Java 学习笔记之 Suspend和Resume

Posted 2020-10-10 AK47Sonic

Suspend和Resume：

 

Suspend和Resume使用方法：

以下例子证明了线程确实被暂停了，而且还可以恢复成运行状态。

public class SuspendResumeThread extends Thread{
    private long i = 0;

    public long getI() {
        return i;
    }

    public void setI(long i) {
        this.i = i;
    }

    @Override
    public void run() {
        while(true){
            i++;
        }
    }
}

public class ThreadRunMain {
    public static void main(String[] args) {
        testSuspendResumeThread();
    }
  public static void testSuspendResumeThread(){
        try {
            SuspendResumeThread srt = new SuspendResumeThread();
            srt.start();
            Thread.sleep(5000);

            srt.suspend();
            System.out.println("A= " + System.currentTimeMillis() + " i=" + srt.getI());
            Thread.sleep(5000);
            System.out.println("A= " + System.currentTimeMillis() + " i=" + srt.getI());

            srt.resume();
            Thread.sleep(5000);

            srt.suspend();
            System.out.println("A= " + System.currentTimeMillis() + " i=" + srt.getI());
            Thread.sleep(5000);
            System.out.println("A= " + System.currentTimeMillis() + " i=" + srt.getI());

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

Suspend和Resume缺点1-独占：

public class SuspendResumeObject {
    synchronized public void printString(){
        System.out.println("begin");
        if(Thread.currentThread().getName().equals("a")){
            System.out.println("a thread will suspend.");
            Thread.currentThread().suspend();
        }
        System.out.println("SuspendResumeObject end");
    }
}

public class ThreadRunMain {
    public static void main(String[] args) {
        testSuspendResumeObject();
    }
   public static void testSuspendResumeObject(){
        try {
            final SuspendResumeObject object = new SuspendResumeObject();
            Thread t = new Thread(){
                @Override
                public void run() {
                    object.printString();
                }
            };
            t.setName("a");
            t.start();
            Thread.sleep(1000);
            Thread t2 = new Thread(){
                @Override
                public void run() {
                    System.out.println("Thread 2 start, but can\'t enter printString()");
                    System.out.println("Because of printString() is blocked by thread a");
                    object.printString();
                    System.out.println("Thread 2 complete");
                }
            };
            t2.start();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

运行结果：

public class SuspendResumePrintStreamIssue extends Thread{
    private long i = 0;
    @Override
    public void run() {
        while (true){
//            try {
                i++;
//                Thread.sleep(1);
                System.out.println(i);
//            } catch (InterruptedException e) {
//                e.printStackTrace();
//            }
        }
    }
}

public class ThreadRunMain {
    public static void main(String[] args) {
        testSuspendResumePrintStreamIssue();
    }
    public static void testSuspendResumePrintStreamIssue(){
        try {
            SuspendResumePrintStreamIssue srpsi = new SuspendResumePrintStreamIssue();
            srpsi.start();
            Thread.sleep(1000);
            srpsi.suspend();
            System.out.println("Main end.");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

 

同样是独占，当程序运行到PrintStream对象println()方法内部停止时，同步锁未被释放。这导致main()方法中的System.out.println("Main end.");不能被执行。

 

Suspend和Resume缺点2-数据不一致：

public class SuspendResumeDataIssue {
    private String userName = "1";
    private String password = "11";
    synchronized public void setValue(String u, String p){
        this.userName = u;
        if(Thread.currentThread().getName().equals("a")){
            System.out.println("Thread a suspend.");
            Thread.currentThread().suspend();
        }
        this.password = p;
    }

    public void printUserNamePassword(){
        System.out.println(userName + " " + password);
    }
}

public class ThreadRunMain {
    public static void main(String[] args) {
        testSuspendResumeDataIssue();
    }


    public static void testSuspendResumeDataIssue(){
        try {
            SuspendResumeDataIssue srdi = new SuspendResumeDataIssue();
            Thread t1 = new Thread(){
                @Override
                public void run() {
                    srdi.setValue("a", "aa");
                }
            };
            t1.setName("a");
            t1.start();
            Thread.sleep(500);
            Thread t2 = new Thread(){
                @Override
                public void run() {
                    srdi.printUserNamePassword();
                }
            };
            t2.start();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

运行结果：