目錄
2 synchronized/wait/notifyAll 機制
3 ReentrantLock/Condition.await()/Condition.signalAll() 機制
1 思路
啓動三個線程,採用多線程間等待/通知的機制來設計。維護一個全局不變數組printArr和變量索引index,printArr[index]就是接下來的線程要打印的字符。三個線程一開始就定好了打印的字符,當線程獲取鎖後,要判斷printArr[index]與指定該線程的字符相等,相等就打印字符同時index = (index+1)%3,不相等表明還沒輪到當前線程打印,當前線程等待。
2 synchronized/wait/notifyAll 機制
public class Test1 {
private static char[] printArr = new char[]{'a','b','c'};
private static volatile int index; // 保證index的可見性
public static void main(String[] args) {
ExecutorService threadPool = Executors.newFixedThreadPool(3);
final Object lock = new Object();
threadPool.execute(new MyThread(lock,printArr[index]));
threadPool.execute(new MyThread(lock,printArr[index+1]));
threadPool.execute(new MyThread(lock,printArr[index+2]));
threadPool.shutdown();
}
private static class MyThread extends Thread{ // 靜態內部打印類
Object lock; // 同步鎖和等待/通知鎖
char printC; // 指定的要打印的字符
MyThread(final Object lock ,char printC){
this.lock = lock;
this.printC = printC;
}
@Override
public void run(){
while(true){
synchronized (lock){
char c = printArr[index];
if (c == printC){
System.out.println(c);
index = (index+1)%printArr.length; // index“+1”
lock.notifyAll(); // 喚醒所有等待在lock上的線程
} else {
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
}
}
3 ReentrantLock/Condition.await()/Condition.signalAll() 機制
public class Test2 {
private static char[] printArr = new char[]{'a','b','c'};
private static volatile int index; // 保證index的可見性
public static void main(String[] args) {
ExecutorService threadPool = Executors.newFixedThreadPool(3);
ReentrantLock lock = new ReentrantLock();
Condition condition = lock.newCondition();
threadPool.execute(new MyThread(lock,condition,printArr[index]));
threadPool.execute(new MyThread(lock,condition,printArr[index+1]));
threadPool.execute(new MyThread(lock,condition,printArr[index+2]));
threadPool.shutdown();
}
private static class MyThread extends Thread{ // 靜態內部打印類
ReentrantLock lock;
Condition condition;
char printC; // 指定的要打印的字符
MyThread(ReentrantLock lock ,Condition condition ,char printC){
if (lock == null || condition == null)
throw new NullPointerException("lock or condition is null");
this.lock = lock;
this.condition = condition;
this.printC = printC;
}
@Override
public void run(){
while(true){
lock.lock();
try {
char c = printArr[index];
if (c == printC){
System.out.println(c);
index = (index+1)%printArr.length;
condition.signalAll();
} else {
try {
condition.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}finally {
lock.unlock();
}
}
}
}
}