Concurrency,Java 並發

//TestLock.javapackage com.test.thread;import java.util.ArrayList;import java.util.List;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;import java.util.concurrent.TimeUnit;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class TestLock {private static int cnt=0;private final int num=cnt++;private static Lock lock=new ReentrantLock();private TestLock(){}private static TestLock ins=null;public static /*synchronized */ TestLock getInstance(){if(ins==null){//若在此處聲明鎖，則不能保證多個線程訪問時，此段代碼的安全//Lock lock=new ReentrantLock();lock.lock();try {if (ins== null) {TimeUnit.MILLISECONDS.sleep(10);ins = new TestLock();}} catch (InterruptedException e) {e.printStackTrace();}finally{lock.unlock();}}return ins;}public int getNum() {return num;}/** * @param args */public static void main(String[] args) {ExecutorService svs = Executors.newCachedThreadPool();List< Future<TestLock> > lstObjs=new ArrayList< Future<TestLock> >();for (int i = 0;i<10;i++){ lstObjs.add( svs.submit(new TestLockThread()) );}for (Future<TestLock> ftl : lstObjs) {try {TestLock tl=  ftl.get();} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();}}svs.shutdown();}}//TestLockThread.javapackage com.test.thread;import java.util.concurrent.Callable;public class TestLockThread implements Callable<TestLock> {@Overridepublic TestLock call() throws Exception {TestLock tl = TestLock.getInstance();System.out.println("call:"+tl.getNum());return tl;}}