java

关注公众号 jb51net

关闭
首页 > 软件编程 > java > Java多线程 两阶段终止模式

Java多线程 两阶段终止模式Two-Phase Termination Patter

作者:冬日毛毛雨

这篇文章主要介绍了Java多线程 两阶段终止模式Two-Phase Termination Patter,该模式有两个角色,分别是Terminator,终止者,负责接收终止请求,执行终止处理,处理完成后再终止自己。TerminationRequester终止请求发出者,用来向Terminator发出终止请求,需要的朋友可以参考一下

1、两阶段终止模式介绍

有时候,我们希望提前结束线程,但安全可靠地停止线程,并不是一件容易的事情,如果立即停止线程,会使共享的数据结构处于不一致的状态,如目前已经废弃使用的Thread类的stop方法(它会使线程在抛出java.lang.ThreadDeath之后终止线程,即使是在执行synchronized方法的时候)。更好的做法是执行完终止处理,再终止线程,即Two-phase Termination,两阶段终止模式。

该模式有两个角色:

2、Terminator代码演示

该模式示例代码如下:

public class CounterIncrement extends Thread {

    private volatile boolean terminated = false;

    private int counter = 0;

    private Random random = new Random(System.currentTimeMillis());
    @Override
    public void run() {

        try {
            while (!terminated) {
                System.out.println(Thread.currentThread().getName()+" "+counter++);
                Thread.sleep(random.nextInt(1000));
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            this.clean();
        }
    }

    private void clean() {
        System.out.println("do some clean work for the second phase,current counter "+counter);

    }

    public void close() {
        this.terminated = true;
        this.interrupt();
    }
}

3、TerminationRequester

public class CounterTest {
    public static void main(String[] args) throws InterruptedException {
        CounterIncrement counterIncrement = new CounterIncrement();
        counterIncrement.start();

        Thread.sleep(15_000L);
        //主动清理
        counterIncrement.close();
    }
}

这段代码可以看出实现两阶段终止模式必须注意的是:

使用线程停止标志和interrupt方法,两者缺一不可

  public void close() {
        this.terminated = true;
        this.interrupt();
    }

这里使用了terminated作为线程停止标志,变量采用volatile修饰,避免了使用显式锁的开销,又保证了内存可见性。线程run方法会检查terminated属性,如果属性为true,就停止线程,但线程可能调用了阻塞方法,处于wait状态,任务也就可能永远不会检查terminated标志;线程也有可能处于sleep()状态,等sleep时间过后再执行终止状态,程序的响应性就下降了。你可以把方法改成如下运行,线程停止明显变慢了许多:

  public void close() {
        terminated = true;
  }

4、模拟客户端或者服务端都可能终止服务的例子

public class AppServer extends Thread {

    private static final int DEFAULT_PORT = 12722;
    private final static ExecutorService executor = Executors.newFixedThreadPool(10);
    private int port;
    private volatile boolean start = true;
    private List<ClientHandler> clientHandlers = new ArrayList<>();
    private ServerSocket server;

    public AppServer() {
        this(DEFAULT_PORT);
    }

    public AppServer(int port) {
        this.port = port;
    }

    @Override
    public void run() {
        try {
            server = new ServerSocket(port);
            while (start) {
                Socket client = server.accept();
                ClientHandler clientHandler = new ClientHandler(client);
                executor.submit(clientHandler);
                this.clientHandlers.add(clientHandler);
            }

        } catch (IOException e) {
            //throw new RuntimeException();
        } finally {
            this.dispose();
        }
    }

    public void dispose() {
        System.out.println("dispose");
        this.clientHandlers.stream().forEach(ClientHandler::stop);
        this.executor.shutdown();
    }

    public void shutdown() throws IOException {
        this.start = false;
        this.interrupt();
        this.server.close();
    }
}

public class ClientHandler implements Runnable {

    private final Socket socket;

    private volatile boolean running = true;

    public ClientHandler(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {


        try (InputStream inputStream = socket.getInputStream();
             OutputStream outputStream = socket.getOutputStream();
             BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
             PrintWriter printWriter = new PrintWriter(outputStream)) {
            while (running) {
                String message = br.readLine();
                if (message == null) {
                    break;
                }
                System.out.println("Come from client >" + message);
                printWriter.write("echo " + message+"\n");
                printWriter.flush();
            }
        } catch (IOException e) {
            //自动关闭的时候 将running
            this.running = false;
        }finally {
            this.stop();
        }

    }

    public void stop() {
        if (!running) {
            return;
        }
        this.running = false;
        try {
            this.socket.close();

        } catch (IOException e) {

        }
    }
}

public class AppServerClient {
    public static void main(String[] args) throws InterruptedException, IOException {
        AppServer server = new AppServer(12135);
        server.start();

        Thread.sleep(20_000L);
        server.shutdown();
    }
}

5、mac telnet模拟客户端输入

bogon:~ kpioneer$ telnet localhost 12135
Trying ::1...
Connected to localhost.
Escape character is '^]'.
hello 
echo hello 
I love you
echo I love you
Connection closed by foreign host.

服务端输出:

Come from client >hello
Come from client >I love you
dispose

总结:

可以看到,在子类使用两阶段终止模式时,其只需要实现各自所需要执行的任务,并且更新当前任务的数量即可。在某些情况下,当前任务的数量也可以不进行更新,比如在进行终止时,不关心当前剩余多少任务需要执行。

到此这篇关于Java多线程 两阶段终止模式Two-Phase Termination Patter的文章就介绍到这了,更多相关Java多线程 两阶段终止模式内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家!

您可能感兴趣的文章:
阅读全文