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java多线程总结2

java多线程总结2

作者: dotdotdotdotbar | 来源:发表于2019-05-02 11:42 被阅读0次

结束线程

线程的状态

  1. 新建（new）：线程被创建时短暂处于该状态，字后调度器将把线程转变为就绪状态或阻塞状态。
  2. 就绪（Runnable）：只要调度器把时间片分给线程，线程就可以运行。
  3. 阻塞（Blocked）：线程能够运行，但是有条件阻止它运行。
  4. 死亡（Dead）：通常是run()方法返回

进入阻塞状态

  1. 调用sleep
  2. 调用wait
  3. 等待输入/输出完成
  4. 视图调用同步方法

通用方法

通常可以在线程的while循环中设置一个布尔值的标志位来控制线程是否需要关闭，当需要关闭时将该标志位设为true即可退出循环，从而关闭线程。如下例所示：

package com.alpha.concurrent.test;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

class Task implements Runnable {
    private volatile static boolean canceled = false;
    private static int taskId = 0;
    private int id = taskId++;

    @Override
    public void run() {
        while (!canceled) {
            System.out.println(this + "running");
            try {
                TimeUnit.MILLISECONDS.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(this + "canceled");
    }

    public static void cancel() {
        canceled = true;
    }

    @Override
    public String toString() {
        return "task " + id + ":";
    }
}

public class StopThread {
    public static void main(String[] args) {
        ExecutorService exec = Executors.newCachedThreadPool();
        for (int i = 0; i < 5; i++) {
            exec.execute(new Task());
        }

        try {
            TimeUnit.MILLISECONDS.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        Task.cancel();

        try {
            TimeUnit.MILLISECONDS.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        exec.shutdown();
    }
}

运行结果如下：

D:\software\java\jdk\bin\java.exe "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\lib\idea_rt.jar=1749:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\bin" -Dfile.encoding=UTF-8 -classpath D:\software\java\jdk\jre\lib\charsets.jar;D:\software\java\jdk\jre\lib\deploy.jar;D:\software\java\jdk\jre\lib\ext\access-bridge-64.jar;D:\software\java\jdk\jre\lib\ext\cldrdata.jar;D:\software\java\jdk\jre\lib\ext\dnsns.jar;D:\software\java\jdk\jre\lib\ext\jaccess.jar;D:\software\java\jdk\jre\lib\ext\jfxrt.jar;D:\software\java\jdk\jre\lib\ext\localedata.jar;D:\software\java\jdk\jre\lib\ext\nashorn.jar;D:\software\java\jdk\jre\lib\ext\sunec.jar;D:\software\java\jdk\jre\lib\ext\sunjce_provider.jar;D:\software\java\jdk\jre\lib\ext\sunmscapi.jar;D:\software\java\jdk\jre\lib\ext\sunpkcs11.jar;D:\software\java\jdk\jre\lib\ext\zipfs.jar;D:\software\java\jdk\jre\lib\javaws.jar;D:\software\java\jdk\jre\lib\jce.jar;D:\software\java\jdk\jre\lib\jfr.jar;D:\software\java\jdk\jre\lib\jfxswt.jar;D:\software\java\jdk\jre\lib\jsse.jar;D:\software\java\jdk\jre\lib\management-agent.jar;D:\software\java\jdk\jre\lib\plugin.jar;D:\software\java\jdk\jre\lib\resources.jar;D:\software\java\jdk\jre\lib\rt.jar;E:\WorkSpace\JAVA\IDEA\concurrent\out\production\concurrent com.alpha.concurrent.test.StopThread
task 0:running
task 1:running
task 2:running
task 3:running
task 4:running
task 3:running
task 4:running
task 1:running
task 2:running
task 0:running
task 0:running
task 2:running
task 1:running
task 4:running
task 3:running
task 3:running
task 1:running
task 4:running
task 2:running
task 0:running
task 1:running
task 3:running
task 4:running
task 2:running
task 0:running
task 0:running
task 2:running
task 4:running
task 1:running
task 3:running
task 0:running
task 2:running
task 4:running
task 1:running
task 3:running
task 2:running
task 4:running
task 0:running
task 1:running
task 3:running
task 3:running
task 1:running
task 2:running
task 0:running
task 4:running
task 0:running
task 1:running
task 2:running
task 4:running
task 3:running
task 1:canceled
task 2:canceled
task 4:canceled
task 0:canceled
task 3:canceled

Process finished with exit code 0

结束阻塞状态的线程

通常情况下可以使用上例所示的方法来终结线程，但是如果线程内部被阻塞的话，只能等线程恢复运行之后才能停止线程，比如上例中只能等sleep过后才能终结线程。但是有时阻塞的时间较长，我们希望立即结束线程，这是就需要了解中断。

中断

Thread类包含interrupt()方法，可以使用它来终止被阻塞的任务，该方法将设置线程的中断状态。如果一个线程已经被阻塞，或者视图执行一个阻塞操作，那么设置这个线程的中断状态将抛出InterruptedException。当抛出该异常或者该线程调用Thread.interrupted()时，中断状态将被复位。Thread.interrupted()提供了离开run()循环而不抛出异常的第二种方式。
在Executor上调用shutdownNow()，它将发送一个interrupt()调用给它启动的所有线程。如果只希望中断Executor启动的某一个任务，可以使用submit()启动任务，从而获得一个Future<?>对象，可以在Future对象上调用cancel方法，传递true给它来中断任务。如下例：

package com.alpha.concurrent.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

class SleepBlocked implements Runnable {
    @Override
    public void run() {
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("exit from sleep");
    }
}

class IOBlocked implements Runnable {
    private InputStream in;

    public IOBlocked(InputStream in) {
        this.in = in;
    }

    @Override
    public void run() {
        try {
            System.out.println("reading...");
            in.read();
        } catch (IOException e) {
            if (Thread.currentThread().isInterrupted()) {
                System.out.println("interrupted form blocked I/O");
            } else {
                throw new RuntimeException(e);
            }
        }
        System.out.println("exit from reading.");
    }
}

class SynchronizedBlocked implements Runnable {

    public SynchronizedBlocked() {
        new Thread() {
            @Override
            public void run() {
                f();
            }
        }.start();
    }

    public synchronized void f() {
        while (true) {
            Thread.yield();
        }
    }

    @Override
    public void run() {
        System.out.println("Trying to call f()");
        f();
        System.out.println("exit from synchronized.");
    }
}

public class Interrupting {
    private static ExecutorService exec = Executors.newCachedThreadPool();

    static void test(Runnable r) throws InterruptedException {
        Future<?> f = exec.submit(r);
        TimeUnit.MILLISECONDS.sleep(100);
        System.out.println("Interrupting " + r.getClass().getSimpleName());
        f.cancel(true);
        System.out.println("Interrupt sent to " + r.getClass().getSimpleName());
    }

    public static void main(String[] args) throws Exception {
        test(new SleepBlocked());
        test(new IOBlocked(System.in));
        test(new SynchronizedBlocked());

        TimeUnit.SECONDS.sleep(4);
        System.out.println("Aborting with System.exit(0)");
        System.exit(0);
    }
}

运行结果如下

D:\software\java\jdk\bin\java.exe "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\lib\idea_rt.jar=1722:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\bin" -Dfile.encoding=UTF-8 -classpath D:\software\java\jdk\jre\lib\charsets.jar;D:\software\java\jdk\jre\lib\deploy.jar;D:\software\java\jdk\jre\lib\ext\access-bridge-64.jar;D:\software\java\jdk\jre\lib\ext\cldrdata.jar;D:\software\java\jdk\jre\lib\ext\dnsns.jar;D:\software\java\jdk\jre\lib\ext\jaccess.jar;D:\software\java\jdk\jre\lib\ext\jfxrt.jar;D:\software\java\jdk\jre\lib\ext\localedata.jar;D:\software\java\jdk\jre\lib\ext\nashorn.jar;D:\software\java\jdk\jre\lib\ext\sunec.jar;D:\software\java\jdk\jre\lib\ext\sunjce_provider.jar;D:\software\java\jdk\jre\lib\ext\sunmscapi.jar;D:\software\java\jdk\jre\lib\ext\sunpkcs11.jar;D:\software\java\jdk\jre\lib\ext\zipfs.jar;D:\software\java\jdk\jre\lib\javaws.jar;D:\software\java\jdk\jre\lib\jce.jar;D:\software\java\jdk\jre\lib\jfr.jar;D:\software\java\jdk\jre\lib\jfxswt.jar;D:\software\java\jdk\jre\lib\jsse.jar;D:\software\java\jdk\jre\lib\management-agent.jar;D:\software\java\jdk\jre\lib\plugin.jar;D:\software\java\jdk\jre\lib\resources.jar;D:\software\java\jdk\jre\lib\rt.jar;E:\WorkSpace\JAVA\IDEA\concurrent\out\production\concurrent com.alpha.concurrent.test.Interrupting
Interrupting SleepBlocked
Interrupt sent to SleepBlocked
java.lang.InterruptedException: sleep interrupted
    at java.lang.Thread.sleep(Native Method)
    at java.lang.Thread.sleep(Thread.java:340)
    at java.util.concurrent.TimeUnit.sleep(TimeUnit.java:386)
    at com.alpha.concurrent.test.SleepBlocked.run(Interrupting.java:14)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
exit from sleep
reading...
Interrupting IOBlocked
Interrupt sent to IOBlocked
Trying to call f()
Interrupting SynchronizedBlocked
Interrupt sent to SynchronizedBlocked
Aborting with System.exit(0)

Process finished with exit code 0

可以看出，由sleep造成阻塞的线程被成功的唤醒，而由IO及同步锁造成的阻塞并没有被唤醒。因此可以知道，我们可以中断由sleep造成的阻塞，但是不能中断由于IO操作或者同步锁所造成的阻塞。

I/O阻塞

但是对于后两者所造成的阻塞该怎么办呢？对于I/O操作造成的阻塞，我们可以通过关闭发生阻塞的底层资源：

package com.alpha.concurrent.test;

import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class CloseResource {
    public static void main(String[] args) throws Exception {
        ExecutorService exec = Executors.newCachedThreadPool();

        ServerSocket server = new ServerSocket(8080);
        InputStream socketInput = new Socket("localhost", 8080).getInputStream();
        exec.execute(new IOBlocked(socketInput));

        TimeUnit.MILLISECONDS.sleep(100);
        System.out.println("shutdown all thread");
        exec.shutdownNow();

        TimeUnit.SECONDS.sleep(1);
        System.out.println("close socket input");
        socketInput.close();
    }
}

输出结果如下：

D:\software\java\jdk\bin\java.exe "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\lib\idea_rt.jar=1987:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\bin" -Dfile.encoding=UTF-8 -classpath D:\software\java\jdk\jre\lib\charsets.jar;D:\software\java\jdk\jre\lib\deploy.jar;D:\software\java\jdk\jre\lib\ext\access-bridge-64.jar;D:\software\java\jdk\jre\lib\ext\cldrdata.jar;D:\software\java\jdk\jre\lib\ext\dnsns.jar;D:\software\java\jdk\jre\lib\ext\jaccess.jar;D:\software\java\jdk\jre\lib\ext\jfxrt.jar;D:\software\java\jdk\jre\lib\ext\localedata.jar;D:\software\java\jdk\jre\lib\ext\nashorn.jar;D:\software\java\jdk\jre\lib\ext\sunec.jar;D:\software\java\jdk\jre\lib\ext\sunjce_provider.jar;D:\software\java\jdk\jre\lib\ext\sunmscapi.jar;D:\software\java\jdk\jre\lib\ext\sunpkcs11.jar;D:\software\java\jdk\jre\lib\ext\zipfs.jar;D:\software\java\jdk\jre\lib\javaws.jar;D:\software\java\jdk\jre\lib\jce.jar;D:\software\java\jdk\jre\lib\jfr.jar;D:\software\java\jdk\jre\lib\jfxswt.jar;D:\software\java\jdk\jre\lib\jsse.jar;D:\software\java\jdk\jre\lib\management-agent.jar;D:\software\java\jdk\jre\lib\plugin.jar;D:\software\java\jdk\jre\lib\resources.jar;D:\software\java\jdk\jre\lib\rt.jar;E:\WorkSpace\JAVA\IDEA\concurrent\out\production\concurrent com.alpha.concurrent.test.CloseResource
reading...
shutdown all thread
close socket input
interrupted form blocked I/O
exit from reading.

Process finished with exit code 0

同步锁阻塞

针对synchronized锁阻塞的线程无法被中断，可以使用ReentrantLock给任务上锁，从而使其具备被中断的能力：

package com.alpha.concurrent.test;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

class BlockedMutex {
    private Lock lock = new ReentrantLock();

    public BlockedMutex() {
        lock.lock();
    }

    public void f() {
        try {
            lock.lockInterruptibly();
        } catch (InterruptedException e) {
            System.out.println("Interrupted from lock acquisition in f()");
        }
    }
}

class LockTask implements Runnable {
    BlockedMutex blockedMutex = new BlockedMutex();

    @Override
    public void run() {
        System.out.println("waiting for f() in BlockedMutex");
        blockedMutex.f();
        System.out.println("Broken out of blocked call");

    }
}

public class Interrupting2 {
    public static void main(String[] args) {
        Thread t = new Thread(new LockTask());
        t.start();
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("interrupt");
        t.interrupt();
    }
}

输出结果如下：

D:\software\java\jdk\bin\java.exe "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\lib\idea_rt.jar=2049:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\bin" -Dfile.encoding=UTF-8 -classpath D:\software\java\jdk\jre\lib\charsets.jar;D:\software\java\jdk\jre\lib\deploy.jar;D:\software\java\jdk\jre\lib\ext\access-bridge-64.jar;D:\software\java\jdk\jre\lib\ext\cldrdata.jar;D:\software\java\jdk\jre\lib\ext\dnsns.jar;D:\software\java\jdk\jre\lib\ext\jaccess.jar;D:\software\java\jdk\jre\lib\ext\jfxrt.jar;D:\software\java\jdk\jre\lib\ext\localedata.jar;D:\software\java\jdk\jre\lib\ext\nashorn.jar;D:\software\java\jdk\jre\lib\ext\sunec.jar;D:\software\java\jdk\jre\lib\ext\sunjce_provider.jar;D:\software\java\jdk\jre\lib\ext\sunmscapi.jar;D:\software\java\jdk\jre\lib\ext\sunpkcs11.jar;D:\software\java\jdk\jre\lib\ext\zipfs.jar;D:\software\java\jdk\jre\lib\javaws.jar;D:\software\java\jdk\jre\lib\jce.jar;D:\software\java\jdk\jre\lib\jfr.jar;D:\software\java\jdk\jre\lib\jfxswt.jar;D:\software\java\jdk\jre\lib\jsse.jar;D:\software\java\jdk\jre\lib\management-agent.jar;D:\software\java\jdk\jre\lib\plugin.jar;D:\software\java\jdk\jre\lib\resources.jar;D:\software\java\jdk\jre\lib\rt.jar;E:\WorkSpace\JAVA\IDEA\concurrent\out\production\concurrent com.alpha.concurrent.test.Interrupting2
waiting for f() in BlockedMutex
interrupt
Interrupted from lock acquisition in f()
Broken out of blocked call

Process finished with exit code 0

检查中断

当你在线程上调用interrupt()时，只有当线程准备进入阻塞或者已经处于阻塞状态时，才会抛出InterruptedException异常，如果只依靠该异常，当线程不处于阻塞状态时调用interrupt()就不能离开run中的循环，因此需要在run()循环中使用interrupted()检查中断状态:

package com.alpha.concurrent.test;

import java.util.concurrent.TimeUnit;

class NeedsCleanup {
    private final int id;

    public NeedsCleanup(int id) {
        this.id = id;
        System.out.println("NeedsCleanup " + id);
    }

    public void cleanup() {
        System.out.println("Cleaning up " + id);
    }
}

class Block3 implements Runnable {
    private volatile double d = 0.0;

    @Override
    public void run() {
        try {
            while (!Thread.interrupted()) {
                // point1
                NeedsCleanup n1 = new NeedsCleanup(1);

                try {
                    System.out.println("Sleeping");
                    TimeUnit.SECONDS.sleep(1);

                    // point2
                    NeedsCleanup n2 = new NeedsCleanup(2);

                    try {
                        System.out.println("Calculating");
                        // time comsuming
                        for (int i = 1; i < 2500000; i++) {
                            d = d + (Math.PI + Math.E) / d;
                        }
                        System.out.println("finished Calculating");
                    } finally {
                        n2.cleanup();
                    }
                } finally {
                    n1.cleanup();
                }
            }
            System.out.println("exit while");
        } catch (InterruptedException e) {
            System.out.println("exit by interrupted");
        }
    }
}

public class InterruptingIdiom {
    public static void main(String[] args) throws Exception {
        Thread t = new Thread(new Block3());
        t.start();

        TimeUnit.SECONDS.sleep(1);
        t.interrupt();
    }
}

输出1：

D:\software\java\jdk\bin\java.exe "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\lib\idea_rt.jar=2300:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\bin" -Dfile.encoding=UTF-8 -classpath D:\software\java\jdk\jre\lib\charsets.jar;D:\software\java\jdk\jre\lib\deploy.jar;D:\software\java\jdk\jre\lib\ext\access-bridge-64.jar;D:\software\java\jdk\jre\lib\ext\cldrdata.jar;D:\software\java\jdk\jre\lib\ext\dnsns.jar;D:\software\java\jdk\jre\lib\ext\jaccess.jar;D:\software\java\jdk\jre\lib\ext\jfxrt.jar;D:\software\java\jdk\jre\lib\ext\localedata.jar;D:\software\java\jdk\jre\lib\ext\nashorn.jar;D:\software\java\jdk\jre\lib\ext\sunec.jar;D:\software\java\jdk\jre\lib\ext\sunjce_provider.jar;D:\software\java\jdk\jre\lib\ext\sunmscapi.jar;D:\software\java\jdk\jre\lib\ext\sunpkcs11.jar;D:\software\java\jdk\jre\lib\ext\zipfs.jar;D:\software\java\jdk\jre\lib\javaws.jar;D:\software\java\jdk\jre\lib\jce.jar;D:\software\java\jdk\jre\lib\jfr.jar;D:\software\java\jdk\jre\lib\jfxswt.jar;D:\software\java\jdk\jre\lib\jsse.jar;D:\software\java\jdk\jre\lib\management-agent.jar;D:\software\java\jdk\jre\lib\plugin.jar;D:\software\java\jdk\jre\lib\resources.jar;D:\software\java\jdk\jre\lib\rt.jar;E:\WorkSpace\JAVA\IDEA\concurrent\out\production\concurrent com.alpha.concurrent.test.InterruptingIdiom
NeedsCleanup 1
Sleeping
NeedsCleanup 2
Calculating
finished Calculating
Cleaning up 2
Cleaning up 1
exit while

Process finished with exit code 0

输出2：

D:\software\java\jdk\bin\java.exe "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\lib\idea_rt.jar=2311:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.6\bin" -Dfile.encoding=UTF-8 -classpath D:\software\java\jdk\jre\lib\charsets.jar;D:\software\java\jdk\jre\lib\deploy.jar;D:\software\java\jdk\jre\lib\ext\access-bridge-64.jar;D:\software\java\jdk\jre\lib\ext\cldrdata.jar;D:\software\java\jdk\jre\lib\ext\dnsns.jar;D:\software\java\jdk\jre\lib\ext\jaccess.jar;D:\software\java\jdk\jre\lib\ext\jfxrt.jar;D:\software\java\jdk\jre\lib\ext\localedata.jar;D:\software\java\jdk\jre\lib\ext\nashorn.jar;D:\software\java\jdk\jre\lib\ext\sunec.jar;D:\software\java\jdk\jre\lib\ext\sunjce_provider.jar;D:\software\java\jdk\jre\lib\ext\sunmscapi.jar;D:\software\java\jdk\jre\lib\ext\sunpkcs11.jar;D:\software\java\jdk\jre\lib\ext\zipfs.jar;D:\software\java\jdk\jre\lib\javaws.jar;D:\software\java\jdk\jre\lib\jce.jar;D:\software\java\jdk\jre\lib\jfr.jar;D:\software\java\jdk\jre\lib\jfxswt.jar;D:\software\java\jdk\jre\lib\jsse.jar;D:\software\java\jdk\jre\lib\management-agent.jar;D:\software\java\jdk\jre\lib\plugin.jar;D:\software\java\jdk\jre\lib\resources.jar;D:\software\java\jdk\jre\lib\rt.jar;E:\WorkSpace\JAVA\IDEA\concurrent\out\production\concurrent com.alpha.concurrent.test.InterruptingIdiom
NeedsCleanup 1
Sleeping
NeedsCleanup 2
Calculating
finished Calculating
Cleaning up 2
Cleaning up 1
NeedsCleanup 1
Sleeping
Cleaning up 1
exit by interrupted

Process finished with exit code 0

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