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Producer and consumer issues

2022-06-22 06:17:00 【Kuxiaoya】

Producer and consumer issues Synchronzied edition

/** *  Communication problems between threads ： Producer and consumer issues ！ *  Threads execute alternately  A B  Operate on the same variable  num = 0 * A num+1 * B num-1 */
public class A {
    
    public static void main(String[] args) {
    
        Data data = new Data();

        new Thread(()->{
    
            for (int i = 0; i < 10; i++) {
    
                try {
    
                    data.increment();
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
            }
        },"A").start();

        new Thread(()->{
    
            for (int i = 0; i < 10; i++) {
    
                try {
    
                    data.increment();
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
            }
        },"B").start();
    }
}
//  Judge wait , Business , notice 
class  Data{
    
    // Numbers   Resource class 
    private int number=0;
    //+1
    public synchronized void increment() throws InterruptedException {
    
        if(number!=0){
    // be equal to  0  when , work 
            // wait for 
            this.wait();
        }
        number++;
        System.out.println(Thread.currentThread().getName()+"=>"+number);
        // Notify other threads , I +1 It's over 
        this.notifyAll();
    }

    //-1
    public synchronized void decrement() throws InterruptedException {
    
        if(number==0){
    // It's not equal to  0  when , work 
            // wait for 
            this.wait();
        }
        number--;
        // Notify other threads , I -1 It's over 
        this.notifyAll();
    }
}

The problem is ,A B C D 4 Threads ！ spurious wakeup

$[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-ZhtqRxFK-1654847938784)(C:\Users\38492\AppData\Local\Temp\1654795628742.png)]$

Solution ： hold if Switch to while that will do !

/** *  Communication problems between threads ： Producer and consumer issues ！ *  Threads execute alternately  A B  Operate on the same variable  num = 0 * A num+1 * B num-1 */
public class A {
    
    public static void main(String[] args) {
    
        Data data = new Data();

        new Thread(()->{
    
            for (int i = 0; i < 10; i++) {
    
                try {
    
                    data.increment();
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
            }
        },"A").start();

        new Thread(()->{
    
            for (int i = 0; i < 10; i++) {
    
                try {
    
                    data.decrement();
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
            }
        },"B").start();

        new Thread(()->{
    
            for (int i = 0; i < 10; i++) {
    
                try {
    
                    data.increment();
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
            }
        },"C").start();

        new Thread(()->{
    
            for (int i = 0; i < 10; i++) {
    
                try {
    
                    data.decrement();
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
            }
        },"D").start();
    }
}
//  Judge wait , Business , notice 
class  Data{
    
    // Numbers   Resource class 
    private int number=0;
    //+1
    public synchronized void increment() throws InterruptedException {
    
        while(number!=0){
    // be equal to  0  when , work 
            // wait for 
            this.wait();
        }
        number++;
        System.out.println(Thread.currentThread().getName()+"=>"+number);
        // Notify other threads , I +1 It's over 
        this.notifyAll();
    }

    //-1
    public synchronized void decrement() throws InterruptedException {
    
        while(number==0){
    // It's not equal to  0  when , work 
            // wait for 
            this.wait();
        }
        number--;
        System.out.println(Thread.currentThread().getName()+"=>"+number);
        // Notify other threads , I -1 It's over 
        this.notifyAll();
    }
}

JUC Producer of version

$[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-8wN0XQYe-1654848042391)(C:\Users\38492\AppData\Local\Temp\1654796413847.png)]$

public class B {
    


/** *  Communication problems between threads ： Producer and consumer issues ！ *  Threads execute alternately  A B  Operate on the same variable  num = 0 * A num+1 * B num-1 */

    public static void main(String[] args) {
    
        Data2 data = new Data2();

        new Thread(()->{
    
            for (int i = 0; i < 10; i++) {
    
                try {
    
                    data.increment();
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
            }
        },"A").start();

        new Thread(()->{
    
            for (int i = 0; i < 10; i++) {
    
                try {
    
                    data.decrement();
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
            }
        },"B").start();

        new Thread(()->{
    
            for (int i = 0; i < 10; i++) {
    
                try {
    
                    data.increment();
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
            }
        },"C").start();

        new Thread(()->{
    
            for (int i = 0; i < 10; i++) {
    
                try {
    
                    data.decrement();
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
            }
        },"D").start();

    }
}
//  Judge wait , Business , notice 
class  Data2{
    
    // Numbers   Resource class 
    private int number=0;

    Lock lock = new ReentrantLock();
    Condition condition = lock.newCondition();
// condition.await(); // wait for 
// condition.signalAll(); // Wake up all 

    //+1
    public synchronized void increment() throws InterruptedException {
    

        try {
    
            lock.lock();// locked 

            // Business code 
            while(number!=0){
    // be equal to  0  when , work 
                // wait for 
                condition.await();
            }
            number++;
            System.out.println(Thread.currentThread().getName()+"=>"+number);
            // Notify other threads , I +1 It's over 
            condition.signalAll();
        } catch (Exception e) {
    
            e.printStackTrace();
        } finally {
    
            lock.unlock();// Unlock 
        }
    }

    //-1
    public  void decrement() throws InterruptedException {
    
        try {
    
            lock.lock();// locked 

            // Business code 
            while(number==0){
    // It's not equal to  0  when , work 
                // wait for 
                condition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName()+"=>"+number);
            // Notify other threads , I -1 It's over 
            condition.signalAll();
        } catch (Exception e) {
    
            e.printStackTrace();
        } finally {
    
            lock.unlock();// Unlock 
        }
    }
}

Any new technology , It's not just about covering the original technology , Advantages and supplements !

Condition Precise notification and wake-up threads

Insert picture description here

How to solve random states ？ Make it an orderly execution ！
Code implementation ：

public class C {
    
    public static void main(String[] args) {
    
        Data3 data = new Data3();

        new Thread(() -> {
    
            for (int i = 0; i < 10; i++) {
    
                data.printA();
            }
        }, "A").start();
        new Thread(() -> {
    
            for (int i = 0; i < 10; i++) {
    
                data.printB();
            }
        }, "B").start();
        new Thread(() -> {
    
            for (int i = 0; i < 10; i++) {
    
                data.printC();
            }
        }, "C").start();
    }
}

class Data3 {
    
    // Resource class  Lock
    private Lock lock = new ReentrantLock();
    private Condition condition1 = lock.newCondition();
    private Condition condition2 = lock.newCondition();
    private Condition condition3 = lock.newCondition();
    private int number = 1;//1A 2B 3C

    public void printA() {
    

        try {
    
            lock.lock();// locked 
            // Business code  ：  Judge  ->  perform  ->  notice 
            while (number != 1) {
    
                // wait for 
                condition1.await();
            }
            System.out.println(Thread.currentThread().getName() + "=>AAA");
            // Wake up the , Wake up the designated person ,B
            number = 2;
            condition2.signal();
        } catch (Exception e) {
    
            e.printStackTrace();
        } finally {
    
            lock.unlock();// Unlock 
        }

    }

    public void printB() {
    

        try {
    
            lock.lock();// locked 
            // Business code  ：  Judge  ->  perform  ->  notice 
            while (number != 2) {
    
                // wait for 
                condition2.await();
            }
            System.out.println(Thread.currentThread().getName() + "->BBB");
            // Wake up the , Wake up the designated person ,B
            number = 3;
            condition3.signal();
        } catch (Exception e) {
    
            e.printStackTrace();
        } finally {
    
            lock.unlock();// Unlock 
        }
    }

    public void printC() {
    

        try {
    
            lock.lock();// locked 
            // Business code  ：  Judge  ->  perform  ->  notice 
            while (number != 3) {
    
                // wait for 
                condition3.await();
            }
            System.out.println(Thread.currentThread().getName() + "->CCC");
            // Wake up the , Wake up the designated person ,C
            number = 1;
            condition1.signal();
        } catch (Exception e) {
    
            e.printStackTrace();
        } finally {
    
            lock.unlock();// Unlock 
        }
    }

}