比如下面这个类
class test{
public void methodA(){
//methodA同时有多个线程在访问,请问如何填充这个方法,使最多只有2个线程调用methodB,当调用完成后,其他那些方法才能继续调用
methodB();
}
private void methodB(){
}
------解决方案--------------------
- Java code
/** * ThreadNoneSync.java * 演示非同步线程访问共享数据带来的问题 * @ kahn178 * @ version 1.0 * create on 2008-10-29 */package ThreadNoneSync;import javax.microedition.midlet.MIDlet;import javax.microedition.midlet.MIDletStateChangeException;public class ThreadNoneSync extends MIDlet { boolean isRunning=true; int a=0;//共享数据 //MIDLet对象实例的引用 ThreadNoneSync instance=this; public ThreadNoneSync() { // TODO 自动生成构造函数存根 super(); //启动线程同进访问共享变量a new Thread("Thread Add"){ public void run(){ //对a进行加1运算 while(isRunning){ String name=Thread.currentThread().getName(); synchronized(instance){ //进行线程的处理，监视器，线程访问时，会加一个锁。避免多线程访问共享数据造成破坏 System.out.print(name + ": " + a); System.out.println("+1=" + ++a); } } } }.start(); //启动线程同进访问共享变量a new Thread("Thread Add"){ public void run(){ //对a进行减1运算 while(isRunning){ String name=Thread.currentThread().getName(); synchronized(instance){//会耗费系统资源，降低程序执行效率。因此一定在需要时才使用 System.out.print(name + ": " +a ); System.out.println("-1="+ --a); } } } }.start(); } protected void startApp() throws MIDletStateChangeException { // TODO 自动生成方法存根 } protected void pauseApp() { // TODO 自动生成方法存根 } protected void destroyApp(boolean arg0) throws MIDletStateChangeException { // TODO 自动生成方法存根 isRunning=false; }}
------解决方案--------------------
- Java code
package sample.concurrent;import java.util.concurrent.Semaphore;public class Test { private final Semaphore available = new Semaphore(2); public void methodA() { try { available.acquire(); methodB(); available.release(); } catch (InterruptedException ex) { } } public void methodB() { System.out.println(Thread.currentThread().getName() + ": " + "Entering methodB ..."); try { Thread.sleep(3000); } catch (InterruptedException ex) { } System.out.println(Thread.currentThread().getName() + ": " + "Leaving methodB ..."); } public static void main(String[] args) { final Test t = new Test(); for (int i = 0; i < 10; i++) { new Thread() { @Override public void run() { t.methodA(); } }.start(); } }}