java线程共享受限资源 解决资源竞争 thinking in java4 21.3
java线程共享受限资源 解决资源竞争 具体介绍请參阅:thinking in java4 21.3
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package org.rui.thread.res; /** * 不对的訪问 资源 * @author lenovo * */ public abstract class IntGenerator { private volatile boolean canceled=false;//取消的 public abstract int next(); // 同意这样的被取消 public void cancel(){canceled =true;} public boolean isCanceled(){return canceled;} }
package org.rui.thread.res; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; /** * 不论什么IntGenerator都能够用以下的EvenCherker类来測试 * @author lenovo * */ public class EvenChecker implements Runnable { private IntGenerator generator; private final int id; public EvenChecker(IntGenerator g,int ident) { this.generator=g; this.id=ident; } @Override public void run() { while(!generator.isCanceled()) { int val=generator.next(); if(val%2!=0) { System.out.println(val+" not even!"); generator.cancel();//cancels all evencheckers } } } ///test any type of intgenerator public static void test(IntGenerator gp,int count) { System.out.println("press control-c to exit"); ExecutorService ex=Executors.newCachedThreadPool(); for(int i=0;i<count;i++) { ex.execute(new EvenChecker(gp,i)); } ex.shutdown(); /*for(int i=0;i<count;i++) { Thread t=new Thread(new EvenChecker(gp,i)); t.start(); }*/ } /// public static void test(IntGenerator gp) { test(gp,10); } }
package org.rui.thread.res; /** * 这个程序终于会失败,由于evenChecker任务在evenGenerator处于 不恰当的 状态时 * 仍可以訪问当中信息 * 假设你希望更快地发现失败。可以尝试着将yield() 的调用放置到第一个和第二个递增操作之间。 * 这仅仅是并发程序的部分部题 * @author lenovo * */ public class EvenGenerator extends IntGenerator { private int currentEvenValue=0; @Override public int next() { ++currentEvenValue;//危急项目》的出版物! danger point here ++currentEvenValue; return currentEvenValue; } public static void main(String[] args) { EvenChecker.test(new EvenGenerator()); } } /** * output: press control-c to exit 13103419 not even! */
package org.rui.thread.res; /** * 同步控制 EvenGenerator * @author lenovo * */ public class SynchronizedEvenGenerator extends IntGenerator { private int currentEvenValue=0; @Override public synchronized int next() { ++currentEvenValue; Thread.yield();//导致失败的更快 暂停当前正在运行的线程对象。并运行其它线程。++currentEvenValue; return currentEvenValue; } public static void main(String[] args) { EvenChecker.test(new SynchronizedEvenGenerator()); } } /** output: press control-c to exit */
package org.rui.thread.res; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * 使用显示的Lock对象 * @author lenovo * */ public class MutexEvenGenerator extends IntGenerator { private int currentEvenValue=0; Lock lock=new ReentrantLock(); @Override public int next() { lock.lock(); try { ++currentEvenValue; Thread.yield();//导致失败的更快 暂停当前正在运行的线程对象,并运行其它线程。++currentEvenValue; return currentEvenValue; } finally { lock.unlock(); } } ////////////////////////////// public static void main(String[] args) { EvenChecker.test(new MutexEvenGenerator()); } } /** output: press control-c to exit */
package org.rui.thread.res; import java.util.concurrent.TimeUnit; import java.util.concurrent.locks.ReentrantLock; /** * synchronizedkeyword不能尝试着获取锁且终于获取锁会失败 * 或都尝试获取一段时间 。然后放弃它。要实现这些。你必须使用concurrent类库: * * * ReentrantLock同意你尝试着获取但终于末获取锁,这样假设其它人已经获取了这个锁, * 那么你就能够决定离开去运行其它一些事件。而不是等待直至这个锁被释放,就像在untimed()方法中所示。 * 在timed中 做出尝试去获取锁。该尝试能够在2秒之后失败 * @author lenovo * */ public class AttemptLocking { //可重入的相互排斥锁 private ReentrantLock lock=new ReentrantLock(); public void untimed()//不计时的 { // 仅在调用时锁未被还有一个线程保持的情况下。才获取该锁。boolean captured=lock.tryLock(); try { System.out.println("tryLock(): "+captured); } finally { if(captured) lock.unlock(); } } ///////////// public void timed()//计时 { boolean captured=false; try { //假设锁在给定等待时间内没有被还有一个线程保持,且当前线程未被中断,则获取该锁。 captured=lock.tryLock(2,TimeUnit.SECONDS); } catch(InterruptedException e) { throw new RuntimeException(e); } try { System.out.println("tryLock(2,TimeUnit.SECONDS) : "+captured); } finally { if(captured) lock.unlock(); } } ///////////////main public static void main(String[] args) throws InterruptedException { final AttemptLocking al=new AttemptLocking(); al.untimed();//true -- lock is available 锁可用 al.timed();//true -- lock is available //如今创建一个单独的任务获取锁 使以下的线程调用产生竞争 new Thread() { {setDaemon(true);} @Override public void run() { al.lock.lock(); System.out.println("acquired"); } }.start(); Thread.sleep(1000); // 暂停当前正在运行的线程对象,并运行其它线程。
//Thread.yield();//give the 2nd task a chance 给第二个任务一个机会 al.untimed();//false--lock grabbed by task 锁了的任务 al.timed();//false--lock grabbed by task } } /** * output: tryLock(): true tryLock(2,TimeUnit.SECONDS) : true acquired tryLock(): false tryLock(2,TimeUnit.SECONDS) : false */