多线程学习--线程通信

客官°小女子只卖身不卖艺 2024-02-19 14:35 91阅读 0赞

线程彼此通信会涉及到等待/通知，其最经典的案例就是“生产者/消费者模式”。原理都是基于wait/notify的。

一生产一消费：

//消费者
    class Consumer {
        private String lock;
    
        public Consumer(String lock) {
            super();
            this.lock = lock;
        }
    
        public void getValue() {
            try {
                synchronized (lock) {
                    if (ValueObject.value.equals("")) {
                        lock.wait();
                    }
                    System.out.println("get的值是" + ValueObject.value);
                    ValueObject.value = "";
                    lock.notify();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    //生产者
    class Producer {
        private String lock;
    
        public Producer(String lock) {
            super();
            this.lock = lock;
        }
    
        public void setValue() {
            try {
                synchronized (lock) {
                    if (!ValueObject.value.equals("")) {
                        lock.wait();
                    }
                    String value = System.currentTimeMillis() + "_" + System.nanoTime();
                    System.out.println("set的值是" + value);
                    ValueObject.value = value;
                    lock.notify();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    
    public class test {
        public static void main(String[] args) {
            String lock = new String("");
            Producer producer = new Producer(lock);
            Consumer consumer = new Consumer(lock);
            new Thread(()->{
                while (true) {
                    producer.setValue();
                }
            },"生产者").start();
            new Thread(()->{
                while (true) {
                    consumer.getValue();
                }
            },"消费者").start();
        }
    }

结果：

set的值是1544676746771_186857371485669
    get的值是1544676746771_186857371485669
    set的值是1544676746771_186857371495584
    get的值是1544676746771_186857371495584
    set的值是1544676746771_186857371515716
    get的值是1544676746771_186857371515716
    。。。。。。。。。。。。。。。。。。。。。

假死：无法不保证唤醒的是非当前线程

class ValueObject {
        public static String value = "";
    }
    
    class Producer {
        private String lock;
    
        public Producer(String lock) {
            super();
            this.lock = lock;
        }
    
        public void setValue() {
            try {
                synchronized (lock) {
                    while (!ValueObject.value.equals("")) {
                        System.out.println("生产者 " + Thread.currentThread().getName() + " WAITING了★");
                        lock.wait();
                    }
                    System.out.println("生产者 " + Thread.currentThread().getName() + " RUNNABLE了");
                    String value = System.currentTimeMillis() + "_" + System.nanoTime();
                    ValueObject.value = value;
                    lock.notify();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    class Consumer {
        private String lock;
    
        public Consumer(String lock) {
            super();
            this.lock = lock;
        }
    
        public void getValue() {
            try {
                synchronized (lock) {
                    while (ValueObject.value.equals("")) {
                        System.out.println("消费者 " + Thread.currentThread().getName() + " WAITING了☆");
                        lock.wait();
                    }
                    System.out.println("消费者 " + Thread.currentThread().getName() + " RUNNABLE了");
                    ValueObject.value = "";
                    lock.notify();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    
    class ThreadP extends Thread {
        private Producer p;
    
        public ThreadP(Producer p) {
            super();
            this.p = p;
        }
    
        @Override
        public void run() {
            while (true) {
                p.setValue();
            }
        }
    }
    class ThreadC extends Thread {
        private Consumer consumer;
    
        public ThreadC(Consumer consumer) {
            super();
            this.consumer = consumer;
        }
    
        @Override
        public void run() {
            while (true) {
                consumer.getValue();
            }
        }
    }
    public class Run8_allWait {
        public static void main(String[] args) throws InterruptedException {
            String lock = new String("");
            Producer producer = new Producer(lock);
            Consumer consumer = new Consumer(lock);
            ThreadP[] pThread = new ThreadP[2];
            ThreadC[] cThread = new ThreadC[2];
            for (int i = 0; i < 2; i++) {
                pThread[i] = new ThreadP(producer);
                pThread[i].setName("生产者" + (i + 1));
                cThread[i] = new ThreadC(consumer);
                cThread[i].setName("消费者" + (i + 1));
                pThread[i].start();
                cThread[i].start();
            }
            Thread.sleep(5000);
            //获取当前活动的线程
            Thread[] threads = new Thread[Thread.currentThread().getThreadGroup().activeCount()];
            Thread.currentThread().getThreadGroup().enumerate(threads);
            for (int i = 0; i < threads.length; i++) {
                System.out.println(threads[i].getName() + " " + threads[i].getState());
            }
    
        }
    }

结果：

生产者 生产者1 RUNNABLE了
    生产者 生产者1 WAITING了★
    生产者 生产者2 WAITING了★
    消费者 消费者1 RUNNABLE了
    消费者 消费者1 WAITING了☆
    生产者 生产者1 RUNNABLE了
    生产者 生产者1 WAITING了★
    生产者 生产者2 WAITING了★
    消费者 消费者2 RUNNABLE了
    消费者 消费者2 WAITING了☆
    消费者 消费者1 WAITING了☆
    main RUNNABLE
    Monitor Ctrl-Break RUNNABLE
    生产者1 WAITING
    消费者1 WAITING
    生产者2 WAITING
    消费者2 WAITING

分析：jps/jstack pid 分析线程问题 jdk自带工具

jsp:

![2018121313265596.png][]

jstack 7444:

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzU0OTU3OA_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzU0OTU3OA_size_16_color_FFFFFF_t_70 1][]

线程根据等待和唤醒进行通信成功，但是无法不保证唤醒的是非当前线程，比如“生产者”唤醒 “生产者” / “消费者” 唤醒 “消费者”，从而导致了程序最后呈“假死状态”。

解决方法:notify()换成notifyAll().

一生产与多消费：

class MyStack {
        private List list = new ArrayList();
    
        synchronized public void push() {
            try {
                if (list.size() == 1) {
                    System.out.println("push操作中的： " + Thread.currentThread().getName() + " 线程呈wait状态");
                    this.wait();
                }
                list.add(Math.random());
                this.notify();
                System.out.println("push = " + list.size());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    
        synchronized public String pop() {
            String returnValue = "";
            try {
                if (list.size() == 0) {
                    System.out.println("pop操作中的： " + Thread.currentThread().getName() + " 线程呈wait状态");
                    this.wait();
                }
                returnValue = list.get(0) + "  " + Thread.currentThread().getName();
                list.remove(0);
                this.notify();
                System.out.println("pop = " + list.size() + "  Mystack的pop方法中 线程" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return returnValue;
        }
    }
    class Producer {
        private MyStack myStack;
    
        public Producer(MyStack myStack) {
            super();
            this.myStack = myStack;
        }
    
        public void pushService() {
            myStack.push();
        }
    
    }
    class Consumer {
        private MyStack myStack;
    
        public Consumer(MyStack myStack) {
            super();
            this.myStack = myStack;
        }
    
        public void popService() {
            System.out.println("pop = " + myStack.pop() + "  Consumer的popService方法中打印pop返回值");
        }
    
    }
    class P_Thread extends Thread {
        private Producer p;
    
        public P_Thread(Producer p) {
            super();
            this.p = p;
        }
    
        @Override
        public void run() {
            while (true) {
                p.pushService();
            }
        }
    }
    class C_Thread extends Thread {
        private Consumer c;
    
        public C_Thread(Consumer c) {
            super();
            this.c = c;
        }
    
        @Override
        public void run() {
            while (true) {
                c.popService();
            }
        }
    }
    public class Run9_oneP_manyC {
        public static void main(String[] args) {
            MyStack myStack = new MyStack();
            Producer p = new Producer(myStack);
            Consumer c1 = new Consumer(myStack);
            Consumer c2 = new Consumer(myStack);
            Consumer c3 = new Consumer(myStack);
            Consumer c4 = new Consumer(myStack);
            Consumer c5 = new Consumer(myStack);
    
            P_Thread p_thread = new P_Thread(p);
            p_thread.start();
            C_Thread c_thread1 = new C_Thread(c1);
            C_Thread c_thread2 = new C_Thread(c2);
            C_Thread c_thread3 = new C_Thread(c3);
            C_Thread c_thread4 = new C_Thread(c4);
            C_Thread c_thread5 = new C_Thread(c5);
            c_thread1.start();
            c_thread2.start();
            c_thread3.start();
            c_thread4.start();
            c_thread5.start();
    
        }
    }

结果：

"C:\Program Files\Java\jdk1.8.0_181\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2018.2.4\lib\idea_rt.jar=51167:C:\Program Files\JetBrains\IntelliJ IDEA 2018.2.4\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_181\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_181\jre\lib\rt.jar;C:\Users\zhw\IdeaProjects\java-learning\java-multithread\target\classes" com.brianway.learning.java.multithread.communication.example9.Run9_oneP_manyC
    Exception in thread "Thread-1" Exception in thread "Thread-2" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    push = 1
    	at java.util.ArrayList.rangeCheck(ArrayList.java:657)
    push操作中的： Thread-0 线程呈wait状态
    pop = 0  Mystack的pop方法中 线程Thread-3
    	at java.util.ArrayList.get(ArrayList.java:433)
    pop = 0.859192167402362  Thread-3  Consumer的popService方法中打印pop返回值
    pop操作中的： Thread-2 线程呈wait状态
    pop操作中的： Thread-1 线程呈wait状态
    	at com.brianway.learning.java.multithread.communication.example9.MyStack.pop(Run9_oneP_manyC.java:41)
    pop操作中的： Thread-3 线程呈wait状态
    push = 1
    	at com.brianway.learning.java.multithread.communication.example9.Consumer.popService(Run9_oneP_manyC.java:73)
    push操作中的： Thread-0 线程呈wait状态
    pop = 0  Mystack的pop方法中 线程Thread-5
    	at com.brianway.learning.java.multithread.communication.example9.C_Thread.run(C_Thread.java:17)
    pop = 0.381657285316201  Thread-5  Consumer的popService方法中打印pop返回值
    pop操作中的： Thread-4 线程呈wait状态
    java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    pop操作中的： Thread-5 线程呈wait状态
    	at java.util.ArrayList.rangeCheck(ArrayList.java:657)
    	at java.util.ArrayList.get(ArrayList.java:433)
    	at com.brianway.learning.java.multithread.communication.example9.MyStack.pop(Run9_oneP_manyC.java:41)
    	at com.brianway.learning.java.multithread.communication.example9.Consumer.popService(Run9_oneP_manyC.java:73)
    	at com.brianway.learning.java.multithread.communication.example9.C_Thread.run(C_Thread.java:17)

原因：

if判断存在弊端，条件发生改变时没有得到及时的响应，多个呈wait状态的线程被唤醒，继而执行list.remove(0)出现异常java.lang.IndexOutOfBoundsException.
    
    解决办法：

if 改为while, while判断解决条件发生改变时没有得到及时的响应，多个呈wait状态的线程被唤醒的问题，但会出现新的问题：假死，同时需要将notify()换成notifyAll()

多生产与一消费:notifyAll()代替notify()，将一直运行下去

class MyStack {
        private List list = new ArrayList();
    
        synchronized public void push() {
            try {
                while (list.size() == 1) {
                    System.out.println("push操作中的： " + Thread.currentThread().getName() + " 线程呈wait状态");
                    this.wait();
                }
                list.add(Math.random());
                this.notifyAll();
                System.out.println("push = " + list.size());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    
        synchronized public String pop() {
            String returnValue = "";
            try {
                while (list.size() == 0) {
                    System.out.println("pop操作中的： " + Thread.currentThread().getName() + " 线程呈wait状态");
                    this.wait();
                }
                returnValue = list.get(0) + "  " + Thread.currentThread().getName();
                list.remove(0);
                this.notifyAll();
                System.out.println("pop = " + list.size() + "  Mystack的pop方法中 线程" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return returnValue;
        }
    }
    class Producer {
        private MyStack myStack;
    
        public Producer(MyStack myStack) {
            super();
            this.myStack = myStack;
        }
    
        public void pushService() {
            myStack.push();
        }
    
    }
    class Consumer {
        private MyStack myStack;
    
        public Consumer(MyStack myStack) {
            super();
            this.myStack = myStack;
        }
    
        public void popService() {
            System.out.println("pop = " + myStack.pop() + "  Consumer的popService方法中打印pop返回值");
        }
    
    }
    class C_Thread extends Thread {
        private Consumer c;
    
        public C_Thread(Consumer c) {
            super();
            this.c = c;
        }
    
        @Override
        public void run() {
            while (true) {
                c.popService();
            }
        }
    }
    class P_Thread extends Thread {
        private Producer p;
    
        public P_Thread(Producer p) {
            super();
            this.p = p;
        }
    
        @Override
        public void run() {
            while (true) {
                p.pushService();
            }
        }
    }
    
    public class test{
        public static void main(String[] args) {
            MyStack myStack = new MyStack();
    
            int pNum = 6;
            Producer[] producers = new Producer[pNum];
            P_Thread[] p_threads = new P_Thread[pNum];
    
            for (int i = 0; i < pNum; i++) {
                producers[i] = new Producer(myStack);
            }
    
            for (int i = 0; i < pNum; i++) {
                p_threads[i] = new P_Thread(producers[i]);
                p_threads[i].start();
            }
    
            Consumer c = new Consumer(myStack);
            C_Thread c_thread = new C_Thread(c);
            c_thread.start();
    
        }
    }

多生产与多消费: 一直运行下去

class MyStack {
        private List list = new ArrayList();
    
        synchronized public void push() {
            try {
                while (list.size() == 1) {
                    System.out.println("push操作中的： " + Thread.currentThread().getName() + " 线程呈wait状态");
                    this.wait();
                }
                list.add(Math.random());
                this.notifyAll();
                System.out.println("push = " + list.size());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    
        synchronized public String pop() {
            String returnValue = "";
            try {
                while (list.size() == 0) {
                    System.out.println("pop操作中的： " + Thread.currentThread().getName() + " 线程呈wait状态");
                    this.wait();
                }
                returnValue = list.get(0) + "  " + Thread.currentThread().getName();
                list.remove(0);
                this.notifyAll();
                System.out.println("pop = " + list.size() + "  Mystack的pop方法中 线程" + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return returnValue;
        }
    }
    class Producer {
        private MyStack myStack;
    
        public Producer(MyStack myStack) {
            super();
            this.myStack = myStack;
        }
    
        public void pushService() {
            myStack.push();
        }
    
    }
    class Consumer {
        private MyStack myStack;
    
        public Consumer(MyStack myStack) {
            super();
            this.myStack = myStack;
        }
    
        public void popService() {
            System.out.println("pop = " + myStack.pop() + "  Consumer的popService方法中打印pop返回值");
        }
    
    }
    class C_Thread extends Thread {
        private Consumer c;
    
        public C_Thread(Consumer c) {
            super();
            this.c = c;
        }
    
        @Override
        public void run() {
            while (true) {
                c.popService();
            }
        }
    }
    class P_Thread extends Thread {
        private Producer p;
    
        public P_Thread(Producer p) {
            super();
            this.p = p;
        }
    
        @Override
        public void run() {
            while (true) {
                p.pushService();
            }
        }
    }
    
    public class test{
        public static void main(String[] args) {
            MyStack myStack = new MyStack();
    
            int pNum = 6;
            Producer[] producers = new Producer[pNum];
            P_Thread[] p_threads = new P_Thread[pNum];
    
            for (int i = 0; i < pNum; i++) {
                producers[i] = new Producer(myStack);
            }
    
            for (int i = 0; i < pNum; i++) {
                p_threads[i] = new P_Thread(producers[i]);
                p_threads[i].start();
            }
    
            int cNum = 8;
            Consumer[] consumers = new Consumer[cNum];
            C_Thread[] c_threads = new C_Thread[cNum];
    
            for (int i = 0; i < cNum; i++) {
                consumers[i] = new Consumer(myStack);
            }
    
            for (int i = 0; i < cNum; i++) {
                c_threads[i] = new C_Thread(consumers[i]);
                c_threads[i].start();
            }
    
        }
    }

[2018121313265596.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/848f46b323da47638a1d8e7e3bdc4f02.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzU0OTU3OA_size_16_color_FFFFFF_t_70]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/d48a10f1e86e4f8eba9447eea8bc089d.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzU0OTU3OA_size_16_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/43e4cc366f8c4ce596cd3024a3060143.png