JUC详解2——生产者消费者

小咪咪 2022-12-17 13:56 213阅读 0赞

### JUC详解2 ###

*   *   *  生产者消费者
         *   *  使用synchronized方法解决
             *  使用lock解决生产者消费者问题
         *  高频面试题：一个主线程三个子线程，如何让三个子线程执行结束再执行主线程

### 生产者消费者 ###

**线程间的通信问题——生产者消费者问题**  
一个简单的生产者消费者模型（使用synchronized）

#### 使用synchronized方法解决 ####

package com.fly.juc.pc;
    
    /** * @Description 生产者、消费者 * 线程间通信问题————生产者、消费者问题：等待唤醒；通知唤醒 * 线程交替执行：P：生产者、C：消费者, 操作同一个变量 * P：+1 * C：-1 * @ClassName ProCon * @Author cai feifei * @date 2020.10.23 20:56 * @Version */
    public class ProCon { 
        public static void main(String[] args) { 
            PC pc = new PC();
            new Thread(()->{ 
                for (int i=0;i<10;i++){ 
                    try { 
                        pc.increment();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            },"P").start();
            new Thread(()->{ 
                for (int i=0;i<10;i++){ 
                    try { 
                        pc.decrement();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            },"C").start();
        }
    }
    
    class PC{ 
        private int number = 0;
    
        public synchronized void increment() throws InterruptedException { 
            if (number!=0){ 
                //等待
                this.wait();
            }
            //业务
            number++;
            System.out.println(Thread.currentThread().getName()+"===="+number);
            //通知
            this.notifyAll();
        }
        public synchronized void decrement() throws InterruptedException { 
            if (number==0){ 
                this.wait();
            }
            number--;
            System.out.println(Thread.currentThread().getName()+"===="+number);
            this.notifyAll();
        }
    }

整齐的输出：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNTEwNTUx_size_16_color_FFFFFF_t_70_pic_center]  
**当存在多个生产者和消费者的时候**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNTEwNTUx_size_16_color_FFFFFF_t_70_pic_center 1]  
源码中的说明  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNTEwNTUx_size_16_color_FFFFFF_t_70_pic_center 2]  
这种线程的虚假唤醒，可以使用while来做判断等待

class PC{ 
        private int number = 0;
    
        public synchronized void increment() throws InterruptedException { 
            while (number!=0){ 
                //等待
                this.wait();
            }
            //业务
            number++;
            System.out.println(Thread.currentThread().getName()+"===="+number);
            //通知
            this.notifyAll();
        }
        public synchronized void decrement() throws InterruptedException { 
            while (number==0){ 
                this.wait();
            }
            number--;
            System.out.println(Thread.currentThread().getName()+"===="+number);
            this.notifyAll();
        }
    }

#### 使用lock解决生产者消费者问题 ####

package com.fly.juc.pc;
    
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    /** * @Description 生产者、消费者 * 线程间通信问题————生产者、消费者问题：等待唤醒；通知唤醒 * 线程交替执行：P：生产者、C：消费者, 操作同一个变量 * P：+1 * C：-1 * @ClassName ProCon * @Author cai feifei * @date 2020.10.23 20:56 * @Version */
    public class ProConJuc { 
        public static void main(String[] args) { 
            PCJ pc = new PCJ();
            new Thread(()->{ 
                for (int i=0;i<10;i++){ 
                    try { 
                        pc.increment();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            },"P1").start();
            new Thread(()->{ 
                for (int i=0;i<10;i++){ 
                    try { 
                        pc.decrement();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            },"C1").start();
            new Thread(()->{ 
                for (int i=0;i<10;i++){ 
                    try { 
                        pc.increment();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            },"P2").start();
            new Thread(()->{ 
                for (int i=0;i<10;i++){ 
                    try { 
                        pc.decrement();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            },"C2").start();
        }
    }
    
    class PCJ { 
        private int number = 0;
    
        Lock lock = new ReentrantLock();
        Condition condition = lock.newCondition();
    
        public void increment() throws InterruptedException { 
            lock.lock();
            try { 
                while (number != 0) { 
                    //等待
                    condition.await();
                }
                //业务
                number++;
                System.out.println(Thread.currentThread().getName() + "====" + number);
                //通知
                condition.signalAll();
            } catch (Exception e) { 
                e.printStackTrace();
            } finally { 
                lock.unlock();
            }
        }
    
        public void decrement() throws InterruptedException { 
            lock.lock();
            try { 
                while (number != 0) { 
                    //等待
                    condition.await();
                }
                //业务
                number--;
                System.out.println(Thread.currentThread().getName() + "====" + number);
                //通知
                condition.signalAll();
            } catch (Exception e) { 
                e.printStackTrace();
            } finally { 
                lock.unlock();
            }
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNTEwNTUx_size_16_color_FFFFFF_t_70_pic_center 3]  
生产者和消费者随机执行，

如何精准唤醒和通知线程，从而按照自己的意愿进行执行
    	Condition：同步监视器
    	使用Condition实现指定唤醒功能

package com.fly.juc.pc;
    
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    /** * @Description 一把锁实现流水线 * @ClassName ProConJuc * @Author cai feifei * @date 2020.10.23 20:56 * @Version */
    public class ProConJuc { 
        public static void main(String[] args) { 
            PCJ pc = new PCJ();
            new Thread(()->{ for (int i=0;i<10;i++){ pc.partA();}},"A").start();
            new Thread(()->{ for (int i=0;i<10;i++){ pc.partB();}},"B").start();
            new Thread(()->{ for (int i=0;i<10;i++){ pc.partC();}},"C").start();
    
        }
    }
    
    class PCJ { 
        private int number = 0;
    
        Lock lock = new ReentrantLock();
        Condition condition1 = lock.newCondition();
        Condition condition2 = lock.newCondition();
        Condition condition3 = lock.newCondition();
    
        public void partA(){ 
            lock.lock();
            try { 
                //业务：判断等待-》执行-》通知
                while (number!=0){ 
                    condition1.await();
                }
                //业务
                System.out.println(Thread.currentThread().getName()+"线程执行了========"+number);
                //唤醒，指定唤醒:condition2=>B
                number=1;
                condition2.signal();
            }catch (Exception e){ 
                e.printStackTrace();
            }finally { 
                lock.unlock();
            }
        }
        public void partB(){ 
            lock.lock();
            try { 
                //业务：判断等待-》执行-》通知
                while (number!=1){ 
                    condition2.await();
                }
                //业务
                System.out.println(Thread.currentThread().getName()+"线程执行了========"+number);
                //唤醒，指定唤醒:condition3=>C
                number=2;
                condition3.signal();
            }catch (Exception e){ 
                e.printStackTrace();
            }finally { 
                lock.unlock();
            }
        }
        public void partC(){ 
            lock.lock();
            try { 
                //业务：判断等待-》执行-》通知
                while (number!=2){ 
                    condition3.await();
                }
                //业务
                System.out.println(Thread.currentThread().getName()+"线程执行了========"+number);
                //唤醒，指定唤醒:condition1=>A
                number=0;
                condition1.signal();
            }catch (Exception e){ 
                e.printStackTrace();
            }finally { 
                lock.unlock();
            }
        }
    }

程序有序依次执行  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNTEwNTUx_size_16_color_FFFFFF_t_70_pic_center 4]

### 高频面试题：一个主线程三个子线程，如何让三个子线程执行结束再执行主线程 ###

package com.fly.juc.pc;
    
    /** * @Description 一个主线程三个子线程，如何让三个子线程执行结束再执行主线程 * @ClassName JoinTest * @Author cai feifei * @date 2020.10.24 08:50 * @Version */
    public class JoinTest { 
        public static void main(String[] args) { 
            Data data = new Data();
    
            try { 
                Thread thread1 = new Thread(()->{ data.test();},"A");
                Thread thread2 = new Thread(()->{ data.test();},"B");
                Thread thread3 = new Thread(()->{ data.test();},"C");
                thread1.start();
                thread2.start();
                thread3.start();
                //让三个线程执行完，如果在调用start方法后面直接调用join方法，那么三个线程将串行
                thread1.join();
                thread2.join();
                thread3.join();
            } catch (Exception e) { 
                e.printStackTrace();
            }
            System.out.println("主线程执行");
        }
    }
    
    class Data{ 
        public void test(){ 
            System.out.println(Thread.currentThread().getName()+"线程执行了");
        }
    }

**上一篇：**[JUC详解1][JUC_1]

**下一篇：**[JUC详解3——8锁问题][JUC_3_8]

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[JUC_1]: https://blog.csdn.net/qq_41510551/article/details/109228266
[JUC_3_8]: https://blog.csdn.net/qq_41510551/article/details/109254112