java线程 同步临界区：thinking in java4 21.3.5
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package org.rui.thread.critical;import java.util.ArrayList;import java.util.Collections;import java.util.List;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.TimeUnit;import java.util.concurrent.atomic.AtomicInteger;/** * 临界区 * * * * Pair不是线程安全的，因为它的约束条件（虽然是任意的） 需要两个变量维护成相同的值。 * 此外，如本章前面所述，自增加操作不是线程安全的， * 并且因为没有任何方法被标记为synchronized，所以不能保证一个pair对象在多线程程序中不会破坏. * @author lenovo * *///org.rui.thread.critical.Criticaldiv.javaclass Pair{private int x,y;public Pair(int x,int y){ this.x=x; this.y=y;}public Pair(){this(0,0);} public int getX() {return x;}public int getY() {return y;}public void incrementX(){x++;}public void incrementY(){y++;}public String toString(){return "x: "+x+" , y:"+y;}/////////////////PariValuesNotEqualExceptionpublic class PariValuesNotEqualException extends RuntimeException{public PariValuesNotEqualException(){super("Pair values not equal:"+Pair.this);}}//任意变,两个变量必须是平等的//Arbitrary invariant --both variables must be equal:public void checkState(){if(x!=y){throw new PariValuesNotEqualException();}}}//Pair end//保护一对在一个线程安全的类//protect a pair inside a thread -safe class: abstract class PairManager { AtomicInteger checkCounter=new AtomicInteger(0); protected Pair p=new Pair(); private List<Pair> storage=Collections.synchronizedList(new ArrayList<Pair>()); public synchronized Pair getPair() { //复制的原始安全: //Make a copy to keep the original safe: return new Pair(p.getX(),p.getY()); } //假设这是一个耗时的操作 //Assume this is a time consuming operation protected void store(Pair p) { storage.add(p); try {TimeUnit.MILLISECONDS.sleep(50);} catch (InterruptedException e) {e.printStackTrace();} } // public abstract void increment(); } //整个同步方法//synchronize the entire methodclass PairManager1 extends PairManager{@Overridepublic synchronized void increment(){p.incrementX();p.incrementY();store(getPair());}}//use a critical div: 使用临界区class PairManager2 extends PairManager{ public void increment() { Pair temp; synchronized(this) { p.incrementX(); p.incrementY(); temp=getPair(); } store(temp); }}///操作者class PairManipulator implements Runnable{ private PairManager pm; public PairManipulator(PairManager pm) { this.pm=pm; }@Overridepublic void run() {while(true)pm.increment();}public String toString(){return "Pair: "+pm.getPair()+" checkCounter= "+pm.checkCounter.get();}}////PairCheckerclass PairChecker implements Runnable{private PairManager pm; public PairChecker(PairManager pm) { this.pm=pm; }@Overridepublic void run() {while(true){pm.checkCounter.incrementAndGet();pm.getPair().checkState();}}}/////////////////////////////////////////////////////////public class Criticaldiv {//测试两种不同的方法//test the two defferent approachesstatic void testApproaches(PairManager pman1,PairManager pman2){ExecutorService exec=Executors.newCachedThreadPool();PairManipulator pm1=new PairManipulator(pman1);PairManipulator pm2=new PairManipulator(pman2);PairChecker pcheck1=new PairChecker(pman1);PairChecker pcheck2=new PairChecker(pman2);exec.execute(pm1);exec.execute(pm2);exec.execute(pcheck1);exec.execute(pcheck2);try {TimeUnit.MILLISECONDS.sleep(500);} catch (InterruptedException e) {System.out.println("InterruptedException");}System.out.println("pm1:"+pm1+"\npm2:"+pm2);System.exit(0);}public static void main(String[] args) {PairManager pman1=new PairManager1(), pman2=new PairManager2();testApproaches(pman1,pman2);}}/**output:(sample)pm1:Pair: x: 8 , y:8 checkCounter= 674247pm2:Pair: x: 8 , y:8 checkCounter= 5043736 */
package org.rui.thread.critical;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;/** * 你还可以使用显示的lock对象来创建临界区 * * 这里利用了Criticaldiv.java的绝大部分， * 并创建了新的使用显式的lock对象的PairManger类型。 * expliciPariManger2展示了如何使用Lock对象来创建临界区，而对store()的调用则在这个临界区的外部 * @author lenovo * */////////////////////////// class ExplicitPairManager1 extends PairManager {private Lock lock =new ReentrantLock();@Overridepublic synchronized void increment() {lock.lock();try{p.incrementX();p.incrementY();store(getPair());}finally{lock.unlock();}}}//use a critical divclass ExplicitPairManager2 extends PairManager{private Lock lock =new ReentrantLock();@Overridepublic void increment() {Pair temp=null;lock.lock();try{p.incrementX();p.incrementY();temp=getPair();}finally{lock.unlock();}store(temp);}}/////////////////public class ExplicitCriticaldiv { public static void main(String[] args) { PairManager pman1=new PairManager1(), pman2=new PairManager2(); Criticaldiv.testApproaches(pman1,pman2);}}/** * output:pm1:Pair: x: 10 , y:10 checkCounter= 195142pm2:Pair: x: 11 , y:11 checkCounter= 4129459 */
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