Java——Java實現生產者消費者

1、生產/消費者模型

生產/消費者問題是個非常典型的多線程問題，涉及到的對象包括“生產者”、“消費者”、“倉庫”和“產品”。他們之間的關系如下：
(01) 生產者僅僅在倉儲未滿時候生產，倉滿則停止生產。
(02) 消費者僅僅在倉儲有產品時候才能消費，倉空則等待。
(03) 當消費者發現倉儲沒產品可消費時候會通知生產者生產。
(04) 生產者在生產出可消費產品時候，應該通知等待的消費者去消費。

2、生產者消費者實現（synchronized ）

// Demo1.java
// 倉庫
class Depot {
    private int capacity;    // 倉庫的容量
    private int size;        // 倉庫的實際數量

    public Depot(int capacity) {
        this.capacity = capacity;
        this.size = 0;
    }

    public synchronized void produce(int val) {
        try {
             // left 表示“想要生產的數量”(有可能生產量太多，需多此生產)
            int left = val;
            while (left > 0) {
                // 庫存已滿時，等待“消費者”消費產品。
                while (size >= capacity)
                    wait();
                // 獲取“實際生產的數量”(即庫存中新增的數量)
                // 如果“庫存”+“想要生產的數量”>“總的容量”，則“實際增量”=“總的容量”-“當前容量”。(此時填滿倉庫)
                // 否則“實際增量”=“想要生產的數量”
                int inc = (size+left)>capacity ? (capacity-size) : left;
                size += inc;
                left -= inc;
                System.out.printf("%s produce(%3d) --> left=%3d, inc=%3d, size=%3d\n", 
                        Thread.currentThread().getName(), val, left, inc, size);
                // 通知“消費者”可以消費了。
                notifyAll();
            }
        } catch (InterruptedException e) {
        }
    } 

    public synchronized void consume(int val) {
        try {
            // left 表示“客戶要消費數量”(有可能消費量太大，庫存不夠，需多此消費)
            int left = val;
            while (left > 0) {
                // 庫存為0時，等待“生產者”生產產品。
                while (size <= 0)
                    wait();
                // 獲取“實際消費的數量”(即庫存中實際減少的數量)
                // 如果“庫存”<“客戶要消費的數量”，則“實際消費量”=“庫存”；
                // 否則，“實際消費量”=“客戶要消費的數量”。
                int dec = (size<left) ? size : left;
                size -= dec;
                left -= dec;
                System.out.printf("%s consume(%3d) <-- left=%3d, dec=%3d, size=%3d\n", 
                        Thread.currentThread().getName(), val, left, dec, size);
                notifyAll();
            }
        } catch (InterruptedException e) {
        }
    }

    public String toString() {
        return "capacity:"+capacity+", actual size:"+size;
    }
} 

// 生產者
class Producer {
    private Depot depot;
    
    public Producer(Depot depot) {
        this.depot = depot;
    }

    // 消費產品：新建一個線程向倉庫中生產產品。
    public void produce(final int val) {
        new Thread() {
            public void run() {
                depot.produce(val);
            }
        }.start();
    }
}

// 消費者
class Customer {
    private Depot depot;
    
    public Customer(Depot depot) {
        this.depot = depot;
    }

    // 消費產品：新建一個線程從倉庫中消費產品。
    public void consume(final int val) {
        new Thread() {
            public void run() {
                depot.consume(val);
            }
        }.start();
    }
}

public class Demo1 {  
    public static void main(String[] args) {  
        Depot mDepot = new Depot(100);
        Producer mPro = new Producer(mDepot);
        Customer mCus = new Customer(mDepot);

        mPro.produce(60);
        mPro.produce(120);
        mCus.consume(90);
        mCus.consume(150);
        mPro.produce(110);
    }
}

運行結果

Thread-0 produce( 60) --> left=  0, inc= 60, size= 60
Thread-4 produce(110) --> left= 70, inc= 40, size=100
Thread-2 consume( 90) <-- left=  0, dec= 90, size= 10
Thread-3 consume(150) <-- left=140, dec= 10, size=  0
Thread-1 produce(120) --> left= 20, inc=100, size=100
Thread-3 consume(150) <-- left= 40, dec=100, size=  0
Thread-4 produce(110) --> left=  0, inc= 70, size= 70
Thread-3 consume(150) <-- left=  0, dec= 40, size= 30
Thread-1 produce(120) --> left=  0, inc= 20, size= 50

3、生產者消費者實現（Lock鎖）

package Thread;



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

class Depot{
    private int capacity; //倉庫容量
    private int size; //倉庫當前產品數量
    private Lock lock; //鎖
    private Condition productCondition; //生產條件
    private Condition consumerCondition; //消費條件

    public Depot(int capacity) {
        this.capacity=capacity;
        this.size=0;
        this.lock = new ReentrantLock();
        this.productCondition = this.lock.newCondition();
        this.consumerCondition = this.lock.newCondition();
    }

    //生產商品
    public void produce(int val) {
        lock.lock();
        try {
            int left=val; //left表示需要生產的數量
            while (left > 0) {
                //當庫存已滿時，則生產者開始等待消費者消費
                while (size == capacity) {
                    productCondition.await();
                }
                int pro= left > (capacity-size) ? (capacity-size) : left;  //如果生產的數量大於倉庫容量，則只生產倉庫容量這么多
                size += pro;
                left -= pro;
                System.out.printf("%s produce(%3d) --> left=%3d, inc=%3d, size=%3d\n",
                        Thread.currentThread().getName(), val, left, pro, size);
                consumerCondition.signal(); //消費者消費時，發現當倉庫產品為零時，此時消費者等待，調用生產者生產，那么生產者生產完成后則需要釋放消費者
            }

        }catch (Exception e){

        }finally {
            lock.unlock();
        }
    }

    //消費商品
    public void consume(int val) {
        lock.lock();
        try {
            int left=val; //left表示需要消費的數量
            while (left > 0) {
                while (size == 0) {  //當前商品數量為零時，消費者需要等待
                    consumerCondition.await();
                }
                int cus=left > size? size : left;
                size -= cus;
                left -= cus;
                System.out.printf("%s consume(%3d) <-- left=%3d, dec=%3d, size=%3d\n",
                        Thread.currentThread().getName(), val, left, cus, size);
                productCondition.signal(); //消費者消費完成后，需要釋放生產者
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            lock.unlock();
        }

    }
}

//生產者
class Producer{

    private Depot depot;

    public Producer(Depot depot) {
        this.depot = depot;
    }

    public void produce(int val){
        new Thread(){
            @Override
            public void run() {
                depot.produce(val);
            }
        }.start();
    }
}


//消費者
class Customer{
    private Depot depot;

    public Customer(Depot depot) {
        this.depot = depot;
    }

    public void consume(int val) {
        new Thread(){
            @Override
            public void run() {
                depot.consume(val);
            }
        }.start();
    }

}




public class LockTest {
    public static void main(String[] args) {
        Depot mDepot = new Depot(100);
        Producer mPro = new Producer(mDepot);
        Customer mCus = new Customer(mDepot);

        mPro.produce(60);
        mPro.produce(120);
        mCus.consume(90);
        mCus.consume(150);
        mPro.produce(110);
    }
}

運行結果

Thread-0 produce( 60) --> left=  0, inc= 60, size= 60
Thread-1 produce(120) --> left= 80, inc= 40, size=100
Thread-2 consume( 90) <-- left=  0, dec= 90, size= 10
Thread-3 consume(150) <-- left=140, dec= 10, size=  0
Thread-4 produce(110) --> left= 10, inc=100, size=100
Thread-3 consume(150) <-- left= 40, dec=100, size=  0
Thread-4 produce(110) --> left=  0, inc= 10, size= 10
Thread-3 consume(150) <-- left= 30, dec= 10, size=  0
Thread-1 produce(120) --> left=  0, inc= 80, size= 80
Thread-3 consume(150) <-- left=  0, dec= 30, size= 50