (this){try {if(x-this.cash>0){wait();}else {this.cash-=x;System.out.println(name+"取款"+x+",当前余额为"+this.cash);}} catch (InterruptedException e) {e.printStackTrace();}notifyAll();}}
}class DrawMoneyThread extends Thread {private String name;    //操作人private MyCount myCount;//账户private int x;          //取款金额DrawMoneyThread(String name,MyCount myCount,int x){this.name=name;this.myCount=myCount;this.x=x;}/*** 取款*/@Overridepublic void run() {this.myCount.drawMoney(this.x,this.name);}
}class SaveMoneyThread extends Thread {private String name;    //操作人private MyCount myCount;//账户private int x;          //存款金额SaveMoneyThread(String name,MyCount myCount,int x){this.name=name;this.myCount=myCount;this.x=x;}/*** 存款*/@Overridepublic void run() {this.myCount.saveMoney(this.x,this.name);}
}

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