java Semaphore实现ABC三个线程循环打印
Semaphore位于java.util.concurrent包下。其中有两个重要的方法acquire()和release()。acquire用来获取一个信号量,并且是阻塞型的,如果当前还有可用的信号量,则获取成功,可用信号量减1,使用完后可用release释放信号量。
下面的例子有ABC三个线程。A负责输出1 4 7 B负责输出2 5 8 C负责3 6 9。要求通过信号量机制 控制这三个线程按照顺序输出。
package test;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
public class SemaphoreTest {
public int i=1;
//设置信号量,用来控制可以同时访问的线程数量
public Semaphore s1 = new Semaphore(1);
public Semaphore s2 = new Semaphore(0);
public Semaphore s3 = new Semaphore(0);
public static void main(String[] args) {
new SemaphoreTest().Print();
}
public void Print() {
//创建一个可缓存线程池
ExecutorService exe = Executors.newCachedThreadPool();
Thread t1 = new Thread(){
@Override
public void run() {
while(i<7) {
try {
s1.acquire();//获取信号量,s1 - 1
System.out.print(i);
i++;
//方便看到运行结果
Thread.sleep(1000);
s2.release();//释放信号量,s2 + 1
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
};
Thread t2 = new Thread(){
@Override
public void run() {
while(i<8) {
try {
s2.acquire();//获取信号量,s2 - 1
System.out.print(i);
i++;
Thread.sleep(1000);
s3.release();//释放信号量,s3 + 1
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
};
Thread t3 = new Thread(){
@Override
public void run() {
while(i<9) {
try {
s3.acquire();//获取信号量,s3 - 1
System.out.print(i);
i++;
Thread.sleep(1000);
s1.release();//释放信号量,s1 + 1
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
};
exe.execute(t1);
exe.execute(t2);
exe.execute(t3);
}
}
运行结果:
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